Question

25.3 g of sodium carbonate, \[\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\] is dissolved in enough water to make 250 mL of solution. If sodium carbonate dissociates completely, molar concentration of sodium ion, Na+ and carbonate ions are:
(Molar mass \[\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\]=106 g mol-1)
A. 0.955M and 1.910M
B. 1.910M and 0.955M
C. 1.90M and 1.910M
D. 0.477M and 0.477M

Answer 1

Hint: In order to solve this question, we have to consider the number of moles of solute and litres of solvent. Using the formula to find the molar concentration we can find the answer to this question.
Formula used: Molar Concentration = Moles of Solute / Litres of solution

Step by step answer:
Hence, molar concentration of sodium ion and carbonate ion can be calculated as:
\[Number\text{ }of\text{ }moles\text{ }of\text{ }N{{a}_{2}}C{{O}_{3}}\text{ }=\text{ }\dfrac{25.3}{106}\text{ }=\text{ }0.239\text{ }moles\]
\[Molarity\text{ }of\text{ }solution\text{ }=\text{ }\dfrac{0.239}{0.25}\text{ }=\text{ }0.956\text{ }mole/litre\]
\[N{{a}_{2}}C{{O}_{3}}\xrightarrow{{}}2N{{a}^{+}}\text{ }+\text{ }C{{O}_{3}}^{2-}\]
\[\therefore \] Concentration of \[C{{O}_{3}}^{2-}\] \[=\text{ }0.956M\]
Concentration of \[N{{a}^{+}}\text{ }=\text{ }2\times 0.956\text{ }=\text{ }1.912M\]

Additional Information:
Molar concentration is also known as molarity. It is the measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solution.
The molar mass is the mass of a given chemical element or chemical compound (g) divided by the amount of substance (mole). The molar mass of a compound can be calculated by adding the standard atomic masses (in \[g/mole\]) of the constituent atoms.

Note: Molarity is very important in chemistry for one reason. That is, it is the measurement of concentration in any mixture. The molarity of any solution is a way to know the specific elements and compounds which are present in any solution.
The importance of molar mass of a compound is that it denotes the mass of a sample of that compound divided by the amount of substance in that sample which is measured in moles.
The molar mass is an intensive property of the substance that does not depend on the size of the sample.