6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Learn this properly: Relative Formula MassIn industry, two different reactions can both be used to make the same useful product. A chemist must choose between them.
Discuss how a chemist would use percentage yield and atom economy to decide which reaction is the better choice for large-scale, sustainable manufacture. In your answer you should explain what each measure tells you, how each is calculated, and why both matter for cost and the environment. (6 marks)
Aluminium reacts with oxygen to form aluminium oxide:
4Al+3O2→2Al2O3
A factory reacts 54 g of aluminium with excess oxygen.
(Relative atomic masses: Al = 27; O = 16.)
(a) Calculate the number of moles of aluminium in 54 g. (2 marks)
(b) Calculate the maximum mass of aluminium oxide (Al2O3) that could be made. Show your working. (2 marks)
A solution of sodium hydroxide (NaOH) was made by dissolving the solid in water.
The solution has a concentration of 2.0 mol/dm³.
(Relative atomic masses: Na = 23; O = 16; H = 1.)
(a) Calculate the number of moles of NaOH in 250 cm³ of this solution. (2 marks)
(b) Convert the concentration of the solution into g/dm³. (1 mark)
In a titration, a student used a pipette to place 25.0 cm³ of sodium hydroxide solution into a conical flask. They titrated it against hydrochloric acid of concentration 0.200 mol/dm³.
The equation for the reaction is:
HCl+NaOH→NaCl+H2O
The mean titre of acid needed was 20.0 cm³.
(a) Calculate the number of moles of HCl used. (1 mark)
(b) Calculate the concentration of the sodium hydroxide solution in mol/dm³. Show your working. (2 marks)
A compound is found by analysis to contain 2.4 g of carbon and 0.8 g of hydrogen, and nothing else.
(Relative atomic masses: C = 12; H = 1.)
Determine the empirical formula of the compound. Show your working. (2 marks)
At room temperature and pressure (rtp), 1 mole of any gas occupies a volume of 24 dm³.
A reaction produces 0.50 mol of carbon dioxide gas.
Calculate the volume of carbon dioxide produced at rtp, in dm³. (1 mark)