SEPARATING TECHNIQUES at a glance

 

TOPIC: STANDARD SEPARATION TECHNIQUE

STANDARD SEPARATION TECHNIQUES
These are the various methods that are available and used to separate components of a mixture from the mixture. they include the following methods discussed below

1. SIEVING

This is used to separate solid particles of different sizes. Particles smaller than the size of the sieve (mesh) pass through leaving behind particles of larger sizes. It is used in gold and diamond mines and in garri industries.

2. MAGNETIC SEPARATION

This method is used to separate magnetic substances from non-magnetic particles. It makes use of a magnet. An example is the separation of a mixture of iron filings  or pins and sugar.

It is used in mining and steel industries. It can be used to remove magnetic impurities from tin ores. It can be used to separate iron filings from sulphur powder.

3. FILTRATION

Filtration is a separation technique that involves separating an insoluble solid from a liquid using a filter. For example, a mixture of chalk particles in water can be separated using filtration technique. 

Filtration is used in industries such as water purification plants and breweries

                                                      fig.1 filtration of muddy water

4. CENTRIFUGATION:

Centrifugation is a standard separation technique used to separate a mixture of insoluble solid from liquid by using a centrifuge. A centrifuge is a machine which can spin test tubes containing suspensions at high speed. Centrifugation is often used when there is only a small amount of material. In hospitals, blood samples are centrifuged to separate the blood cells from the plasma.                                        

5. DECANTATION

Decantation is a separation technique used to separate a mixture containing insoluble solid from a liquid. This is done when the mixture is allowed to settle down with the upper clear liquid carefully poured or decanted into a clean container thereby leaving the lower solid in the container originally containing the mixture. This is a quick but inaccurate method of separating the components of a mixture.

6. EVAPORATION

Evaporation is a separation technique used to recover soluble solute from its solvent. For example, salt can be separated from salt solution by evaporation.

fig.3. Evaporation of a salt solution0

Evaporation is used in salt –making industries.

7. CRYSTALLIZATION

Crystallization is used to obtain pure crystals of salts which decompose easily on heating, from its solution. 

The solution is concentrated by heating until it is concentrated, and it is then allowed to cool down, the crystals start to form as the solution cools down. To induce crystal formation:

(i). some crystals of the salt are added (seedling)

(ii). use a glass rod to scratch the inside of the container.  

Crystallization is used in drug industries and sugar industries, industries where purity of a substance is important.

8. FRACTIONAL CRYSTALLIZATION

It is used to separate two or more solutes (solids) which are present in the same solution. The solutes to be separated must have different solubilities at different temperatures. Starting from a particular temperature, as cooling of the solution begins the solutes that is least soluble begins to appear, that is, the crystals that are least soluble at that particular temperature begins to crystalize out leaving the more soluble salts in the solution.

9. PRECIPITATION

In precipitation, a difference in the solubility of a solid in two different miscible liquids is used. For example, FeS0₄ is soluble in water but not on ethanol. If ethanol is added to a solution of FeS0₄ in water, the FeS0₄ will be precipitated out of the solution and filtered out.

10. SUBLIMATION

Sublimation is the change of state from solid to gas directly on application of heat. Examples of substances that sublime are iodine and ammonium chloride. Sublimation can be used to separate these substances. The pure crystal recovered is the sublimate.

    Fig. 

 

11. DISTILLATION

              

This method is used to recover a solvent from a solution. It involves heating the liquid until it vapourizes and then condensing the vapour with the aid of a condenser into a liquid called distillate. The solute and other impurities remain in the distillation flask. This method is used in gin/brandy and water distilleries to manufacture gin and distilled water.

FRACTIONAL DISTILLATION

This method is used to separate a mixture of two or more miscible liquids with close boiling points. When two liquids have boiling points that are very close (less than 10^oC ) it becomes difficult to use simple distillation. A fractionating column is inserted into the distillation flask.the fractionating column does the actual separation

How the fractionating column works: - As the mixture boils and enters the fractionating column, the vapours loss their heat to the glass beads in the fractionating column and falls back into the mixture, (i.e by returning components whose boiling point is less than that of the fractionating column). Only components whose boiling point is the same as the fractionating column are allowed to pass into the condenser. This method is used in the refinery to separate crude oil into its various fractions, also the extraction of oxygen and nitrogen from Liquified air, the manufacture of ethanol and to separate benzene and methyl benzene mixture.           

SEPARATING FUNNEL

This method is used to separate a mixture of two immiscible liquids or a polar liquid from a non-polar liquid. It depends on the densities of the two liquids. The less dense liquid will float on top and the denser below. It is used to separate water and kerosene

Diag.  Separation of a mixture of kerosene and water.

CHROMATOGRAPHY

This method uses a solvent moving over an adsorbent medium (paper) which is porous to separate mixtures of solutes.

                 

A chemist uses liquid chromatography to analyze a complex mixture of substances. The chromatograph utilizes an adsorptive medium, which when placed in contact with a sample, adsorbs the various constituents of the sample at different rates. In this manner, the components of a mixture are separated. Chromatography has many valuable applications, such as determining the level of pollutants in air, analyzing drugs, and testing blood and urine samples.

Types

1.            Paper chromatography

2.            Thin layer chromatography

3.            Gas chromatography

4.            Column chromatography

In paper chromatography, a solution, such as ink, is spotted into the paper (stationary phase) near one end. The paper is then dipped into an appropriate solvent such as water or ethanol (mobile phase) in a closed air-tight jar. The solvent moves up the paper and separates the substance into various spots.The paper is removed and dried. The different spots on the paper show the different constituents the substance (ink, dye or chlorophyl) contains.

USES

i). It is used in medicine to analyze blood.

ii). It is used in the industry to identify petroleum fractions.

iii). It is used in scientific research.

CRITERIA FOR PURITY

1.            The melting point and boiling point of a pure substance are fixed but change in the presence of impurities. Impurities lower the melting point of a substance and increase its boiling point.     

And the criteria for purity is 

1. Sharp melting point: substance must melt at a specific temperature 

2. Sharp boiling point: substance must boil at a specific temperature called the boiling point.

3. Substance must have a constant density 

4. Substance must show only one spot on a chromatographic plate.

 

                                            OBJECTIVE QUESTIONS

1.  A mixture of oil and water can be separated by 

(a) sublimation

 (b) evaporation to dryness 

(c) using a separating funnel

 (d) fractional distillation

2.  Fractional distillation is used to separate

(a) an insoluble substance from a soluble volatile substance 

(b) liquids with differing boiling points

 (c) gas, liquid or solid impurities from a mixture 

(d) liquid with close boiling points

3. Which of the following separating techniques can be used to separate a mixture of iodine and sodium chloride? 

(a) distillation 

(b) evaporation  

(c) sublimation  

(d) decantation

4.  Which of the following is not a type of chromatography?

(a) thin layer 

(b) gas  

(c) paper 

(d) glass

5. Which of the following is a quick but inaccurate way of separating mixture?

 (a) decantation      (b) evaporation   (c) filtration     (d) distillation 

6. How can you separate a mixture of iron filings and sulphur powder?

 (a) distillation 

(b) chromatography 

(c) magnetization  

(d) evaporation

7.  A mixture of calcium chloride and calcium trioxocarbonate (IV) in water can be separated by

(a)Evaporation

(b) Sublimation

(c) Distillation

(d) Filtration

8.  CuSO4.5H2O can be obtained from an aqueous solution of copper (II) tetraoxosulphate (VI) by

(a) evaporation to dryness

(b) Using chromatography

(c) precipitation

(d) crystallization.

9. Which of this separation technique can be used to separate an insoluble solid from a liquid

(a) centrifugation

(b) chromatography

(c) distillation

(d) sublimation

10. Which of these techniques would you use to obtain pure water from sea water?

(a) chromatography

(b) crystallization

(c) distillation

(d) filtration

11. Ethanol is a product of fermentation of simple sugars. Which method is used to separate ethanol from other products?

(a) boiling off the ethanol

(b) filtration

(c) precipitation

(d) fractional distillation

12.  A spot of oil paint on a shirt can best be removed using

(a) brine.

(b) detergent

(c) kerosene

(d) warm water.

13. Which of these techniques would you use to separate a mixture of ammonium chloride and sodium chloride

(a) centrifugation

(b) chromatography

(c) distillation

(d) sublimation

14. Which of the following is not a separation technique?

(a) Crystallization

(b) Distillation

(c) Evaporation

(d) Hydration

15. Fractional distillation of petroleum depends on differences in

(a) boiling points

(b) densities

(c) freezing points

(d) solubilities

16. Pure solvents are obtained by

(a) evaporation

(b) extraction

(c) condensation

(d) distillation

17.  The constituents of leaf pigment can be separated by

 (a) chromatography

(b) filtration

(c) fractional crystallization

(d) fractional distillation

18. The separation of Oxygen from nitrogen by fractional distillation of air is possible because 

a). nitrogen is less dense than oxygen

b). oxygen is more reactive than nitrogen

c). of the difference in their boiling points.

d). they belong to the same period. 

19. The purity of a solid sample can best be determined by its 

a). boiling point

b). melting point 

c). conductivity.

d). solubility.

20.  A sample of orange juice is suspected to have been contaminated with a yellow dye. Which of

the following methods can be used to detect the dye.

a). Decantation 

b). Chromatography 

c). Distillation 

d). Evaporation

                                            THEORY

1.(a) The diagrams labelled I to IV below illustrate different laboratory set-ups used in the separation of mixtures. 

i). Name the separation technique illustrated by each diagram 

ii). Which of the set-ups is used for concentrating dilute salt solutions, for the purpose of crystallization  

iii). Which of the set-ups is used in obtaining pure water from muddy water?

iv). Mention the set-up you would use to separate a polar solvent from a non-polar solvent 

v). State the modification you would make to the set-up labelled IV in order to use it for separating a mixture of NaCl and NH4Cl [waec]

2.  The set-up shown in the diagram below was used to separate a drop of universal indicator into the constituent dyes using ethyl ethanoate as the solvent. 

(a) what name is given to the separation technique illustrated in the diagram? 

(b)  State:   

(i). How many components are resolved in the separation 

 (ii). The material normally used in the laboratory as the absorbent medium.

(iii) Which of the labels indicate the point of application of the indicator.

1.        Explain the following separation techniques. Magnetic separation, paper chromatography and sieving

2.            Describe how you would separate a mixture of NaCl, PbCl₂ and NH₄Cl

3.            What method can be applied to separate a mixture of iron filings and sulphur

4.            Mention two criteria for purity of a substance.

PARTICULATE NATURE OF MATTER

TOPIC: PARTICULATE NATURE OF MATTER

CONTENT

- ATOMS AND MOLECULES

- IONS

- DALTON’S ATOMIC THEORY

- MODIFICATIONS OF DALTONS ATOMIC THEORY

ATOMS AND MOLECULES

Matter is made up of discrete particles. The main ones are atoms, molecules, and ions.

An atom is the smallest part of an element which can take part in a chemical reaction.

A molecule is the smallest particle of a substance that can exist alone and still retains the chemical properties of that substance. 

Molecules are made up of atoms. These atoms may be the same or may be different

ATOMICITY: - This is the number of atoms in one molecule of an element or a compound

We have monatomic, diatomic and triatomic for those elements that contain one atom, two atoms and three atoms respectively in their molecules.

Examples:

Element            Atomicity

Neon                Monoatomic    Ne

Helium            Monoatomic    He

Argon              Monoatomic    Ar

Hydrogen        Diatomic         H2

Oxygen           Diatomic          O2

Nitrogen         Diatomic          N2

Ozone             Triatomic        O3

Sulphur           Polyatomic      S8

Water               triatomic          H2O   

Limestone        pentatomic      CaCO3

IONS

An ion is an atom or group of atoms which carries an electric charge. They are formed when atoms loss or gain electrons. 

Generally, ions are grouped as cations and anions. 

Cations are positively charged ions e.g. Ca²⁺, Na⁺, NH₄⁺ etc.

Anions are negatively charged ions e.g. C0₃^2-, S0₄^2-, Cl^-, OH^-, etc.

We also have group of atoms that carry a single charge, whether positive or negative charge, they are called RADICALS.

An acid radical is thus a small group of atoms carrying a negative charge that keeps, 

Examples include S0₄^2-, N0₃^- e.t.c

DALTON’S ATOMIC THEORY

John Dalton, a British Physicist and Chemist (1808) proposed the atomic theory thus: 

1.            All elements are made up of small indivisible particles called atoms.

2.            Atoms can neither be created nor destroyed in any chemical reaction.

3.            Atoms of a particular element are exactly alike in all aspect and are different from atoms of all other elements.

4.            Atoms of different elements combine in simple whole number ratios to form compounds.

5.            All chemical changes result from the combination or separation of atoms

MODIFICATIONS OF DALTON’S ATOMIC THEORY

Due to new discoveries in the twentieth century, Dalton’s atomic theory cannot hold in its totality.  setting new modifications have been made There is need for its modification.

i.  Due to the discovery of the sub-atomic particles, (protons and electrons) the atom is no longer believed to be indivisible.

ii. Due to the discovery of radioactivity and radioisotopes which involves the destruction of atoms and formation of new elements during nuclear reactions, the atom is no longer believed to be indestructible. however. This second statement still holds good for ordinary chemical reactions

iii.  Due to the discovery of isotopes and isotopy, the third statement is no longer acceptable. 

iv.  Due to the discovery of very large organic molecules such as proteins, starch and fats which contain thousands of atoms. The fourth statement is no longer true for organic compounds but still remains true for inorganic compounds which contain a few atoms per molecule.

Objective Questions

1. Which of the following is not a constituent of the atom

 (a) proton  

(b) electron

 (c) neutron

 (d) isotope

2. Which of the following statement about an atom is not correct?

 (a) it is indivisible

(b) it is destructible in some cases 

(c) it is the smallest part of a substance that takes part in a reaction 

(d) it is made up of protons, neutrons and electrons

3.  Which of the following is a liquid at room temperature? 

(a) copper (b) gold  (c) mercury

 (d) silver

4.   What is the atomicity of neon? (a) monoatomic (b) diatomic (c) triatomic  (d) polyatomic

THEORY

1.(a)i  State any two postulates of the Dalton’s atomic theory.

ii. state the modification of the postulates mentioned above

2.(a)i. Differentiate an atom from a molecule.

ii. How will an atom become an ion?

1.  Define an atom.

2.  Give two examples of diatomic molecules.

EVALUATION

1. What are ions?
2. State the cation and anion present in (I) H₂S0₄   (ii) NaCl (iii) FeS0₄

pH at a glance

 

DEFINITION OF pH

pH is defined as the negative logarithm to the base 10 of the hydrogen ion [H⁺] concentration.

It is also defined as the degree of acidity or alkalinity of a solution

i.e. pH = -log₁₀ [H⁺].

Thus: If [H⁺] = 0.00001 or 10^-5.

log [H⁺] = log10^-5 = -5

pH= -log [H⁺] = - (-5) = 5.

If [H⁺] =10^-x

Therefore, pH= -log10^-x = - (-x) = x

If [H⁺] = 10^-2, pH = 2

DEFINITION OF pOH

pOH is defined as the negative logarithms of the hydroxide ion [OH^-] concentration to the base of 10.

i.e. pOH= -log [OH^-].

A solution with pH 7 is neutral.

A solution with pH less than 7 i.e. pH 6,5,4, 3, 2, 1 or 0 indicates increasing acidity as the numbers decreases.

A solution with pH greater than 7, i.e. pH 8,9,10, 11, 12, 13, or 14 indicate increasing alkalinity as the numbers increase.

 1< 2 <3< 4< 5< 6        7          8< 9<10< 11<12<13<14

Increasing acidity    Neutral     Increasing alkalinity

A solution with pH 1 is very acidic [with high concentration of H⁺]. A solution with pH 13 is very alkaline [with low concentration of H+, but high concentration of OH-].

Note that: If pH is 1, it has concentration of H+ 10 times greater than pH 2 and 100 times greater than pH 3 e.t.c.

pH 1 > pH 2 > pH 3.

Concentration of H⁺    10^-1      10^-2      10^-3.

                                      0.1       0.01     0.001.

Relationship between pH and pOH.

                 H₂O →   H⁺    +   OH^-

From conductivity measurement [H⁺] =10^-7moldm^-3, [OH^-]=10^-7moldm^-3.

[H⁺] [OH^-] = Kw=10^-7 x 10^-7=10^-14mol²dm^-6.

Taking logarithm of both sides

log ([H⁺] [OH^-]) = logKw

log [H⁺] + log[OH^-] =logKw

Subtracting both sides

-(log[H⁺]  +  [OH^-]) = -logKw

-log [H+] – log[OH^-] = -logKw

-log [H⁺] + (-log [OH^-]) = -logKw

pH + pOH = PKw

pKw = -log10^-14 = -(-14) = 14

Therefore, pH + pOH = 14.

Worked examples

1. Find the hydrogen and hydroxide ion concentrations in

(a) 0.01moldm^-3 tetraoxosulphate (vi) acid solution.

(b) 0.001moldm^-3 potassium hydroxide solution.

Solution

(a).  H₂SO_4(aq)→ 2H⁺_(aq)+SO₄^2-_(aq)

From the equation, 1 moldm^-3 H₂SO₄ ionizes to give 2moldm^-3 H⁺

Therefore, 0.01moldm^-3 H₂SO₄ would ionize to give (2x0.01) moldm^-3 H⁺

[H⁺] = 2x10^-2moldm^-3

[H⁺] [OH^-] = 10^-14

(2x10^-2) [OH^-] = 10^-14

[OH^-] =    10^-14

                2 x 10^-2

[OH-] = 0.5x (10^{-14- -2})

[OH-] =0.5 x10^-14+2

[OH-] =0.5x10^-12moldm^-3.

(b).     KOH_(aq)→ K⁺_(aq)+  OH^-_(aq)

From the equation,

1moldm^-3 of KOH ionizes to give 1moldm^-3 of OH-

10^-3moldm^-3 of KOH would ionize to give 10^-3moldm^-3 of OH

[OH^-]=10^-3moldm^-3.

[H⁺] [OH^-]=10^-14

[H⁺] (10^-3) = 10^-14.

[H⁺] = 10^-14

            10^-3

[H+] = 10^-14+3

[H+] = 10^-11moldm^-3

2.  A glass cup of orange juice is found to have a POH of 11.40. Calculate the concentration of the hydrogen ions in the juice.

Solution

pH + pOH = 14.

pH = 14 – 11.4.

pH = 2.6.

pH = -log [H⁺]

2.6 =-log [H⁺].

[H+] = Antilog (-2.6)

[H+] = 0.0025moldm^-3

[H+] = 2.5x10^-3moldm^-3.

Measuring pH of a solution.

We use the pH meter or a universal indicator to measure the pH of a solution. 

A universal indicator shows different colours at specific pH or hydrogen ion concentrations.

                          OBJECTIVE QUESTIONS

1. 

CHEMICAL BONDING at a glance

Chemical bonding deals with the various types of forces of attraction that binds atoms and molecules together.  There are two major types: -

Electrovalent bonding/Ionic bonding 

2.Covalent bond bonding.

I. Ordinary covalent

II. Dative covalent

Electrovalent bonding or IONIC BOND: - This is a type of bonding that involves the total transfer of electrons from one atom (usually a metal) to another atom (usually a non-metal).

It is also called ionic bonding because the compound splits into ions when dissolved in water or when molten

This type of bond is usually identified by looking at the two atoms involved in the bonding. It is usually between a metal and a non-metal. 

Examples include the bonding between sodium and chlorine

Using Lewis electron dot symbol:  Lewis dot electron symbol uses the symbol of the element surrounded by the valence electrons of the 

Characteristics of Electrovalent bonds

1.   They have high melting and high boiling points.

II.   They are soluble in polar solvents (e.g water)

III.   They conduct electricity when molten or in solution

IV.   They are crystalline in nature

V.    They are solids at room temperature.

Covalent bonding 

Covalent bonding can be of two types

 i. ordinary covalent bonding and

 ii. dative or coordinate covalent bonding.

Ordinary COVALENT BONDING: - This is a type of bonding that involves the sharing of electrons between two atoms (usually non-metals).

Ordinary covalent bonds can be identified by looking at the two atoms involved in the bonding. If the two atoms involved in the bonding are both non-metals then the bond is possibly covalent bond.

Ordinary covalent bonding can be grouped into three types 

i. Single covalent bond: - In this type of covalent bond each atom donates one electron each to the shared pair. Examples include the bonding between two hydrogen atoms to form a hydrogen molecule or two chlorine atoms to form a chlorine molecule 

i.

ii.

                     

Here you can see only one dash (representing the b0ond between the hydrogen atoms and the chlorine atoms).

ii. Double Covalent Bond: - In this type of covalent bonding each atom donates two electrons to the shared electron pair. Examples include the bonding between two Oxygen atoms to form an Oxygen molecule, and also the bonding between carbon and oxygen to form Carbon (IV) oxide 

i.

      O      +      O →     O=O      (O₂)

Covalent bonding does not exist only between atoms of the same element, it can occur between atoms of different elements. For example, the combination of carbon and oxygen to form carbon (IV) oxide 

using Lewis dot electron symbol

      C + O₂  →    O==C==O

Here there are two lines/dash (representing double covalent bonds) between the the two atoms 

iii. Triple Covalent bond: - In this type of bonding, each atom donates three electrons each to the shared electron pair. An example includes the bonding between nitrogen atoms to form the molecule (N2)

                                        

    1.   N + N →  N2

    

Note: In all these examples of covalent combinations, each atom is contributing the same number of electrons it needs to acquire an octet or a duplet (in the case of hydrogen) structure.

Characteristics of Covalent bond

I. Solids have low melting and low boiling points.

2. They are insoluble in polar solvents but soluble in organic solvents.

3. They are mainly volatile liquid or gases at room temperature.

4. They form molecules not ions.

5. They are non-electrolytes.

DATIVE COVALENT BOND: - This is a type of covalent bond that involves the sharing of electrons between two atoms, but unlike ordinary covalent bonding the shared electron pair is donated by only one of the two atoms.

Example of dative covalent bond is the bond in ammonium ion NH4+ and hydroxonium ion H3O+.

So, the basic difference between ordinary covalent and dative covalent bond is that the shared electron pair is donated by only one of the two atoms involved in the bonding.

METALLIC BONDING: - This is the attraction between the positive nuclei of metals and the electron cloud or sea of electrons enveloping the nucleus 

       Positively charged electrons embedded in a sea of delocalized electrons 

HYDROGEN BONDING: - Hydrogen bonding is a type of force (bond) that arises when hydrogen is bonded covalently to a strongly electronegative element.

Hydrogen bond can only exist in compounds where hydrogen is bonded to another nonmetal which is highly electronegative. Example of electronegative elements include Fluorine, Oxygen, Chlorine, Nitrogen.

Electronegativity is the tendency of an element to attract electrons to itself in a molecule

H-F.......H-F,,,,,,H-F   the dotted lines represent hydrogen bonding. hydrogen bonding gives added properties to compounds they occur in such as higher boiling points; and such covalent compounds usually exist in the liquid state. example is water.

Van der Waals Forces:

These are Weak intermolecular forces of attraction arising from temporary dipoles in molecules.

 Van der Waals forces are weaker than covalent bonds.

They arise sometimes from temporary uneven distribution of electrons. ( temporary dipoles)

Examples of substances where van der waals are found include Iodine crystals,  between graphite layers.

 

OBJECTIVE QUESTIONS 

1. What is responsible for metallic bonding?                        

 (a). Shearing of electrons between the metal atoms.          

 (b). Attraction between the atomic nuclei and cloud of electrons.        

(c). Transfer of electrons from one atom to another                   

 (d).  Attraction between negative and positive ions.

2. Electrostatic forces of attraction between sodium ion and halide are greatest in                                

 (a) NaCl.            

 (b) NaBr.                  

 (c) NaF .                      

 (d) NaI

3. Which of the following compounds is covalent?      

 (a). CaCl₂     

(b).  MgO 

 (c).  NaH      

 (d).  CH₄.

4. The type of chemical bond that exist between potassium and oxygen in potassium oxide is     

 (a) Ionic

 (b) metallic 

(c) covalent 

(d) dative

5. Which type of bond is represented by the dotted lines in the following structure?        

H-F''''''''H-F''''''''H-F'''''''H-F

(a) Covalent bond

(b) Dative bond 

(c) Electrovalent bond 

(d) Hydrogen bond.

6. What type of bond will be formed between elements P and Q if their electronegativity values are 0.8 and 4.0 respectively

(a) Covalent bonding 

(b) Co-ordinate covalent bonding 

(c) Electrovalent bonding 

(d)Hydrogen bonding

7. A solid substance with high melting and boiling points is likely to be a/an   

(a) covalent compound 

(b) dative covalent compound 

(c) electrovalent compound 

(d) non-metal

8. Which of the following molecules has a triple bond  

(a) CH₄   

(b) NH₃  

(c) N2   

(d) O2

9. Which of the following molecules has a linear shape? 

(a) CH₄ 

(b) CO₂ 

(c) H₂S 

(d) NH₃.

10. Hydrogen bonds are formed between molecules containing a hydrogen atom bonded to a 

(a) strongly electronegative atom 

(b) non-polar species 

(c) diatomic element 

(d) complex ion.

11. Element X with electronic configuration 2,8,2 and an element Y with electronic configuration 2,8,7 are likely to combine by

(a)  bonding 

(b) covalent bonding

(c) electrolpvalent bonding 

(d) dative bonding

12. Which of the following statements is correct about sodium chloride in the solid state?

(a) It exists as aggregates of ions 

(b) it conducts electricity

(c) its melting point is below 100⁰C

(d) it exists as discrete molecules.

13. If an element with high electron affinity combines with another element with low ionization energy, the bond formed will be mainly 

(a) covalent 

(b) ionic 

(c) dative 

(d) metallic

14. The bond formed when two electrons that are shared between two atoms are donated by only one of the atoms is

 (a) covalent dative 

(b) dative 

(c) ionic 

(c) metallic.

15. When element ₂₀A combines with element ₈Y.

 (a) a covalent compound AY is formed 

(b) an ionic compound AY is formed 

(c) an ionic compound A₂Y is formed 

(d) a covalent compound AY₂ is formed.

16. In metallic solids the forces of attractions are between the mobile valence electrons and 

(a) Atoms

 (b) Neutrons

 (c) The negative electrons 

(d) positively charged nuclei.

17. which of the following compounds has hydrogen bonds between its molecules

(a).  HF      

(b).  HBr        

(c).  HCl        

(d).  HI

18. The bonds in crystalline ammonium chloride are

 (a) covalent and dative 

(b) ionic and covalent 

(c) ionic, covalent and dative 

(d) ionic, covalent and hydrogen bond.

19. Which of the following properties of covalent compounds is not correct? They

 (a) are non-electrolytes 

(b) are mostly gaseous and volatile liquids.  

(c) Have low melting points 

(d) have high boiling points.

20. Which of the following molecules is not linear in shape? 

(a) CO₂ 

(b) O₂ 

(c) NH₃  

(d)HCl.

21. In bonded atoms, increase in electronegativity difference, 

(a) increases polarity 

(b) decreases polarity 

 (c) has no effect on polarity 

(d) brings the polarity to zero.

22. If the difference between the electronegativities of two element is large, the type of bond that can be formed between them is 

(a) covalent    

(b) dative

(c) ionic

 (d) metallic.

23. Which of the following species does not contain a co-ordinate bond? 

 (a) Al₂Cl ₃

(b) CCl₄

(c) H₃O⁺ 

(d) NH₄⁺

24. What type of chemical bonding is involved in the formation of NH₄⁺ from a molecule of  ammonia and a proton? 

(a). Covalent bonding 

(b). Co-ordinate covalent bonding 

(c). Electrovalent bonding 

(d). Hydrogen bonding 

25

THEORY QUESTIONS

1a) Define i. electrovalent bond

ii. Give two properties of electrovalent bond

iii. With the aid of a diagram show the bonding between sodium and chlorine to form sodium chloride.

(b)i Define covalent bond

ii. Give three properties of covalent bond

iii. With the aid of a diagram show how ammonia molecule is formed

(c). State the type of bonds that exist in

i. ammonia

ii. ammonium ion.

2a) Define the following terms 

 i. electrovalent bonding  

 ii. ordinary covalent bonding

iii. give two properties of electrovalent bond

iv. with the aid of a diagram show the bonding between magnesium and chlorine to form magnesium chloride.

bi) differentiate between ordinary covalent and dative covalent bond

ii. Define hydrogen bonding

3.a(i) Why do electrovalent compounds have high boiling points

     (ii).  Name two compounds that can react with hydrogen ion to form dative bond

    (iii).  State two physical properties of electrovalent compounds   [Neco 2025]

ACIDS at a glance

 

ACIDS

Definition: 

By Arrhenius: -An acid is a substance which in aqueous solution produces hydrogen ion (H⁺)or  hydroxonium ion (H₃O⁺) as the only positive ion. 

By Bronsted-Lowry: -An acid is a proton donor.

By  Lewis:- an acid is a substance that donates a pair of electron    

CLASSES OF ACIDS

There are two classes of acids:

(1). Organic acids: - this are naturally occurring acids found in plants and animal material.

	ORGANIC ACIDS	SOURCES
1.	Ethanoic Acid	vinegar
2.	Citric acid	Lime, lemon
3.	Amino acids	proteins
4.	Fatty acids	Fats and Oils
5.	Ascorbic acids (vitamin C)	oranges

(2). Inorganic acid: Inorganic acid can be prepared from mineral elements or inorganic matter.

	Inorganic Acids	Formula	constituents
1.	Hydrochloric acid	HCl	Hydrogen and chlorine
2.	Tetraoxosulphate  acid	H2SO4	Hydrogen, oxygen and Sulphur
3	Trioxonitrate (V) acid me	HNO3	Hydrogen, Nitrogen and Oxygen
4.	Trixocarbonate (IV) acid	H2CO3	Carbon, Hydrogen and Oxygen
5.	Tetraoxophosphate (V) acids	H3PO4	Hydrogen, Oxygen and Phosphorus

An acid is also defined as a substance which produces hydroxonium ion as the only positive ion when dissolved in water.

  H₂O_(l) →  H3O⁺_(aq)

Acids can be dilute or concentrated depending on the amount of water it contains.

A dilute acid is acid is one that contains a large amount of water added to a small amount of the acid.

 A concentrated acid is acid one that contains only a little amount of water added to a relatively large amount of the acid.

STRENGTH OF AN ACID

The strength of an acid can either be weak or strong.

1.  Strong acids: are acids which ionize completely in aqueous solution. 

Such acid solutions have a high concentration of H⁺ are HCl, H₂SO₄ and HNO₃.

H₂SO_4(aq) → 2H⁺_(aq) + SO₄^2-_(aq)

HNO_3(aq) → H⁺_(aq) + NO₃^-_(aq)

HCl_(aq) → H⁺_(aq) + Cl^-_(aq)

2.  Weak acids: are acids which ionize or dissociate slightly or partially in aqueous solution. 

Such acid solutions have a low concentration of hydrogen ions.

        Examples of weak acids are ethanoic acid CH₃COOH, H₂CO₃, H₃PO₄, H₂SO₃.

H₂CO_3(aq) → 2H⁺_(aq) + CO₃^2-_(aq)

H₃PO_4(aq) → 3H⁺_(aq) + PO₄^3-_(aq)

CH₃COOH_(aq) → H⁺_(aq) + CH₃COO^-_(aq)

H₂SO_3(aq) → 2H⁺_(aq) +   SO₃^2-_(aq)

BASICITY OF AN ACID: This is the number of replaceable hydrogen atoms in one molecule of an acid

Examples: -

1. HCl_(aq) →    H⁺_(aq) + Cl^-_(aq)

2. HNO_3(aq) → H⁺_(aq)+ NO₃^-_(aq)

3. H₂SO_4(aq) → 2H⁺_(aq) + SO₄^2-_(aq)

4. H₂CO_3(aq) → 2H⁺_(aq) + CO₃² _(aq)

5. H₃PO_4(aq) → 3H⁺_(aq) + PO₄^2-_(aq)

_{That is the number of hydrogen ions that dissociates or separates out or ionizes.}

The Table below shows some acids and thier Basicity 

	ACID	BASICITY
1.	Hydrochloric acid	1 or Monobasic
2.	Trioxonitrate V acid	1 or Monobasic
3	Tetraoxosulphate VI acid	2 or Dibasic
4	Trioxocarbonate IV acid	2 or Dibasic
5	Trioxophosphate V acid	3 or tribasic

PHYSICAL PROPERTIES OF ACID

1. They have a sour taste.

2. They are corrosive in nature especially the strong acid.

3. In aqueous solution, they conduct electricity.

4. Most acids are colourless

CHEMICAL PROPERTIES OF ACID

1.      Reaction with metals: They react with metals to liberate hydrogen gas and salt of metal i.e

QAcid    +    Metal → Salt + Hydrogen gas.

 E.g.  2HCl_(aq) + Zn_(s)→ZnCl_2(aq) + H_2(g)

 H₂SO_4(aq) + Mg_(s)→MgSO_4(aq) + H_2(g)

2. They react with soluble bases to form salt and water only. This reaction is known as neutralization.

      Acid + Base → salt + water

  E.g  

H₂SO_4(aq) + 2KOH_(aq) → K₂SO_4(aq) + 2H₂O_(l)

   2HCl_(aq) + CaO_(s) →CaCl_2(aq) + H₂O_(l)

3.  They react with  trioxocarbonates (iv) salts to liberate carbon (iv) oxide, salt and water i.e.

    Acid +  trioxocarbonate (iv) → Salt + Water + CO_2(g)

  E.g  2HCl_(aq) + Na₂CO_3(aq) → 2NaCl_(aq) + H₂O_(l) + CO_2(g)

PREPARATION OF ACIDS

Acid can be prepared by using the following methods:

1.      Dissolving an acid anhydride in water: Acid anhydride is oxides of non-metal that dissolve in water to produce the corresponding acids e.g SO₂, CO₂, NO₂, SO₃.

SO_2(g) + H₂O_(l)   →     H₂SO_3(aq)

CO2 +  H₂O_(l) →    H₂CO_3(aq)

SO_3(g) + H₂O_(l) →    H₂SO_4(aq

2. Combination of constituent elements.

(a). Burning hydrogen in chlorine, in the presence of activated charcoal as the catalyst, yields HCl gas which dissolves readily in water to give HCl acid.

                 _{Activated charcoal}
  H2+ Cl_2(g)      →       2HCl_(g)

                            _Platinum
     H_2(g) + Br_2(g)      →      2HBr_(g)

(3). By displacement of a weak or more volatile acid from its salt by a stronger or less volatile acid. For Example

Displacement of the more volatile hydrogen chloride from metallic chloride by the less volatile concentrated tetraoxosulphate (VI) acid.

NaCl_(s) + H₂SO_4(aq) → NaHSO_4(aq) + HCl_(aq)

Uses of acid

(1) Acids are useful chemicals, used in many industries to make other consumer chemicals such as fertilizers, detergent and drugs.

(2) They are used in industrial process as drying agents, oxidizing agents and catalysts.

USES OF ORGANIC AND INORGANIC ACID

	Acids	uses
1.	HCl	i.   Needed by industries to make chemicals used to remove rust. ii.  it is used in the production of batteries
2.	H2SO4	Used as an electrolyte in lead-acid accumulators
3	HNO3	Needed by industries for making fertilizers, explosives etc.
4	Boric acid	Used as mild antiseptic or germicide.  Used as mild antiseptic or germicide.
5	Tartaric acid	Used in making baking soda, soft drinks and health salts
6	Acetic acid (ethanoic acid)	Used in preserving food.
7	Citric acid	Used in making fruits juice.
8	Fatty acid	Used in the manufacture of soap. This process is known as saponification.
9.	Phosphoric acids	Used in most soft drinks as the main ingredients
10.

OBJECTIVE  QUESTIONS 

1. An acid is a substance that

A. accepts protons
B. donates protons
C. produces hydroxide ions in water
D. neutralizes bases only

2. Which of the following is a mineral acid?
A. Ethanoic acid
B. Citric acid
C. Hydrochloric acid
D. Lactic acid

3. Acids turn blue litmus paper
A. green
B. red
C. colourless
D. yellow

4. Which ion is responsible for the acidic property of acids?
A. OH⁻
B. Cl⁻
C. H⁺
D. Na⁺

5. Which of the following is a weak acid?
A. Sulphuric acid
B. Nitric acid
C. Hydrochloric acid
D. Ethanoic acid

6. The pH value of an acidic solution is
A. always greater than 7
B. equal to 7
C. less than 7
D. equal to 14

7. Which acid is present in vinegar?
A. Methanoic acid
B. Ethanoic acid
C. Citric acid
D. Tartaric acid

8. Acids react with metals to produce
A. salt and water
B. hydrogen and oxygen
C. salt and hydrogen
D. base and water

9. Which of the following acids is used in car batteries?
A. Nitric acid
B. Hydrochloric acid
C. Sulphuric acid
D. Ethanoic acid

10. Which substance can be used to neutralize an acid?
A. Salt
B. Alkali
C. Another acid
D. Distilled water

11. Which indicator gives a red colour in acidic solution?
A. Phenolphthalein
B. Methyl orange
C. Universal indicator (blue)
D. Litmus (blue)

12. What is formed when an acid reacts with a base?
A. acid and salt
B. salt and hydrogen
C. salt and water
D. base and water

13. Which of the following is a property of acids?
A. Bitter taste
B. Slippery feel
C. Sour taste
D. Soapy nature

14. Which acid is found in ant stings?
A. Oxalic acid
B. Ethanoic acid
C. Methanoic acid
D. Citric acid

15. Which gas is produced when acids react with carbonates?
A. Hydrogen
B. Oxygen
C. Carbon monoxide
D. Carbon dioxide

16. The strength of an acid depends on its
A. concentration only
B. colour
C. degree of ionization
D. taste

17. Which of the following is an organic acid?
A. Hydrochloric acid
B. Sulphuric acid
C. Nitric acid
D. Citric acid

18. Acid rain is mainly caused by the oxides of
A. nitrogen and sulphur
B. hydrogen and oxygen
C. carbon and hydrogen
D. sodium and chlorine

19. Which acid is commonly used in the manufacture of fertilizers?
A. Hydrochloric acid
B. tetraoxosulphate VI acid
C. Ethanoic acid
D. Trioxocarbonat IV acid

20. Which statement about acids is correct?
A. All acids are strong
B. Acids produce OH⁻ ions in water
C. Acids have pH values less than 7
D. Acids do not react with metals

21. The colour of phenolphthalein indicator in dilute HNO₃ is 

a. Colourless

b. Orange

c. Pink

d. Purple

22. When concentrated H₂SO₄, is added to NaCl(s), the gas evolved 
a. Bleaches damp blue litmus paper
b. Forms a white precipitate with AgNO_3(aq)
c. Forms a white precipitate with BaCl2(aq)
d. Turns moist blue litmus paper blue

23. Which of the following processes involves neutralization?
a. Hardening of oils 
b. Souring of milk
c. Charring of sugar
d. Liming of soils

24. Bees inject an acid substance when they sting. Which of the following chemical compounds could be used to treat bee stings?
a. CH₃COOH
b. NaHCO₃

c. C₂H₅OH
d. H₂O₂

25. Which of the following acid is dibasic
a. Hydrochloric acid
b. Trioxisulphate (IV) acid
c. Dioxonitrate V acid
d. Ethanoic acid

26. The pH values of the solutions resulting from the dissolution of oxides of elements M, N, O, P and Q in water are as indicated in the table below 

Oxide of	pH value
M	3
N	5
O	6
P	7
Q	9

Which of the above elements is likely to be a metal
a). M
b). N
c). O
d).P






THEORY QUESTIONS
1(a)i. What is an acid?

 ii. What is the name of the process used for the industrial preparation of tetraoxosulphate VI acid?

(iii). State the catalyst used in the process mentioned above 
 

iv. List three chemical properties of tetraoxosulphate (VI) acid.

2(a) What is the acid anhydride of each of the following acids? 

(i). H₂SO₄  (ii). HNO₃ 

 

WATER

TOPIC: WATER

WATER

Water is regarded as a universal solvent, because it can dissolve almost all other substances.

SOURCES OF WATER

The following are some of  the sources of water:

1.             Natural water: - Rainwater, Well water, Spring water and Sea water

2.             Treated water: - Distilled water, Pipe-borne water and chlorinated water.

STRUCTURE OF WATER

Water with the molecular formula H₂O, has Oxygen bonded to two hydrogen atoms. The oxygen atom with the  following electronic configuration: 1s² 2s² 2p⁴  has two lone pairs of electrons in the valence  (2s²2p²) and two unpaired electrons (2p_y¹2p_z¹). Each unpaired electron forms a covalent bond with one electron from a hydrogen atom. The water molecule has two lone pairs and two bonded pairs. Ideally, the four electron pairs should be directed towards corners of a tetrahedron. However, when lone pairs of electrons are located near another lone pair, the repulsion between them is so great that they tend to push the two bond pairs of electrons closer together. As a result, the bond angle in water is compressed to approximately 105^o, making the structure of the water molecule is V-shaped or angular shape.

                                                                            O

                                                                   H              H

LABORATORY PREPARATION OF WATER 

Water can be prepared in the  laboratory when  dry hydrogen gas is ignited in air. It burns with a pale blue flame to give steam, which will condense on contact with any cold surface to form water.

PHYSICAL PROPERTIES OF WATER

1.   Water boils at 100^oC and freezes at 0^oC

2.   It has a maximum density of 1gcm^-3 at 4^oC

3.   It is neutral to litmus.

CHEMICAL PROPERTIES

1.  Water reacts with electropositive metals to form alkalis and liberate hydrogen gas. E.g

Na_(s) + H₂O_(aq)→ NaOH_(aq)+ H_2(g)

  Mg & Zn react with steam to also liberate hydrogen gas

 Mg_(s) + H₂O_(g) → Mg(OH)_2(s) + H_2(g)

       Cu, Au, Ag, Hg do not react with water.

2.   Non-metal like chlorine reacts with water to form acid solution.

H₂O_(aq) + Cl_2(g)→ HCl_(aq) + HOCl_(aq)

TEST FOR WATER

1. White anhydrous copper (II) tetraoxosulphate (VI), it turns blue and 

2. Blue cobalt (II) chloride paper  turns pink in the presence of water.

 TREATMENT OF WATER FOR MUNICIPAL SUPPLY

The following are the processes of treating river water for town supply

1. Coagulation (or Floculation): Chemicals like potash alum, KAl(SO₄)₂, or sodium aluminate III, NaAlO₂ is added to water in a large settling tank. This causes the large dirt to coagulate or clog together¹¹¹¹

2. Sedimentation: The coagulated solid particles or flocs are allowed to settle in the settling tank to form sediments at the bottom of the tank.

3. Filtration: The water above the sediment still contains some suspended particles.  The water is passed through a filter bed of layers of sand to remove the remaining fine dirt particles.

4.  Chlorination (Disinfection): Chlorine is then added to the water to kill germs.

 Iodine and fluorine are also added as food supplements to prevent goiter and tooth decay respectively. 

 The treated water is then stored in a reservoir and distributed to the town.

HARDNESS OF WATER 

water may be grouped into hard water and soft water.

HARD WATER:- Hard water is any water that does not form lather (foam) easily in water. 

We have two types of Hardness 

 I. Temporary hardness and 

II. Permanent hardness 

I. Temporary hardness is caused by the presence of Ca(HCO3)2 or Mg(HCO3)2 

REMOVAL OF TEMPORARY

 HARDNESS

1.  Physical method: By boiling

Ca(HCO₃)_2(aq) → CaCO_3(s) + H₂O_(l) + CO_2(g)

2.  Chemical method: By using of slaked lime (calcium hydroxide solution)

                   Ca(HCO₃)_2(aq) + Ca(OH)_2(aq) →2CaCO_3(s)  + 2H₂O_(l)

3 Addition of washing soda :-

Ca(HCO₃)_2(aq)  +  Na₂CO_3(aq) → CaCO_3(s)  +  2NaHCO_{3 (aq)8}

EFFECTS OF TEMPORARY HARDNESS:  It causes

1. Furring of kettles and boilers.

2. Stalagmites and stalactites in caves.

PERMANENT HARDNESS

Permanent hardness  is caused by the presence of Ca2+ or  Ma2+ ions in the form of soluble tetraoxosulphate (VI) and chlorides (i.e. CaSO₄, MgSO₄, MgCl₂, CaCl₂)

Removal of permanent hardness: 

1. Physical method: by distillation.

⁰By chemical method only

1. Addition of washing soda          Na₂CO_3(aq) + CaSO_4(aq) → CaCO_3(s) + Na₂SO_4(aq)

2.  Addition of caustic soda

  2NaOH_(aq)+ CaSO_4(aq) → Ca(OH)_2(s)+  Na₂SO_4(aq)

3. Ion exchange resin

  CaSO_4(aq) + Sodium zeolite →Calcium zeolite + NaSO_4(aq)

           (insoluble)

ADVANTAGES OF HARD WATER

i.   It taste better than soft water because of the presence of ions

ii. Provides calcium for the development of bones and teeth of animals

iii.  It provides CaCO₃, that crab and snail use to build their shells.

iv. Reduce heart disease

v.  It does not dissolve lead, hence, it can be supplied in lead pipes. (it is less likely to cause corrosion in pipes.

DISADVANTAGES OF HARD WATER

i. It causes furring of kettles and boilers.

ii.  It wastes soap.

iii. It cannot be used in dying and tanning.

iv. Effects is seen in stalactites and stalagmite

v. It cause dry itchy skin

   

Objective questions 

1. Treated town water undergoes the following steps except 

(A). coagulation 

(B). precipitation 

(C). sedimentation 

(D). chlorination

 

2.  Water is temporarily hard because it contains 

(A). CaSO₄

(B). MgSO₄

(C). Chlorine 

(D). Ca(HCO₃)₂

 

3. Temporary hardness of water is removed by the use of one of the following 

(A). boiling

 (B). use of use of Ca(OH)₂  

(C). use of Na₂CO₃ 

(D). use of alum

 

4. A substance that turns white anhydrous CuSO₄ blue is

 (A). water 

(B) liquid ammonia 

(C). hydrochloric acid 

(D). molten sulphur

 

5. Distilled water is different from deionized water because 

(A). distilled water is a product of condensed steam while deionized water is filtered laboratory water 

(B). distilled water is always pure and sold in packs while deionized is not packaged for consumption 

(C). distilled water is condensed steam, but deionized water is produced using ion-exchange resins which absorbs undesired ions. 

(D). distilled water is man-made while deionized water is both natural and artificial

6. When a sample of water was boiled, it lathered more readily with soap. it can be concluded that the sample most likely contained 

(a). magnesium and tetraoxosulphate (VI) 

(b). suspended solids 

(c). organic impurities 

(d). calcium hydrogentetraoxocarbonate (IV)

7.  What are the gases associated with the formation of acid rain? 

(a). CO₂ and HCl 

(a)  CO₂ and NO

(c). SO₂ and NO 

(d). which of the following processes will pollute water? 

(a) Exposure of a body of water to ultraviolet rays

(b) Discharge of industrial effluents into waterways

(c). Passage of river water through a sand bed 

(d). Addition of measured quantity of chlorine                                                    

SECTION B

1.     State the steps involved in the treatment of river water for town supply ?

2.     Give two ions that causes hardness of water?

3.      Write two equations to show the removal of permanent hardness of water?

4.      Mention two compounds that causes permanent hardness in water ?

5.      State two ways of removing permanent hardness in water?

6.       List two advantages of hard water and two disadvantages of hard water?