Question

How do you determine the mass of potassium in 33.5 g of KCl?

Answer 1

Hint: There is a formula to calculate the number moles of a compound and it is as follows.
Number of moles of a compound $\text{=}\frac{\text{weight of the compound}}{\text{molecular weight of the compound}}$. We should know the weight and molecular weight of the compound to get the number moles of the compound.

Complete answer:
- In the question it is asked to find the mass of the potassium in 33.5 g of potassium chloride (KCl).
- The molecular weight of the potassium chloride (KCl) is 74.55 g/mol.
- The given weight of the potassium chloride (KCl) is 33.5 gram.
- We know that the atomic weight of the potassium is 17.56 g.
- Number of moles of potassium chloride $\text{=}\frac{\text{weight of the compound}}{\text{molecular weight of the compound}}=\frac{33.5}{74.55}$
- We know that x mole of potassium chloride contains y moles of potassium atoms.
- Then mass of the potassium in potassium chloride = (moles of potassium) ( molar mass of the potassium.
- Number of moles of potassium $=\frac{33.5}{74.55}$
- Molar mass of the potassium = 39.0983
- Substitute the known values in the above formula to get the mass of the potassium in the given sample and it is as follows.
 \[\begin{align}
  & =\frac{33.5}{74.55}\times 39.0983 \\
 & =17.569g \\
\end{align}\]
Therefore, the mass of potassium in 33.5 g of KCl is 17.569 g.

Note: We should know some basic values while calculating the mass of a particular element. Without knowing the values and formulas we cannot go forward to calculate the number of moles of a particular substance or compound.