A student masses a green crystal sample and records 1.253 grams. He then dissolves the green crystal in water and does a titration, and calculates that his sample has 7.35x10-3 moles of C2O4-2. What is the percent of C2O4-2 in the sample?
a. not enough information is given
b. 51.63%
c. 129%
d. 0.5866%
e. 20.62%

b. 51.63%

Explanation:

Step 1: Given data

Step 2: Calculate the mass corresponding to 7.35 × 10⁻³ moles of oxalate

The molar mass of C₂O₄²⁻ is 88.02 g/mol.

7.35 × 10⁻³ mol × 88.02 g/mol = 0.647 g

Step 3: Calculate the mass percent of oxalate in the sample

% w/w = mass of oxalate / mass of the sample × 100%

% w/w = 0.647 g / 1.253 g × 100%

% w/w = 51.63%

law of conservation of matter