Chemistry Form 5 Chapter 1

Measuring the volume of gas release

Measuring the changes in mass of the reactants

FORM 5 THEME: INTERACTION BETWEEN CHEMICALS

CHAPTER 1: RATE OF REACTION

1.1 Rate of Reaction

1. The speed at which a reaction occurs is called the rate of reaction.2. The faster the reaction, the higher the rate of the reaction. Whereas the slower the reaction,

the lower the rate of the reaction.3. Below are some examples of fast and slow reaction:

4. To investigate the rate of a chemicals reaction, we need to record some observable changes taking place such as:

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5. Measuring the rate of reaction includes the rate of reaction determined by measuring the amount of reactant used up or the amount of product produced per unit time.

6. The rate of reaction can be expressed in:a) The average rate of reaction

This is determined by measuring the amount of reactant used up or the amount of product produced over a period of time.

b) The rate of reaction at any given time or instantaneous rate of reaction at the given timeThis is determined by determining the gradient of the tangent to a graph at a particular time of the reaction.


Formation of Precipitate

Example 1

2g (in excess) of marble is added into 50 cm3 of 0.15 mol dm-3of dilute nitric acid in a conical flask. The total volume of carbon dioxide gas released is recorded at every half-minute interval.

The reaction is presented by the equation:




The graph of the total volume of carbon dioxide gas collected against time is shown below:

a) What is the total volume of CO2 gas collected?b) What is the time taken for the reaction to be completed?c) Determine the average rate of reaction.

d) Determine the rate of reaction at 3.7 minutes.



1.2 Factors that Affect the Rate of Reaction

1. The factors that affect the rate of reaction are:a) Particle size (or surface area) of a solid reactant b) Concentration of the reactantsc) Temperature of the reactiond) Presence of catalyste) Pressure (for reactions involving gases only)


EXPERIMENT 1.1AimTo study the effect of particle size on the rate of reaction.Problem StatementHow does the particle size of the marble chips affect the rate of reactions?HypothesisThe smaller the particle size of the marble chips, the higher the rate of reaction.Variable

a) Manipulated: Size of marble chips used.b) Responding: Rate of reactionc) Controlled: Temperature, volume and concentration of hydrochloric acid, mass of marble

chips.Materials6g of small marble chips, 6 g of large marble chips, 100 cm3 of 0.2 mol dm-3 hydrochloric acid.Apparatus100cm3 conical flask , delivery tube, burette, retort stand, basin, stopwatch.Procedure

1. A burette is filled with water and inverted in a basin of water. The burette is clamped vertically to a retort stand.

2. The volume of the burette is adjusted to the 50.00cm3 mark.3. 50cm3 of 0.2 mol dm-3 hydrochloric acid is poured into a conical flask.4. 6g of small marble chips is weighed out. The marble chips are added into the conical flask.5. Then, the delivery tube with a rubber stopper is inserted into the mouth of the conical flask

and the stopwatch is immediately started.6. The burette readings are recorded at every 30-second intervals.7. Steps (a)-(f) are repeated using 6g of large marble chips.8. The total volume of CO2 gas collected against time for both experiments are plotted on the

same axes.

9. The results are tabulated below:

I. Small marble chips




9. The results are tabulated below:

I. Small marble chips




SPM CLONE 2006The diagram shows two experiments to investigate one of the factors that Influences the rate of a reaction.

a) What is the factor investigated?

b) Write an equation for the reaction occurring in the conical flasks.

c) State variables that must be controlled.

d)

Graph I and II shows the result of both experiments on the same axes.

i. What has happened at time X and Y?

ii. State which graph corresponds to Experiment X and which to Experiment Y? Explain your answer.

iii. Explain why the total volume of carbon dioxide gas collected in the same for both experiments.

AimTo study the effect of concentration of reactants on the rate of reaction Problem StatementHow does the concentration of sodium thiosulphate solution affect the rate of reaction?HypothesisThe higher the concentration of the reactant, the higher the rate of reaction.Variables

a) Manipulated: Concentration OF Sodium thiosulphate solution.b) Responding: Rate of reaction.c) Temperature, volume and concentration of hydrochloric acid.

EXPERIMENT 1.2




AimTo study the effect of concentration of reactants on the rate of reaction Problem StatementHow does the concentration of sodium thiosulphate solution affect the rate of reaction?HypothesisThe higher the concentration of the reactant, the higher the rate of reaction.Variables

a) Manipulated: Concentration OF Sodium thiosulphate solution.b) Responding: Rate of reaction.c) Temperature, volume and concentration of hydrochloric acid.

Result

The graph of concentration of sodium thiosulphate against time, t and 1/t are shown below:




Result

The graph of concentration of sodium thiosulphate against time, t and 1/t are shown below:




Graphs I and II show the results of experiment for the reactions between

Reaction X: 0.65g of zink reacts with 100cm3 of 0.2 mol dm-3 hydrochloric acidReaction Y: 0.65g of zink reacts with 100cm3 of 0.2 mol dm-3 sulphuric acid

a) State which graphs correspond to reaction X and Y? Explain your answer.b) Calculate the average rate of reaction for both reactions X and Y.

Solution

a) Graph I corresponds to reaction Y and graph II corresponds to reaction X. Hydrogen ions react with zink to produce hydrogen hydrogen gas according to the equation:

Sulphuric acid is a diprotic acid whereas hydrochloric acid is mono protic.

One mole of sulphuric acid produces two moles of hydrogen ions whereas one mole of hydrochloric acid produces one mole of H+ ions. Thus, the concentration of hydrogen ions is higher in sulphuric acid solution. The frequency of eefective collision by the H+ ions on zinc is higher in H2S04 than in HCL solution. Thus, the rate of reaction is higher in sulphuric acid solution.

b) Average rate of reaction X=240/200=1.2 cm3s-1c) Average rate of reaction X=240/140=1.7 cm3s-1

SPM CLONE 2007




EXPERIMENT 1.3AimTo study the effect of temperature on the rate of reactionProblem statement How does the temperature of sodium thiosulphate solution after the rate of reaction?HypothesisThe higher the temperature of sodium thiosulphate solution, the higher the rate of reaction.Variable

a) Manipulated: temperature of sodium thiosulphate solution.b) Responding: Rate of reactionc) Controlled: The concentration of sodium thiosulphate and hydrochloric acid solution.

Materials25cm3 of 2mol dm-3 hydrochloric acid solution, 250cm3 of 0.1 mol dm-3 sodium thiosulphate solution.Apparatus100cm3 conical flask, 100cm3 and 10cm3 measuring cylinder, stopwatch, a cupboard with a mark ‘X’, thermometer, Bunsen burner, wire gauze and tripod stand.Procedure

1. 50cm3 of 0.1 mol dm-3 sodium thiosulphate solution is poured into a 100 cm3 conical flask.2. The temperature of the sodium thiosulphate solution is measured with a thermometer.3. 5cm3 of 2 mol dm-3 hydrochloric acid is added into the sodium thiosulphate solution.4. The stopwatch is immediately started.5. The mixture is swirled once and then placed on a cardboard with a “X” mark.6. The conical flask is viewed from above.7. When the “X” mark disappears from sight, the stopwatch is stopped and the time of reaction

(t) is recorded.8. The contents is the conical flask is then poured out and the flask is washed thoroughly.9. Four experiments are repeated but the solution of 50 cm3 0.1 mol dm-3 sodium

thiosulphate solution is now heated to 35⁰C, 40⁰C, 45⁰C and 50⁰C respectively.10. The result of the experiment are tabulated below and the value of 1/t calculated.

Tabulation




Discussion

1. The graph of temperature of sodium thiosulphate solution against time, t is shown below.

a) From the graph, we can see that the higher the temperature, the shorter of time of reaction.

b) Hence the higher the temperature, the higher the rate of reaction.2. The graph of temperature of sodium thiosulphate solution against 1/time, 1/t is shown as

follows.

a) From the graph we see that for every increase of 10⁰C, the value of 1/t doubles.

Hence, at 60⁰C, the value of 1/t is expected to be 0.08 s-1.

b) Thus, we can conclude that for every increase of 10⁰C, the rate of reaction doubles.

Aim To study the affect of catalyst on the rate of reactionProblem StatementHow does catalyst affect the rate of affect the rate of decomposition of hydrogen peroxide?HypothesisManganese (IV) oxide increases the rate of decomposition of hydrogen peroxide.Variables

a) Manipulated: Presence of manganese (IV) oxideb) Responding: Rate of decomposition of hydrogen peroxide.

EXPERIMENT 1.4

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Chemistry Form 5 Chapter 1