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:

CO32-  + 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:

CO32- + 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)