Question

a) What is the law of constant proportion?
b) What is molality? Why is it superior over molarity?
c) How are 0.50 $N{a_2}C{O_3}$ and 0.50M $N{a_2}C{O_3}$ different?

Answer 1

a) Law of constant proportion states that compound always consists of the same elements that are combined together in a fixed proportion by mass.
b) Volume changes with the temperature and mass is constant at any temperature.
c) Use the molar mass of $N{a_2}C{O_3}$.

Complete step by step answer:
A.The law of constant proportion states that, “for any particular chemical compound, all samples of that particular compound will be made up of the same elements in the same proportion or ratio. For example, ${H_2}O$ molecule is made of hydrogen and oxygen atoms in ratio 2:1.
B.Molality can be defined as the number of moles solute per kilogram of solvent. The S.I unit for molality is mol/kg.
Molality depends upon mass of solvent whereas, the molarity depends upon the volume of solution. Volume varies with the variation in temperature and pressure. So, molarity also depends upon the temperature and pressure. We know that mass does not vary with temperature and pressure. Hence, molality is superior over molarity.
C.First, we need to find the molar mass of $N{a_2}C{O_3}$.
So, the molar mass of $N{a_2}C{O_3}$ is $106g/mol$.
Now, 0.5 moles of $N{a_2}C{O_3}$ means $0.5 \times 106 = 53g$, and
0.5 M of $N{a_2}C{O_3}$ means 0.5 moles of $N{a_2}C{O_3}$, that is, 53g of $N{a_2}C{O_3}$ are present in one liter of the solution.

Note:
The relationship between volume and temperature was stated by Charles's Law which states that the, “volume of given amount is directly proportional to the temperature”, this is how the volume depends upon the temperature.