Question

Explain how you will find the mass of sodium needed to make $5.68L$ of hydrogen gas STP after the reaction, described in the following equation:
$2Na + 2H_2O \to 2NaOH + H_2$

Answer 1

We need to make sure that the given equation is always balanced, if not, we should balance it. Only from a balanced equation we can correctly associate the number of moles of the target elements, which are sodium and hydrogen here. The steps we follow to get the final answer would be to first find the total number of moles required from hydrogen’s volume, then to find mass of sodium by the molar ratio.

Complete step by step answer:
Let us look at what is given to us;
The volume of hydrogen gas at STP required $= 5.68L$
To find, the mass of sodium $= ?$
We also have a balanced equation provided in the question, let us note it down again;
$2Na + 2H_2O \to 2NaOH + H_2$
Now we need to understand from the balanced equation that, from the left hand side, $2$ moles of sodium ( $2Na$ ) is able to make $1$ mole of hydrogen gas ( $H_2$ ) as given on the right hand side.
We need to know the relationship between mole and litres;
By result: $22.4L$ of volume comprises $1$ mole of a gas
If that is the case then; $1L$ is equivalent to $\dfrac{{1\;mol}}{{22.4\;L}}$
Consequently, for $5.68L$ of hydrogen gas there will be $\dfrac{{5.68\;L}}{{22.4\;L/mol}}$ moles of hydrogen.
$\therefore 5.68L\;H_2$ contains $0.254$ moles of $H_2$ .
Since we know from the balanced equation that the ratio of $Na:H_2$ is $2:1$ , for sodium we need twice the number of moles, that is $0.507$ moles.
Let us consider sodium’s molecular weight now, that is $23\;g/mol$
Therefore to find mass of sodium we need to apply a formula:
$Mass\; = Number\;of\;moles \times Molecular\;weight$
$Mass\;of\;Na = 0.507mol \times 23g.mo{l^{ - 1}}$
$\therefore$ $Mass\;of\;Na$ needed to make $5.68L\;of\;H_2$ $= 11.67g$

Note: The mole concept is a widely used concept in Chemistry. Mole is similar to generic units like dozen, pair, etc. A mole gives an accurate quantity for the number of atoms or molecules in the given matter. A universally accepted constant, Avogadro’s number is said to be the number of entities inside a mole, the number has been calculated to be $6.023 \times {10^{23}}$ . In a balanced equation the number given to the left of the components in the equation is said to describe the number of moles of that component required to produce the entities on the product side.