Chapter U4, Problem C15.5RE

(a)

Interpretation Introduction

Interpretation: The steps to make 0.5 M solution of sodium hydroxide needs to be explained.

Concept Introduction: Mole concept is used to calculate the moles, mass, number of atoms and moles of a compound. The relation between these values can be shown as:

  $\begin{array}{l}\text{Moles = }\frac{\text{mass}}{\text{molar mass}}\\ {\text{1 mole = N}}_{\text{a}}\text{ atoms}\\ {\text{N}}_{\text{a}}\text{ = 6}\text{.022 }\times {\text{ 10}}^{\text{23}}\end{array}$

Answer to Problem C15.5RE

• Take 19.9 g of solid NaOH solution.
• Measure 1 L of water with the help of measuring cylinder
• Add water in beaker containing 19.9 g of solid NaOH
• Stir the solution till complete NaOH dissolved in it.

Explanation of Solution

To make 0.5 M solution of NaOH; 0.5 M stands for 0.5 moles of NaOH dissolves in 1 L of water.

Molar mass of NaOH = 39.9 g/mol

Calculate the mass of NaOH required:

  $\begin{array}{l}\text{Moles = }\frac{\text{mass}}{\text{molar mass}}\\ \text{Mass = moles×molar mass}\\ \text{Mass = 0}\text{.5 M × 39}\text{.9 g/mol }\\ \text{Mass = 19}\text{.9 g}\end{array}$

Thus to make 0.5 M solution of 1 L of NaOH:

• Take 19.9 g of solid NaOH.
• Measure 1 L of water with the help of measuring cylinder
• Add water in beaker containing 19.9 g of solid NaOH
• Stir the solution till complete NaOH dissolves in it.

(b)

Interpretation Introduction

Interpretation: The use of 1 L of water while making 0.5 M solution of sodium hydroxide needs to be explained.

Concept Introduction: The molecular mass of compound is the sum of atomic mass of all the atoms present in the given chemical compound. Mole concept is used to calculate the moles, mass, number of atoms and moles of a compound. The relation between these values can be shown as:

  $\begin{array}{l}\text{Moles = }\frac{\text{mass}}{\text{molar mass}}\\ {\text{1 mole = N}}_{\text{a}}\text{ atoms}\\ {\text{N}}_{\text{a}}\text{ = 6}\text{.022 }\times {\text{ 10}}^{\text{23}}\end{array}$

Answer to Problem C15.5RE

The volume of water depends on the volume of solution required. If less than 1 L volume of solution required, less volume of water and corresponding mass of NaOH can be used.

Explanation of Solution

To make 0.5 M solution of NaOH; 0.5 M stands for 0.5 moles of NaOH dissolves in 1 L of water. Thus to make 0.5 M solution of 1 L of NaOH take 19.9 g of solid NaOH and dissolve it in 1 L of water.

Thus the volume of water depends on the volume of solution required. If less than 1 L volume of solution required, less volume of water and mass of NaOH can be used.