RR3 How do changes in temperature affect the
speed of a chemical reaction ?
IDEA
The reaction between sodium thiosulphate and dilute hydrochloric acid will be used.
In this reaction a precipitate of sulphur is formed slowly.
The solution becomes milkier and milkier until you cannot see through it.
WORD EQUATION
sodium
+ hydrochloric
thiosulphate
acid
sodium
chloride
(salt)
+
sulphur
2NaCl
+
S
CHEMICAL EQUATION
2HCl
Na2S2O3 +
+
+
water
H 2O
+
+ sulphur
dioxide
SO2
The temperature of the sodium thiosulphate will be changed by heating the solution to a known
temperature.
The concentration of the acid remains unchanged.
DIAGRAM
PROCEDURE
 Put 50 mls of sodium thiosulphate in to the
conical flask.
 Place this solution on a tripod and gauze and
heat the solution for a few minutes.
 Draw a small cross on the piece of paper and
put the flask on top of it.
 Pour the acid into the hot sodium
thiosulphate solution and start the clock.
 Record the temperature.
 Time (in seconds) how long it takes for the
cross to disappear.
 Wash out the flask thoroughly .
 Repeat using the same volumes of sodium
thiosulphate and acid as given in the results
table.
 Vary the temperature of the sodium
thiosulphate
THE RESULTS:
Fill in the table below
Volume of sodium
thiosulphate (mls)
50
Volume of acid
used (mls)
5
Temperature
(oC)
.
Time
(secs)
.
50
5
.
.
50
5
.
.
50
5
.
.
50
5
.
.
50
5
.
.
Using the graph paper below plot a graph of temperature of sodium thiosulphate solution
(vertical axis ) against the time taken for the cross to disappear (horizontal axis).
QUESTIONS
1.
At what temperature was the reaction at its
(i)
fastest ?
(ii)
slowest ?
2.
How does the speed of reaction vary with temperature ?
3.
Explain why a change in temperature can alter the speed of a reaction ?
Talk about the reacting particles.
FOR THE TECHNICIAN
HAZARDS
 50 ml measuring cylinder (plastic)
Sulphur dioxide
 10 ml measuring cylinder (glass)
Produced in this reaction is
 test tube
toxic by inhalation.
 bunsen burner
Students suffering from
 tripod
asthma need to take care.
 gauze
Hydrochloric acid
 stopclock
Corrosive
 thermometer -10 - 110 oC
May also cause burns
 sheet of white paper
 2M hydrochloric acid (DANGER)
sodium thiosulphate containing 40 g / litre
Also an irritant.