Review Material for Exam #2 1. a. Calculate the molarity of a solution made with 184.6 mg sample of potassium dichromate dissolved in enough water to give 500.0 mL of solution.

2 2 72 2 7

2 2 7

1 mole K Cr O1 g184.6 mg K Cr O x x 1000 mg 294.181 g K Cr O

1 L500.0 mL x 1000 mL

= 1.255 x 103 M

b. What is the molarity of potassium ion? K2Cr2O7(aq) 2 K+(aq) + Cr2O72(aq)

3 +

2 2 7

2 2 7

1.255 x 10 mole K Cr O 2 mole K x L 1 mole K Cr O

= 2.510 x 103 M K+

2. Calculate the mass of sodium hydroxide needed to make 250.0 mL of a 0.4000 M solution.

0.4000 mole NaOH 39.997 g NaOH x 0.2500 L x L 1 mole NaOH

= 4.000 g NaOH

3. How would you prepare 1.0 L of 0.50 M sulfuric acid from concentrated (18 M) sulfuric acid?

2 42 4

0.50 mole H SO 1 L 1000 mL x 1.0 L x x L 18 mole H SO 1 L

= 28 mL concentrated H2SO4 diluted to 1.0 L 4. Predict the solubility of each substance in water using solubility rules. Write the ionization reaction when each soluble substance is dissolved in water. 1. All Li+, Na+, K+, and NH4+ salts are soluble. 2. All NO3, C2H3O2, ClO3, and ClO4 salts are soluble. 3. All Ag+, Pb2+ , and Hg22+ salts are insoluble. 4. All Cl , Br , and I salts are soluble.

5. All CO32, O2, S2, OH, SO32, CrO42, Cr2O72, and PO43 salts insoluble, except CaS, SrS, BaS and Ba(OH)2. 6. All SO42 salts are soluble except Ca2+, Sr2+, and Ba2+. a. Ba(NO3)2 soluble (2) Ba(NO3)2(aq) Ba2+(aq) + 2 NO3(aq) b. ZnS insoluble (5) c. (NH4)2CO3 soluble (1) (NH4)2CO3(aq) 2 NH4+(aq) + CO32(aq)

d. Fe2O3 insoluble (5) e. PbCl2 insoluble (3) f. NaClO4 soluble (1) NaClO4(aq) Na+(aq) + ClO4(aq) g. BaCrO4 insoluble (5) h. FeBr2 soluble (4) FeBr2(aq) Fe2+(aq) + 2 Br(aq) i. Ag2SO4 insoluble (3) j. Ca(OH)2 insoluble (5) k. Hg2(ClO3)2 soluble (2) Hg2(ClO3)2(aq) Hg22+(aq) + 2 ClO3(aq) l. K3PO4 soluble (1) K3PO4(aq) 3 K+(aq) + PO43(aq) m. Mg3(PO4)2 insoluble (5) n. NH4NO3 soluble (1) NH4NO3(aq) NH4+(aq) + NO3(aq) o. ZnCrO4 insoluble (5) p. NiSO4 soluble (6) NiSO4(aq) Ni2+(aq) + SO42(aq) q. AlCl3 soluble (4) AlCl3(aq) Al3+(aq) + 3 Cl(aq) r. AgI insoluble (3) s. CaBr2 soluble (4) CaBr2(aq) Ca2+(aq) + 2 Br(aq) t. CuS insoluble (5) u. K2SO3 soluble (1) K2SO3(aq) 2 K+(aq) + SO33(aq) 5. Predict the products (include phase state), balance and write the net ionic equations for each of the following. Classify each as precipitation, acid-base or oxidation-reduction. Na3PO4(aq) + 3 AgNO3(aq) Ag3PO4(s) + 3 NaNO3(aq) 3 Ag+(aq) + PO43(aq) Ag3PO4(s) precipitation K2SO4(aq) + BaCl2(aq) BaSO4(s) + 2 KCl(aq) Ba2+(aq) + SO42(aq) BaSO4(s) precipitation Hg2(NO3)2(aq) + CaCl2(aq) Hg2Cl2(s) + Ca(NO3)2(aq) Hg22+(aq) + 2 Cl(aq) Hg2Cl2(s) precipitation Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + 2 NaNO3(aq) Pb2+(aq) + SO42(aq) PbSO4(s) precipitation AgClO3(aq) + KCl(aq) AgCl(s) + KClO3(aq) Ag+(aq) + Cl(aq) AgCl(s) precipitation 3 KOH(aq) + H3PO4(aq) K3PO4(aq) + 3 H2O() H3PO4(aq) + 3 OH(aq) PO43(aq) + 3 H2O() acid-base

ZnCl2(aq) + H2S(aq) ZnS(s) + 2 HCl(aq) Zn2+(aq) + S2(aq) ZnS(s) precipitation 2 Na3PO4(aq) + 3 CaCl2(aq) Ca3(PO4)2(s) + 6 NaCl(aq) 3 Ca2+(aq) + 2 PO43(aq) Ca3(PO4)2(s) precipitation 2 HBr(aq) + Ca(OH)2(aq) CaBr2(aq) + 2 H2O() H+(aq) + OH(aq) H2O() acid-base 2 Na(s) + S(s) Na2S(s) Same redox 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g or ) Same redox Mg(s) + Cu(NO3)2(aq) Cu(s) + Mg(NO3)2(aq) Mg(s) + Cu2+(aq) Mg2+(aq) + Cu(s) redox 6. Determine the oxidation state of each element and identify which element is oxidized and which is reduced. Identify the oxidizing and reducing agents. a. Fe2O3 + 3 CO 2 Fe + 3 CO2 +3 2 +2 2 0 +4 2 Fe reduced, C oxidized Fe2O3 oxidizing agent CO reducing agent b. PbS + 4 H2O2 PbSO4 + 4 H2O +2 2 +1 1 +2 +6 2 +1 2 O reduced, S oxidized H2O2 oxidizing agent PbS reducing agent c. 8 H2O + 3 P4 + 20 HNO3 12 H3PO4 + 20 NO +1 2 0 +1 +5 2 +1 +5 2 +2 2 N reduced, P oxidized HNO3 oxidizing agent P4 reducing agent

d. 2 MnSO4 + 5 PbO2 + 3H2SO4 2 HMnO4 + 5 PbSO4 + 2 H2O +2 +6 2 +4 2 +1 +6 2 +1 +7 2 +2 +6 2 +1 2 Pb reduced, Mn oxidized PbO2 oxidizing agent MnSO4 reducing agent e. 3 Cu + 2 HNO3 + 6 HCl 3 CuCl2 + 2 NO + 4 H2O 0 +1 +5 2 +1 1 +2 1 +2 2 +1 2 N reduced, Cu oxidized HNO3 oxidizing agent Cu reducing agent f. 2 Bi(OH)3 + 3 K2SnO2 3 K2SnO3 + 2 Bi + 3 H2O +3 2 +1 +1 +2 2 +1 +4 2 0 +1 2 Bi reduced, Sn oxidized Bi(OH)3 oxidizing agent K2SnO2 reducing agent 7. If 30.0 mL of 0.150 M aluminum chloride is added to 15.0 mL of 0.100 M silver(I) nitrate, what mass of precipitate will be formed? 3 AgNO3(aq) + AlCl3(aq) 3 AgCl(s) + Al(NO3)3(aq)

33

0.150 mole AlCl 3 mole AgCl 143.321 g AgCl x 0.030 L x x L 1 mole AlCl 1 mole AgCl

= 1.94 g AgCl

33

0.100 mole AgNO 1 mole AgCl 143.321 g AgCl x 0.015 L x x L 1 mole AgNO 1 mole AgCl

= 0.215 g AgCl

limiting 8. A 10.00 mL sample of barium hydroxide solution was titrated with 31.24 mL of 0.1250 M HCl. Calculate the molarity of the barium hydroxide solution. 2 HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2 H2O()

21 mole Ba(OH)0.1250 mole HCl x 0.03124 L x L 2 mole HCl

0.01000 L = 0.1953 Ba(OH)2

9. Calcium in blood is determined by precipitating calcium oxalate, CaC2O4, followed by dissolving in acid and titrating the oxalic acid (H2C2O4) with KMnO4: 5 H2C2O4(aq) + 2 MnO4(aq) + 6 H+(aq) 10 CO2(g) + 2 Mn2+(aq) + 8 H2O() What is the concentration of Ca2+ (mg/dL) in a 10.0 mL sample of blood if 10.54 mL of 9.88 x 104 M KMnO4 solution is needed for the titration.

44 4 2 2 4

4 4

9.88 x 10 mole KMnO 1 mole MnO 5 mole H C O x x 0.01054 L x L 1 mole KMnO 2 mole MnO

0.01000 L

x2+ 2+

2+2 2 4

1 mole Ca 40.078 g Ca 1000 mg 1 L x x x 1 mole H C O 1 mole Ca 1g 10 dL

= 10.4 mg/dL

10. Acetylene is a gas used as a fuel for some welding torches. If 0.52 L of acetylene has a pressure of 1824 torr, what is the pressure (in atms) if the volume is decreased to 0.39 L? Boyles Law: P1V1 = P2V2;

1 12

2

1 atm1824 torr x 0.52 LP V 760 torrP V 0.39 L

3.2 atm

11. A sample of carbon dioxide has a volume of 19.4 L at 10.8 C. What is the volume of the same sample of carbon dioxide at 14.6 C.

Charles Law: 1 21 2

V V T T

; 1 2

21

19.4 L (14.6 + 273.15) KV TV T (10.8 + 273.15) K

19.7 L

12. A balloon at 23 C contains 0.32 moles of helium gas at 2432 torr. The volume of the helium is 2.43 L. If an additional 0.14 mole of He is injected into the balloon while holding the temperature and pressure constant, what is the volume of the balloon?

Avogadros Law: 1 21 2

V V n n

; 1 2

21

2.43 L 0.46 moleV nV n 0.32 mole

3.5 L

13. A sample of Ar has a pressure of 0.63 atm at 26.4 C and a volume of 0.79 L. If the temperature is lowered by 5.2 C and the pressure is increased to 0.96 atm, what is the new volume?

1 1 2 21 2

P V P V T T

;

1 1 22

2 1

0.63 atm 0.79 L (26.4 + 273.15P V TV P T 0.96 atm ((26.4 5.2) + 273.15)

0.53 L

14. Magnesium metal reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas. What mass of Mg reacted with excess hydrochloric acid if 255 mL of hydrogen gas is produced at 756.4 torr and 25.0 oC?

1 atmP 756.4 torr 23.76 torr x 0.9640 atm760 torr

1 LV 255 mL x 0.255 L1000 mL

n ?

L atmR 0.08206 mole K

T 25.0 oC + 273.15 = 298.15K PV = nRT

0.9640 atm 0.255 LPVn L atmRT 0.08206 298.15 K

mole K

= 0.01005 mole H2

Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g)

22

1 mole Mg 24.305 g Mg0.01005 mole H x x 1 mole H 1 mole Mg

= 0.244 g Mg

15. Styrene oxide is a fairly simple aromatic organic compound that has a pleasant odor and is often used in the perfume industry. If 2.07 g of the compound is vaporized completely into a closed 1.04 L flask at 435 C, the pressure in the flask is found to be 735 torr. Calculate the formula weight of styrene oxide.

1 atmP 735 torr x 0.967 atm760 torr

V 1.04 L g 2.07 g

L atmR 0.08206 mole K

T 435 oC + 273.15 = 708.15 K FW ?

gRTPV FW

L atm2.07 g 0.08206 708.15 KgRT mole KFW PV 0.967 atm 1.04 L

= 120 g/mole

(3 sig. figs.) 16. a. A sample of dichloroethane, a dry cleaning solvent, is vaporized into a 266.4 mL flask at 99.8 oC. Some of the sample leaves the flask through a pinhole through the stopper until the pressure in the flask is the same as the outside pressure. A barometer shows the pressure to be 745.3 torr. When the flask is cooled, the mass of dichloroethane in the flask is measured to be 0.8447 g. Calculate the formula weight of dichloroethane.

1 atmP 745.3 torr x 0.9807 atm760 torr

1 LV 266.4 mL x 0.2664 L1000 mL

g 0.8447 g

L atmR 0.08206 mole K

T 99.8 oC + 273.15 = 372.95 K FW ?

gRTPV FW

L atm0.8447 g 0.08206 372.95 KgRT mole KFW PV 0.9807 atm 0.2664 L

= 98.95 g/mol

b. Is the formula of dichloroethane CH2Cl2, C2H4Cl2, or C4H8Cl2? 84.933 g/mole, 98.960 g/mole, 127.014 g/mole 17. Diborane, B2H6, is a highly explosive compound formed by the reaction 3 NaBH4(s) + 4 BF3(g) 2 B2H6(g) + 3 NaBF4(s) What mass of NaBH4 is required to give 1.00 L of diborane at 0.0 oC and 1.00 atm? P 1.00 atm V 1.00 L n ?

L atmR 0.08206 mole K

T 0.0 oC + 273.15 = 273.15 K PV = nRT

1.00 atm 1.00 LPVn L atmRT 0.08206 273.15 K

mole K

= 0.0446 mole B2H6

4 42 62 6 4

3 mole NaBH 37.833 g NaBH0.0446 mole B H x x 2 mole B H 1 mole NaBH

= 2.53 g NaBH4

18. For the reaction, as written: S8(s) + 8 O2(g) 8 SO2(g) H = 2368 kJ a. How much heat is evolved when 25 moles of sulfur is burned in excess oxygen?

88

2368 kJ25 mole S x 1 mole S = 5.9 x 104 kJ

b. How much heat is evolved when 275 grams of sulfur is burned in excess oxygen?

888 8

1 mole S 2368 kJ275 g S x x 256.52 g S 1 mole S

= 2.54 x 103 kJ

c. How much heat is evolved when 150.0 grams of sulfur dioxide is produced?

8222 2 8

1 mole S1 mole SO 2368 kJ150.0 g SO x x x 64.063 g SO 8 mole SO 1 mole S

= 693.1 kJ

19. In a calorimetry experiment, 0.1277 g of Mg ribbon was added to 200.0 mL 0.500 M HCl at 24.12 oC. The water temperature increased to 27.10 oC. Calculate H for this reaction, as performed, and H per mole of HCl.

2 2

o oH O H O o

JH C T (m x s ) T (200.0 g x 4.184 )(27.10 C 24.12 C)g C

H = 2493.66 J

Mg(s) + 2 HCl(aq) MgCl2(s) + H2(g)

1 mole Mg 2 mole HCl0.1277 g Mg x x 24.305 g Mg 1 mole Mg

= 0.0105 mole HCl needed

0.500 mole HCl x 0.2000 L

L = 0.100 mole HCl available; Mg limiting

2493.66 JH

0.0105 mole HCl

237,491 J/mole = 237 kJ/mole HCl

20. A 2.50 g sample of sucrose (C12H22O11) was burned in excess oxygen in a calorimeter which contained 2.19 kg of water. The temperature of the water increased from 20.50 oC to 25.01 oC. Determine the molar heat of combustion of sucrose. C12H22O11(s) + 12 O2(g) 12 CO2(g) + 11 H2O(g)

2 2

o oH O H O o

JH C T (m x s ) T (2190 g x 4.184 )(25.01 C 20.50 C)g C

H = 41,324.9 J

12 22 1112 22 1112 22 11

1 mole C H O2.50 g C H O x 342.297 g C H O

= 7.30 x 103 mole C12H22O11

312 22 11

41,324.9 JH 7.30 x 10 mole C H O

5,658,162.51 J/mole

= 5.66 x 103 kJ/mole C12H22O11

21. The burning of 5.08 g benzene (C6H6) releases enough heat to raise the temperature of 5.00 kg of water from 10.1 oC to 19.6 oC. Calculate the molar heat of combustion of benzene. 2 C6H6() + 15 O2(g) 12 CO2(g) + 6 H2O(g)

2 2

o oH O H O o

JH C T (m x s ) T (5000 g x 4.184 )(19.6 C 10.1 C)g C

H = 198,740 J

6 66 66 6

1 mole C H5.08 g C H x 78.114 g C H

= 0.065 mole C6H6

6 6

198,740 JH 0.065 mole C H

3,055,979.6 J/mole = 3.1 x 103 kJ/mole C6H6

22. Given the following equations and H values, H H3BO3(aq) HBO2(aq) + H2O() 0.02 kJ H2B4O7(s) + H2O() 4 HBO2(aq) 11.3 kJ H2B4O7(s) 2 B2O3(s) + H2O() +17.5 kJ calculate Horxn for the following reaction: 2 H3BO3(aq) B2O3(s) + 3 H2O() 2 H3BO3(aq) 2 HBO2(aq) + 2 H2O() 2(0.02 kJ) 2 HBO2(aq) 1/2 H2B4O7(s) + 1/2 H2O() (11.3 kJ) 1/2 H2B4O7(s) B2O3(s) + 1/2 H2O() (+17.5 kJ) +14.4 kJ 23. The following reaction is one that occurs in a blast furnace when iron is extracted from its ores: Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g) find Horxn for this reaction given the following information: H 3 Fe2O3(s) + CO(g) 2 Fe3O4(s) + CO2(g) 46.4 kJ FeO(s) + CO(g) Fe(s) + CO2(g) 9.0 kJ Fe3O4(s) + CO(g) 3 FeO(s) + CO2(g) 41.0 kJ Fe2O3(s) + 1/3 CO(g) 2/3 Fe3O4(s) + 1/3 CO2(g) 1/3(46.4 kJ) 2 FeO(s) + 2 CO(g) 2 Fe(s) + 2 CO2(g) 2(9.0 kJ) 2/3 Fe3O4(s) + 2/3 CO(g) 6/3 FeO(s) + 2/3 CO2(g) 2/3(41.0 kJ) 24.8 kJ 24. Calculate Horxn for the following reaction: C2H4(g) + H2(g) C2H6(g) from the following information: H C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O() 1401 kJ

C2H6(g) + 7/2 O2(g) 2 CO2(g) + 3 H2O() 1550 kJ H2(g) + 1/2 O2(g) H2O() 286 kJ C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O() 1401 kJ 2 CO2(g) + 3 H2O() C2H6(g) + 7/2 O2(g) (1550 kJ) H2(g) + 1/2 O2(g) H2O() 286 kJ 137 kJ 25. Give the formation reactions for the following compounds: Al2O3, NH3, N2O5, C2H3Cl. 2 Al(s) + 3/2 O2(g) Al2O3(s)

1/2 N2(g) + 3/2 H2(g) NH3(g)

N2(g) + 5/2 O2(g) N2O5(g) 2 C(s) + 3/2 H2(g) + 1/2 Cl2(g) C2H3Cl()