Na2S + 2 AgNO3
A. 41.37 g AgNO3
B. 13.00 g Na2S
C. 26.00 g Na2S
D. 74.27 g AgNO3
8. Using a given mass of KClO3, how would one calculate the mass of oxygen produced in the following reaction, assuming it goes to completion?
2 KClO3
9. Aluminum metal can be used to remove tarnish from silver when the two solid metals are placed in water, according to the following reaction.
3 AgO + 2 Al
This reaction is a
I. double-displacement reaction.
II. single-displacement reaction.
III. redox reaction.
IV. combination reaction.
A. II only
B. I and III
C. II and III
D. IV only
10. Which of the following type(s) of reaction(s) generally has/have the same number of reactants and products?
I. Single-displacement reaction
II. Double-displacement reaction
III. Combination reaction
A. I only
B. II only
C. II and III
D. I and II
11. Which of the following is the correct net ionic reaction for the reaction of copper with silver nitrate?
A. Cu + AgNO3
B. Cu + 2 Ag+ + NO3-
C. 2 Ag+ + 2 NO3-
D. Cu + 2 Ag+
12. In the process of photosynthesis, carbon dioxide and water combine with energy to form glucose and oxygen, according to the following equation.
CO2 + H2O + Energy
What is the theoretical yield, in grams, of glucose if 30.00 grams of water are reacted with excess carbon dioxide and energy, in the balanced equation?
A. 50.02 grams glucose
B. 300.1 grams glucose
C. 30.03 grams glucose
D. 1,801 grams glucose
13. One way to test for the presence of iron in solution is by adding potassium thiocyanate to the solution. The product when this reagent reacts with iron is FeSCN2+, which creates a dark red color in solution via the following net ionic equation.
Fe3+ (aq) + SCN-
How many grams of iron sulfate would be needed to produce 2 moles of FeSCN2+?
A. 400 grams
B. 800 grams
C. 200 grams
D. 500 grams
Small Group Questions
1. Can the Law of Constant Composition be applied to solutions?
2. What is the purpose of calculating a reactant’s gram equivalent weight?
Explanations to Practice Questions
1. D
Ionic compounds are composed of atoms held together by ionic bonds. Ionic bonds associate charged particles with disparate electronegativities; for example, sodium (Na+) with chloride (Cl-). In ionic bonds, electrons are not really “shared” but are rather donated from the less electronegative atom to the more electronegative atom. As a result, ionic compounds are not formed from true molecules, as are covalent compounds. (A) and (B) both describe covalent compounds; their smallest unit is a molecule, which is typically described in terms of molecular weight and moles. In contrast, ionic compounds are measured using “formula weights” and are made of three-dimensional arrays of their charged particles, as indicated in (D). (C) is incorrect because ionic compounds do not share electrons equally; equal sharing occurs in covalent bonds.
2. A
Of the compounds listed, only (A) and (C) are ionic compounds, which are measured in “formula weights.” The other options, (B) and (D), are covalent compounds and thus are measured in “molecular weight.” This clues us in to the fact that we don’t really even need to examine choices (B) and (D). (A) consists of potassium (39.0983 g) plus chloride (35.453 g), which has a total weight of 74.551 grams. (C) is made up of 2 lithiums (2 × 6.941 g) and 2 chlorides (2 × 35.4527 g), whose sum exceeds 75 grams.
3. B
First, it is helpful to know the molecular weight of one mole of H2SO4, which is found by adding the molecular weight of the atoms that constitute the molecule: 2 × (molecular weight of hydrogen) + 1 × (molecular weight of sulfur) + 4 × (molecular weight of oxygen) = 2 × 1.00794 g + 32.065 g + 4 × 15.9994 g = 98.078 g. Next, you must understand what the term gram equivalent weight means. Gram equivalent weight is the weight (in grams) that would release one acid equivalent. Because H2SO4 has two hydrogens per molecule, the gram equivalent weight is 98.078 g/mole divided by 2, or 49.039 g/mole. All of the other answer choices are multiples of this number.
4. C
The definition of an empirical formula is a formula that represents a molecule with the simplest ratio, in whole numbers, of the atoms/elements comprising the compounds. In this case, given the empirical formula CH, any molecule with carbon and hydrogen atoms in a 1:1 ratio would be accurately represented by this empirical formula. Benzene, C6H6 (A), is thus correct, as is ethyne, C2H2 (B). (D) has eight carbon atoms and eight hydrogen atoms, making it correct as well. (C) is incorrect, and thus the right answer, because it has three carbon atoms while having four hydrogens. Both its molecular and empirical formulas would be C3H4, because this formula represents the smallest whole number ratio of its constituent elements.
5. A
The percent composition of any given element within a molecule is equal to the molecular mass of that element in the molecule, divided by the formula or molecular weight of the compound, times 100%. In this case, acetone, C3H6O, has a total molecular weight of (12.0107 g × 3 + 1.00794 g × 6 + 15.994 g × 1) = 58.074 g/mol, of which 12.0107 g × 3 = 36.0321 g/mol is from carbon. Thus, the percent composition of carbon is 63.132%. With this calculation serving as an example, you can calculate the percent composition for ethanol (C2H6O; MW = 41.023 g/mol) to be 58.556%; for C3H8 (MW = 44.096 g/mol) to be 81.713%; and for methanol (CH4O; MW = 32.036 g/mol) to be 37.491%. These calculations make it clear that although both acetone (A) and ethanol (B) have percent compositions of carbon close to 63%, acetone is closer (within 1%).
6. B
This reaction is a classic example of a neutralization reaction, in which an acid and a base react to form water and a new aqueous compound. Although this reaction may also appear to fit the criteria for a double-displacement reaction, in which two molecules essentially “exchange” with each other, neutralization is a more specific description of the process. A single-displacement reaction is typically a redox (reduction/oxidation) reaction in which one element is replaced in the molecules; thus (A) and (D) are incorrect.
7. B