Chemistry I

Part B (Comprehensive Questions: 20 points) 

 

36.A 1.345 g sample of a compound of barium and oxygen was dissolved in hydrochloric acid to give a solution of barium ion, which was then precipitated with an excess of potassium chromate to give 2.012 g of barium chromate, BaCrO₄.  What is the formula of the compound?(4 points)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

37a. Phenol, commonly known as carbolic acid, was used by Joseph Lister as an antiseptic for surgery in 1865.  Its principle use today is the manufacture of phenolic resins and plastics.  Combustion of 5.23 mg of phenol yields 14.67 mg CO₂ and 3.01 mg H₂O.  Phenol contains only C, H, and O.  What is the percentage of each element in this substance?(2 points)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

37.b.How many milliliters of 0.250 M KMnO4 are needed to react with 4.40 g of iron(II) sulfate, FeSO₄? (Hint: Volumetric analysis)

The reaction is as follows:

 

10FeSO₄(aq) + 2KMnO₄(aq) + 8H₂SO₄(aq)   

5Fe₂(SO₄)₃(aq) + 2MnSO₄(aq) + K₂SO₄(aq) + 8H₂O(l)

(2 points)

 

 

 

 

 

 

 

 

 

 

 

 

 

38.Two compounds have the same composition: 85.62% C and 14.38% H.

 

. a. Obtain the empirical formula corresponding to this composition.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b. One of the compounds has a molecular mass of 28.03 amu; the other, of 56.06 amu.  Obtain the molecular formulas of both compounds.( 4 points)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

39.a.For the given aqueous reaction, write the molecular and net ionic equations, including phase labels..(2 points)

 

The neutralization of acetic acid by calcium hydroxide, both in aqueous solution

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

39.b.Balance the following oxidation-reduction reaction by the half-reaction method…(2 points)

 

FeI₃(aq) + Mg(s)       Fe(s) + MgI₂(aq)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

40.a.One step in the isolation of pure rhodium metal (Rh) is the precipitation of rhodium(III) hydroxide from a solution containing rhodium(III) sulfate according to the following balanced chemical equation:

Rh₂(SO₄)₃(aq) + 6NaOH(aq)     2Rh(OH)₃(s) + 3Na₂SO₄(aq)

What is the theoretical yield of rhodium(III) hydroxide from the reaction of 0.590 g of rhodium(III) sulfate with 0.366 g of sodium hydroxide?  Show detailed work.

(3 points)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

40.b.   Using questions 40a, calculate the percentage yield ofrhodium(III) hydroxide, Rh(OH)3 ; given that the actual yield ofRh(OH)3 is 0.320 g.