Question

The number of millimoles of solute present in 10ml of decimolar solution is:
(A) 1
(B) ${10^{ - 3}}$
(C) ${10^{ - 2}}$
(D) ${10^{ - 1}}$

Answer 1

Hint: Molarity is defined as the number of moles of solute dissolved in 1 litre of solution.
Molarity= $\dfrac{{n \times 1000}}{V}$

Step by step explanation:
Step1: Given: molarity= 0.1 M
                          V=volume of solution in ml= 10ml
                         N=number of moles of solute=?
Step 2: Moles of solute= given mass/molar mass
$0.1M = \dfrac{{x \times 1000}}{{10ml}}$
X=0.001 moles=$0.001 \times 0.0001 = 0.000001 = {10^{ - 5}}$moles
There are 0.000001 millimoles present in 10 ml of solution.

Additional information: There are many ways to express concentration of a solution- molarity, molality, normality, mass percentage , volume percentage etc. Normality is another term used for expressing the concentration of a solution. As per the standard definition , normality is defined as the number of mole or gram equivalent of solute present in 1 liter of solution. It is denoted by ‘N’. in simple words, normality is equal to molality divided by valency. Or we can say that normality is the number of moles of solute present in equivalent weight of solution. Equivalent weight is molar mass of a substance divided by the valency.

Note: In these types of questions we simply put the given values in the formula and calculate the unknown. Molarity and molality are two terms which look alike but have different meanings. Molarity is defined as the number of moles of solute dissolved in 1 liter of solution. Molality is defined as the number of moles of solute dissolved in 1 Kg of solvent.