An igneous rock originally has 3 grams of uranium 238 in it. When dated the rock only contains 1.8 grams. What are the parent and daughter concentrations (in percentages) and what is its age?

Answer :

The parent and daughter concentrations (in percentages) is, 60 % and 40 % respectively.

The age of rock is

Explanation :

First we have to calculate the parent and daughter concentrations (in percentages).

and,

As we know that, the half-life of uranium-238 = years

Now we have to calculate the rate constant, we use the formula :

Now we have to calculate the time passed.

Expression for rate law for first order kinetics is given by:

where,

k = rate constant  =

t = time passed by the sample  = ?

a = initial amount of the reactant  = 3 g

a - x = amount left after decay process = 1.8 g

Now put all the given values in above equation, we get

Therefore, the age of rock is