Chapter 10, Problem 155A

Interpretation Introduction

Interpretation:

The information needed for the chemist to find a molecular formula of an unknown compound should be predicted.

Concept introduction:

The representation of atoms of a compound in simple whole number ratio is known as empirical formula.

Chemical formula or molecular formula represents the type of atoms and number of atoms present in a molecule using numerical subscripts and atomic symbol.

Answer to Problem 155A

The percent composition, mass of elements present in the compound, empirical formula and empirical formula mass of the compound should be known.

Explanation of Solution

The rules for determining empirical formula is given as follows:

• Determine the mass of elements in given compound.
• Calculate number of moles using molar mass of each compound or element.
• Divide each number of moles by smallest number of mole value calculated in second step.
• Round the value calculated in step 3 to nearest whole number.

Now, n that is the ratio of given molar mass and empirical formula mass is calculated as follows:

$\text{n}=\frac{\text{Molecular}\text{formula}\text{mass}}{\text{Empirical}\text{formula}\text{mass}}$

Now, the number obtained will be multiplied to empirical formula as follows:

$\text{Molecular}\text{formula}=2\times \text{n}$

Thus, the mass of elements, molar mass of the compound, and empirical formula and its mass should be known to determine the molecular formula for an unknown compound.