Brass is an alloy of copper and zinc. A student finds the percentage of zinc in a sample of brass. She adds 2.00 g of powdered brass to excess dilute hydrochloric acid. The zinc reacts but the copper does not.
Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)\mathrm{Zn(s)} + \mathrm{2HCl(aq)} \rightarrow \mathrm{ZnCl_{2}(aq)} + \mathrm{H_{2}(g)}Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)
She collects 240 cm3\mathrm{cm^{3}}cm3 of hydrogen at room temperature and pressure.
Explain why copper does not react with dilute hydrochloric acid.
Calculate the percentage by mass of zinc in the brass. Relative atomic mass: Zn = 65. One mole of any gas occupies 24 000 cm3\mathrm{cm^{3}}cm3 at room temperature and pressure.
Describe how the student could obtain a pure, dry sample of the copper left at the end, and state the mass of copper she should expect.
The manufacturer states that the brass contains 30.0 % zinc. Suggest one reason why the student's value is higher.
Brass is used to make water taps. Suggest two properties of brass that make it suitable for this use.
42 exam-style questions on Edexcel GCSE Chemistry 6.1 Transition metals, alloys and corrosion, covering 6.1.1 Properties of transition metals, 6.1.2 Corrosion and its prevention, and 6.1.3 Alloys and the uses of metals. Each one has a worked solution and a mark scheme showing where the marks go.