Rates of Reaction - Molarity.

Temperature - when the temperature is increased the particles gain kinetic energy, which means the particles vibrate more which in turn means they are more likely to collide successfully.

Surface Area - a larger surface are means more particles are exposed. Therefore as larger number of collisions occur

Catalyst - the catalyst lowers the amount of energy needed for a collision without taking part therefore more successful collisions will take place.

However I am only testing concentration so from this knowledge I know that the higher the concentration the more likely that the particles will collide.

Prediction:

I believe that as the molarity decreases so will the speed at which the gas collects. I predict this because of my preliminary work and scientific knowledge. This knowledge is that as the concentration increases there are more particles in the same volume so then there will be more successful collision. This means the volume of gas collected in the first minute should decrease as the concentration decreases.

* Set up the experiment as shown above

* Add 2 cm of magnesium strip to 20 cm3 of HCl

* Write down the volume of the gas every 5 secs for 1 minute

* Use concentrations 1, 0.9, 0.8, 0.7, 0.6 M

To make the different concentrations I added water to 1M hydrochloric acid:

Molarity

Water/Acid cm3

0/20

0.9

2/18

0.8

4/16

0.7

6/14

0.6

8/12

Fair test/Reliability:

By controlling all the other variables (temperature, surface area and using a catalyst) I am leaving only one thus making my results accurate and reliable and easier to test. I am also using the same amount of acid (variable) and magnesium each time making it a fair test. I have also repeated my experiment so that I can average out my results making it fair, as extremities will be averaged out. To make it a reliable and fair test I have made sure that the gas syringe is always at 0 at the beginning of each experiment and I will start the clock as soon as the Magnesium meets the HCl and always make sure that the Mg is cut to exactly to 2 cm

Safety:

Always wear goggles - so that no acid can go in your eye

Wash acid after using acid - so that acid does not transfer onto things that you touch and worse in your mouth (from the food that you eat).

Results:

Test 1

Molarity (M)

Water/Acid cm3

T

5s

I

0s

M

5s

E

20s

25s

I

30s

N

35s

40s

S

45s

E

50s

C

55s

S

60s

0/20

2

4

6

8

0

2

4

6

7

9

20

21

0.9

2/18

2

4

5

7

8

9

1

2

3

5

6

7

0.8

4/16

2

3

4

5

5

6

7

8

8

9

0

1

0.7

6/14

2

3

5

6

7

9

0

1

2

3

4

5

0.6

8/12

2

2

3

4

4

4

5

5

6

6

7

Test 2

Molarity (M)

Water/Acid cm3

T

5s

I

0s

M

5s

E

20s

25s

I

30s

N

35s

40s

S

45s

E

50s

C

55s

S

60s

0/20

2

5

7

9

1

3

5

6

7

9

20

21

0.9

2/18

2

4

6

8

9

1

2

3

5

6

7

8

0.8

4/16

2

3

3

4

5

6

6

7

8

8

9

0

0.7

6/14

2

3

4

5

6

7

8

9

1

2

3

3

0.6

8/12

2

3

4

5

6

66

7

7

8

9

Average (2dp)

Molarity (M)

Water/Acid

cm3

T

5s

I

0s

M

5s

E

20s

25s

I

30s

N

35s

40s

S

45s

E

50s

C

55s

S

60s

0/20

2

4.5

6.5

8.5

0.5

2.5

4.5

6

7

9

20

21

0.9

2/18

2

4

5.5

7.5

8.5

0

1.5

2.5

4

5.5

6.5

7.5

0.8

4/16

2

3

3.5

4.5

5

6

6.5

7.5

8

8.5

9.5

0.5

0.7

6/14

2

3

4.5

5.5

6.5

8

9

0

1.5

2.5

3.5

4

0.6

8/12

.5

2

4

4

4.5

5

5.5

6

6.5

7

8

= Volume of H2 collected

Rate of Reaction:

The rate of a reaction is how quickly the reactants turn into products. To work out the rate of reaction I have decided to find the time that each reaction took to reach 8 ml of H2 and converting it into a rate.

The formula for Rate of Reaction is 1/time (secs)

Molarity (M)

Calculation

Rate (3dp)

/18.75

0.053

0.9

/23

0.044

0.8

/42

0.024

0.7

/36

0.028

0.6

/60

0.17

The rate of reaction tell you how fast each reaction takes to get to point as you can see from my rate of reaction graph as the molarity increases the reaction is quicker apart from 0.8 (sources of error in evaluation). This graph is useful, as initially I has thought 0.7 moles was the incorrect result but this graph proved otherwise. Also from this graph I can find out what the rate should have been for 0.9 ideally which is 0.036 so the time it would have taken for this experiment to reach 8 ml of H2 is 1/rate = 1/0.036 = 28.7 seconds. I can also predict other results:

0.5 = 0.0125 1/0.0125 = 80 s = 1 min 20 s

0.4 = 0.0095 1/0.0095 = 105.3 (1dp) = 1 min 45.3 s

0.3 = 0.0065 1/0.0065 = 153.8 (1dp) = 2 min 33.8 s

0.1 = 0.00225 1/0.0025 = 444.4 (1dp) = 7 min 24.4 s

Conclusion

As my graphs and results show the volume of gas produced in the first minute increases with the increase in molarity apart from 0.8 moles, this anomaly occurred both times which is unusual but apart from that result I know that Molarity is proportional to volume of gas collected per minute.

E.g. it takes longer for 8 ml of gas to be collected as the concentration reduces, which proves my prediction right. This is because there are more particles in the same volume if the concentration is increased. Here is a diagram:

Less moles More moles

Evaluation

I believe the plan was good and enabled me to get the results that I needed. My experiment went very well apart from my one anomaly (0.8 Moles) this is unusual as it happened both time as but these are some reasons why this happened:

Sources of Error

Gas syringe - was only to the nearest ml

Magnesium - it used up the HCl around it and turned it into MgCl but did not react with the acid at the bottom making the reaction slower

Heat - as the Mg reacts with HCl heat is given off speeding up the reaction

Human Error - reading the gas wrong, starting or stopping the clock at the wrong time etc.

Solving these Errors

Gas syringe - use a position sensor on the gas syringe, which is attached to a computer. This will record the results with no anomalies.

Magnesium - shake the test tube every so often

Heat - can't solve this, the reaction is exothermic

Human Error - use a position sensor on the gas syringe, which is attached to a computer. This will record the results with no human anomalies.

Extension

To extend the investigation I would do the experiment again put try and put right all the sources of error and see if my results come out perfect.