A manufacturer checks the rate at which antacid granules neutralise stomach acid. Fig. 1 shows the pH probe placed in a beaker while a stirrer mixes the sol...
Question 1 Report
A manufacturer checks the rate at which antacid granules neutralise stomach acid. Fig. 1 shows the pH probe placed in a beaker while a stirrer mixes the solution. Table 1 records pH values after a fixed mass of granules is added.
| Time / s | pH |
|---|---|
| 0 | 1.5 |
| 15 | 2.8 |
| 30 | 4.1 |
| 45 | 5.0 |
| 60 | 5.3 |
| 75 | 5.3 |
(a) What does the rise in pH show about the acid solution? [1]
(b) Use Table 1 to state when the pH stops changing. [1]
(c) Suggest why stirring can increase the rate of neutralisation. [2]
(d) Give two variables that should be controlled when comparing different antacid brands. [2]
Answer Details
- (a) The rising pH shows that the solution becomes less acidic, so its hydrogen ion concentration decreases. [1]
- (b) The pH is 5.3 at both 60 s and 75 s, so it stops changing after 60 s. [1]
- (c) Stirring brings fresh acid into contact with the antacid granules [1], increasing the frequency of collisions [1].
- (d) Any two appropriate controls are: mass of antacid [1], volume or concentration of acid [1], temperature [1], or particle size [1]. These must be kept constant so that brand is the only variable changed.
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