Investigate the factors, which affect the rate of reaction between Calcium carbonate and Hydrochloric acid.

I will change the concentration of the acid. To get reliable results I need to chose a good range of dilutions. I will make 5 different dilutions of hydrochloric acid from a stock bottle provided which is of Known concentration i.e. 2M.

Below is a table, which shows the ratio of water to hydrochloric acid I will use to get my 5 different results so I can draw a graph.

Volume of hydrochloric acid (cm3)

Volume of Distilled water (cm3)

50

0

40

0

30

20

20

30

0

40

Dependant variable

In this reaction we can trace the rate by looking at the amount of carbon dioxide gas that is produced. I will collect the gas that is produced in the initial stage of the reaction. I will time using an electronic stop clock how long it takes to produce 100cm3 of the gas.

Equipment

* Burettes - We will be using the burette because we can measure to the nearest cm³.

* Gas Syringe - We choose this because it will be used to collect the gas.

* Side Arm Conical Flask - This used so the gas syringe can be connected up to it.

* Electronic Balance - To weigh the mass accurately to 2 decimal places.

* Filter Funnel - to fill the burettes safely.

* Calcium Carbonate

* Hydrochloric acid

* Distilled Water - to change the concentration of the hydrochloric acid.

* Filter paper - it there to have something to weigh the chips on

* Electronic Stop Watch - The time will be measured o the nearest millisecond we will not be able to record the volume at exactly this time though so we will probably measure the time to a two second accuracy.

* In this investigation we will be recording how long it takes for 100mls of gas to be produced.

Prediction

I predict that if I increase the concentration the time taken to produce 100cm3 of carbon dioxide will decrease. I further predict that the higher the concentration the faster the reaction If I double the concentration I will double the rate of the reaction as rate is directly proportional to concentration. This will occur because in a higher concentration there will more hydrogen ions and chloride ions per set volume. This means that there will be a higher chance of the hydrogen ions and chloride ions colliding with the calcium ions and carbonate ions in the calcium carbonate lattice and reacting. This should in theory increase the rate of reaction as the concentration is increased.

The reaction rate, however, should decrease as the experiment progresses because as the reaction time increases the number of hydrogen ions and chlorine ions present will decrease as they have been reacted to form water, calcium chloride and carbon dioxide. The additional water and calcium chloride present as the experiment progresses should decrease the rate of reaction because of decrease in concentration.

The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrogen ions and chlorine ions present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially. This can be thought of as like people in a refined space, if there is twice the number of people there will be twice the chance of people colliding. This situation may change over time, however, depending on the situation. This shows how a higher concentration produces more collisions.

Method

To make the test a fair test we had to carry out the same method each time this is what we did.

* First we will collect the apparatus

* Using electronic balance weigh out 20g of small marble chips

* Set up burettes fill one with distilled water the other with Hydrochloric acid

* Measure out 50cm3 of Hydrochloric acid into the side armed flask.

* Add 20g of marble chips stopper flask start stop clock

* Record time to produce 100cm3 of carbon dioxide in gas syringe

* Repeat for accuracy

* Repeat with different dilution of acid

* Underneath is a diagram of how the experiment was set-up

Safety

To make sure we are safe in the lab here are some of the things we will do in more detail.

* Wear safety goggles because we are dealing with bleach

* Tuck stools in to make sure mo-one falls in the lab

* Put all bags under the table to make sure no-one falls

* Never run in the lab

* Always stand up when carrying out experiments so we can move away if we are in any danger

* Carefully fill burette by using the filter funnel

We will be able to get precise results because we will be using accurate equipment like the burette, electronic balance that measures up to 2 decimal places and the digital stop clock that will also give us an accurate result.

Strategy of Results

Here is the table we will record our results on

Volume of hydrochloric acid (cm3)

Volume of Distilled water (cm3)

Time taken for 100 cm3 of carbon dioxide gas to be produced (s)

Concentration of hydrochloric acid (gdm-3)

Rate of reaction (1/s)

2

Av

50

0

40

0

30

20

20

30

0

40

To calculate concentration of acid in the solution:

The concentration of the acid can be found by finding the ratio of acid to total solution and multiplying by the concentration of the acid in the stock bottle.

50/50 x 2 = 2

40/50 x 2 = 1.6

30/50 x 2 = 1.2

20/50 x 2 = 0.8

10/50 x 2 = 0.4

I will plot a graph of concentration against average time taken to produce a 100 mls of carbon dioxide.

I will work out the average by adding my two results together and dividing by two.

The graph will look like this

I will then use this graph to draw a second graph of concentration against rate of reaction. Having checked that I have no anomalous results I will take the time taken and divide the values into 1 to calculate rate.

My new graph will look like this:

From this graph I will be able to prove my hypothesis that if you double the concentration you double the rate of reaction.

Obtaining Evidence

This our table of raw data

Volume of hydrochloric acid (cm3)

Volume of Distilled water (cm3)

Time taken for 100 cm3 of carbon dioxide gas to be produced (s)

2

50

0

4

4

40

0

5

6

30

20

23

9

20

30

28

33

0

40

09

06

To calculate the average time we will take the time of the first time and add it to the second time and divide by 2.

(14 + 14) / 2 = 14

(15 + 16) / 2 = 15.5

(23 + 19) / 2 = 21

(28 + 33) / 2 = 30.5

(109 + 106) / 2 = 107.5

Average

4

5.5

21

30.5

07.5

The concentration of the acid can be found by finding the ratio of acid to total solution and multiplying by the concentration of the acid in the stock bottle.

(50/50) x 2 = 2

(40/50) x 2 = 1.6

(30/50) x 2 = 1.2

(20/50) x 2 = 0.8

(10/50) x 2 = 0.4

Concentration of hydrochloric acid (moldm-3)

2

.6

.2

0.8

0.4

I will plot a graph of concentration against time taken to produce a 100 cm3 of carbon dioxide.

Average (s)

(y)

Concentration of hydrochloric acid

(moldm-3)

(x)

4

2

5.5

.6

21

.2

30.5

0.8

07.5

0.4

To work out the rate of reaction you divide the average time taken into 1.

Rate of reaction (1/s)

0.071

0.065

0.048

0.033

0.009

1 / 14 = 0.071

1 / 15.5 = 0.065

1 / 21 = 0.048

1 / 30.5 = 0.033

Concentration of hydrochloric acid (moldm-3)

(x)

Rate of reaction (1/s)

(y)

2

0.071

.6

0.065

.2

0.048

0.8

0.033

0.4

0.009

/ 107.5 = 0.009

I will then use this table to draw a second graph of concentration

against rate of reaction.

Interpretation

Graphs

The first graph shows the average time against concentration. The graph is a curve, which is steeper at the beginning and gentler near the end. This shows the concentration is indirectly proportional to the time, as concentration increases the less time it takes to produce 100cm3 of carbon dioxide. The curve becomes less steep because after a certain increase in concentration the change in time to collect 100cm3 of the carbon dioxide gas is not changing very much i.e. it will no longer make any difference to my results whether the concentration is increased. This is because in this reaction the collisions are occurring on the surface of the calcium carbonate chips. When I increase the concentration of the acid I increased the number of hydrogen ions to collide with the surface of the calcium carbonate. Hydrogen ions have to come in contact with the surface for the reaction to occur. My reaction will only get faster if more collisions occur in the same period of time. This levelling out of my graph suggests there is a limit to the number of increased collisions that occur in a given unit of time and this is due to the surface area available for increased number of collisions to occur.

My second graph shows a straight line through the origin showing that concentration is directly proportional to rate. If concentration is doubled so is the rate.

Conclusion

Essentially my results show that the rate of reaction is directly proportional to the concentration. If the concentration is doubled so too is the rate. I can prove this by looking at my results and how they lie on the line of best fit. When the concentration is 0.8M the rate of reaction is 0.033cm3 per minute. When the concentration is 1.6M, the rate is 0.065. The rates of reactions have almost doubled each other.

This conclusion proves that I was correct in my original prediction. My graph shows a straight line through the origin indicating my results being directly proportional as expected. This conclusion can be explained using this diagram.

This diagram shows the reaction between calcium carbonate and hydrochloric acid. It shows how calcium carbonate molecules are bombarded with hydrogen and chloride ions. The more hydrogen and chloride ions the easier it is for the calcium carbonate molecules to break down into calcium ions and carbonate ions. This is because there are more hydrogen and chloride ions and therefore more chance of a successful collision, which will result in these bonds being broken.

The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrogen ions and chlorine ions present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially. This can be thought of as like people in a refined space, if there is twice the number of people there will be twice the chance of people colliding. This situation may change over time, however, depending on the situation. This shows how a higher concentration produces more collisions.

This evidence proves my original prediction correct. When I stated if I double the concentration I double the rate of reaction.

Are my results reliable?

As an inspection of my graphs they show anomalies but only in my rate against concentration. 0.4M should be 0.016 instead of 0.009. This will co-inside with my result for 0.8M and will support my prediction. The other anomaly was 2.0M, which was 0.071 but should really be 0.081.

This shows that during the experiment there were some errors. The points however do not deviate too far of the line of best fit so the evidence is still reliable.

To explain these anomalous results I will go back to my result table. When I compare my replication of the experiment I find that 0.4M and 2.0M are not identical this suggests there were errors in my method. Again the difference is not significant to affect the reliability of my evidence.

These errors could come about through human errors for example:

* Weighing out the marble chips and trying to get them the same size from one run to the next.

* I used burettes to make up the dilutions so these should be accurate.

This is an instantaneous reaction; once the marble chips inter the dilution of acid the reaction between the two starts instantly. This caused some problems because there was a delay sometimes to get the stopper on the conical flask and some gas could have escaped by then. Both reactions should be in the flask and kept separate e.g have the calcium carbonate in a test tube or a divided flask.

If I was to repeat the experiment I think I might get more information if I traced the reaction to completion. I was only studying the first few minutes of the reaction. I could use a larger measuring cylinder inverted in water I could then trace the reaction with the amount of water displaced from the cylinder.

In conclusion my results are reliable as they support my prediction at the start.

By Colm Killough 12B