Question

A solution was made by dissolving 12.5 g of solid Na2C2O4 in enough water to make 750 ml of solution. Calculate the molarity of Na in the solution.

A. 0.2 M
B. 0.5 M
C. 1.0 M
D. 2.0 M

Answer 1

The molarity of Na in the solution is calculated by determining the moles of Na from the given mass of Na2C2O4, accounting for the 2:1 ratio of Na to Na2C2O4, and then dividing by the volume of the solution in liters. The result is 0.250 M, which doesn't match any of the given options.

Step-by-step explanation:

To calculate the molarity of Na in a solution made by dissolving 12.5 g of solid Na2C2O4 (sodium oxalate) in enough water to make 750 ml of solution, follow these steps:

1. Determine the molar mass of Na2C2O4. The atomic weights are Na (22.99 g/mol) and C2O4 (88.02 g/mol), giving a total of (2 × 22.99) + 88.02 = 133.00 g/mol for sodium oxalate.
2. Calculate the number of moles of Na2C2O4: 12.5 g ÷ 133.00 g/mol = 0.0940 mol.
3. Since there are 2 moles of Na for every mole of Na2C2O4, multiply the moles of Na2C2O4 by 2 to find the moles of Na: 0.0940 mol × 2 = 0.188 mol Na.
4. Convert the volume of the solution to liters: 750 mL is 0.750 L.
5. Finally, divide the moles of Na by the volume of the solution in liters to find the molarity: 0.188 mol Na ÷ 0.750 L = 0.250 M Na.

This result indicates that the molarity of Na in the solution is 0.250 M, which is not one of the options provided. It's important to double-check the calculation, the molecular weight used, and the volume of solution to ensure accuracy.