Question

Calculate the volume of hydrogen gas evolved when 460g of sodium is reacted with excess water at STP.

Answer 1

Hint:
STP stands for standard temperature and pressure. These are set by the IUPAC(International Union of Pure and Applied Chemistry) as $0^{\circ }C$ temperature and $1bar$ pressure. When sodium reacts with water, a salt is formed and hydrogen gas is liberated.

Complete step by step answer:
STP conditions are mostly assigned to gases because their characteristics or properties change drastically with change in temperature or pressure. At STP , one mole of any gas occupies $22.4litres$ .
When sodium reacts with water the reaction can be written as-
$2Na(s)+2H_{2}O(l)\to 2NaOH+H_2(g)$
The above reaction is a balanced chemical equation. We can see that in the reaction when two moles of sodium reacts with water, one mole of hydrogen gas is evolved.
Now it is given that $460g$ of sodium reacts with water, first let us calculate the number of moles of sodium in $460g$ .
We know that molar mass of sodium is $23gmo{l}^{-1}$ . So the number of moles in $460g$ of sodium is
$=46023=20moles$ of sodium.
There are $20moles$ of sodium in $460g$ of sodium samples. Now from the reaction we know that two moles of sodium releases one mole of hydrogen gas. So , $20moles$ of sodium will release $10moles$ of hydrogen gas.
We know that at STP one mole of any gas occupies $22.4litres$ . It means that one mole of hydrogen also occupies $22.4litres$ of volume at STP. So $10moles$ of hydrogen gas will occupy $=22.4\times 10=224litres$ of volume at STP.
So the volume of hydrogen gas evolved is $224litres$ or $224000mL$ when $460g$ of sodium reacts with excess water at STP.
Therefore, the correct option is (A) .

Additional information:
There are two conditions-STP and NTP. NTP stands for normal temperature and pressure. NTP uses a temperature of ${20}^{\circ }C(293.15K)$ and $1atm$ pressure.

Note:The mass of one mole of a substance is equal to its molar mass. One mole of any substance contains Avogadro’s number of particles. Remember at STP, volume of one mole of gas occupies $22.4litres=22.4d{m}^3=22400mL=22400c{m}^3$