Question

How many moles are in $2.5$ grams of KCN?

Answer 1

Hint: We can calculate the moles of KCN using the grams of KCN and the molar mass of KCN. When we divide the grams of KCN with molar mass of KCN, we will obtain the moles of KCN. We can calculate the molar mass of KCN using the atomic mass of potassium, carbon, and nitrogen. The sum of the atomic masses of all these elements would give the molar mass of KCN.

Complete step by step answer:
Given data contains,
Mass (in grams) is $2.5$ g.
Let us now calculate the molar mass of KCN.
The atomic mass of potassium is $39g$
The atomic mass of carbon is $12g$
The atomic mass of nitrogen is $14g$.
When we add up, all the atomic masses of these elements, we get the molar mass of KCN as $65g/mol$.
So, we can write the formula to calculate the moles of KCN as,
${\text{Moles of KCN}} = \dfrac{{{\text{Grams of KCN}}}}{{{\text{Molar mass of KCN}}}}$
We have that the grams of KCN is $2.5$ and the molar mass of KCN is $65g/mol$. Let us now substitute these values in the above expression to get the moles of KCN.
We could calculate the moles of KCN as,
${\text{Moles of KCN}} = \dfrac{{{\text{Grams of KCN}}}}{{{\text{Molar mass of KCN}}}}$
Now we can substitute the known values we get,
Moles of $KCN = \dfrac{{2.5g}}{{65g/mol}}$
On simplification we get,
Moles of $KCN = 0.038mol$
The moles of KCN in $2.5$ grams of KCN is $0.038mol$ which on approximation could be $0.04mol$.

Note:
We can say that a mole contains $6.022 \times {10^{23}}$ particles. These particles could be molecules, atoms, electrons, (or) ions. Generally, we could define one mole as the amount of substance that is present in 12 grams of carbon-12, an isotope of carbon. Using the moles, we can calculate the molar concentration, mole fraction, and molality. We can say that the SI unit to measure the amount of substance is one mol.