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Category: Science

Autor: anton 20 November 2010

Words: 2436 | Pages: 10

Investigating the factors affecting the rate of a chemical reaction.

Introduction:

In my coursework I will be mainly concentrating on the reaction between dilute hydrochloric acid with marble chips (calcium carbonate).

Calcium carbonate (marble chips) + hydrochloric acid ==> calcium chloride + water + carbon dioxide

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

Aim:

The aim of the experiment is to investigate how the concentration of hydrochloric acid affects the rate of reaction with marble chips, i.e. how quickly/how much hydrogen is produced.

Firstly I would like to establish the term ‘rate of reaction’, the term means how fast a reaction occurs it could also mean in other aspects how slow the reaction occurring takes place.

There are a number of factors that determine the rates of reaction, listed below are the factors affecting the rate of reaction:

(a) the solution concentration,

(b) the temperature of the reactants,

(c) the size of the solid particles (surface area effect),

(d) a catalyst

A chemical reaction can only occur between particles if only they collide he reactant particles must collide therefore this only occurs in the collision theroy, the collision theory is the process in which reactant particles collide with each other, the collision must have enough energy for the particles to react. The minimum energy needed for particles to react is called the activation energy, however not all particles bring about a chemical change. More collision increases the rate of reaction.

• Temperature increases the number of collisions, as the temperature is increased the particles move quicker. Reactions get faster as the temperature is increased in this case the same mass of gas would be given off because you still have the same quantities of everything in the mixture.

• As a catalyst is placed in a chemical it speeds up a reaction without changing the original solution in a chemical., therefore in practical it looks like the diagram below:

• The size of the particle also has an affect on the rate of reaction, in this case if a solid particle is broken down into smaller pieces the rate of reaction increases, hence if the particles are large the rate of reaction decreases, The speed increase happens because smaller pieces of the same mass of solid have a greater surface area compared to larger pieces of the solid. Therefore the greater the surface area the faster the rate if reaction.

Safety: During the practical a number of measures have to be taken, to determine that the experiment is carried out safely and precisely, these are:

• Safety goggles to be worn at all times to ensure no chemicals make contact with eyes.

• Wear a lab coat, so no corrosive chemicals come into contact with skin and clothes, as well as spillages.

• Avoid contact with any chemicals, as they can be harmful in a number of ways.

• Tie long hair back.

• Make sure you have no loose fitting clothes, jewellery etc hanging around

• Place bags and overcoats in suitable place.

• Not to eat or drink in the lab.

• If using Bunsen burner make sure not near flammable gases.

• If using Bunsen burner must use a safety mat, make sure that its nowhere near the apparatus.

Hypothesis: If you increase the concentration of the reactants, the reaction becomes faster, increasing the concentration increases the chances of particles hitting each other, increasing the number of collisions, hence increases the rate of reaction therefore, I predict that if I increase the concentration of the hydrochloric acid the rate of reaction will also increase.

Apparatus:

• Measuring cylinder

• Weighting scale

• Marble chips

• Dilute Hydrochloric acid

• Safety goggles

• Stop clock

• Water

• Result sheet

• Pen

• Gas syringe

• Conical flask

Item: Amount Reason for using equipment

Measuring cylinder 1 Measuring out hydrochloric acid required

Weighting scale 1 To measure the size of marble chips to be at 3g

Marble chips 15g Main material required to determine rate of reaction, 3grams for each experiment.

Dilute hydrochloric acid 150ml Raw material required determining whether concentration affects reaction.

Safety goggles 1 Safety issues, due to dealing with acids which can be corrosive.

Stop clock 1 Time how long it takes for each experiment to reach 50cm3 of hydrogen gas.

Water 100ml To dilute with hydrochloric acid as to change concentration.

Results tables 1 To record results of the finalised experiment.

Gas syringe 1 to record how long it takes for gas to be produced at 5ocm3

Conical flask 1 To place hydrochloric acid and marble chips in.

Reasons why using particular equipment:

Method:

1. Collect all equipment; required.

2. Weight 3g of marble chips, and record the measurement as for the chips to be of the same weight, so that it’s more likely for the test to be fair as well as precise.

3. Collect the hydrochloric acid and measure out 10cm3 at 0.2molar in the measuring cylinder then pour into the conical flask.

4. Place the 3g of marble chips into the conical flask place lid As soon as the chip touches the acid start the stop clock, and time how long it takes for hydrogen gas to reach 50cm3.

5. Record results on results sheet.

6. Place another 3g of marble chips, repeat procedure again but with 40ml of Hydrochloric acid diluted with 10ml of water. As soon as the chip touches the acid start the stop clock, and time how long it takes for hydrogen gas to reach 50cm3.

7. Record results on results sheet.

8. Repeat the same procedures as above but with different concentration of hydrochloric acid and water. And so forth.

9. To make the experiment a fair test repeat two more times. Collect observations/results, on prepared results sheet.

Fair test:

As to make sure that the test is fair I will double check the measurements of the products, I will also make sure the test tube I am using does not contain any unwanted products i.e. solutions, as if any remaining products can cause reactions which can alter the experiment greatly in a negative way.

I will also carry out the experiment twice for a precise and more accurate result.

Results table:

Original table without conversion of minutes into seconds.

Time (m) taken for hydrogen gas to reach 50cm3

Concentration (ml) Test 1 Test 2

50 ml Hcl

0 ml H20 1.33 1.16 1.45

40 ml Hcl

10 ml H20 2.43 2.54 2.44

30 ml Hcl

20 ml H20 3.49 4.31 4.12

20 ml Hcl

30 ml H20 9.23 8.41 8.21

10 ml Hcl

40 ml H20 25.12 28.8 27.3

Table converted from minutes into seconds.

Time (m) taken for hydrogen gas to reach 50cm3

Concentration (ml) Test 1 Test 2 Test 3 Mean= test 1+2+3/3

In Seconds only

50 ml Hcl

0 ml H20 1.33m 1.16m 1.45m 78.8 (s)

79.8 (s) 69.6 (s) 87 (s)

40 ml Hcl

10 ml H20 2.43m 2.54m 2.44m 148.2 (s)

145.8 (s) 152.4 (s) 146.4 (s)

30 ml Hcl

20 ml H20 3.49m 4.31m 4.12m 238.4 (s)

209.4 (s) 258.6 (s) 247.2 (s)

20 ml Hcl

30 ml H20 9.23m 8.41m 8.21m 517 (s)

553.8 (s) 504.6 (s) 492.6 (s)

10 ml Hcl

40 ml H20 25.12m 28.8m 27.3m 1624.2 (s)

1,507.2 (s) 1,728 (s) 1,638 (s)

Working out concentration values:

Solution of hydrochloric acid 0.2mol dm3 = Concentration.

2.0 mole of acid in 1000cm3

No of moles in 50cm3

2.0

1000 = no of moles in 1cm3

Therefore in 50cm3 = 2.0 x50 = no of mol = 0.1 mol

1000

Volume of acid cm3 No of moles concentration Working out:

50 0.1 2.0 0.1 x100 = 2.0

50

40 0.08 1.6 0.08 x100 = 1.6

50

30 0.06 1.2 0.06 x100 = 1.2

50

20 0.04 0.8 0.04 x100 = 0.8

50

10 0.02 0.4 0.02 x100 = 0.4

50

The results table above is just to determine the concentration values I have been working with as you can see the highest being of 2.0 moles, which is also equal to 50cm3, this was the highest concentration I have use

Rate is equal to gas collected therefore in my case 50cm3 divided by the time for each concentration.

Rate = Gas collected

Time

This is just the same as saying:

Speed = Distance

Time

Time (m) taken for hydrogen gas to reach 50cm3

Concentration (mole) Average time (seconds)

2.0 78.8 (s)

1.6 148.2 (s)

1.2 238.4 (s)

0.8 517 (s)

0.4 1624.2 (s)

Analysis of results:

Above is the graph showing the different concentrations in which I have been investigating, from this graph I can conclude that as the concentration of hydrochloric acid decreases the time it takes for the reaction to occur takes much longer but as the concentration increases the rate at which the reaction occurs also increases, this proves to me that my prediction is correct, therefore the higher the concentration the faster the reaction.

From the graph as you can see at 2.0 moles concentration, it takes just over a minute for a reaction to take place in this case 78.8 seconds but at already only 1.6 moles of concentration there is a difference of 69.4 seconds, which is actually quite a big difference however at 0.8moles of concentration there is already a very major difference in which it took 517 seconds for hydrogen gas to reach 50cm3 therefore around 8 minutes which is quite long to wait and at 0.4 moles of concentration it takes almost half as much time as 0.8 moles of concentration therefore very slow, it took about 27 minutes, hence proving my prediction right.

Results table for rate factor.

Concentration Time (seconds) Rate=gas collected/time Rate

2.0 78.8 (s) Rate=50/78.8 0.63s

1.6 148.2 (s) Rate=50/148.2 0.33s

1.2 238.4 (s) Rate=50/238.4 0.20

0.8 517 (s) Rate=50/517 0.09

0.4 1624.2 (s) Rate=50/1624 0.03

Graph:

Rate is equal to gas collected therefore in my case 50cm3 divided by the time for each concentration.

Rate = Gas collected

Time

This is just the same as saying:

Speed = Distance

Time

Analysis of results:

The graph above is just the same as the one earlier but its showing that any rate of a reaction is affected by a number of factors in this case the factor being concentration, as the concentration of the reactant is increased the rate at which it reacts is very high, therefore faster, but if the concentration is decreased the rate at which solution reacts is very slow.

In general terms if you increase the concentration of the reactants, the reaction becomes faster; increasing the concentration increases the chances of particles hitting each other. At 2.0 moles of concentration the rate at which hydrogen produced reaches 50cm3 is 0.63seconds, at 1.2 moles of concentration it takes 0.2 seconds, from here there is a difference of 0.43 seconds, showing that as concentration decreases the rate of reaction also decreases.

In conclusion to all this, I have finally proved that as the concentration is increased collision rate increases which therefore increases the rate at which particles are moving.

Evaluation

From my results both theoretically and practically I have come to conclusion that the research worked out pretty well, in which my prediction proved to be correct. Although I believe that it would have been better for me to collect a wider range of results, even though this would have been too time consuming, if I had time I would have also repeated the test more to at least 5 times as to get a very precise average.

Despite what I have said earlier that my results were pretty good, I believe that from the concentration 0.8 the rate of reaction was 517 seconds, but at 0.4 moles of concentration the rate of reaction was double that at 1624.2 seconds from here it took about 27 minutes which is a long time to wait, I can say that this was the only anomaly in the whole of the experiment.

From what I can remember during the experiment is that the tubing in which holds the gas cylinder to the conical flask contained a little amount of water, in which I did not quite notice, for the first trial, this caused a difficulty in the movement of the gas syringe which was supposedly meant to measure up to 50cm3 of hydrogen gas being produced, it caused it to take time to move the gas up, the water came from the solution being poured into the sink via the tubing, then being placed back onto the conical flask, this must have obviously caused the anomaly.

The equipment I was provided with was very good and provided very accurate measurements, although the marble chips were of varying sizes it would have been better to have one size to measure from, the weighting scales in which I had to measure 3g of marble chips was very reliable, it was just the fact that the sizes of the chips varied. Although I have used a measuring cylinder to measure out the hydrochloric acid and water, a burette would have been a much better and a more accurate piece of equipment to use as not to cause anomalies within the results.

If I had to change anything in the experiment I would have measured the hydrogen gas produced on a weighting scale, as I think that it is not time consuming, I would have also changed the factor in which I am investigating, temperature and surface area would have been my first choices, as to determine which facto works well I would have investigated a variety of factors, to provide me with very accurate prediction.

In conclusion I do believe that my prediction was correct, my prediction being the higher the concentration the faster the rate of reaction.

Therefore proved to me that the whole of the experiment went really well.

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