1.Determine the mass of sodium thiosulfate needed to prepare 200 mL of a 0.25 M

Question

1.Determine the mass of sodium thiosulfate needed to prepare 200 mL of a 0.25 M sodium thiosulfate solution.

2. Why is it necressary to keep the total volume of the reagents after mixing constant in the the kinetic runs (i.e., why was it necressary to add distilled water to keep the volume constant)?

3. Why is it necressary for the two solutions being mixed to be at the same temperature prior to mixing? What error will be introduced if hte solutions are not at the same temperature?

Please explain thoroughly

Explanation / Answer

1.No.of moles of Sodium thiosulfate required = 0.2*0.25 = 0.05 moles

Mass of Sodium thiosulfate required = 0.05*158.11 = 7.79 gms

2,3)the factors that affect mixing
1)concentration
2)temperature
3)surface area
4)catalyst
5)light(in photochemical reactions)

In the experiments we are checking the effect of changing one of these factors on the rate of reaction.All the other factors like volume of reactants should be kept constant to do a fair test and comparison of results.eg. If you are testing for the effect of increasing surface area,then all the other four factors and the volume of reactants should be kept constant.
Even when testing for the effect of changing the concentration,we do not change the volume because concentration does not depend on volume(no.of moles) but no.of moles per given volume.

When temperature is increases reacting particles gain more kinetic energy and move faster.Therefore more frquent and effective collisions between particles.So rate of reaction increases.

I hope you got the answers for second and third questions

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