Question

Which one of the following is the lightest : a) 0.2 moles of H2 gas b) 6.023X 1022 molecules of nitrogen c)0.1 g of silver d) 0.1 mole of oxygen gas e) 1 gofwater

Answer 1

0 2 hydrogen because it is obvious that hydrogen is lightest known gas

Answer 2

Answer: The correct answer is Option a.

Explanation:

To calculate the mass of the given compound, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$    ....(1)

• For a: 0.2 moles of $H_2$ gas

Moles of hydrogen gas = 0.2 mol

Molar mass of hydrogen gas = 2 g/mol

Putting values in equation 1, we get:

$0.2=\frac{\text{Mass of }H_2\text{ gas}}{2g/mol}\\\\\text{Mass of }H_2\text{ gas}=0.4g$

Mass of hydrogen gas = 0.4 grams

• For b: $6.023\times 10^{22}$ molecules of nitrogen

According to mole concept:

$6.022\times 10^{23}$ molecules constitute 1 mole of a substance

So, $6.023\times 10^{22}$ molecules will occupy = $\frac{1}{6.022\times 10^{23}}\times 6.023\times 10^{22}=0.1mol$

Molar mass nitrogen = 14g/mol

Putting values in equation 1, we get:

$0.1=\frac{\text{Mass of nitrogen}}{14g/mol}\\\\\text{Mass of nitrogen}=1.4g$

Mass of nitrogen = 1.4 grams

• For c: 0.1 g of silver

It is given only silver has 0.1 grams of mass.

• For d: 0.1 mole of oxygen gas

Moles of oxygen gas = 0.1 mole

Molar mass of oxygen gas = 32g/mol

Putting values in equation 1, we get:

$0.1mol=\frac{\text{Mass of oxygen gas}}{32g/mol}\\\\\text{Mass of oxygen gas}=3.2g$

Mass of oxygen gas = 3.2 grams

• For e: 1 g of water

it is given that the mass of water is 1 grams.

From the above calculation, we conclude that the lightest compound is hydrogen gas.

Hence, the correct answer is Option a.