Question

2H2 +O2 → 2H2O

What mass of water forms when 1.45 × 10-3 g O2 react completely? (Molar mass of O2 = 32.00 g/mol; molar mass of H2O = 18.02 g/mol)

1.63 × 10-3 g

8.16 × 10-4 g

1.29 × 10-3 g

Answer 1

1.63 x 10 ^3 g is the correct answer 

Answer 2

Answer : The correct option is,
`1.63* 10^(-3)g`

Explanation : Given,

Mass of oxygen gas =
`1.45* 10^(-3)g`

Molar mass of oxygen gas = 32 g/mole

Molar mass of water = 18.02 g/mole

First we have to calculate the moles of
`O_2`.

`\text{Moles of }O_2=\frac{\text{Mass of }O_2}{\text{Molar mass of }O_2}=(1.45* 10^(-3)g)/(32g/mole)=4.53* 10^(-5)moles`

Now we have to calculate the moles of
`H_2O`.

The balanced chemical reaction is,

`2H_2+O_2\rightarrow 2H_2O`

From the balanced reaction we conclude that

As, 1 mole of
`O_2` react to give 2 mole of
`H_2O`

So,
`4.53* 10^(-5)`moles of
`O_2` react to give
`4.53* 10^(-5)* 2=9.06* 10^(-5)` moles of
`H_2O`

Now we have to calculate the mass of
`H_2O`

`\text{Mass of }H_2O=\text{Moles of }H_2O* \text{Molar mass of }H_2O`

`\text{Mass of }H_2O=(9.06* 10^(-5)mole)* (18.02g/mole)=1.63* 10^(-3)g`

Therefore, the mass water produced is,
`1.63* 10^(-3)g`