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A sample of 25.3 g of sodium carbonate, Na2CO3, is dissolved in water and the total volume is made up to 250 mL. Assuming complete dissociation, what are the molar concentrations of Na+ and CO3²− ions, respectively? (Molar mass of Na2CO3 = 106 g mol−1)

1. 0.955 M and 1.910 M
2. 1.910 M and 0.955 M
3. 1.90 M and 1.910 M
4. 0.477 M and 0.477 M

Correct answer: 1.910 M and 0.955 M

Solution

The correct option is right because when sodium carbonate (Na2CO3) dissolves, it dissociates into two sodium ions (Na+) and one carbonate ion (CO3²−). Therefore, the concentration of Na+ ions is twice that of CO3²− ions, leading to 1.910 M for Na+ and 0.955 M for CO3²− in a 250 mL solution.

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