CHEMICAL REACTIONS II
UNIT 8 ACIDS AND BASES
ANSWER KEY
Aspirations High School
Ms. Kasia Room 109
Friday, June 03, 2011
TOTAL POINTS
Part A /16
Part B /22
Bonus /5
TOTAL /38
PART A
Answer all questions in this part.
Directions (1-19): For each statement or question, circle the number of the word or expression that, of those given, best completes the statement or answers the questions. Some questions may require the use of the Reference Tables for Physical Setting/ Chemistry. [40 points
1. A atom is electrically neutral because the
(1) number of protons equals the number of electrons
(2) number of protons equals the number of neutrons
(3) ratio of the number of neutrons to the number of electrons is 1:1
(4) ratio of the number of neutrons to the number of protons is 2:1
2. At STP, which sample contains the same number of molecules as 11.2 liters of CO2 (g) at STP?
(1) 5.6 L of NO2 (g)
(2) 7.5 L of H2 (g)
(3) 11.2 L of N2 (g)
(4) 22.4 L of CO (g)
3. Which formula represents an ionic compound?
(1) H2
(2) CH4
(3) CH3OH
(4) NH4Cl
4. Which formula represents a hydronium ion?
(1) H3O+
(2) NH4+
(3) OH-
(4) HCO3-
5. Which compound is an Arrhenius acid?
(1) H2SO4
(2) KCl
(3) NaOH
(4) NH3
6. At standard pressure, a certain compound has a low boiling point and is insoluble in water. At STP, this compound most likely exists as
(1) ionic crystals
(2) metallic crystals
(3) nonpolar molecules
(4) polar molecules
7. Sulfuric acid, H2SO4 (aq), can be used to neutralize barium hydroxide, Ba(OH)2 (aq). What is the formula for the salt produced by this neutralization?
(1) BaS
(2) BaSO2
(3) BaSO3
(4) BaSO4
8. According to one acid-base theory, a water molecule acts as an acid when the water molecule
(1) accepts an H+
(2) accepts an OH-
(3) donates an H+
(4) donates an OH-
9. Which equation represents a neutralization reaction?
(1) 4Fe (s) + 3O2 (g) à 2 Fe2O3 (s)
(2) 2H2 (g) + O2 (g) à 2H2O (l)
(3) HNO3(aq) + KOH(aq) à KNO3(aq) + H2O(l)
(4) AgNO3(aq) + KCl(aq) à KNO3(aq) + AgCl(s)
10. Which substance is an Arrhenius base?
(1) CH3OH
(2) CH3Cl
(3) LiOH
(4) LiCl
11. Information related to a titration experiment is given in the balanced equation and table below.
H2SO4(aq) + 2KOH(aq) à
K2SO4(aq) + 2H2O(l)
Titration Experiment Results
Volume of H2SO4(aq) used / 12.0 mLConcentration of H2SO4(aq) / ?
Volume of KOH(aq) used / 36.0 mL
Concentration of KOH (aq) / 0.16 M
Based on the equation and the titration results, what is the concentration of the H2SO4(aq)?
(1) 0.12 M
(2) 0.16 M
(3) 0.48 M
(4) 0.96 M
12. In which solution will thymol blue indicator appear blue?
(1) 0.1 M CH3COOH
(2) 0.1 M KOH
(3) 0.1 M HCl
(4) 0.1 M H2SO4
13. Which indicator, when added to a solution, changes color from yellow to blue as the pH of the solution is changed from 5.5 to 8.0?
(1) bromcresol green
(2) bromthymol blue
(3) litmus
(4) methyl orange
14. The pH of an aqueous solution changes from 4 to 3 when the hydrogen ion concentration in the solution is
(1) decreases by a factor of ¾
(2) decreased by a factor of 10
(3) increased by a factor of 4/3
(4) increased by a factor of 10
15. Which volume of 0.10 M NaOH(aq) exactly neutralizes 15.0 mililiters of 0.20 M HNO3 (aq)?
(1) 1.5 mL
(2) 7.5 mL
(3) 3.0 mL
(4) 30. mL
16. A nuclear fission reaction and a nuclear fusion reaction are similar because both reactions
(1) form heavy nuclides from light nuclides
(2) form light nuclides from heavy nuclides
(3) release a large amount of energy
(4) absorb a large amount of energy
PART B
Directions (17-18): For each question make sure to show your work or provide and explanation. Some questions may require the use of the Reference Tables for Physical Setting/ Chemistry. [40 points]
Base questions 20 through 21 on the information below:
In a titration, 15.65 milliliters of a KOH(aq) solution exactly neutralized 10.00 milliliters of a 1.22 M HCl(aq) solution.
17. Complete the equation below for the titration reaction by writing the formula for each product.
KOH (aq) + HCl (aq) à KCl + H2O
18. Show a correctly numerical setup for calculating the molarity of the KOH (aq) solution.
(15.65mL)(x) = (10mL)(1.22M)
Base questions 19 to 21 on the information below:
A truck carrying concentrated nitric acid overturns and spills its contents. The acid drains into a nearby pond. The pH of the pond water was 8.0 before the spill. After the spill, the pond water is 1,000 times more acidic.
19. Name an ion in the pond water that has increased in concentration due to this spill.
hydrogen
20. What is the new pH of the pond water after the spill?
1,000 times so that is 10x10x10=1000 since hydrogen increased, the pH had to decrease
8à7à6
The new pH is 6
21. What color would bromthymol blue be at this new pH?
Yellow turning into blue
Base questions 22 through 23 on the information below:
Sulfur dioxide, SO2, is one gas produced when fossil fuels are burned. When this gas reacts with water in the atmosphere, an acid is produced forming acid rain. The pH of the water in a lake changes when acid rain collects in the lake.
Two sample of the same rainwater are tested using two indicators. Methyl orange is yellow in one sample of this rainwater. Litmus is red in the other sample of this rainwater.
22. Identify a possible pH value for the rainwater that was tested.
Since methyl orange is yellow that means the pH has to be at least 3.0 Since litmus paper is red, the solution must be at most 5.5
The Ph ranges between 3.0-5.5
23. Write the formula for one substance that can neutralize the lake water affected by acid rain.
NaOH
Base questions 24 through 26 on the information below:
A laboratory worker filled a bottle with a hydrochloric acid solution. Another bottle was filled with methanol, while a third bottle was filled with a sodium hydroxide solution. However, the worker neglected to label each bottle. After a few days, the worker could not remember which liquid was in each bottle.
The worker needed to identify the liquid in each bottle. The bottles were labeled A, B, and C. Using materials found in the lab (indicators, conductivity apparatus, and pieces of Mg metal), the worker tested samples of liquid from each bottle. The test results are shown in the table below.
24. Using the test results, state how the worker differentiated the bottle that contained methanol from the other two bottles.
Methyl orangeà every bottle is at least at a pH of 3
Bromthymol blue-à A is at least 6.0, B is between 6.0-7.6, and C is below 6.0
Electrical Conductivityà if ionic, will conduct electricity in a solution, so Bottle B has to have the methanol
25. The worker concluded that bottle C contained hydrochloric acid. Identify one test and state the corresponding test result that supports this conclusion.
Bromthymol blue-à A is at least 6.0, B is between 6.0-7.6, and C is below 6.0
Since bottle C is below a pH of 6.0, it definitely must be an acid.
26. Explain, in terms of pH, why methyl orange indicator test results were the same for each of the three liquids.
The methyl orange color was the same in each bottle because all the substance had a pH greater than 3.0.
Given the reaction at equilibrium:
27. Explain, in terms of energy, why the forward reaction is exothermic.
It is exothermic because energy is a product. Energy is released
28. Explain, in terms of Le Chatelier’s principle, why the equilibrium shifts to the right to relieve the stress when the pressure on the system is increased at constant temperature.
When the pressure is increased, the reaction favors less gas particles. There are 2 gas moles on the left side and 1 gas mole on the right side. The reaction will favor the right side. That is why forward reaction is favored.
Base questions 29 through 30 on the information given below:
Using burets, a student titrated a sodium hydroxide solution of unknown concentration with a standard solution of 0.10 M hydrochloric acid. The data are recorded in the table below.
29. Determine both the total volume of HCl (aq) and the total volume of NaOH (aq) used in the titration.
HClà 25.00-15.50=9.50mL
NaOHà 8.80-5.00= 3.80mL
30. Show a correct numerical setup for calculating the molarity of the sodium hydroxide solution.
MAVA=MBVB (0.10M)(9.50mL)=(x)(3.80mL)
BONUS: 1. Why did foam and bubbles form in the bucket when we mixed acid and base in yesterday’s lab?
Chemical reactions
2. What are the subatomic particles and what are their charges? (NAME ALL!)
Electronsà negative Neutronsàneutral Protonsà positive