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Biology · May / June 2024 · Paper 62 · Question 1

0610

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The question as text

A student investigated the effect of acid concentration on the rate of diffusion in agar jelly. The student was given three test￿tubes containing bromothymol blue indicator in agar jelly. Bromothymol blue is a blue indicator that turns yellow in the presence of an acid. The student used this method: Step 1 label three beakers A1, A2 and A3 Step 2 put 20 cm3 of 1 mol per dm3 hydrochloric acid solution into beaker A1 Step 3 put 2 cm3 of 1 mol per dm3 hydrochloric acid solution into beaker A2 Step 4 add 18 cm3 of distilled water to the hydrochloric acid solution in beaker A2 Step 5 use a clean syringe to transfer 2 cm3 of the solution from beaker A2 to beaker A3 Step 6 add 18 cm3 of distilled water to beaker A3 Table 1.1 shows the final concentrations of the hydrochloric acid solution in each beaker. Table 1.1 beaker final concentration of the hydrochloric acid solution / mol per dm3 final volume of the solution / cm3 A1 1.00 20 A2 0.10 ………. A3 0.01 20

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  • 1(a)(i)[1]

    20 (cm3) ;

  • 1(a)(ii)[4]

    1

    table drawn with headings underlined

    and

    minimum of two, columns / rows ;

    2

    suitable headings with units for:

    (final acid) concentration (in) mol per dm3

    and

    height (of yellow agar) (in) mm / cm ;

    3

    three concentrations and three heights recorded ; 4

    all heights correct ±1 mm ;

  • 1(a)(iii)[1]

    an increase in the concentration (of the hydrochloric acid solution) increases the rate of diffusion ;

    ora

  • 1(a)(iv)[2]

    IV: concentration (of hydrochloric acid solution) ;

    DV: height of yellow (agar) ;

  • 1(a)(v)[1]

    23 (°C) ;

  • 1(a)(vi)[1]

    any change in temperature would affect all three test-tubes equally / AW ;

  • 1(a)(vii)[2]

    any one from:

    use water instead of acid ;

    only add water to the agar jelly ;

  • 1(b)(i)[1]

    64 ;

  • 1(b)(ii)[4]

    axes labelled with units ;

    suitable linear scale and plotting area occupies at least half the grid in both directions ;

    five points plotted accurately ± half small square ; suitable line drawn ;

  • 1(b)(iii)[2]

    any indication on graph at 3 mm / indication of correct value on the time axis ;

    correct value recorded from candidate’s graph ;

  • 1(b)(iv)[2]

    any two from:

    temperature
    concentration of acid
    volume of acid
    type / pH, of acid
    type of agar
    density / solidity / concentration, of agar
    concentration of indicator
    volume of indicator
    type of indicator

    ;;

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