Question

What is $1M$ $NaOH$ ?

Answer 1

We need to know the Molarity if the term often used to describe concentration of the solution. $1M$ solution means $1$ mol of solution in $1L$ of solution.
Concentration is the relative amount of solute in a solution.
The concentration of a substance in solution is expressed as the number of moles of solute per liter of solution. In chemistry, molar concentration is calculated by dividing the moles of solute (n) by the total volume of the solution (V).

Complete answer:
Two solutions with same amount of moles of solute can be represented by the formula:
${C_1}{V_1} = {C_2}{V_2}$
Where, C is the concentration and V is volume.
Molarity indicates the number of moles of solute per litre of solution and is one of the most common units used to measure the concentration. Molarity can be used to determine the volume of solvent or amount of solute. The SI unit for molar concentration is $mol/{m^3}$. However, $mol/L$ is a more commonly used unit for molarity.
While Calculating molarity first we have to find the no. of moles. If the substance is given in grams, then the no. of moles can be found out by dividing mass of the substance with molar mass of the substance.
Given that we have to prepare a $1M$ $NaOH$ solution. The molar mass of $NaOH$ is $40g/mol$ . To prepare $1M$ solution we will dissolve one mole of $NaOH$ in $1L$ of water.
${\text{No}}{\text{. of moles}} = \dfrac{{{\text{Mass of solute}}}}{{{\text{Molar mass}}}}$
Hence for $1M$ mass of solute will be = $40g$
When, $40g$ of $NaOH$ is dissolved in $1L$ of water, we get a $1M$ $NaOH$ solution.

Note:
We have to require that a solution containing 1 mol of solute in $1L$ of solution is called ‘1 Molar solution’. The unit conversion of mol/L to $mol/{m^3}$ is as follows:
$1mol/L = 1mol/d{m^3} = 1M = 1000mol/{m^3}$