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.
A reaction takes place between small pieces of a solid and a dilute acid.
Using collision theory, explain why each of the following increases the rate of the reaction:
A student carried out a titration. They used a pipette to place 25.0 cm³ of sodium hydroxide solution into a conical flask, and titrated it with hydrochloric acid of concentration 0.150 mol/dm³.
The equation is:
HCl+NaOH→NaCl+H2O
The mean titre of acid was 22.0 cm³.
(a) Calculate the number of moles of hydrochloric acid used. (2 marks)
(b) Calculate the concentration of the sodium hydroxide solution in mol/dm³. Show your working. (2 marks)
In a reaction to make a useful product, the theoretical (maximum) yield is 15.0 g. A student actually obtains 11.4 g of product.
(a) Calculate the percentage yield. (2 marks)
(b) Give one reason why the percentage yield is less than 100 %. (1 mark)
A student measured the volume of hydrogen gas produced over time when magnesium reacted with excess dilute hydrochloric acid. They plotted the volume of gas against time.
The graph was steepest at the start, then became less steep, and finally levelled off to a horizontal line.
Explain the shape of this graph. (3 marks)
A catalyst can be added to a reaction to increase its rate.
Explain how a catalyst increases the rate of a chemical reaction. (2 marks)
The Haber process is used to manufacture ammonia. It is a reversible reaction:
N2+3H2⇌2NH3
State what the symbol ⇌ tells you about this reaction. (1 mark)