RP3

Question 1

Independent variable and how it’s varied:

Answer 1

• Temperature
• varied by using a water bath at different temperatures

Question 2

Write the reaction between sodium thiosulfate and hydrochloric acid

Answer 2

Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + SO₂(g) + S(s) + H₂O(l)

Question 3

What causes the cross to disappear?

Answer 3

The formation of sulfur precipitate obscures the cross

Question 4

Dependent variable and how it’s accurately measured

Answer 4

• Time taken for ‘X’ to disappear
• Time measured using a stop clock

Question 5

control variables

Answer 5

-Volume and conc. of Na₂S₂O₃ (Sodium thiosulfate)
-Volume and conc. of HCl

Question 6

Why is it important to control these control variables?

Answer 6

• Different concentrations of reactant will affect the time taken for ‘X’ to disappear.
• Different Volumes mean you are not producing a fixed amount of sulfur for each experiment.

Question 7

Why does rate of reaction increase when temperature increases?
Explain using collision theory

Answer 7

At higher temp
1. Significantly higher proportion of particles with E greater or equal to Ea
2. Particles have more KE
3. So more frequent collisions
4. More frequent successful collisions, so faster RoR

Question 8

Why are we able to calculate rate by using 1/time taken?

Answer 8

amount of sulfur produced is constant for each experiment therefore we can assume this change in concentration is = 1.
- As rate is change in concentration/time. Rate can simplify to = 1/time

Question 9

Why should the temperature not exceed 55°C?

Answer 9

• Gases become less soluble at higher temperatures, above 55°C, the SO₂ is starts to become insoluble and will be released into the air.
• SO₂ is toxic so this should not be allowed to happen.