Answer : The initial mass of the sample is, 31.9 mg
Explanation :
Half-life = 4 days
First we have to calculate the rate constant, we use the formula :
Now we have to calculate the initial mass of sample.
Expression for rate law for first order kinetics is given by:
where,
k = rate constant =
t = time passed by the sample = 12 days
a = initial amount of the reactant = ?
a - x = amount left after decay process = 4 mg
Now put all the given values in above equation, we get
Therefore, the initial mass of the sample is, 31.9 mg