Chapter U4.78, Problem 1E

Interpretation Introduction

Interpretation:

The method for conversion between moles of substance to grams of a substance should be determined.

Concept Introduction:

Mole is SI unit which is used to measure the quantity of the substance. It is the quantity of a substance which contains same number of atoms as present in accurately 12.00 g of carbon-12 is known as mole.

The one mole of any substance is equal to the Avogadro number i.e. $6.022\times {10}^{23}$ atoms.

Answer to Problem 1E

Mass of substance in g is obtained by multiplying molar mass of a substance with number of moles of substance.

Explanation of Solution

Number of moles is defined as the ratio of mass to the molar mass of the substance.

The mathematical expression is given as:

  $\text{Number of moles =}\frac{\text{mass (g)}}{\text{molar mass}}$

Since, unit of number of moles = mole

Unit of molar mass = g/mole

Therefore,

  $\text{mole =}\frac{\text{g}}{\text{g/mole}}$

  $\text{<menclose notation="horizontalstrike"> m </menclose><menclose notation="horizontalstrike"> o </menclose> l<menclose notation="horizontalstrike"> e </menclose> }\times \frac{\text{g}}{\text{<menclose notation="horizontalstrike"> m </menclose><menclose notation="horizontalstrike"> o </menclose> l<menclose notation="horizontalstrike"> e </menclose>}}\text{= g}$

Thus, number of moles of a substance is converted into grams of a substance.

For an example:

Number of moles of a substance = 2 moles

Molar mass of a substance = 2 g/mole

Conversion of number of moles to mass is shown as:

  $\text{Number of moles =}\frac{\text{mass (g)}}{\text{molar mass}}$

Put the values,

  $\text{2 mole =}\frac{\text{mass (g)}}{\text{2 g/mole}}$

  $\text{2 mole}\times \text{2 g/mole = mass (g)}$

  $\begin{array}{l}\text{ Mass (g) =2 <menclose notation="horizontalstrike"> m </menclose><menclose notation="horizontalstrike"> o </menclose> l<menclose notation="horizontalstrike"> e </menclose> }\times \text{2 g/<menclose notation="horizontalstrike"> m </menclose><menclose notation="horizontalstrike"> o </menclose> l<menclose notation="horizontalstrike"> e </menclose> }\\ \text{ = 4 g}\end{array}$

Thus, by multiplication between molar mass and number of moles, mass of a substance in g is obtained.