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Kami Export - Rate of Reaction 1 QP

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Module

Biological psychology (5PSYC002)

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University

University of Westminster

Academic year: 2019/2020

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Khamis Othoman Mohammed

University of Westminster

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1 When aqueous sodium thiosulfate and dilute hydrochloric acid are mixed, a precipitate

of insoluble

sulfur is produced. This makes the mixture difficult to see through.

Na 2

S

O

(aq) + 2HCl (aq)  S(s) + 2NaCl (aq) + H 2

O(l) + SO 2

(g)

The time taken for the cross to disappear from view is measured.

A student adds the following volumes of aqueous sodium thiosulfate, dilute

hydrochloric acid and

distilled water to the conical flask.

The time taken for the formation of the precipitate of sulfur to make the cross

disappear from view is recorded.

experimen

t number

volume of

sodium

thiosulfate

/ cm

volume of

hydrochloric acid

/ cm

volume of

distilled water

/ cm

time taken for

cross to

disappear from

view / s

1 10 10 40 56

2 20 10 30 28

3

(a) State the order in which the aqueous sodium thiosulfate, hydrochloric acid and

distilled water

should be added to the flask.

.......................................................................................................................................

.............

.............................................................................................................................. [1]

(b) In experiment 3 the student wanted the sodium thiosulfate to be double the

concentration used in experiment 2.

(i) Complete the table to show the volumes which should be used and the

expected time taken for the cross to disappear from view in experiment 3.

[2]

(ii) Use collision theory to explain why increasing the concentration of sodium

thiosulfate would change the rate of reaction.

................................................................................................................................

.............

................................................................................................................................

.............

................................................................................................................................

.............

....................................................................................................................... [2]

Use collision theory to explain why the rate of reaction would increase.

......................................................................................................................................

..............

......................................................................................................................................

..............

......................................................................................................................................

..............

.............................................................................................................................. [3]

[Total: 8]

P h y s i c s A n .

d ..

M

...

a ..

t .

h ..

s ..

T

..

u ..

t .

o ..

r .

.

c ..

o ..

.......................................................................................................................................................

....................................................................................................................... [1]

(iv) Where is hydrogen produced in the electrolytic cell?

(v) Describe a test for chlorine.

test ......................................................................................................................................

result ...................................................................................................................................

[2]

(f) The electrolysis of concentrated aqueous sodium chloride can be represented by

the following word equation.

sodium chloride + water  sodium hydroxide + hydrogen +

chlorine Construct a chemical equation to represent this reaction. Do not

include state symbols.

............................................................................................................................. [2]

(g) State one use of

chlorine, ......................................................................................................................

...............

sodium hydroxide,

.....................................................................................................................

hydrogen. ................................................................................................................................

...

[3]

[Total: 18]

....................................................................................................................... [1]

................. mol [1]

(ii) Use your answer to (c)(i) and the equation to calculate the number of moles of

oxygen produced in the reaction.

2H

O

(aq)  2H 2

O(l) + O 2

(g)

................. mol [1]

(iii) Calculate the volume (at r.t.) of oxygen produced.

................. dm

[1]

(iv) What would be the effect on the volume of oxygen produced if the mass of

catalyst was increased?

....................................................................................................................... [1]

(v) Deduce the volume of oxygen that would be produced if 20 cm

of 0 mol /

hydrogen peroxide was used instead of 20 cm

of 0 mol / dm

hydrogen peroxide.

................. dm

[1]

20 40 60 80 100

gas syringe hydrochloric acid

zinc foil

4 (a) The reactions between metals and acids are redox reactions.

Zn + 2H

 Zn

(i) Which change in the above reaction is oxidation, Zn to Zn

or 2H

to H 2

?

Give a reason for your choice.

.................................................................................................................................

............

....................................................................................................................... [2]

(ii) Which reactant in the above reaction is the oxidising agent? Give a reason for

your choice.

.................................................................................................................................

............

....................................................................................................................... [2]

(b) The rate of reaction between a metal and an acid can be investigated using the

apparatus shown below.

A piece of zinc foil was added to 50 cm

of hydrochloric acid, of concentration 2.

mol / dm

. The acid was in excess. The hydrogen evolved was collected in the gas

syringe and its volume measured every minute. The results were plotted and

labelled as graph 1.

graph 2 (with copper)

volume

0

time

The experiment was repeated to show that the reaction between zinc metal and

hydrochloric acid is catalysed by copper. A small volume of aqueous copper(II)

graph 1

chloride was added to the acid before the zinc was added. The results of this

experiment were plotted on the same grid and labelled as graph 2.

20406080100

oxygen collects

in syringe

sodium chlorate(I) solution

5 (a) Sodium chlorate(I) decomposes to form sodium chloride and oxygen. The rate of

this reaction is very slow at room temperature provided the sodium chlorate(I) is

stored in a dark bottle to prevent exposure to light.

2NaCl O  2NaCl + O 2

The rate of this decomposition can be studied using the following experiment.

Sodium chlorate(I) is placed in the flask and 0 g of copper(II) oxide is added.

This catalyses the decomposition of the sodium chlorate(I) and the volume of

oxygen collected is measured every minute. The results are plotted to give a

graph of the type shown below.

volume

of oxygen

0

time

(i) Explain why the gradient (slope) of this graph decreases with time.

.................................................................................................................................

............

....................................................................................................................... [2]

(ii) Cobalt(II) oxide is a more efficient catalyst for this reaction than

copper(II) oxide. Sketch, on the grid, the graph for the reaction

catalysed by cobalt(II) oxide.

All other conditions were kept constant. [2]

(iii) What can you deduce from the comment that sodium chlorate(I) has to be

shielded from light?

................................................................................................................................

.............

....................................................................................................................... [1]

(iv) Explain, in terms of collisions between particles, why the initial gradient

would be steeper if the experiment was repeated at a higher temperature.

................................................................................................................................

.............

................................................................................................................................

.............

................................................................................................................................

.............

....................................................................................................................... [3]

(b) The ions present in aqueous sodium chloride are Na

(aq), Cl

(aq), H

(aq) and OH

(aq).

The electrolysis of concentrated aqueous sodium chloride forms three products.

They are hydrogen, chlorine and sodium hydroxide.

(i) Explain how these three products are formed. Give ionic equations for the

reactions at the electrodes.

................................................................................................................................

.............

................................................................................................................................

.............

................................................................................................................................

.............

................................................................................................................................

.............

....................................................................................................................... [4]

(ii) If the solution of the electrolyte is stirred, chlorine reacts with sodium

hydroxide to form sodium chlorate(I), sodium chloride and water.

Write an equation for this reaction.

Cl 2 + ..  ..................... + ..................... + .....................

[2]

[Total: 14]

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