(^100) › STEP 4. Review the Knowledge You Need to Score High
- D—The KMnO 4 is the limiting reagent. Each mole of KMnO 4 will produce a mole of
MnSO 4. - A—The balanced equation is 2 C 8 H 18 (g) + 25 O 2 (g) → 16 CO 2 (g) + 18 H 2 O(g).
The calculation is
(^) ()
1.00 mol C H25 mol O(^818) 2 mol C H
2
818
= 12.5 mole O 2
14. B—()
0.200 mol Ca
1 mol H
1 mol Ca22.4 L at STP
1 mol H2
2 = 4.48 L. Be careful to only use 22.4
when at STP.- C—There are 5.00 × 10 -^3 mole of CrO 42 - and an equal number of moles of SnO 22 -.
Thus, SnO 22 - is the limiting reactant (larger coefficient in the balanced reaction).
()×
−−
−
5.00 10 mol SnO −
2 mol OH
3 mol SnO3
2
2
22 = 3.33 ×^10
- (^3) mole OH-
- D—The volume of water is irrelevant. 0.20 mole of KBr will require 0.10 mole of
Pb(NO 3 ) 2 , and 0.20 mole of MgBr 2 will require 0.20 mole of Pb(NO 3 ) 2. Total the two
yields to get the final answer. - A—One mole of a cycloalkane, CnH 2 n, will form n moles of water. It is possible to
determine the value of n by dividing the mass of the cycloalkane by the empirical for-
mula mass (CH 2 = 14 g/mole). This gives
0.560 g
14 g/mol
= 4 (0.140) g
14 g/mol
= 0.040 mole- C—For the formula mass of the empirical formula to be the same as that of the molec-
ular formula, the two formulas must be the same. All the molecular formulas except
CO 2 can be simplified to give an empirical formula that is different from the molecular
formula.
❯ Free-Response Question
You have 15 minutes to answer the following question. You may use a calculator and the
tables in the back of the book.Question
The analysis of a sample of a monoprotic acid found that the sample contained 40.0% C
and 6.71% H. The remainder of the sample was oxygen.
(a) Determine the empirical formula of the acid. Show all work.
(b) A 0.2720-g sample of the acid, HA, was titrated with standard sodium hydroxide,
NaOH, solution. Determine the molecular weight of the acid if the sample required
45.00 mL of 0.1000 M NaOH for the titration. Show all work.
(c) A second sample was placed in a flask. The flask was placed in a hot water bath until
the sample vaporized. It was found that 1.18 g of vapor occupied 300.0 mL at 100°C
and 1.00 atm. Determine the molecular weight of the acid. Show all work.
(d) Using your answer from part a, determine the molecular formula for part b and for part c.
(e) Account for any differences in the molecular formulas determined in part d.