People with indigestion have too much hydrochloric acid in their stomach. Indigestion remedies contain a base that neutralises some of the acid.
A student compares three powdered indigestion remedies, A, B and C.
This is the student's method:
Put 25 cm³ of dilute hydrochloric acid into a conical flask and add a few drops of universal indicator.
Add one remedy, 0.2 g at a time, and swirl the flask after each addition.
Stop when the indicator turns green.
Record the total mass of remedy added.
The table shows the results.
| Remedy | Main substance in the remedy | Total mass of remedy added (g) | Observations |
|---|---|---|---|
| A | magnesium hydroxide | 0.4 | no fizzing |
| B | calcium carbonate | 0.8 | fizzing |
| C | sodium hydrogencarbonate | 1.2 | a lot of fizzing |
What colour is the universal indicator in the acid at the start?
Explain why the student stops adding remedy when the indicator turns green.
Complete the word equation for the reaction in remedy A.
magnesium hydroxide + hydrochloric acid → ...... + ......
The student concludes: "Remedy A is the best indigestion remedy."
Evaluate the student's conclusion and method.
Use the results and your knowledge of neutralisation.
53 exam-style questions on OCR GCSE Chemistry 3.3 Types of chemical reactions, covering 3.3.1 Oxidation and reduction in terms of oxygen, 3.3.2 Acids, alkalis and neutralisation, 3.3.3 The pH scale and measuring pH, 3.3.4 Oxidation and reduction in terms of electrons, 3.3.5 Dilute and concentrated, weak and strong acids, and 3.3.6 Hydrogen ion concentration and pH. Each one has a worked solution and a mark scheme showing where the marks go.