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