General Chemistry, Chapters 4-6 Practice Problems Dr. Badger
1. A solution contains 2.0 moles of solute in mL of solution. What is its molarity? 2.0 mol 200 mL 1000 mL 1 L =10.0 mol/L
2. How many grams of Ca(OH) 2 are required to make 1.00 L of a 0.750M Ca(OH) 2 solution? g Ca(OH) 2 1 mol Ca(OH) 2 1 L =55.6 g Ca(OH) 2 mm Ca(OH) 2 = g Ca(OH) 2 / mol mol Ca(OH) 2 That is, 55.6 g Ca(OH) 2 per liter of solution is 0.750M Ca(OH) 2
3. How many grams of CO 2 are in 15.0 L of CO 2 at STP? 15.0 L of CO g CO 2 mol CO L =29.5 g CO mol Could you use PV = nRT to solve this? Why didn’t we use it?
4. 50 mL of an H 3 PO 4 solution was titrated with 0.50 M KOH. 235 mL of the base were required to neutralize the sample. What is the molarity of this acid solution? H 3 PO 4 + KOH K 3 PO 4 + H 2 O Is this equation balanced? Why do we need a balanced chemical equation?
4. 50 mL of an H 3 PO 4 solution was titrated with 0.50 M KOH. 235 mL of the base were required to neutralize the sample. What is the molarity of this acid solution? H 3 PO KOH K 3 PO H 2 O 0.50 mol KOH L 3 mol KOH 1 mol H 3 PO L = 3.92 mol H 3 PO mol H 3 PO 4 = mol/L 1 L
5. What volume of conc hydrochloric acid (12.0 M) is required to make 350 mL of 1.5 M hydrochloric acid? M i V i = M f V f 12.0 M V i = 1.5 M 350 mL V i = 12.0 M 1.5 M 350 mL = = 44 mL
mol NH 3 occupies 2.25 L at 175ºC. Calculate the pressure of NH 3 in the flask. PV = nRT P = 175ºC = 448 K V nRT = mol L atm mol -1 K -1 448 K 2.25 L P = 12.3 atm
7. A sample of a gas occupies 2.50 10 3 mL at 25ºC and 560 mmHg. What volume will it occupy at the same temperature and 690 mmHg? P 1 V 1 = P 2 V mmHg 2.50 10 3 mL V 2 = 690 mmHg atm 2.50 10 3 mL V 2 = atm = 2.03 10 3 mL
8. Calculate the mass of 3.54 L of CO gas measured at 29ºC and 800 mmHg. 29ºC = 302K PV = nRT n = RT PV = L atm mol -1 K -1 302 K 1.05 atm 3.54 L n = mol CO g CO 1 mol CO = 4.20 g CO
9. Calculate the amount of heat necessary to raise the temperature of 26.0 g of water from 13.4ºC to 81.0ºC. The specific heat of water = 4.18 J/g·ºC. q = msΔt Δt = t f - t i q = 26.0 g 4.18 J/g ºC (67.6 ºC) q = 7.35 10 3 kJ
10. A sample of oxygen gas was collected over water at 25ºC and 725 mmHg. The volume of the container was 4.80 L. Calculate the mass of O 2 (g) collected. P T = P ox + P w P ox = P T - P w P ox = 725 mmHg – mmHg n = RT PV = L atm mol -1 K -1 298 K atm 4.80 L = 18.1 mol n = 18.1 mol O g O 2 1 mol O 2 = 579 g O 2 P ox = mmHg = atm
11. Calculate the amount of heat required to raise the temperature of 41.7 g of Al from 20.0ºC to 145ºC. (Al has a specific heat of J/g·ºC.) q = msΔt Δt = t f - t i q = 41.7 g J/g ºC (125 ºC) q = 4.80 10 3 kJ
12. Determine the molar mass of an unknown gas if a sample weighing g is collected in a flask with a volume of L at 90ºC. The pressure of the gas is 682 mmHg. n = RT PV = L atm mol -1 K -1 363 K atm L = 3.52 mol 3.52 mol g = 59.9 g / mol PV = nRT
13. Given: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) Calculate the heat evolved when 88.2 g of SO 2 (g) is oxidized to SO 3 (g). H = –198.2 kJ/mol 88.2 g SO 2 = -273 kJ 1 mol SO g SO 2 1 mol kJ Is this -273 kJ/mol? Explain.