Question

What will be the molarity of a $200mL$ solution containing $1.2gm$ of urea?
a.$0.05M$
b.$0.2M$
c.$0.1M$
d.$0.4M$

Answer 1

In this, we need to find out the molarity of the solution which can be calculated using a formula by dividing mass of solute by volume of solution. Molarity is basically the amount of solutes present in the solution.

Complete step by step answer:
Since, we need to find out the molarity of the solution, so we will take a formula:
$Molarity = \dfrac{M}{V}$, where M stands for number of moles solute and V stands for the volume of solution in litres.
We are given the volume of the solution, that is , $200mL$ and mass in grams, that is, $1.2grams$
So, first we need to find out number of moles of Urea and we will find this out using a formula:
$n = \dfrac{m}{M}$, where n stands for the no. of moles, m stands for the mass given and M stands for the molecular weight.
Let’s find out the molecular weight of Urea and water.
Urea: its molecular formula is $N{H_2}CON{H_2}$,
Molecular weight= $14 + 2(1) + 12 + 16 + 12 + 2(1) = 60moles{g^{ - 1}}$
Water: its molecular formula is ${H_2}O$,
Molecular weight= $2(1) + 16 = 18moles{g^{ - 1}}$
No. of moles of urea= given mass by its molecular weight, so
$n = \dfrac{{1.2}}{{60}} = 0.02moles$
Volume of the solution is given $200mL$, first we need to convert the it from $mL$ to $L$
$\therefore$ $0.1M$ $Volume = \dfrac{{200}}{{1000}} = 0.2litre$
Now, we can put these values in the formula of molarity, after putting the values, we get:
$Molarity = \dfrac{{0.02}}{{0.2}} = 0.1M$

$\therefore$ The molarity of the given solution is $0.1M$.

Note:
Before putting the values into the formula we must change the units into those units given in the formula of molarity after changing the units put those values into the formula and then we will get the accurate result.