Question

What is the percent by weight of sodium in sodium sulfate?

Answer 1

Hint: Percent by weight of any substance is the mass of that substance upon the total mass of the compound multiplied by hundred. It is also denoted by m/m %. Sodium sulfate consists of sodium and sulfate ion and has the formula, $N{{a}_{2}}S{{O}_{4}}$ . The molar mass of $N{{a}_{2}}S{{O}_{4}}$is 142.04 g/mol.

Complete answer:
We have been given to find the weight percent of sodium sulfate which is $N{{a}_{2}}S{{O}_{4}}$. Percent by weight of any substance is the mass of the substance whose percent is to be found upon the total mass of the compound into hundred. So, we will divide the molar mass of sodium by molar mass of sodium sulfate and multiply it into hundred.
But as from the formula of sodium sulfate, $N{{a}_{2}}S{{O}_{4}}$the sodium atoms are present in an amount of 2. This is because the sulfate ion has a charge of -2 which needs to be neutralized by the 2 sodium ions. So, the amount of sodium that is its molar mass will be taken 2 times (multiplied by 2). Therefore, the mass percent will be,
Percent of sodium = $\dfrac{2\times mass\,of\,sodium}{mass\,of\,sodium\,sulfate}\times 100%$
Percent of sodium = $\dfrac{2\times 23\,g\,mo{{l}^{-1}}}{142.04\,g\,mo{{l}^{-1}}}\times 100%$
Percent of sodium $\simeq 30\,%$
Hence, the approximate percent by weight of sodium in sodium sulfate is 30%.

Note:
The mass of sodium (Na) is 22.99 g per mole, which is taken as 23 gram per mole. Percent by weight is also called mass by mass percent, denoted by m/m %. Also there is volume by volume percent that involves only volume as v/v %. While mass by volume percent involves mass and volume, as m/v %.