Rate Of Reaction

Question 1

Why cotton should be loosely plugged at the neck of the flask,
to increase the accuracy of weighing result?

Answer 1

1. To prevent acid from splashing out (trapped by the cotton)
2. To allow gas evolves to escape from the reaction mixture

Question 2

Calculate rate of reaction in g s^-1

Then in mol dm^-3 s^-1

Answer 2

1. g/time(s) = rate in g s^-1
2. Find rate of reaction in mol s^-1
   (n=mass/molar mass)
3. mol s^-1/dm^3 = mol dm^-3 s^-1
   (n=MV)

Question 3

2H2O2→ 2H2O + O2
What percentage of the hydrogen peroxide(H2O2) had decomposed at the 4th minute
(1. 120cm^3 O2(g) produced at 4th min)
(2. 150cm^3 O2(g) produced is MAX pt)

Answer 3

120(O2(g) produced :/=H2O2(aq) decomposed)
/
150(reaction stops: H2O2(aq) is completely decomposed)
x100%
=74.7%

Question 4

Y the initial rate of the reaction is lower than expected? ( By measuring total mass change)

Answer 4

1. CO2(g) evolved HAS TO BE saturated with the conical flask (with reaction mixture) first.
2. So, the total mass of the conical flask & its content does not change much at initial