(A) Composition (B) Decomposition (C) Single replacement (D) Double replacement: Acid-base (E) Combustion

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1 AP Chemistry - Problem Drill 08: Chemical Reactions No. 1 of What type is the following reaction: H 2 CO 3 (aq) + Ca(OH) 2 (aq) CaCO 3 (aq) + 2 H 2 O (l)? (A) Composition (B) Decomposition (C) Single replacement (D) Double replacement: Acid-base (E) Combustion Composition is more than one compound forming one compound. Decomposition is one compound breaking apart into more than one compound. Single replacement reactions involve a compound and an element as reactants. D. Correct! This is an acid and base reacting. A combustion reaction has O 2 as one of the two reactants. H 2 CO 3 is an acid and Ca(OH) 2 is a base. This is an acid-base double replacement reaction. The correct answer is (D).

2 No. 2 of Determine the oxidation number of nitrogen in N 2 O 4. (A) +2 (B) +3 (C) +4 (D) +5 (E) Cannot be determined without the other reactant in the reaction. The 2 indicates 2 atoms, not a +2 charge. Check the charges again. C. Correct! Each oxygen atom has a -2 oxidation number, which leaves each nitrogen atom with +4. Check the charges again. You cannot determine if an atom is being oxidized or reduced without the remainder of the equation, but you can determine the oxidation number of an atom in a molecule without the rest of the equation. Rule 3: O = -2 Rule 1: compound must add up to 0 2 N + 4 O = 0 2 N = 0 N = +4 The correct answer is (C).

3 No. 3 of Which of the following is a reduction reaction? I. Sr e - Sr II. 2 Cl - Cl e - (A) I (B) II (C) I and II (D) Neither I nor II (E) Cannot be determined without the complete reaction. A. Correct! Reduction reduces the charge. Strontium is going from +2 to 0, which is a reduction in charge. Reduction reduces the charge. Chloride is going from -1 to 0, which is not reduction. Reduction reduces the charge. Although strontium is being reduced from +2 to 0, the chloride is being oxidized from -1 to 0. Look closely one of them is a reduction reaction. Reduction and oxidization reactions can be identified from half-reactions. The whole reaction is not necessary. Reduction is the gain of electrons to reduce the charge of the species. Strontium is being reduced. The correct answer is (A).

4 No. 4 of Which of the following is insoluble in water? (A) NaOH (B) K 3 PO 4 (C) Ba(OH) 2 (D) CaSO 4 (E) KCl Sodium is soluble with most anions. Potassium is soluble with most anions. Hydroxide is soluble with barium. D. Correct! Sulfate is not soluble with calcium. Potassium is soluble with most anions. Use the solubility rules. Look up the anion and determine if it is soluble or insoluble with the particular cation. All these choice are soluble except calcium sulfate. The correct answer is (D).

5 No. 5 of What would the products of the following reaction be? CaCl 2 (aq) + Na 2 SO 4 (aq)? (A) CaSO 4 (aq) + 2 NaCl (aq) (B) CaSO 4 (s) + 2 NaCl (aq) (C) CaSO 4 (s) + Na 2 Cl 2 (aq) (D) CaNa 2 (aq) + Cl 2 SO 4 (aq) (E) Na 2 Ca (aq) + SO 4 Cl 2 (aq) You have the correct products, but one of them is insoluble. B. Correct! This is a double replacement reaction and calcium sulfate is not soluble. Your formula for sodium chloride is incorrect. Do not combine two cations and two anions. Cations only bond to anions. Do not combine two cations and two anions. Cations only bond to anions. This is a double replacement reaction. The cation of the first compound combines with the anion of the second. CaSO 4. Ca is +2 and SO 4 is -2 so the compound is neutral as written. The cation of the second combines with the anion of the first to form NaCl, which is neutral as written. Use solubility rules to determine if one is insoluble. NaCl is soluble, but CaSO 4 is not. The correct answer is (B).

6 No. 6 of What is the net ionic reaction for the following: CaCl 2 (aq) + Na 2 SO 4 (aq) CaSO 4 (s) + 2 NaCl (aq) (A) Ca Cl Na + + SO 4 2- CaSO Na Cl - (B) Ca 2+ + Cl Na SO 4 2- Ca 2+ + SO Na Cl 2 - (C) Ca 2+ + SO 4 2- CaSO 4 (D) 2 Cl Na + 2 NaCl (E) There is no net reaction. You can cancel out the spectator ions. Only keep subscripts that are in polyatomic ions, not with single atom ions. C. Correct! You crossed out the spectator ions correctly. The soluble product dissociates. With double displacement reactions, as long as both products are not soluble ionic compounds, there is a reaction. Net ionic equations separate all aqueous ionic compounds into ions. The spectator ions are then cancelled out. The correct answer is (C).

7 No. 7 of An example of an oxidation reaction is? (A) Na + + e - Na (B) Cu 2+ + e - Cu + (C) Cu e - Cu (D) Cu + Cu 2+ + e - (E) None of these reactions are oxidation reactions. Oxidation reactions have an increase in charge. Sodium is going from +1 to 0 this is a reduction reaction. Oxidation reactions have an increase in charge. Copper is going from +2 to +1 this is a reduction reaction. Oxidation reactions have an increase in charge. Copper is going from +2 to 0 this is a reducation reaction. D. Correct! Oxidation reactions have an increase in charge. Copper s charge is going from +1 to +2 this is an oxidation reaction. There is an oxidation reaction among the choices. Oxidation is the release of an electron. The above reactions are called half reactions because they only show half of the story. The correct answer is (D).

8 No. 8 of What type of reaction is the following: 2 C 2 H O 2 4 CO H 2 O (A) Combination (B) Decomposition (C) Single displacement (D) Double displacement (E) Redox Combination reactions combine more than one compound into one compound. Decomposition reactions have one compound breaking down into more than one compound. Single displacement reactions involve a compound and a single element replacing one of the ions in the compound. Double displacement reactions involve two compounds switching anions. E. Correct! This is a redox reaction as oxygen is reduced from 0 to -2 and carbon is oxidized from -3 to +4. Oxygen is changing charge from 0 to -2 and carbon is changing charge from -3 to +4. This is redox. The correct answer is (E).

9 No. 9 of Which atom is most likely to replace the calcium in our bones? (A) Na (B) F (C) O (D) Pb (E) Sr There s another atom in the list that is more similar to calcium. There s another atom in the list that is more similar to calcium. There s another atom in the list that is more similar to calcium. There s another atom in the list that is more similar to calcium. E. Correct!. Strontium is in the same group and can have the same cation charge as calcium. The element most like calcium is strontium (same group, same possible cation charge, etc.). The correct answer is (E).

10 No. 10 of Which is a spectator ion in the following reaction: Ca(OH) 2 (aq) + 2 HCl (aq) CaCl 2 (aq) + 2 H 2 O (l) (A) Ca 2+ (B) Cl 2 2- (C) H + (D) OH - (E) there are no spectator ions in this reaction. A. Correct! Calcium is in soluble compounds on both sides of the reaction. This is not an ion, but instead you have 2 separate chloride ions (Cl - ). This element is in a pure liquid on the product side therefore it will not dissociate on that side. This polyatomic ion is in a pure liquid on the product side and therefore it does not dissociate on that side. There is a spectator ion (one that is in a soluble compound on both sides of the reaction) among these choices. A spectator ion is in a soluble compound on both sides of the reaction. In this equation, Ca 2+ is a spectator ion. The correct answer is (A).