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Method:

  1. Pour limewater into one of the test tubes and seal with a rubber stopper.
  2. Carefully pour a small amount of hydrochloric acid into the remaining test tube.
  3. Add a small amount of sodium carbonate to the acid and seal the test tube with the rubber stopper.
  4. Connect the two test tubes with a delivery tube.
  5. Observe what happens to the colour of the limewater.
  6. Repeat the above steps, this time using sulfuric acid and calcium carbonate.

Observations:

The clear lime water turns milky meaning that carbon dioxide has been produced.

When an acid reacts with a carbonate a salt, carbon dioxide and water are formed. Look at the following examples:

  • Nitric acid reacts with sodium carbonate to form sodium nitrate, carbon dioxide and water. 2 HNO 3 + Na 2 CO 3 2 NaNO 3 + CO 2 + H 2 O
  • Sulfuric acid reacts with calcium carbonate to form 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. 2 HCl + CaCO 3 CaCl 2 + CO 2 + H 2 O

Acids and bases

  1. The compound NaHCO 3 is commonly known as baking soda. A recipe requires 1.6 g of baking soda, mixed with other ingredients, to bake a cake.
    1. Calculate the number of moles of NaHCO 3 used to bake the cake.
    2. How many atoms of oxygen are there in the 1.6 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 )
    3. Identify the reactant which acts as the Bronsted-Lowry base in this reaction. Give a reason for your answer.
    4. Use the above equation to explain why the cake 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 3 2 - + 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 acid in the stomach. The balanced equation for the reaction is: NaHCO 3 + HCl NaCl + H 2 O + CO 2 The hydrochloric acid in the stomach has a concentration of 1.0 mol.dm - 3 . Calculate the volume of the hydrochloric acid that can be neutralised by the antacid tablet. (DoE Grade 11 Paper 2, 2007)
  4. A learner is asked to prepare 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 .
    1. Calculate the mass of oxalic acid which the learner has to dissolve to make up the required standard solution. The leaner titrates this 0.2 mol.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 hydroxide solution.
    2. Calculate the concentration of the sodium hydroxide solution.
  5. A learner finds some sulfuric acid solution in a bottle labelled 'dilute sulfuric acid'. He wants to determine the concentration of the sulphuric acid solution. To do this, he decides to titrate the sulfuric acid against a standard potassium hydroxide (KOH) solution.
    1. What is a standard solution?
    2. Calculate the mass of KOH which he must use to make 300 cm 3 of a 0.2 mol.dm - 3 KOH solution.
    3. Calculate the pH of the 0.2 mol.dm - 3 KOH solution (assume standard temperature).
    4. Write a balanced chemical equation for the reaction between H 2 SO 4 and KOH.
    5. During the titration he finds that 15 cm 3 of the KOH solution neutralises 20 cm 3 of the H 2 SO 4 solution. Calculate the concentration of the H 2 SO 4 solution.
    (IEB Paper 2, 2003)

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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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