Question

Q1 For a first order reaction it takes 5 minutes for the initial concentration of 0.6 molL-1 . how long will it take for the initial concentration to become 0.3 molL-1 ?


Q2 0.5g of KCl was dissolved in 100g of water and the solution originally at 20*C froze at -0.24*C. Calculate the percentage of dissociation of salt ( Kf for water per 1000g= 1.86 K). Hence calculate its molality.


Q3 . Why are carbohydrates generally optically active?

pls answer all the questions

Answer 1

Rate law follows first order kinetics.

N=N_o\times e^{-\lambda t}N=N

o

×e

−λt

N = amount left after time t = 0.4 M

N_0N

0

= initial amount = 0.6 M

\lambdaλ = rate constant

t= time = 5minutes

0.4=0.6\times e^{-\lambda\times 5minutes}0.4=0.6×e

−λ×5minutes

\lambda=0.083minutes^{-1}λ=0.083minutes

−1

Now, N = amount left after time t = 0.3 M, we need to find t

Again putting in the values:

0.3=0.6\times e^{-0.083minutes^{-1}\times tminutes}0.3=0.6×e

−0.083minutes

−1

×tminutes

t=8.35minutest=8.35minutes

It will take 8.35 minutes to reduce 0.6 m to 0.3 m.