1) Samples of a mixture of Ca3(PO4)2 and CaF2 were analyzed to determine calcium and phosphorus.
a) Calcium was determined by conversion to CaC2O4, dissolution in H2SO4, and titration with KMnO4.
Reactions are as follows:
CaC2O4 + H2SO4 ---> CaSO4 + H2C2O4
5H2C2O4 + 2KMnO4 + 3H2SO4 ---> 10CO2 + K2SO4 + 2MnSO4 + 8H2O
Data for one determination were as follows:
| Weight of mixture | 1.165 grams |
| Volume of 0.105-molar KMnO4 | 47.18 milliliters |
Calculate the per cent of calcium in the mixture.
b) Phosphorus was determined by conversion to MgNH4PO4 and ignition to Mg2P2O7.
Data for one determination were as follows:
| Weight of mixture | 1.684 grams |
| Weight of Mg2P2O7 | 0.847 gram |
Calculate the per cent of phosphorus in the mixture.
2) The following reactions are carried out successively, a product of one step being a reactant in the following step:
MgCl2 (molten, electrolysis) ---> Mg + Cl2
3Cl2 + 6OH¯ ---> ClO3¯ + 5Cl¯ + 3H2O
2K+ + ClO3¯ + Cl¯ (evaporation) ---> KClO3(s) + KCl (s)
2KClO3 (heat) ---> 2KCl + 3O2
a) Suppose that 36.5 grams of magnesium is produced in the electrolysis step and that the succeeding steps are 100% efficient.
1. What volume will the oxygen produced in the final step occupy when collected over water at 29 °C (v.p. = 30.0 mm Hg) and at a barometric pressure of 765 millimeters of mercury?
2. How many milliliters of a 4.00-molar potassium hydroxide solution will be needed to provide the hydroxide ion required in the second step?
b) If a current of 1.00 x 103 amperes is used when electrolysis is carried out and if the efficiency is 100%, how many minutes will be required to produce 36.5 grams of magnesium?
6) PbCrO4(s) + Na+ + OH- --->
7) LiH(s) + H2O --->
9) Na+ + C2H3O2¯ + H+ + Cl¯ --> (The acid is present in excess.)
10) K+ + Cr2O72- + H+ + SO42- + Na+ + I¯ --->
11) BaCO3(s) + H+ + NO3¯ ---> (The acid present in excess.)
12) Al2S3(s) + H2O --->
13) Ag(s) + H+ + NO3¯ ---> (The nitric acid is 6-molar.)
14) The second ionization potentials of the alkaline earth metals are about twice as great as the first ionization potentials; nevertheless, the cation produced when the metal reacts with water is the dipositive ion (M2+). Explain.
15) Two students construct galvanic cells from identical materials and the following chemicals: Ag(s), AgNO3(s), Hg(l), Hg2(NO3)2(s), and distilled water. One student reports that for his cell the electrons flow through the external circuit from the mercury electrode to the silver electrode. The other student reports that the electron flow for his cell is from silver to mercury. Propose an explanation for this difference. The half-reactions and their E° values are as follows:
| 2Hg(l) ---> Hg22+ + 2e¯ | -0.79 volt |
| Ag(s) ---> Ag+ + e¯ | -0.80 |
16) Using an appropriate example, state how a buffer solution works and indicate the limits of its effectiveness.
17) Describe the energy distribution of molecules at two appreciably different temperatures.
18) Discuss differences in the bonding between atoms in the following compounds: NaH, CH4, HCl
19) Draw the structures for four of the isomers of C4H6.