Question

What is the mass of crystalline oxalic acid (molar mass = 126 g/mol) present in 50 mL of 0.02N aqueous oxalic acid solution?

• A. 63 mg
• B. 6.3 mg
• C. 31.5 mg
• D. 0.063 mg
• E. 310 mg

Hint:

In solutions, normality (N) is used to express the equivalent concentration of a solution. Remember, normality is related to molarity by the number of replaceable ions or equivalents in the solution.

Answer 1

The Correct Option is A

We are given the following information:

- Normality (N) = 0.02 N
- Volume of solution = 50 mL = 0.050 L
- Molar mass of oxalic acid = 126 g/mol

We know that normality \( N \) is related to molarity \( M \) by the equation:

\[ N = n \times M \] where \( n \) is the number of equivalents per mole. For oxalic acid (H$_2$C$_2$O$_4$), the number of replaceable hydrogen ions \( n \) is 2, because each molecule of oxalic acid can donate two protons (H$^+$) in a reaction.

Therefore, the molarity of the oxalic acid solution is:

\[ M = \frac{N}{n} = \frac{0.02}{2} = 0.01 \, \text{mol/L} \] Now, the amount of substance (in moles) present in 50 mL (0.050 L) of the solution is:

\[ \text{moles of oxalic acid} = M \times \text{Volume} = 0.01 \times 0.050 = 0.0005 \, \text{mol} \] Finally, to find the mass, we use the molar mass of oxalic acid:

\[ \text{mass} = \text{moles} \times \text{molar mass} = 0.0005 \times 126 = 0.063 \, \text{g} = 63 \, \text{mg} \]
Thus, the mass of oxalic acid in 50 mL of the solution is:

\[ \boxed{63 \, \text{mg}} \]