Lesson 10: Additional Challenges
By now, you should have completed all the objectives for this lesson. Only exercise 18 remains. It is intended for you, if you reach this point in the lesson and still have time to kill and/or have an interest in figuring out some problems which are not quite so direct. If you are not interested in doing exercise 18, please feel free to skip it. The reason for including it is to show you the kinds of questions that can be answered by doing the kinds of things that we've dealt with. The way the questions are phrased is intended to make you think about which of the skills that you've learned in the past several lessons and reviewed in this lesson would be applicable to figuring out the answer to these particular questions. Because of that, this page does not include any worked-out examples.
If you do choose to work on these exrcises, you can check your answers on the listed page. If you need help with them check with one of the instructors and we'll give you a hand working on them.
Exercise 18:
Extra questions:
a. Which has the higher percentage of magnesium in it--magnesium oxide or magnesium nitride?
b. When magnesium is burned in oxygen, magnesium oxide is formed. When magnesium is burned in air, some magnesium nitride is formed along with magnesium oxide. Will this make the product from burning in air weigh more or less than the product from burning in oxygen?
c. Which compound has the heaviest molecules--sulfur hexafluoride or carbon tetrachloride? Which of those compounds has the most atoms per molecule?
d. Would the weight of magnesium oxide formed by burning 1.23 g of magnesium in ozone (O3) be any different than the weight of magnesium oxide formed by burning 1.23 g of magnesium in molecular oxygen (O2)?
e. Which would yield the larger amount of iron--44 kg of ferrous oxide or 38 kg of ferric oxide?
Answers to Exercise 18
a. Which has the higher percentage of magnesium in it--magnesium oxide or magnesium nitride?
Magnesium oxide is 60.3% Mg and magnesium nitride is 72.2% Mg, so the percentage of magnesium is higher in magnesium nitride.
b. When magnesium is burned in oxygen, magnesium oxide is formed. When magnesium is burned in air, some magnesium nitride is formed along with magnesium oxide. Will this make the product from burning in air weigh more or less than the product from burning in oxygen?
From the previous question, the percentage of magnesium in magnesium nitride is higher than in magnesium oxide, therefore the percentage of the other element in magnesium nitride is less than in magnesium oxide, therefore the increase in mass will be less in forming magnesium nitride than in forming magnesium oxide.
c. Which compound has the heaviest molecules--sulfur hexafluoride or carbon tetrachloride? Which of those compounds has the most atoms per molecule?
SF6 has 7 atoms per molecule and a formula weight of 146.
CCl4 has 5 atoms per molecule and a formula weight of 154.CCl4 has heavier molecules and SF6 has more atoms per molecule.
d. Would the weight of magnesium oxide formed by burning 1.23 g of magnesium in ozone (O3) be any different than the weight of magnesium oxide formed by burning 1.23 g of magnesium in molecular oxygen (O2)?
Because the same product is formed in each case and the same amount of magnesium is the limiting reagent in each case, the weight of the product will be the same.
e. Which would yield the larger amount of iron--44 kg of ferrous oxide or 38 kg of ferric oxide?
44 kg of FeO will yield 34 kg of Fe
38 kg of Fe2O3 will yield 27 kg of FeMore iron can be obtained from 44kg of ferrous oxide.