How the concentration of hydrochloric acid affects the rate of the reaction with magnesium.

Varying concentrations of hydrochloric acid; 0.5M, 1.0M, 1.5M, 2.0M, 2.5M

Dependent Variable

Time taken for reaction for all the magnesium to react with HCl

Controlled Variables

Volume of HCl used

Length of magnesium ribbon used

Temperature is at room temperature (Thermostat at a constant level)

Method

1. Connect side armed flask to gas syringe
2. Connect pipette pump to pipette
3. On the pipette pump, press A and squeeze the pump
4. The pump should now be ‘deflated’; Press S and the pump should draw up the HCl.
5. Draw up 25 ml of 0.5M HCl until it crosses the meniscus and then empty out excess HCl so the acid level is exactly at the meniscus(be sure to check from eye-level)
6. Empty HCl into the side armed flask. Do not ‘flick’ or ‘shake’ the few drops of HCl that is gathered at the mouth of the pipette as it is calibrated that way to measure exactly 25 ml ±0.060
7. Measure and cut 4 cm of the magnesium ribbon
8. Place magnesium into HCl and start timer
9. Immediately place stopper on the flask to prevent any hydrogen gas from escaping
10. Record the time taken for all the magnesium to react and the gas evolved to reach a maximum (Should be approximately 60 cm3)
11. Dispose of the magnesium chloride solution down the drain and push out the hydrogen gas from the gas syringe
12. Remove the pipe from the side armed flask and wash it, so none of the products from the previous reaction is left
13. Dry the water with tissue paper
14. Repeat steps 1-13 with 1.0M, 1.5M, 2.0M, 2.5M HCl

Data

Table 1-Raw Data Table: Time taken for 4cm of magnesium ribbon to completely react with changing concentrations of hydrochloric acid and evolve approximately a maximum of 60 cm3

Qualitative Observations

It was observed that during the reaction with 0.5M the reaction was only a little effervescent and the reaction was really slow which was evident by the bubbles being produced. However as the concentration was increased, the reaction became more effervescent. A pattern can be observed in the time by which each reaction takes to go to completion. As the concentration is increased by 0.5 mol/L, the time taken for the reaction to go to completion almost goes to half its previous value. For example, when the concentration is increased from 2.0 mol/L to2.5 mol/L, the time taken for the reaction to go to completion decreases from 1 min 05 seconds to 34 seconds. This is almost half the time taken for 2.0 mol/ L. If we double 32 seconds, we get 1 min 04 seconds which is almost the value obtained from the results. At 2.5M the reaction produced a lot of bubbles and was most effervescent and more violent than the reaction of magnesium with the lower concentrations.

Calculations

Volume of gas produced= 60.00cm3 ± 0.05

Volume of HCl reacted= 25.00ml ± 0.060

0.5 mol HCl

Rate of reaction= increase in product volume/ time taken

                        = (60cm3/1000)/460s

                  = 1.3 x 10-4 dm-3 s-1 ± 0.05

1.0 mol HCl

Rate of reaction= increase in product concentration/ time taken

                        = (60cm3/1000)/292s

                  = 2.0 x 10-4 dm-3 s-1 ± 0.05

1.5 mol HCl

Rate of reaction= increase in product concentration/ time taken

                        = (60cm3/1000)/148s

                  = 4.0 x 10-4 dm-3 s-1 ± 0.05

2.0 mol HCl

Rate of reaction= increase in product concentration/ time taken

                        = (60cm3/1000)/65s

                  = 9.2 x 10-4 dm-3 s-1± 0.05

2.5 mol HCl

Rate of reaction== increase in product concentration/ time taken

                        = (60cm3/1000)/32

                  = 1.8 x 10-3 dm-3 s-1± 0.05

Table 2-Processed data: Rate of reaction of a 4cm magnesium ribbon and changing concentrations of hydrochloric acid

Graph 1- The concentration of HCl plotted against the rate of reaction

Conclusion

In conclusion, the results I obtained supported my hypothesis because as it can be seen from the graph and the results above, the rate of reaction increases as the concentration of hydrochloric acid increases. This can be observed when one looks at the difference in the rate of reaction of magnesium with 0.5M and 2.5M HCl. We can see from the data obtained that the rate of reaction for 2.5M HCl is 1.8 x 10-3 whereas the rate of reaction for 0.5M is 1.3 x 10-4. The difference in the rates is a big difference and the reason for this difference is because as the concentration of hydrochloric acid is increased, there are more HCl particles in the solution. Consequently, there are more HCl particles to react with the magnesium particles and form more products. This reasoning is supported by the Collision Theory because since there are more reacting particles, the probability of particles colliding in the correct geometry with energy greater than activation energy is higher so therefore there is a higher frequency of more successful collisions.  Therefore as the concentration of hydrochloric acid increased, so did the rate of reaction.

Evaluation

Table 3- Limitations and errors in the experiment and how it can be improved

Bibliography

[1] Ford, Mike. "Chapter 6-Kinetics." Heinemann Baccalaureate Standard Level Chemistry. By Catrin Brown. 2008. 114-25. Print.