Solution pH Gas volume after 60 s / cm3 Observation dilute hydrochloric acid 1 38 magnesium dissolves rapidly dilute ethanoic acid 3 11 slow bubbles water 7...
Question 1 Report
| Solution | pH | Gas volume after 60 s / cm3 | Observation |
|---|---|---|---|
| dilute hydrochloric acid | 1 | 38 | magnesium dissolves rapidly |
| dilute ethanoic acid | 3 | 11 | slow bubbles |
| water | 7 | 0 | no visible change |
| sodium chloride solution | 7 | 0 | no visible change |
The table below shows observations made when a student added equal masses of magnesium ribbon to equal volumes of four aqueous solutions at 20 degrees C. The student collected any gas in an inverted measuring tube. Each tube was cleaned before use. The solutions were not all acids, although each was clear at the start.
| Solution | pH | Gas volume after 60 s / cm3 | Observation |
|---|---|---|---|
| dilute hydrochloric acid | 1 | 38 | magnesium dissolves rapidly |
| dilute ethanoic acid | 3 | 11 | slow bubbles |
| water | 7 | 0 | no visible change |
| sodium chloride solution | 7 | 0 | no visible change |
(a) Which solution has the greatest concentration of hydrogen ions? [1]
(b) Give the name of the gas collected from magnesium and hydrochloric acid. [1]
(c) State two observations showing that a reaction occurs in the first tube. [2]
(d) Explain why ethanoic acid produces less gas than hydrochloric acid in 60 s. [3]
Answer Details
(a) Dilute hydrochloric acid has the greatest hydrogen-ion concentration: it has the lowest pH, 1. [1]
(b) Magnesium reacting with hydrochloric acid produces hydrogen. [1]
(c) Two valid observations are bubbles/fizzing, magnesium dissolving or becoming smaller, and gas being collected. [2]
(d) Ethanoic acid is a weak acid. It only partly ionises in water, so the same volume has fewer hydrogen ions available to react with magnesium in 60 seconds. Therefore it produces less hydrogen gas than hydrochloric acid. [3]
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