CIE iGCSE Co-Ordinated Science C6.1 Physical and chemical changes Exam Style Questions Paper 4
Question
A student investigates the reaction between zinc and dilute nitric acid, HNO$_{2}$.
Zinc nitrate, Zn(NO$_{3}$)$_{2}$, and hydrogen gas, H$_{2}$, are made.
(a) Construct the balanced symbol equation for this reaction.
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(b) The student performs two reactions, X and Y, using different concentrations of nitric acid.
They use the same mass of zinc granules and the same temperature of nitric acid in each reaction.
Fig. 8.1 shows a graph of their results.
(i) State which reaction, X or Y, uses a higher concentration of nitric acid.
Use Fig. 8.1 to explain your answer.
reaction …………………………….
explanation …………………………………………………………………………………………………………
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(ii) Determine the average rate of reaction X during the first 50 seconds.
average rate = ………………………………………. cm$^{3}$/ s
(c) Reactions X and Y both produced 46cm$^{3}$ of hydrogen gas measured at room temperature and pressure (r.t.p.).
Calculate the mass of 46cm$^{3}$ of hydrogen gas.
The volume of one mole of any gas is 24dm$^{3}$ at room temperature and pressure (r.t.p.).
Show your working.
[M$_{4}$: H$_{2}$, $_{2}$]
mass of 46cm$^{3}$ of hydrogen gas = ……………………………………………… g
(d) The student repeats reaction Y at a higher temperature.
State and explain how the rate of reaction changes.
Use ideas about collisions between particles.
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▶️Answer/Explanation
Ans : 8(a) Zn + 2HNO$_{3}$ → Zn(NO$_{3}$)$_{2}$ + H$_{2}$ ;;
1 mark for correct formulae
1 mark for correct balanced equation
8(b)(i) (Y)
curve has a steeper gradient / reaction finishes sooner ;
8(b)(ii) (gradient calculation)16 ÷ 50 ;
0.32 (cm $^{3}$ / s) ;
8(c) (46 cm$^{3}$ =) 0.046 (dm$^{3}$) ;
(moles of H$_{2}$ = 0.046 ÷ 24 =) 0.0019 ;
(mass of H$_{2}$ = 2 × 0.0019 =) 0.0038 (g) ;
8(d) (reaction will be) faster ;
(because)
any two from:
molecules have higher (average) energy / molecules are moving faster ;
more molecules with activation energy ;
frequency of collision (of molecules) is higher / more collisions per second ;
more successful collisions ;