Chem5HW1 - First Homework set for chem 5 PDF

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First Homework set for chem 5...

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Graded Homework Set #1 (15 pts) Collaboration policy: You may (and are encouraged to) work with other students on the problem sets. You may also seek help from the class TF. However, your write-up of your final solutions must be your own. Submit this homework by the start of lecture on Friday, January 18th. 1. (4 pts) In order to determine the amount of Fe2+ in an aqueous solution, an acidic solution of K2Cr2O7 can be added to it, which oxidizes the Fe2+ and changes the color of the solution. a) Write a balanced equation for the reaction of Cr2O7 2- (aq) with Fe2+ (aq), which has the products Cr3+ (aq) and Fe3+ (aq). b) If it takes 26.0 mL of a 0.0250 M solution of K2Cr2O7 to react with 25.0 mL of a solution containing Fe2+ (aq), what is the concentration of Fe2+ (aq) in this solution?

2. (3 pts) A binary compound (let’s call it X) containing only Mn and O consists of 63.6% Mn. When X is heated, oxygen gas is evolved and a new binary compound (let’s call it Y), which consists of 72.0% Mn, is formed. a) Determine the empirical formulae of X and Y. b) Write a balanced equation for the conversion of X to Y.

3. (3 pts) Elemental analysis shows that a molecule contains C, H, and Cl. 1.00 g of this compound was combusted in excess oxygen and the carbon dioxide and water were collected. The water was condensed to liquid and found to have a mass of 68.6 mg. The carbon dioxide was placed in an evacuated 1.000 L bulb at 25 degrees C and found to have a pressure of 283 torr. What is the empirical formula of this compound?

4. (5 pts) At elevated temperatures, sodium chlorate decomposes to produce sodium chloride and oxygen gas. A 0.8765g sample of impure sodium chlorate was heated until the production of oxygen gas ceased. The oxygen gas collected over water occupied 57.2 mL at a temperature of 22oC and a pressure of 734 torr. Calculate the mass percent of NaClO3 in the original sample. (At 22oC the vapor pressure of water is 19.8 torr.)

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