A student investigated the reaction between calcium carbonate (marble chips) and dilute hydrochloric acid. The equation for the reaction is:
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g) \text{CaCO}_3(\text{s}) + 2\text{HCl}(\text{aq}) \rightarrow \text{CaCl}_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g}) CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)The student used a conical flask connected to a gas syringe. They added 30 cm330\text{ cm}^330 cm3 of hydrochloric acid to a chosen mass of calcium carbonate chips, quickly inserted the stopper, and recorded the volume of gas collected after the reaction finished. They repeated this for several different masses of calcium carbonate. The table below shows the volume of gas collected in four trials using a mass of 2.0 g2.0\text{ g}2.0 g of calcium carbonate chips:
| Trial | Volume of gas produced (cm3\text{cm}^3cm3) |
|---|---|
| 1 | 42 |
| 2 | 45 |
| 3 | 18 |
| 4 | 44 |
Answer the following questions:
Identify the gas produced and collected in this investigation.
What was the independent variable in this investigation?
Give one control variable that must be kept constant to ensure a fair test.
Which trial gave an anomalous result? Calculate the mean volume of gas produced using only the non-anomalous trials (give your answer to 1 decimal place).
Suggest one practical error that could explain this anomalous result.
53 exam-style questions on AQA GCSE Chemistry 3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, covering 3.1.1 Conservation of mass and balanced chemical equations, 3.1.2 Relative formula mass, 3.1.3 Mass changes when a reactant or product is a gas, and 3.1.4 Chemical measurements. Each one has a worked solution and a mark scheme showing where the marks go.