Everything Science Grade 11

CHAPTER 8. TYPES OFREACTIONS 8.1

• Nitric acid reacts withsodium carbonate to form sodium nitrate, carbon dioxide and water.

2HNO 3 + Na 2 CO 3 → 2NaNO 3 + CO 2 + H 2 O

• Sulphuric acid reacts with calcium carbonate toform calcium sulfate, carbon dioxide and water.

H 2 SO 4 + CaCO 3 → CaSO 4 + CO 2 + H 2 O

• Hydrochloric acid reacts with calcium carbonate to form calcium chloride, carbon dioxide and
  water.

2HCl + CaCO 3 → CaCl 2 + CO 2 + H 2 O

Exercise 8 - 2

1. The compound NaHCO 3 is commonly known asbaking soda. A recipe requires 1.6 g of baking
   soda, mixed with otheringredients, to bake a cake.

(a) Calculate the number of moles of NaHCO 3 used to bake the cake.

(b) How many atoms ofoxygen are there in the1.6 g of baking soda?

During the baking process, baking soda reacts with an acid to produce carbon dioxide and

water, as shown by the reaction equation below:

HCO− 3 (aq) + H+(aq)→ CO 2 (g) + H 2 O(l)

(c) Identify the reactantwhich acts as the Bronsted-Lowry base in this reaction. Give a reason

for your answer.

(d) Use the above equation to explain why thecake rises during this baking process.

(DoE Grade 11 Paper 2,2007)

2. Label the acid-base conjugate pairs in the following equation:

HCO− 3 + H 2 O� CO^23 −+ H 3 O+

3. A certain antacid tablet contains 22.0 g of baking soda (NaHCO 3 ). It is used to neutralise the
   excess hydrochloric acidin the stomach. The balanced equation for the reaction is:

NaHCO 3 + HCl→ NaCl + H 2 O + CO 2

The hydrochloric acid inthe stomach has a concentration of 1.0 mol.dm−^3. Calculate the vol-

ume of the hydrochloricacid that can be neutralised by the antacid tablet.

(DoE Grade 11 Paper 2,2007)

4. A learner is asked toprepare a standard solution of the weak acid, oxalic acid (COOH) 2 2H 2 O
   for use in a titration. The volume of the solution must be 500 cm^3 and the concentration 0.2
   mol.dm−^3.

(a) Calculate the mass of oxalic acid which the learner has to dissolve tomake up the required

standard solution. Theleaner titrates this 0.2mol.dm−^3 oxalic acid solution against a

solution of sodium hydroxide. He finds that 40 cm^3 of the oxalic acid solution exactly

neutralises 35 cm^3 of the sodium hydroxidesolution.

(b) Calculate the concentration of the sodium hydroxide solution.

5. A learner finds somesulphuric acid solution in a bottle labelled ’dilute sulphuric acid’. He wants
   to determine the concentration of the sulphuricacid solution. To do this, he decides to titrate
   the sulphuric acid against a standard potassiumhydroxide (KOH) solution.

(a) What is a standard solution?