Rate of reaction is the measure of how fast or slow the reactants are converted into products. Hydrochloric acid reacts with sodium Thiosulphate to form Sulphur (solid), water (liquid), sodium chloride (aqueous), and sodium dioxide (gas).
Sodium Thiosulphate + Hydrochloric acid >>>>>> Sulphur +Sulphur Dioxide + Water + Sodium Chloride.
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NA2S2O3 (aq) + 2HCL (aq) >>>>> S (s) + 2NaCl (aq) + SO2 (g) + H2O (l)
Sulfur is yellow in color. The reactants are colorless. The deposition of sulfur crystal makes the product yellowish in color. The rate of reaction of sodium Thiosulfate and hydrochloric acid is directly proportional to the concentration of the reactants and inversely proportional to the products. Caution-hydrochloric acid is corrosive to eyes and skin and also is it do irritate when inhaled. Sulfur gas is an irritant. The experiment must be carried out in a fume chamber or a well-ventilated room. Five 100ml beakers were cleaned and labeled 1-5 respectively. A large letter “X” was drawn on a piece of paper which was stuck at the bottom of each beaker. The beakers were placed on an overhead light box such that one could have a clear view of the letter “X” from above the beaker.
Using different graduated cylinders different solutions of sodium thiosulphate and distilled were measured as accurately as possible. The table below shows the different measurements
| beaker | 1 | 2 | 3 | 4 | 4 |
| 0.15M NA2S2O3 | 50 mL | 40 mL | 30 mL | 20 mL | 10 mL |
| Distilled water | 0 mL | 10 mL | 20 mL | 30 mL | 40 mL |
Each of the final concentrations of the sodium thiosulphate was calculated as follows 0.15M is contained in 1000mL
Hence 1ml contains 0.15 M/1000 mL = 0.0015 M/ mL
Beaker 1 had 50 mL of thiosulphate therefore its concentration is 50 mL x 0.0015 M/mL =0.075M
Beaker 2. 40 mL x 0.15 M/1000 mL =0.060 M
Beaker 3. 30 mL x0.15 M/1000 mL = 0.045 M
Beaker 4. 20 mL x 0.15 M/1000 mL = 0.030 M
Beaker 5. 10 mL x 0.15 M/1000 mL =0.015 M
Reaction time was recorded when 5 mL of 2M was added into each beaker containing a solution of sodium thiosulphate and distilled water.
| Beaker | 1 | 2 | 3 | 4 | 4 |
| 0.15M NA2S2O3 | 50 mL | 40 mL | 30 mL | 20 mL | 10 mL |
| Distilled water | 0 mL | 10 mL | 20 mL | 30 mL | 40 mL |
| Reaction Time |
It is evident that the higher the concentration the shorter the time the reaction takes for X to disappear. The reaction proceeds faster and slows down with time. This is due to a reduction in the concentration of sodium thiosulphate and an increase in the concentration of sulfur. The concentration of hydrochloric acid was constant. The turbidity increases with an increase in sulfur (solid)
The hypothesis was correct the higher the level of the product the lower the time. The higher the concentration of the reactants the faster the rate of reaction.
Conclusion
When the concentration of Sodium thiosulphate increased the rate of reaction increased. The time taken to reach equilibrium decreased with reduced concentration of the product. The rate of reaction is directly proportional to the concentration of reactants.
