Question

2. How many grams of solid lithium must be added to liquid water in order to obtain 15.0 L of

hydrogen gas at STP? (Answer: 9.29g)
2 Li + 2H20 → 2LiOH + H2

Answer 1

9.4g

Step-by-step explanation:

Given parameters:

Volume of hydrogen gas at STP = 15L

Unknown:

Mass of solid lithium = ?

Solution:

The reaction equation is shown below;

2Li + 2H₂O → 2LiOH + H₂

To solve this problem, lets work from the known to the unknown. The known here is hydrogen gas;

At STP;

number of moles =
`(volume of gas)/(22.4)` =
`(15)/(22.4)` = 0.67mole

From the balanced reaction equation;

1 mole of hydrogen gas is produced from 2 moles of Li;

0.67 moles of hydrogen will be produced from 0.67 x 2 = 1.34moles

Mass of solid lithium = number of moles x molar mass

= 1.34 x 7

=9.4g