Some stoichiometry problems

1. How many milligrams are in 0.250 mmol Fe₂O₃? (39.9 mg).

2. A solution is prepared by dissolving 1.26 g AgNO₃ in a 250 mL volumetric flask and diluting to volume. Calculate the molarity of the AgNO₃ solution. How many mmoles AgNO₃ were dissolved? (0.0297 mmol/ml, 7.42 mmol).

3. How many grams of Na₂SO₄ should be weighed out to prepare 500 mL of a 0.100 M solution? (7.10 g).

4. A 2.6 g sample of plant tissue was analyzed and found to contain 3.6 micrograms of zinc. What is the concentration of zinc in the plant in ppm? In ppb? (1.4 ppm, 1400 ppb).

5. A 0.4671 g sample containing sodium bicarbonate was dissolved and titrated with standard 0.1067 M HCl, requiring 40.72 mL. The reaction is

HCO₃^- + H⁺ --> H₂O + CO₂

Calculate the % sodium bicarbonate in the sample. (78.14%)

6. A 0.2638 g soda ash sample is analyzed by titrating with sodium carbonate with standard 0.1288 M HCl solution, requiring 38.27 mL. The reaction is:

CO₃^2- + 2H⁺ --> H₂O + CO₂

Calculate the % sodium carbonate in the sample. (Hint: pay attention to reaction stoichiometry. 99.02%)

7. How many mL of 0.25 M H₂SO₄ solution will react with 10 mL of 0.25 M NaOH?

H₂SO₄ + 2NaOH --> Na₂SO₄ + 2H₂O

(5 mL).

8. An approximately 0.1 M hydrochloric acid solution is prepared by 120-fold dilution of concentrated hydrochloric acid. It is standardized by titrating 0.1876 g of dried primary standard sodium carbonate:

CO₃^2- + 2H⁺ --> H₂O + CO₂

The titration required 35.86 mL acid. Calculate the molar concentration of hydrochloric acid. (0.09872 mmol/mL).

9. You wish to prepare 500 mL of a 0.100 M K₂Cr₂O₇ solution from a 0.250 M solution. What volume of the 0.250 M solution must be diluted to 500 mL? (200 mL)