Question

How do you determine the formula and molar mass of lead II sulfate?

Answer 1

The answer to this question depend on the concept of the formula mass and the molar mass calculation using the definition that sum of atomic mass of all the atoms in formula unit gives formula mass and the quantity of the substance is the molar mass in grams.

Complete answer:
In the classes of basic concepts of chemistry from the previous chapters, we have come across some of the basic concepts like the empirical formula calculation, molecular formula calculation, formula mass, molar mass and also many other terms.
Let us now see the calculation of molar mass and formula mass according to their definitions.
- Formula mass is defined as ‘the sum of the atomic masses of all the atoms in the formula unit in an ionic crystal’.
- Molar mass of a substance is defined as the quantity of the substance which is equal to the molecular mass in grams.
Now, lead II sulfate has the molecular formula $PbS{{O}_{4}}$ and the molar mass of this compound can be calculated using the individual masses of the atoms present in it which is as shown below,
Mass of lead that is $Pb=207.2g/mol$ .
Mass of sulphur that is $S=32.06g/mol$
and mass of oxygen is $16g/mol$
$\Rightarrow 207.2+32.06+4\times 16=303.26gmo{{l}^{-1}}$
Therefore, molar mass of lead II sulfate is $303.26gmo{{l}^{-1}}$
Now, the formula mass according to the definition says that the sum of atomic masses of all the units in the given compound will give the formula mass and if we calculate, we get the same answer as above.
Thus, formula mass of lead II sulfate is also $303.26gmo{{l}^{-1}}$

Note:
Note that formula mass and the molar mass are one and the same as they are having the different terms but the calculation is based on the same data and definition and therefore will give the same answer.