Acids and Bases
Acids and bases are important to chemistry. We use them every day, like when we clean with soaps and detergents or bake with baking soda. There are two types of corrosive things: acids and bases (alkaline earth metal chemical elements). Any compound with a pH value from 0 to 7 is considered acidic, and any compound with a pH value from 7 to 14 is considered basic. A base is called a proton acceptor, while an acid is called a proton donor.
Definition: Acidic things are usually easy to spot because they taste sour. Acids are made up of molecules that can give up an H+ ion and still have positive energy after losing the H+. It is known that acids will turn blue litmus paper red.
Bases, on the other hand, taste and feel bitter and slimy. A base that can be dissolved in water is an alkali. Salts are made when these things have a chemical reaction with acids. Red litmus has been seen to turn blue when put on bases.
Acids and Bases Chemistry Questions with Solutions
Q1. Which one of the following is the strongest acid?
a) CH2ClCOOH
b) CH3COOH
c) CHCl2COOH
d) CCl3COOH
Correct Answer. (d) CCl3COOH
Explanation. Strong acid means weak conjugate base. CCl3COO– < CHCl2COO– < CH2ClCOO– < CH3COO–. Therefore, the strongest acid is CCl3COOH.
Q2. Lime water is-
a) CaO
b) Ca(OH)2
c) CaCO3
d) CaCI2
Correct Answer. (b) Ca(OH)2
Explanation. A saturated aqueous solution of calcium hydroxide is known as limewater.
Q3. The chemical formula of caustic potash is–
a) NaOH
b) Ca(OH)2
c) NH4OH
d) KOH
Correct Answer. (d) KOH
Explanation. Potassium hydroxide, also known as caustic potash, is an inorganic compound with the formula KOH.
Q4. Bleaching powder gives the smell of chlorine because it-
a) is unstable.
b) gives chlorine on exposure to the atmosphere.
c) is a mixture of chlorine and slaked lime.
d) contains an excess of chlorine.
Correct Answer. (d) contains an excess of chlorine.
Q5. Arrange these acids in order of increasing strength.
acid A: pKa = 1.52
acid B: pKa = 6.93
acid C: pKa = 3.86
Given solutions with the same initial concentration of each acid, which would have the highest percent ionization?
Answer. Acids are listed in ascending order of strength: acid B < acid C < acid A. Acid A has the highest percent of ionisation given the same initial concentration of each acid because it is the strongest acid.
Q6. Arrange these bases in order of increasing strength:
base A: pKb = 13.10
base B: pKb = 8.74
base C: pKb = 11.87
Given solutions with the same initial concentration of each base, which would have the highest percent ionization?
Answer. Bases are listed in ascending order of strength: base A < base C < base B. Since base A is the weakest base, it has the highest percent of ionisation in solutions with the same initial concentration of each base.
Q7. (a) Write the name given to bases that are highly soluble in water. Give an example.
(b) How is tooth decay related to pH? How can it be prevented?
(c) Why does bee sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?
Answer. (a) Alkali, such as NaOH (Sodium hydroxide).
(b) A lower pH in the mouth promotes the growth of bad bacteria, which eventually leads to tooth decay.
It is preventable by avoiding foods that cause acidity.
(c) It is caused by formic acid. Formic acid is neutralised by sodium hydrogen carbonate (baking soda), giving relief.
Q8. “Sodium hydrogen carbonate is a basic salt”. Justify the statement. How is it converted into washing soda? Explain.
Answer. Sodium hydrogen carbonate is a salt formed by the reaction of sodium hydroxide (a strong base) and carbonic acid (weak acid). It is a basic salt. Heating and crystallisation are used to convert it to washing soda.
2NaHCO3 → Na2CO3 → CO2 +H2O.
Q9. What are the conjugate bases of the Bronsted acids HF, H2SO4, and HCO3–?
Answer. The conjugate bases for the Bronsted acids are F–, HSO4–, and CO32–.
Q10. Why do 1 M HCl solutions have a higher concentration of H+ ions than 1M CH3COOH solution?
Answer. HCl is more strong than CH3COOH. There is complete dissociation of HCl, which produces more H+ ions than CH3COOH, a weak acid. The concentration is determined by the presence of H+ ions. As a result, 1 M HCL has a greater concentration than 1 M CH3COOH.
Q11. How is the concentration of hydroxide ions(OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer. When a base is dissolved in a sodium hydroxide solution, the concentration of OH– ions per unit volume in the solution increases.
Q12. Give Arrhenius’s definition of an acid and a base.
Answer. Acids are defined by Arrhenius as substances that release H+ ions when dissolved in water.
Bases are substances that, when dissolved in water, release OH– ions.
Q13. What do you mean by the water of crystallization of a substance? Describe an activity to show that blue copper sulphate crystals contain water of crystallization.
Answer. The fixed number of water molecules present in one formula unit of salt in its crystalline form is referred to as water of crystallisation.
CuSO4.5H2O is an example.
It means that one formula unit of copper sulphate contains five water molecules.
Activity to demonstrate the crystallisation of water:
1) Place a few copper sulphate crystals in a dry test tube and heat it.
2) We see water droplets on the test tube walls, and the salt turns white.
3) Place 2 – 3 drops of water on the heated copper sulphate sample.
4) We notice that the blue colour of copper sulphate crystals has been restored.
Reason:
1) In the above activity, copper sulphate crystals that appear to be dry contain water of crystallisation; when heated, the water present in the crystals evaporates and the salt turns white.
2) The blue colour returns when the crystals are moistened with water.
Q14. State the reason for the following statements:
(i) Tap water conducts electricity whereas distilled water does not.
(ii) Dry hydrogen chloride gas does not turn blue litmus red whereas dilute hydrochloric acid does.
(iii) During the summer season, a milkman usually adds a very small amount of baking soda to fresh milk.
(iv) For a dilution of acid, acid is added into water and not water into acid.
(v) Ammonia is a base but does not contain a hydroxyl group.
Answer.
(i) Tap water contains ions that conduct electricity, whereas distilled water does not.
(ii)While dry HCl does not form ions, it does produce H+ and Cl–.
(iii) Baking soda prevents milk from converting to lactic acid, which causes milk to sour.
(iv) Adding water to acid produces a strong exothermic reaction. As a result, water is slowly added to acid while it cools.
(v) Because ammonia dissolves in water and forms H, it is basic in nature.
Q15. (i) Explain why is hydrochloric acid a strong acid and acetic acid, is a weak acid. How can it be verified?
(ii) Explain why the aqueous solution of an acid conducts electricity.
(a) Identify the most acidic and most basic solutions.
(b) Arrange the above four solutions in the increasing order of H+ ion concentration.
(c) State the change in colour of pH paper on dipping in solutions C and D.
Answer.
(i) In aqueous solution, HCl is completely ionised, whereas acetic acid is partially ionised. With pH paper, HCl produces a dark red colour, whereas CH3COOH produces an orange colour
(ii) This is due to acid ionisation in an aqueous solution, and these ions conduct electricity.
(a) ‘A’ is the most acidic, while ‘C’ is the most basic.
(b) C (10–12) < B (10–9) < D (10–7) < A (10–6)
(c) pH paper turns blue in ‘C’ and green in ‘D.’
Q.16 With the help of an example explain what happens when a base reacts with a non- metallic oxide. What do you infer about the nature of non-metal oxide? (Board Term I, 2017)
Answer:
Oxides of non-metals react with bases to form salt and water. For example, the reaction between carbon dioxide and calcium hydroxide. Calcium hydroxide, which is a base, reacts with carbon dioxide to produce salt and water.
Hence, oxides of non-metals are acidic in nature.
