Question

A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the empirical formula of the compound?

Answer 1

Answer: The empirical formula of the compound is
`Ca(OH)_2`

Step-by-step explanation:

To find the empirical formula of the compound, we follow following steps:

• Step 1: Finding the number of moles of the given elements.

To calculate the number of moles, we use the formula:

`\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}`

• For Calcium:

Molar mass of calcium = 40 g/mol

Given mass of calcium = 13.5 g

Putting values in above equation, we get:

`\text{Number of moles}=(13.5g)/(40g/mol)=0.3375`

• For Oxygen:

Molar mass of oxygen = 16 g/mol

Given mass of oxygen = 10.8 g

Putting values in above equation, we get:

`\text{Number of moles}=(10.8g)/(16g/mol)=0.675`

• For Hydrogen:

Molar mass of hydrogen = 1 g/mol

Given mass of hydrogen= 0.675 g

Putting values in above equation, we get:

`\text{Number of moles}=(0.675g)/(1g/mol)=0.675`

• Step 2: Now, to obtain the mole ratio, we divide the moles of each element by the smallest number of moles calculated.

For Ca =
`(0.3375)/(0.3375)=1`

For H =
`(0.675)/(0.3375)=2`

For O =
`(0.675)/(0.3375)=2`

The ratio of Ca : O : H = 1 : 2 : 2

• Step 3: Now, the ratio of the elements is represented as the subscripts in the empirical formula.

The formula becomes:
`CaO_2H_2\approx Ca(OH)_2`

Hence, the empirical formula of the compound is
`Ca(OH)_2`