Question

How many grams of hydrogen are needed to produce 1.80 g of water according to this equation? 2H2 + O2 → 2H2O

A) 0.100 g B) 0.180 g C) 0.200 g D) 2.00 g E) 4.00 g

Answer 1

Answer is c

Work out the moles of 2H2O: 1.80/ (16+1+1) = 0.1
The moles of 2H2 are the same (0.1)
The Mr of H2 is 2

So the mass needed to produce 1.80g of water is
0.1 x 2 = 0.2

Answer 2

Answer : The correct option is, (C) 0.200 g

Explanation : Given,

Mass of water = 1.80 g

Molar mass of water = 18 g/mole

Molar mass of
`H_2` = 2 g/mole

First we have to calculate the moles of water.

`\text{Moles of }H_2O=\frac{\text{Mass of }H_2O}{\text{Molar mass of }H_2O}=(1.80g)/(18g/mole)=0.1mole`

Now we have to calculate the moles of hydrogen gas.

The given balanced reaction is,

`2H_2+O_2\rightarrow 2H_2O`

From the balanced reaction we conclude that

As, 2 mole of water obtained from 2 mole of
`H_2` gas

So, 0.1 mole of water obtained from 0.1 mole of
`H_2` gas

Now we have to calculate the mass of hydrogen gas.

`\text{Mass of }H_2=\text{Moles of }H_2* \text{Molar mass of }H_2`

`\text{Mass of }H_2=(0.1mole)* (2g/mole)=0.2g`

Therefore, the mass of hydrogen gas required will be, 0.2 grams