Rates of reaction

Question 4

A group of students investigated the reaction between zinc granules and dilute sulfuric acid:

\text{Zn}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{H}_2(g)

They wanted to determine how changing the concentration of sulfuric acid affects the rate of reaction. The teacher provided a solution labelled 100% sulfuric acid.

All experiments were performed at room temperature by timing how long it took to collect 50 cm³ of hydrogen gas.

The students kept the amount of zinc constant by using exactly 5 zinc granules in each experiment. State two other physical properties of the zinc granules that should be kept constant in each experiment.

[2]

The table below shows what each student wrote down in their lab notebook:

Student A (Reference): 'I used 5 zinc granules with 100% sulfuric acid and collected 50 cm³ of gas in 25 seconds.'
Student B: 'In my experiment there were 5 zinc granules and 80% sulfuric acid and I collected 50 cm³ of hydrogen gas by the end of the experiment.'
Student C: 'The zinc granules and 60% sulfuric acid formed 50 cm³ of gas in 42 seconds.'
Student D: 'I used 40% sulfuric acid and 5 zinc granules. It took 65 seconds to collect the gas.'
Student E: 'I collected 50 cm³ of gas in 80 seconds when I used 5 zinc granules.'

Identify the missing piece of information that each student (B, C, D, and E) failed to record.

[4]

The students repeated the experiment using a different supply of sulfuric acid. Their results are shown in the table below:

Percentage concentration of sulfuric acid (%)	Time to collect 50 cm³ of gas (s)	Rate of reaction ( $cm3/s\text{cm}^3/\text{s}$ )
10	90.9	0.55
30	71.4	0.70
50	41.7	1.20
70	29.4	1.70
90	22.7	2.20
100	20.8	2.40

Identify which concentration has an anomalous rate of reaction.

[1]

Suggest two experimental errors that could have caused this anomalous result.

[2]

Using a linear best-fit trend for the other five data points, estimate the rate of reaction at an acid concentration of 60%.

[2]

The table below shows what each student wrote down in their lab notebook:

Student A (Reference): 'I used 5 zinc granules with 100% sulfuric acid and collected 50 cm³ of gas in 25 seconds.'
Student B: 'In my experiment there were 5 zinc granules and 80% sulfuric acid and I collected 50 cm³ of hydrogen gas by the end of the experiment.'
Student C: 'The zinc granules and 60% sulfuric acid formed 50 cm³ of gas in 42 seconds.'
Student D: 'I used 40% sulfuric acid and 5 zinc granules. It took 65 seconds to collect the gas.'
Student E: 'I collected 50 cm³ of gas in 80 seconds when I used 5 zinc granules.'

Identify the missing piece of information that each student (B, C, D, and E) failed to record.

Percentage concentration of sulfuric acid (%)

Time to collect 50 cm³ of gas (s)

Rate of reaction (

cm3/s\text{cm}^3/\text{s}

)

90.9

0.55

71.4

0.70

41.7

1.20

29.4

1.70

22.7

2.20

100

20.8

2.40

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