Chemistry Final Answer Key 2018
1. Potassium permanganate and glycerin react explosively according to the following equation: 14 KMnO4 + 4 C3H5(OH)3 → 7 K2CO3 + 7 Mn2O3 + 16 H2O + 5CO2
a) How many moles of carbon dioxide can be produced from 4.44 mol of KMnO4?
1.59 mol CO2
b) If 5.21 g of H2O are produced, how many moles of glycerin, C3H5((OH)3 , were used? 0.0723 mol C3H5((OH)3
c) If 3.39 mol of potassium carbonate are made, how many grams of manganese(III) oxide are also made? 535 g Mn2O3
d) How many grams of glycerin will be needed to react with 50.0 g KMnO4? How many grams of CO2 will be produced in the same reaction? 8.33 g C3H5(OH)3 ; 4.97 g CO2
2. A reaction such as the one shown here is often used to demonstrate a single replacement reaction.
3CuSO4(aq) + 2 Fe(s) → 3 Cu(s) + Fe2(SO4)3(aq)
If you place 0.092 mol of iron filings in a solution containing 0.158 mol of CuSO4, what is the limiting reactant? How many moles of Cu will be formed? Fe is limiting, 0.138 mol Cu
3. In the commercial production of the element arsenic(III) oxide is heated with carbon, which reduces the oxide to the metal according to the following equation:
2As2O3 + 3C → 3CO2 + 4 As
a) If 8.87 g of As2O3 is used in the reaction and 5.33 g of As is produced, what is the percentage yield? 79.3% yield
b) If 67 g of carbon is used up in a different reaction and 425 g of As is produced, calculate the percentage yield of this reaction. 76% yield
4. The reaction N2(g) + 3H2(g) → 2 NH3(g) is used to produce ammonia commercially. If 5.6 L of N2 are used in the reaction, how many liters of NH3 are produced? 11.2 L NH3
5. Explain on the molecular level why liquids have a definite volume but no definite shape.
According to molecular theory, the molecules of a liquid are in motion and are able to slide over one another making them flow, but they are much closer together than a gas’ particles so they do have a definite volume.
6. What determines the boiling point of a substance? The boiling point is the temperature where the vapor pressure of the liquid is equal to the atmospheric pressure of the air around it.
7. What phase transition occurs as a gas becomes a solid? It goes through deposition.
8. For the diagram above:
a. In what state is point A? solid
b. What are the pressure and temperature for the triple point? .08 atm and 150 K
c. If a liquid at 1 atm and 300 K is cooled to 150 K, what transition does it go through? It goes through the process of freezing.
9. Using the chart above, calculate the amount of heat transfer as 200 g Benzene is heated from 0° C to 80° C. 51536 J do not do
10. How much heat is released as 50 g water cools from 100° C to 50° C? 10450 J
11. Explain how the specific heat of water affects the weather at the shore. The ocean water takes longer to warm up than the air and the land. So onshore breezes keep the shore cooler than the land further in from the coast.
12. A child receives a balloon filled with 2.30 L of helium from a vendor at an amusement park. The temperature outside is 311 K. What will the volume of the balloon be when the child brings it home to an air-conditioned house at 295 K? Assume that the pressure stays the same. 2.18 L
13. A sample of carbon dioxide gas occupies 638 mL at 0.893 atm and 12° C. What will the pressure be at a volume of 881 mL and a temperature of 18° C? 0.660 atm
14. A gas has a pressure of 4.62 atm when its volume is 2.33 L. If the temperature remains constant what will the pressure be when the final volume is changed to 1.03 L? Express the final answer in Torrs. 7940 Torrs (with sig. figs.)
15. A container holds 265 mL of chlorine gas, Cl2. If the gas sample is at STP, what is its mass? 0.839 g
16. At a certain temperature and pressure, chlorine molecules have an average velocity of 324 m/s. What is the average velocity of sulfur dioxide molecules under the same conditions? 358 m/s Do not do
17. A mixture of 2 gases is at a total pressure of 5.21 atm. The partial pressure of the first gas is 3.87 atm. What is the pressure of the second gas? 1.34 atm
18. Compare the rates of diffusion of carbon monoxide, CO and sulfur trioxide, SO3. CO diffuses approximately 1.7 times faster than SO3 , smaller molecules move faster. ( to get rate take square root of molar mass)√28 and √80 = 5.29 and 8.94, 8.94 ÷ 5.29 = 1.7
19. What type of solvent would dissolve oil, a non-polar substance? A non-polar solvent would dissolve it.
20. What factors affect the dissolution rate? Temperature, agitation, pressure, and surface area are all factors that affect the rate of dissolution.
21. If 110 g of potassium nitrate is dissolved in 100 g of water at 50° C, is the solution saturated, supersaturated or unsaturated? It is supersaturated.
22. Using the above chart, how many grams of potassium chloride will saturated 200 g of water at 80° C? 100g
23. What does it mean that a solution system is at equilibrium? The rates of the solute going into the solution and out of the solution are equal.
24. A solution of (NH4)2SO4 is made by dissolving 26.42 g in enough water to make 50 mL of solution. What is the molarity of the solution? 4.00 M
25. Determine the number of grams needed to make a 4.5 m solution of HNO3 in 2.00 kg of water. 567.12 g
26. Write the net ionic equation for the word equation:
a. Sodium + water yields sodium hydroxide + hydrogen gas. Na+ (aq) + 2H2O(l) → Na+(aq) + 2 OH-(aq) + H2(aq)
b. Barium chloride + sodium sulfate yields sodium chloride + barium sulfate Ba2+ + SO42- (aq) → BaSO4(s)
27. Identify the spectator ions for the equation:
a. Iron(III) bromide + ammonium sulfide yields iron(III) sulfide + ammonium bromide
Net ionic: 2 Fe+3(aq) + 3S2-(aq) → Fe2S3(s)
Spectator ions: NH3+ (aq) , Br – (aq)
b. Potassium phosphate + Lead(II) nitrate yields potassium nitrate and lead phosphate
Net ionic: 3Pb2+(aq) + 2PO4-3(aq) → Pb3(PO4)3(s)
Spectator ions: K+(aq) , NO3-(aq)
28. How many ions are produced from KCl? Ions produced= 1 mole K+ + 1 mole Cl- = 2 mol ions
29. How many moles of ions are produced from K3PO4? Ions produced = 3 mol K+ + 1 mol PO43- = 4 mol ions
30. How many moles of ions are produced from 2 moles of MgCl2? Ions produced 2 mol Mg2+ + 4 mol Cl- = 6 mol ions
31. Find the freezing point depression of 1.50 m of sucrose , C12H22O11. Use the freezing point constant of -1.86 °C/m. ∆ tf = Kf m
= (-1.86 °C/m) (1.50 m) = -2.79° C
32. Find the freezing point depression of a 1.00 m solution of KI. The Kf = -1.86 °C/m. (-1.86° C/m) (1.00 m KI) (2 mol) = -3.72°C
33. Calculate the boiling point of a solution containing 5.70 g sugar, C12H22O11, dissolved in 50.0 g of water. The Kb = .51 °C/m.
5.7 g C12H22O11 X 1000g X 1 mol X .51°C/m = 0.170 °C
50 g 1 kg 342.2948 g
34. Which graph shows an endothermic reaction? Graph B
35. What does arrow 5 show? Energy of the products
36. What is the ∆H for the reaction in graph A? -150 kJ
37. What does the dotted line in graph B represent? The dotted line represents the catalyst for the reaction.
38. Is the reaction at the top of the graphs illustrated by graph A or Graph B? Graph A
39. How are the two graphs related? The graphs are the reverse reaction of each other.
40. Is the ∆H of an exothermic reaction negative or positive? The ∆H is always negative for an exothermic reaction.
41. What is the enthalpy change for Cl2(g) + 2HBr(g)→ 2HCl2(g) + Br2(g) ? The ∆Hf are as follows: HBr = -36.4 KJ/mol, HCl = -92.3KJ/mol, Cl2= 0, Br2 = 0. 2mol (-92.3 kJ/mol) – 2 mol ( 36.4 kJ/m) = 72.8 kJ ∆H = Hproducts- Hreactants H= -257.4kJ
42. Find the ∆S for the following reactions
a. Zn(NO3)2(aq) + 2NaOH(aq) → Zn(OH)2(cr) + 2NaNO3(aq) Stays the same
c. 4H3PO4(aq) → P4O10(cr) + 6 H2O(l) increase in entropy
43. Predict the spontaneity of the following reaction at 298 K:
a. Sn(cr) + 4HNO3(aq) → SnO2(cr) + 4NO2(g) + 2H2O(l) ∆H = -192 kJ spontaneous
b. 2N2O5(g) → 4 NO2(g) + O2(g) ∆H = 110 kJ, ∆S = 839kJ spontaneous sometimes
44. Name the following as acids or bases
a. HCl acid
b. NaOH base
c. H3PO4 acid
d. KOH base
45. Name the following acids as monoprotic, diprotic or triprotic.
a. Sulfuric acid diprotic
b. Acetic acid monoprotic
c. Hydrosulfuric acid diprotic
46. If an acid has a H3O+ concentration of 1.00 x 10-2 , what is the pH of the solution? pH = 2
47. If a base has a OH- concentration of 1.00 x 10-8, what is the pH of its conjugate acid? pH = 6
48. Explain the three acid-base theories of the Arrhenius theory, Brønsted and Lowery theory and the Lewis Theory. Do not do
The Arrhenius theory explains acids and bases by the ion formation. Acids ionize to produce H+ ions and bases produce OH- ions. The Brønsted and Lowery theory defines acids and bases by the donation or acceptance of a proton (H+). Acids are the donors and bases are the acceptors. The Lewis theory of acids and bases defines them as electron pair acceptors and donors. This allows for non-ionizing molecules to be treated as acids or bases
49. If a substance has a bitter taste, turns red litmus paper blue and conducts electricity, is it an acid or a base? It is a base.
50. Which is more acidic, a solution with a pH of 3 or a solution with a pH of 1? A pH of 1 is more acidic.