GCSEChemistry: Combined ScienceOCR GatewayExam Questions5. Monitoring & Controlling Chemical Reactions5.2 Controlling Reactions

Controlling Reactions (OCR Gateway GCSE Chemistry: Combined Science)

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5.2 Controlling Reactions

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5.2 Controlling Reactions

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11 mark

A student investigates the reaction between sodium carbonate and dilute nitric acid.

She does all the experiments using the

  • same temperature
  • same mass of sodium carbonate
  • same volume of nitric acid.

She uses four different concentrations (A, B, C and D) of nitric acid.

For each concentration, she measures the time for the reaction to complete.

Which concentration of nitric acid gives the fastest reaction?

Concentration Time for reaction to complete (in seconds)
A 41
B 74
C 135
D 67

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    1
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    The rate of a reaction was monitored by recording the volume of gas produced every 5 seconds.

    TIUbhf1t_q1

    What is the mean rate of reaction in the first 10 seconds of the reaction, in cm3/s?

    • 2.9

    • 3.0

    • 3.5

    • 2.5

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    2
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    Hydrogen peroxide, H2O2, quickly decomposes to produce water and oxygen when a catalyst is added to the solution:

    2H2O2 (aq) → 2H2O (l)  + O2 (g)

    The volume of gas produced was measured and is shown in the graph below:

    TIUbhf1t_q1

    Which statement is not true for this reaction?

    • The reaction finishes after 30 seconds

    • The mean rate of reaction in the first 5 seconds is 2.5 cm3/s

    • The final volume of gas produced is 60 cm3

    • The concentration of the hydrogen peroxide decreases during the reaction

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    3
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    Magnesium metal reacts with an excess of hydrochloric acid solution to form magnesium chloride and hydrogen:

    Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

    Which of the following will not increase the rate of this reaction?

    • Increase the temperature of the acid

    • Increase the surface area to volume ratio of the pieces of magnesium

    • Increase the concentration of the hydrochloric acid

    • Increase the volume of hydrochloric acid solution used

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    41 mark

    Catalysts are often used in chemical reactions.

    Which letter represents two correct features of catalysts?

      Feature 1 Feature 2
    A Lower activation energy for the reaction More products made in total
    B Alternative pathway for the reaction is provided Not used up over the course of the reaction
    C Makes industrial processes cheaper Metal catalysts are cheap to buy
    D Reduce the overall energy change of the reaction Can be present in biological systems as enzymes

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      51 mark

      Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide:

      CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)

      Which statement is not true if the temperature of the reaction decreases?

      • The frequency of the collisions between particles decreases

      • The collisions are less energetic

      • The activation energy increases

      • There are fewer particles with the minimum energy to react

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      6
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      Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas:

      Mg (s) + 2HCl (aq) rightwards arrowMgCl2 (aq) + H2 (g)

      During the first 10 s of the reaction, 1.2 g of magnesium was used up.

      Calculate the mean rate of reaction in mol/s for this part of the reaction.

      The relative atomic mass, Ar, of H is 1, of Mg is 24 and of Cl is 35.5.

      • 2.9 mol/s

      • 2.0 mol/s

      • 0.05 mol/s

      • 0.005 mol/s

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      71 mark

      The rate of a reaction can be changed by adding a catalyst to the reaction mixture.

      Which line of the table shows how the rate of reaction and the mass of the catalyst change as the reaction takes place?

        Change in rate of reaction Change in mass of catalyst
      A decreases no change
      B no change decreases
      C increases no change
      D increases decreases

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        81 mark

        Which statement about catalysts is correct?

        • A catalyst decreases the activation energy of a reaction.

        • A catalyst increases the activation energy of a reaction.

        • A catalyst increases the time for a reaction to go to completion.

        • A catalyst slows down a reaction.

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        91 mark

        A student investigates the decomposition of hydrogen peroxide.

        2H2O2 (aq) → 2H2O (l) + O2 (g)

        0.2 g of oxygen gas is produced in the reaction.

        The student uses 0.5 g of manganese(IV) oxide as a catalyst in the reaction.

        How much manganese(IV) oxide remains at the end of the reaction?

        • 0.2 g

        • 0.3 g

        • 0.5 g

        • 0.7 g

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        101 mark

        Enzymes are a type of catalyst.

        Which of the following catalysts is an example of an enzyme?

        • Amylase – a catalyst found in human saliva.

        • Iron – a catalyst used in the Haber process.

        • Manganese(IV) oxide – a catalyst used in the decomposition of hydrogen peroxide.

        • Vanadium(V) oxide – a catalyst used in the Contact process.

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        11
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        A student investigates the reaction between calcium carbonate and hydrochloric acid.

        He measures the total volume of gas made every minute.

        Look at the graph. It shows his results for the experiment.

        q8-paper-4-specimen-2016-ocr-gcse-chem

        What is the rate of reaction between 0 and 2 minutes, in cm3/minute?

        • 7.5

        • 15

        • 30

        • 60

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        121 mark

        A catalyst can be used to increase the rate of a reaction.

        Which graph shows the mass of the catalyst as the reaction takes place?

        • q8a-paper-4-june-2019-ocr-gcse-chem

        • q8b-paper-4-june-2019-ocr-gcse-chem

        • q8c-paper-4-june-2019-ocr-gcse-chem

        • q8d-paper-4-june-2019-ocr-gcse-chem

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        13
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        A student investigates the reaction between 1.0 g of calcium carbonate and 20 cm3 of 1.0 mol/dm3 hydrochloric acid at 25 ºC.

        The student does two experiments.

        • He uses different sized pieces of calcium carbonate for each experiment.
        • The rate of reaction is greater in the first experiment.

        Which is the best explanation for this result?

        • Large pieces of calcium carbonate have a larger surface area resulting in less frequent collisions.

        • Large pieces of calcium carbonate have a smaller surface area resulting in more frequent collisions.

        • Small pieces of calcium carbonate have a larger surface area resulting in less frequent collisions.

        • Small pieces of calcium carbonate have a larger surface area resulting in more frequent collisions.

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        11 mark

        A student investigates the reaction between zinc and dilute sulfuric acid.

        He measures the time taken to collect 50 cm3 of hydrogen gas. This time is 65 seconds.

        The student investigates four substances which are possible catalysts for the reaction.

        Substance Appearance of
        substance        		 Time to collect 50 cm3
        of hydrogen (g)        		 Other observations
        A red-brown powder 19 red-brown powder remains
        B blue solid 15 colourless solution formed
        C red-brown lumps 65 red-brown lumps remain
        D white solid 65 colourless solution formed

        Which substance, A, B, C or D, is a catalyst for the reaction?

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          21 mark

          The rate of reaction of marble chips with dilute hydrochloric acid depends on the surface area of the marble chips.

          Which surface area of the marble chips gives the highest rate of reaction?

          • 0.673 mm2

          • 1030 mm2

          • 2.18 × 103 mm2

          • 4.98 × 10–2 mm2

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