investigation of how rate chanbes with concentration

Question 1

equipment

Answer 1

 thermometer  400 cm3 beaker (for use as a water bath)  plastic container with lid  2 glass tubes to hold 12–14 cm3 of liquid  0.05 mol dm–3 sodium thiosulfate solution  1.0 mol dm–3 hydrochloric acid (or 0.5 mol dm–3 sulfuric acid)  10 cm3 measuring cylinder  plastic graduated pipette  stopwatch  graph paper.

Question 2

method

Answer 2

a) Add about 10 cm3 of 1 mol dm–3 hydrochloric acid (or 0.5 mol dm–3 sulfuric(VI) acid) to the ‘acid’ tube. Place this tube into the correct hole in the plastic container (ie the one without the cross under it). b) Use a measuring cylinder to add 10.0 cm3 of 0.05 mol dm–3 sodium thiosulfate solution to the second tube. Place this tube into the correct hole in the plastic container (ie the one with the cross under it) and carefully place a thermometer in this tube. c) Note the start temperature and then add 1 cm3 of the acid to the thiosulfate solution and start timing. d) Look down through the tube from above and record the time for the cross to disappear from view. e) Record the temperature of the reaction mixture. Pour the cloudy contents of the vial into the sodium carbonate solution (the ‘stop bath’). f) Now add water from a very hot water tap (or kettle) to the plastic container. The water should be no hotter than 55 °C. Add cold water if necessary. g) Measure another 10.0 cm3 of 0.05 mol dm–3 sodium thiosulfate solution into a clean tube. Insert this tube into the correct hole in the plastic container (ie the one with the cross under it). h) Leave the tube to warm up for about 3 minutes. i) Repeat steps (c) to (e) above. j) Repeat to obtain results for at least 5 different temperatures in total

Question 3

how would you analyse these results

Answer 3

In these experiments at different temperatures, the concentrations of all the reactants are the same. You are investigating the time taken to produce the same amount of sulfur at different temperatures. If you were to plot a graph of the amount of sulfur produced against time, it would initially be a straight line because the reaction has only just started. Therefore,

the initial rate of reaction = (amount of sulfur)/time

so the initial rate of reaction is proportional to 1/time ( 1 𝑡 ).

Question 4

dditonal info

Answer 4

A lid is advised in this experiment. Two holes should be made in the lid using a hot wide cork borer. These holes should securely hold the glass tubes and vertically in the plastic container. A cross should be marked on the inside base of the plastic container below one of the larger holes using a permanent black marker pen.

Alternatives include using clear A4 plastic wallets to use as a lid over the plastic container. Also, rather than marking the bottom of the plastic container directly, a laminated sheet marked with a black cross could be used