Question

Given that the molar mass of NaOH is 40.00 g/mol, what mass of NaOH is needed to make 2.500 L of a 2.000 M NaOH solution?

Answer 1

Mass = 200 g

Solution:

Molarity is the amount of solute dissolved per unit volume of solution. It is expressed as,

Molarity = Moles / Volume of Solution ----- (1)

Data Given;

Molarity = 2.0 mol.L⁻¹

Volume = 2.5 L

M.Mass = 40.0 g.mol⁻¹

First calculate Moles as,

Moles = Molarity × Volume

Putting Values,

Moles = 2.0 mol.L⁻¹ × 2.5 L

Moles = 5 mol

Secondly, calculate Mass using following formula,

Moles = Mass ÷ M.Mass

Solving for Mass,

Mass = Moles × M.Mass

Putting Values,

Mass = 5 mol × 40.0 g.mol⁻¹

Mass = 200 g

Solution Preparation:

Add 200 g of NaOH in a Volumetric Flask and add distilled water upto the mark of 2.5 L. Shake it and you have prepared a 2.5 L of 2.0 M solution of NaOH.

Answer 2

There are a number of ways to express concentration of a solution. This includes molarity. Molarity is expressed as the number of moles of solute per volume of the solution. The mass of NaOH needed for the solution is calculated as follows:

2 M = amount in moles of solute / 2.5 L

amount in moles of solute = 5 mol NaOH

amount in grams = 5 x 40 = 200 grams NaOH