Question

How many grams of NaCl will be required to make 100 millilitres of 2M solution?
(A) 5.85
(B) 11.7
(C) 29.2
(D) 58.5
(E) 117

Answer 1

Hint: The concentration of a solution expressed is describing the composition of a solution. These expressions may be either quantitatively or qualitatively. For example, the solution is a dilute or concentrated solution that will describe the quantity of solute. There are several ways of describing the concentration of the solution quantitatively.

Complete step by step solution:
The concentration of the solution is expressed quantitatively as follows,
(1) Molarity
(2) Normality
(3) Mole fraction
(4) Molality
Molarity: it is defined as the number of moles of solute dissolved in one litre of solution. Molarity of solution expressed units in moles/litre or M/L.
Molarity = $\dfrac{moles\text{ }of\text{ }solute}{volume\text{ }of\text{ }solution\text{ }in\text{ L}}$
Given solute is sodium chloride, NaCl.
Molar mass of NaCl = $23 + 35.5$ $= 58.5$ $g/mol$
Weight of NaCl, w =?
Given volume of solution = $100$ $mL$ = $0.1 L$
Molarity of solution (given) = $2M$
Moles of solute = moles of NaCl = $\dfrac{Weight\text{ }of\text{ }NaCl}{Molar\text{ }mass\text{ }of\text{ }NaCl}=\dfrac{w}{58.5}$
Substitute these values in molarity formula, then
$2M =$ $\dfrac{(\dfrac{w}{58.5})}{0.1L}$
$0.2=$ $\dfrac{w}{58.5}$
$w =$ $11.7 grams$
Hence, 11.7 grams of NaCl will be required to make 100 millilitres of 2M solution.

The correct answer is option B.

Note: One of the most common units to measure the concentration of the solution is molarity, which indicates the number of moles of solute per litre of solution. A specific element or compound dissolved or prepared a certain amount of solution is calculated by the molarity of the solution in the chemistry laboratory.