Question

In a first order reaction, the reactant has a half-life period of ten minutes. What fraction of the substance will be left after an hour of the reaction has occured?

• A. $\frac{1}{6}$ of the initial the concentration
• B. $\frac{1}{64}$ of the initial the concentration
• C. $\frac{1}{12}$ of the initial the concentration
• D. $\frac{1}{32}$ of the initial the concentration

Answer 1

The correct option is B $\frac{1}{64}$ of the initial the concentration

In a first order reaction, fraction of the substance $=\frac{1}{2^n}$ of the initial the concentration, where n is the number of half lives.
As the half life of the reaction is 10 minutes, in an hour there are 6 half lives. So, the fraction of the substance =$\frac{1}{2^6}=\frac{1}{64}$