Chem 113 Recitation – Week 3
Solubility Rules: (This is the wording from another book (Silberberg, Chemistry, 3rd Edition, just in case someone might find it useful.)
Soluble Ionic Compounds:
1. All common compounds of Group 1A ion and ammonium ion are soluble.
2. All common nitrates, acetates, and most perchlorates are soluble.
3. All common chlorides, bromides, and iodides are soluble, except those of Ag+ Pb2+, Cu+ and Hg22+.
4. All common sulfates are soluble, except those of Ca2+, Sr2+, Ba2+ and Pb2+.
Insoluble Ionic compounds:
1. All common metal hydroxides are insoluble, except those of Group 1A and the larger members of Group 2A.
2. All common carbonates and phosphates are insoluble, except those of Group 1A and ammonium ion.
3. All common sulfides are insoluble except those of Group 1A, Group 2A and ammonium ion.
(A) (GTQ) An active ingredient of a traditional Chinese medicine (tu-jin-pa) for the treatment of athlete’s foot is pseudolaric acid-A, which contains C, H, and O. When 1.000 g of the compound is subjected to combustion analysis 2.492 g of CO2 and 0.6495 g of H2O are produced. [MM: CO2 = 44.01; H2O = 18.02 g/mol]
(a) Find the empirical formula of pseudolaric acid-A
(b) The mass spectrum of pseudolaric acid-A showed a parent mass peak at 388.46 g/mol. What is the molecular formula of pseudolaric acid-A?
Mol C = 0.6801g/12.011 g/mol = 0.05662 mol/0.0155 = 3.65x3 = 11
Mol H = 0.07266g/1.008 g/mol = 0.07208 mol/0.0155 = 4.65x3 = 14
Mol O = 0.247g/15.999 g/mol = 0.0155 mol/0.0155 = 1x3 = 3
E.F. = C11H14O3
388.46/194 = 2
M.F. = C22H28O6
(B) (GTQ) The treatment of scrap aluminum with chlorine, according to the following equation produces aluminum chloride, a white solid, that is used in many industrial processes.
Al (s) + Cl2 (g) → AlCl3 (s)
(a) How many grams of AlCl3 can be produced from the reaction of 2.70 g of Al and 4.05 g of Cl2?
(b) If the reaction produces only 4.32 g of AlCl3, what is the actual yield of the reaction?
2Al (s) + 3Cl2 (g) → 2AlCl3(s)
Cl2 is the limiting reagent, so 5.08 g of AlCl3 can be produced.
4.32/5.08*100% = 85.2% yield
(C) Diborane (B2H6), a useful reactant in organic synthesis, may be prepared by the following reaction, which occurs in a nonaqueous solvent:
NaBH4(s) + BF3(g) B2H6(g) + NaBF4(s)
If the reaction has a 75.0% yield of diborane, how many grams of NaBH4
are needed to make 25.0g of B2H6?
3NaBH4(s) + 4BF3(g) 2B2H6(g) + 3NaBF4(s)
(D) What is the formula for the following compounds:
(i) potassium carbonate dihydrate (ii) ammonium perchlorate (iii) ammonium hydrogen phosphate (iv) iron nitrate (v) magnesium dichromium heptaoxide
(i) K2CO3*2H2O; (ii) NH4ClO4; (iii) (NH4)2HPO4; (iv) Fe(NO3)2; (v) MgCr2O7
(E) Give the oxidation number of each element in the following:
(i) Na2C2O4 (ii) Cr2(SO4)3 (iii) MnO4- (iv) CBr4
(i) Na = +1, C = +3, O = -2; (ii) Cr = +3, S = +6, O = -2; (iii) Mn = +7, O = - 2; (iv) C = +4, Br = -1
(F) (GTQ) (a) Classify the following compounds as either strong electrolytes, weak electrolytes or nonelectrolytes in aqueous solution:
(i) HClO2 (ii) C3H7OH (ii) (NH4)2S
(i) weak; (ii) non; (iii) strong
(b) Which of the following compounds are considered soluble in water;
(i) UO2(NO3)2 (ii) (NH4)3PO4 (iii) Al(OH)3
(i) soluble; (ii) soluble; (iii) insoluble