If the relative molecular mass of NaNO3 is 85, then find the percentage of oxygen it contains. (Atomic weight of sodium=23, nitrogen=14 and oxygen=16)
Answers
Answer:
The relative formula mass of a substance is the sum of the relative atomic masses of the elements present in a formula unit. The symbol for relative formula mass is Mr.
If the substance is made of simple molecules, this mass may also be called the relative molecular mass.
How to calculate the relative formula mass?
Example:
What is the relative mass formula of hydrogen gas? (Relative atomic mass: H = 1)
Solution:
The formula for hydrogen gas is H2. Each molecule contains 2 hydrogen atoms.
The relative mass formula of hydrogen gas is
Mr(H2) = 2 × Ar(H) = 2 × 1 = 2
Example:
What is the relative mass formula of water? (Relative atomic masses: H = 1, O = 16)
Solution:
The formula for water is H2O. Each molecule contains 2 hydrogen atoms and 1 oxygen atom.
The relative mass formula of water is
Mr(H2O) = 2 × Ar(H) + Ar(O) = 2 × 1 + 16 = 18
Example:
What is the relative mass formula of sodium chloride? (Relative atomic masses: Na = 23, Cl = 35.5)
Solution:
Sodium Chloride is an ionic solid with the formula Na+Cl-.
The relative mass formula of sodium chloride is
Mr(NaCl) = Ar(Na) + Ar(Cl) = 23 + 35.5 = 58.5