Questions on pH regulation of the stomach

1. Give the equations for the reactions of aluminium hydroxide, magnesium hydroxide and sodium hydrogencarbonate with hydrochloric acid.

2. Two well known antacids go by the name of ‘Rennies’ and ‘Milk of magnesia’. Rennies are essentially calcium carbonate and Milk of magnesia is essentially magnesium hydroxide. If stomach acid has a pH of 2 calculate the mass of calcium carbonate required to neutralise 10 cm³ of stomach acid. Would more or less magnesium hydroxide (in grams) be required to neutralise the same amount of acid?

3. (a) Explain how heartburn is caused.

(b) One medicine that is stated to be safe for pregnant women to take hasthe trade name ‘Gaviscon cool’. The active ingredients in Gaviscon cool are sodium alginate, sodium hydrogencarbonate and calcium carbonate.

The advertising for Gaviscon states that it:

“forms a 'raft' over the stomach contents which helps prevent acid coming back up into the oesophagus (food pipe). As such it is effective at treating the classic symptoms of heartburn (a burning pain in the chest and mild acid regurgitation)."

Identify the ingredient that helps to “form a ‘raft’ over the stomach contents”.

4. Two drugs used to treat dyspepsia are ranitidine and omeprazole which are marketed under the trade names of Zantac and Prilosec respectively. Explain the different ways in which these two drugs function in the body.

5. The pK_a value for ethanoic acid is 4.76. Calculate the pH of the buffer solution formed when:

(a) 25.0 cm³ of 0.100 mol dm^-3 sodium hydroxide solution is added to 50.0 cm³ of 0.100 mol dm^-3 ethanoic acid solution.

(b) 0.500 g of sodium ethanoate is added to 50.0 cm³ of 0.100 mol dm^-3 ethanoic acid solution (assume no volume change occurs when the salt is added).

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