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Answers:
Solutions: Instructions: Read the whole examination before starting to work on individual problems. Some problems are easier than others; work those first. Budget your time to insure that you finish the examination. Dont waste time on problems that you find hard to finish until you have worked the others.1. Which of the following is an example of a chemical change?
Solution: The only answer where a substance is changing chemical composition is steel rusting. 2. The number of protons in the nucleus determines the
Solution: The number of protons tells us the identity of the element and is equal to the atomic number. 3. The formulae of the hydroxide, the nitrite, and the sulfite ions are represented respectively as
Solution: Recall the table that you needed to memorize! The correct
answer is 4. The formula for aluminum carbonate is Al2(CO3)3. On the basis of this information, the formula for the phosphate of aluminum would be expected to be
Solution: the formula tells you that Al has a +3 charge. Phosphate also has a +3 charge so that the formula that would give a neutral molecule is AlPO4. 5. The net ionic equation for the reaction of Mg(OH)2(s) with HCl is (recall which are strong and weak acids and bases).. a. H+(aq) + OH- (aq) ® H2O(l)b. 2HCl(aq) + Mg2+(aq) + 2OH- (aq) ® MgCl2(s) + 2H2O(l)c. 2H+ (aq) + 2Cl- (aq) + Mg(OH)2(s) ® MgCl2(s) + 2H2O(l).d. 2Cl- (aq) + Mg2+(aq) ® MgCl2(s)Solution: HCl is a strong acid. This makes it ionic. Both H+ (aq) and Cl- are ionic. and are involed in the reaction. They form water with the magnesium hydroxide and the chloride of magnesium (which should have been soluble). 6. Name the following compound: N2O3.
Solution: Dinitrogen trioxide. 7. The formula of the perclorate anion is
Solution: Use table! Per- tells us there is a lot of oxygen.
The correct answer is 8. The molecular formula of a compound is (NH4)2C2O4.· H2O. Its molecular mass is
Solution: Sum the masses of all elements present in the molecule . 9. When 1.68 g of benzene was burned, 5.68 g of CO2 was produced. Determine the mass of benzene burned if 15.0 g CO2 were produced.
Solution: Use law of definite proportions. Let mB = mass of benzene. 10. The mass of an atom X is 1.54x10- 22g; the atomic number of this element is
Solution: 1 mol of X is avAvagadros # of atoms. Thus FM=1.54x10- 22g· 6.02x1023 = 92.6; This is the mass of element number 41. 11. Convert 3.44 kPa· dm3 to J if 1 J = 1 kg· m2/s2 and 1 Pa = 1kg/(m· s2)
Solution: Hopefully you recognize this as a unit conversion problem. Use definitions provided. 12. Naturally occurring boron consists of two isotopes, 10B and 11B with atomic masses 10.013 and 11.009 respectively. The observed atomic mass of boron is 10.811. Calculate the abundance of 10B.
Solution: remember that the atomic mass on the periodic table is the weighted average of the isotopic masses. Set up an equation for this. 13. If y = (3.15x10- 23)1/24, then y =
Solution: Use your calculator to obtain 0.115 14. In chapter 5 we will discuss that pressure, P, and volume, V, are inversely proportional to each other according to the equation: PV = nRT. Determine the final pressure (in atm) of a cylinder if the initial pressure was 1.00 atm and the volume slowly decreased to exactly 1/3 of its initial volume. Assume all other conditions were constant.
Solution: This should be recognized as a math skills problem.
15. Determine the volume of concentrated solution required to produce 500.0 mL of 1.00 M NaCl from 3.00 M NaCl.
Solution:This is a dilution problem and then you need to do some unit analysis to determine which answer is correct.
16. Given that y = ln x - 2.303log 2x
Solution: This is a math skills problem.
17. When the equation 2 C5H6NS(l) + 17O2(g) ® 10 CO2(g) + 6 H2O(l) + 2NO2(g) + 2SO2(g)is balanced, the sum of the coefficients (simplest whole number) is
Solution: Sum is 39. 18. Which of the following is a strong acid?
Solution: From table in book HCl is a strong acid. |