Download Practice Exam for Test 2 (answers) How many Hydrogen atoms are in

Practice Exam for Test 2 (answers)
1.
How many Hydrogen atoms are in 12g of H2O?
12gH2O x 1molH2O x 6.022*1023 x 2molH
= 8.03*1023 H atoms in 12g water
18gH2O
1mol
1molH2O
2.
Balance the combustion reaction of C8H18 (octane).
C8H18 + 25/2O2  8CO2 + 9H2O so for whole numbers x2 gives 2 C8H18 + 25O2  16CO2 + 18H2O
3.
Calculate the theoretical yield of FeO (rust) in the double-displacement reaction between 5.0g
Aluminum Oxide and 3.75g Iron(II) Chloride. Al2O3 + 3FeCl2  3FeO + 2AlCl3
5.0g x 1mol x 3mol FeO x 72g FeO = 3.53g FeO
102g 1mol Al2O3 1mol
3.75g x 1mol x 3mol FeO x 72g FeO = 2.15g FeO
126g 3mol FeCl2 1mol
4.
Calculate the percent yield of the reaction given 20ml of 2.00M Sulfuric acid reacting with 3.45g
of Barium Hydroxide. Assume that the volume difference after adding the Barium hydroxide is
negligible and that your precipitate’s mass was 3.93g.
H2SO4(aq) + Ba(OH)2(aq)  2H2O(l) + BaSO4(s)
2.00mol x .02L x 1mol BaSO4 x 233.39g = 9.34g
1L
1mol H2SO4
1mol
3.45g x 1mol x 1mol BaSO4 x 233.39g BaSO4 = 4.699g theoretical yield
171.35g 1mol Ba(OH)2 1mol
% = 3.93 x 100 = 84%
4.699
5.
Calculate the percent yield of the reaction between 5.3g of Magnesium hydroxide and excess
hydrofluoric acid given the mass of the precipitate was 4.75g.
Mg(OH)2(aq) + 2HF(aq) MgF2(s) + 2H2O(l)
5.3g Mg(OH)2 x 1mol x 1mol MgF2 x 62.3g = 5.66g MgF2
58.316g 1mol Mg(OH)2 1mol
% = 4.75 x 100 = 84%
5.66
6.
Write the total ionic equation for the double displacement reaction between Potassium acetate
and Phosphorous acid.
3CH3COOK(aq) + H3PO3(aq)  3CH3COOH(aq) + K3PO3(s)
3CH3COO-(aq) + 3K+(aq) + 3H+(aq) + PO33-(aq)  3CH3COO-(aq) + 3H+(aq) + K3PO3(s)
7.
Write the net ionic equation for the reaction above.
3K+(aq) + PO33-(aq)  K3PO3(s)
8.
Liquid phosphorus trichloride is poured into a large excess of water. Write the net ionic
equation for this reaction.
PCl3(l) + H2O  H3PO3(aq) + H+(aq) + Cl-(aq)
Remember water IS aqueous when participating in the reaction
3OH-(aq) + PCl3(l)  PO33-(aq) + 3H+(aq) + 3Cl-(aq)
Write the redox reactions for the remaining problems (just answers, follow work from lecture
notes)
9. CuS(aq) + HNO3(aq)  Cu SO4(aq) + NO (g) + H2O(l)
3CaS(aq) + 8HNO3(aq)  4H2O(l) + 3CaSO4(aq) +8NO(g)
10. Zn(s) + HCl(aq)  ZnCl2(aq) + H2 (g)
2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g)