##### How many moles of each of the following substance are present:

##### (a) A balloon filled with 5g of hydrogen

##### (b) A block of ice that weighs 100 g

Difficulty: Easy

**Problem solving strategy:**

Hydrogen and ice both are molecular substances. Determine their molar masses. Use the molar mass of each to convert masses in grams to moles.

**(a) **Molar mass of H_{2 } = 1.008 x 2 = 2.016 g

1 mole of H_{2} = 2.016 g

$\therefore$ 2.016g of H_{2 }= 1 mole of H_{2}

1 g of H_{2 }= $\frac{1}{2.016}$ moles of H_{2}

5 g of H_{2 }= $\frac{1}{2.016} \times 5$ moles of H_{2}

**= 2.48 moles of H _{2}**

**(b)** 1 mole of ice (H_{2}O) = (2 x 1.008) + 16 = 2.016 +16 = 18.016 g

1 mole H_{2}O = 18.016 g

$\therefore$ 18.016g of H_{2}O = 1 mole

1 g of H_{2}O = $\frac{1}{18.016}$ moles

100 g of H_{2}O_{ }= $\frac{1}{18.016} \times 100$ moles

**= 5.55 moles of H _{2}O**