Question

25.3 g of sodium carbonate, `Na_(2)CO_(3)` is dissolved in enough water to make 250 mL of solution. If sodium carbonate dissociates completely, molar concentration of sodium ions, `Na^(+)` and carbonate ions, `CO_(3)^(2-)` are respectively (Molar mass of `NaCO_(3)=106g mol^(-1)`)
A. 0.477 M and 0.477 M
B. 0.955 M and 1.910 M
C. 1.910 M and 0.955 M
D. 1.90 M and 1.910 M

Answer 1

Correct Answer - C
Molarity `(M)=(wt)/(mol.wt.)(1000)/("vol(in ml)")`
`=(25.3)/(106)xx(1000)/(250)=0.955` mol/L of `Na_(2)CO_(3)`
and `Na_(2)CO_(3)rarr 2Na^(+)+CO_(3)^(-2)`
therefore `[Na^(+)]=2xx0.955=1.910 M`
`[CO_(3)^(-2)]=0.955 M`