CHAPTER
6
Self-Quiz
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1.
(b); Choice (b) is a balanced chemical equation, which has the same number of atoms of each element
on both sides of the equation. Choices (a), (c), and (d) are incorrect because they do not have the same
number of atoms of each element on both sides of the equation.
2.
(d); Choice (d) is a double displacement reaction. Elements in different compounds displace each other.
Choice (a) is incorrect because it is a decomposition reaction. Choice (b) is also incorrect. It is a single
displacement reaction. Choice (c) is incorrect because it is a synthesis reaction.
3.
(b); The reaction produces 25 g 2 15 g 5 10 g of CO2. Choice (a) is incorrect because 5 grams of CO2
and 15 g of CaO would form from 20 g, not 25 g of CaCO3. Choice (c) is also incorrect. If 15 g of CO2
were produced along with 15 g of CaO, then 30 g, not 25 g of CaCO3 would have reacted. Choice (d) is
incorrect because 25 g of CO2 and 15 g of CaO would be produced from 40 g, not 25 g of CaCO3.
4.
(b); Choice (b) shows the correctly balanced equation. It shows the correct formulas for the products and
reactants and contains equal numbers of atoms of each element on both sides of the equation. Choice (a)
is incorrect because although it shows the correct formulas of the reactants and products, it is not
balanced. Choice (c) is also incorrect. The equation is unbalanced, and the formula for sulfur dioxide is
wrong. Choice (d) is incorrect because although it is balanced, it does not show the correct formulas of the
reactants and products.
5.
True. An equation is balanced if it contains the same number of atoms of each element on both sides of
the equation.
6.
False. Changing the formula of a substance would change the identity of the substance. A true version of
the statement would be: Equations are balanced by adding coefficients before the chemical formulas.
7.
coefficient; Coefficients are added before chemical formulas in a chemical reaction to ensure that the
number of atoms on each side of the arrow are balanced.
8.
product; The product is the chemical that is produced during a chemical reaction.
9. (a)(iv) Two
reactants combine to make a single product; (b)(iii) An element displaces another element in
a compound; (c)(ii) Elements in different compounds displace each other; (d)(i) A larger compound is
broken down into smaller compounds or elements; (e)(v) A substance reacts with oxygen to produce oxides
and energy.
10. (a)
CaO and H2O are reactants because they are on the left side of the arrow.
(b)
Ca(OH)2
(c)
The product, Ca(OH)2 is a solid that precipitates in the water and turns it cloudy.
(d)
The test tube will become warmer because energy is given off by this reaction.
11. (a)
sodium bicarbonate → sodium carbonate 1 carbon dioxide 1 water
(b)
A gas (carbon dioxide) is given off.
(c)
2NaHCO3 → Na2CO3 1 CO2 1 H2O
12.
Changing the formula would change the identity of the substance, and MgO2 is a substance that does not
actually exist. Magnesium oxide can only be written as MgO.
13.
The products and the reactants, their ratios, and their states.
14.
Sample answer: Corrosion is the breakdown of a metal as a result of chemical reactions with its
environment. Rusting is one form of corrosion. Rusting is the corrosion of metals that contain iron.
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15. (a)
Sample: In a synthesis reaction, one product is made from two or more reactants.
(b)
A
16.
⫹
B
A
B
Sample answer: I could apply a layer of protective coating, such as rust-inhibiting paint, to my bicycle.
This would prevent rusting as long as the protective layer does not get chipped or scratched. Other answers
might include “Drying my bike when it gets wet or keeping my bike in a garage.”
17. (a)
Hydrocarbons are compounds composed of hydrogen and carbon.
(b) Sample
18. (a)
(b)
answer: benzene (C6H6), octane (C8H18), and acetylene (C2H2)
Sample answer: Five chemical reactions are lighting of a match, rusting of iron, leaves changing colour,
digesting food, and baking bread
Sample answer: In the lighting of a match the reactants are red phosphorus and oxygen. The products
are white phosphorus and energy.
19.
Sample answer: The presence of salt in the air would increase the rate of corrosion. Also, the wetter climate
would increase the rate of corrosion.
20.
The combustion reaction from the grill requires oxygen. Without enough oxygen, the combustion reaction
may be incomplete, which would produce poisonous carbon monoxide. The garage may not let enough
oxygen near the grill, so it could create poisonous gas.
21.
Sample answer: The chemical reaction of iron with oxygen is harmful in the case of automobiles. When
the body of a car rusts, it becomes weaker. But the reaction of iron and oxygen produces compounds that
are useful in paint, cosmetics, and explosives.
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