F10Q4W5

# F10Q4W5 - CHEM 0110 QUIZ 4 WEEK 5 MONDAY, 1:00 PM September...

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CHEM 0110 QUIZ 4 WEEK 5 MONDAY, 1:00 PM September 27, 2010 NAME_______________________________________________________________________ 1. A 28.61 g sample of a compound of chromium and oxygen contained 14.88 g of Cr. Determine the empirical formula of the compound. 2. As you know, ionic compounds in aqueous solution split completely into their ions. Determine the total molar concentration of Cl - ions in 1.00L of a solution which is a mixture of 0.100M KCl and 0.200M BaCl 2 . ANSWERS 1. Mass of Cr = 14.88 g; Mass of O = 28.61 - 14.88 = 13.73 g # mol Cr = 14.88 g Cr x Cr g 52.0 Cr mol 1 = 0.2862 mol # mol O = 13.73 g O x O g 16.0 O mol 1 = 0.8581 mol 2862 . 0 8581 . 0 Cr mol # O mol # = = 2.998 ~ 3 Empirical formula is CrO 3 2. KCl(aq) K + (aq) + Cl - (aq). The concentration of Cl - due to the KCl is 0.100M BaCl 2 (aq) Ba 2+ (aq) + 2 Cl - (aq). The concentration of Cl - due to the BaCl 2 is 0.400M [i.e. concentration of Cl - = 2 2 0.200 mol BaCl 2 mol Cl x 1 L 1 mol BaCl - = 0.400M] Then total Cl - concentration = 0.100 + 0.400M = 0.500M For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:

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CHEM 0110 QUIZ 4 WEEK 5 MONDAY, 6:00 PM September 27, 2010 NAME_______________________________________________________________________ 1. Given the reaction: 4 Fe + 3O 2 2Fe 2 O 3 a) Determine the mass of Fe 2 O 3 formed by reaction of 259.4 g of Fe with excess oxygen. b) Discuss how you would check that your answer makes sense. 2. 35g of solid Na 2 SO 4 were mixed with 250mL of distilled water and completely dissolved. Using this information only (and molar masses), can you determine the molarity of the resulting solution? Give your reasoning. 3. Give the names of Fe 2 O 3 and Na 2 SO 4 ANSWERS 1. a) # mol Fe 2 O 3 = 259.4 g Fe x Fe mol 4 O Fe mol 2 x Fe g 55.85 Fe mol 1 3 2 = 2.322 mol Fe 2 O 3 Mass of Fe 2 O 3 = 2.322 mol Fe 2 O 3 x 3 2 3 2 O Fe mol 1 O Fe g 159.7 = 370.9 g Fe 2 O 3 b) The mass is somewhat larger than the initial mass of Fe of 259.4g. This is as expected as the Fe has picked up some oxygen. 2. No. Molarity is mol of solute divided by volume of the solution. We know the moles of Na 2 SO 4 , but do not know the final volume of the solution – it will be larger than 250mL. 3. Iron(III) oxide; sodium sulfate For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
CHEM 0110 QUIZ 4 WEEK 5 TUESDAY, 8:00 AM September 28, 2010 NAME_______________________________________________________________________ 1. In a recent homework question, we were told that a sample of ammonia, NH 3 , contained 7.933g N and 1.712g H. From this information only, what is the ratio of the atomic mass of N relative to that of H? One student replied that we should multiply the mass of H by 3 to get 1.712 x 3g = 5.136g H,

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## This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

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F10Q4W5 - CHEM 0110 QUIZ 4 WEEK 5 MONDAY, 1:00 PM September...

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