Apparatus and chemicals

  • 200 cm3 of 2 mol/dm3 hydrochloric acid and deionised water
  • 10 x 3 cm strips of magnesium
  • 100 cm3 beaker, 250 cm3 beaker, watch glass, measuring cylinder (25 cm3)
  • Stop clock

Method

  1. Carefully collect 200 cm3 of hydrochloric acid using the 250cm3 beaker, and 10 strips of magnesium using a watch glass.
  2. Using the measuring cylinder, measure out 25 cm3 of hydrochloric acid and add to the small beaker. Remember to use the measuring cylinder accurately.
  3. Drop the piece of magnesium ribbon into the beaker and start the stop watch, swirl once to ensure the magnesium is fully coated in the acid. Stop the watch when all the magnesium disappears.
  4. Repeat the experiment to ensure reliability of results.
  5. Repeat steps 2-4 except using a total of five different volumes of acid and water to ensure different concentrations of acid. The proportions you need to use are given in the results table:
Volume of hydrochloric acid / cm3Volume of deionised water / cm3Time taken for magnesium to disappear / sTime taken for magnesium to disappear / sTime taken for magnesium to disappear / s
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀12Average
250⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
205⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
1510⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
1015⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
520⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀

Analysis of results

In this experiment we can use the times to calculate an approximate value for the rate of each reaction by using the formula:-

Rate~= \frac {1}{time}

Using your average times calculate the rate of reaction for each experiment:-

Average time / sRate / s-1
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀

We can also calculate the percentage of acid used, or, since we know the original concentration of the acid is 2 mol/dm3, we can calculate the concentrate for each experiment:-

Volume of acid / cm3Percentage acidConcentration /mol/ dm3
251002.0
20801.6
15601.2
10400.8
5200.4

Finally, we can plot a graph of our Independent Variable (x-axis) against our Dependent Variable (y-axis). Your Independent Variable will be either % Acid, or Concentration. Your Dependent Variable will either be time or rate. Your teacher will instruct you on which to use.

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