AP Chemistry Unit 3- Homework Problems Gas Laws and Stoichiometry

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1 AP Chemistry Unit 3- Homework Problems Gas Laws and Stoichiometry STP 1. What is standard pressure for each of the following: atm, mm Hg, Torr, kpa, PSI 2. Convert each of the following: a. 700 mm Hg to atm b. 1.5 atm to Torr c. 97 kpa to PSI d. 750 Torr to mm Hg 3. What is a barometer and how does it work? 4. What pressure is on this open-ended manometer? 50 mm 5. What would the pressure be if #4 was a closed-end vacuum manometer? 6. What is standard temperature? 7. How is the Kelvin scale different from the Celcius and Fahrenheit scale? 8. Why is the Kelvin scale called the absolute scale? Pressure and the Atmosphere 1. What is the relationship between altitude and atmospheric pressure? 2. Why does it take longer to cook food in Denver than in Palatine? 3. How does a pressure cooker work? 4. How far under water do you have to go to increase pressure by 1 atm? 5. What are The Bends?

2 Gas Laws 1. A gas is at 10 L and 700 mm Hg. What is the volume at 350 mm Hg? 2. A gas is at 80 ml and 75 kpa. What is the pressure at 50 ml? 3. A gas is at 2.4 L and 25 o C. What volume is the gas at 50 o C? 4. A gas is at 400 ml and 15 o C. What temperature ( o C) will cause the gas to be 100 ml? 5. A gas is at 2.3 atm and 0 o C. What pressure will cause the gas to be -50 o C? 6. A gas is at 18 psi and 20 o C. What temperature will cause the gas to be 50 psi? 7. A gas has 2.4 moles and 5 L. How many moles will cause the gas to be 8 L? 8. A gas has 1.7 moles and 350 ml. How many ml will the gas occupy if it is 7.8 moles instead? 9. A gas has 5.4 L at 800 mm Hg and 20 o C. What volume will the gas occupy if the pressure drops to 600 mm Hg while the temperature increases to 80 o C? 10. A gas has 650 ml at 15 o C and 3.4 atm. What pressure will the gas be if the volume increases to 1000 ml while the temperature drops to -20 o C? 11. A gas has 400 ml at 5 o C and 6.5 psi. What temperature will the gas be if the volume is dropped to 200 ml while the pressure is increased to 20 psi? 12. For each of the questions above, state whether the gas law is: Charles, Gay-Lussac s, Boyle s, Avagadro s, or Combined. 13. Write the Ideal Gas Law. What is the value for R? What are the units of R? 14. What is the pressure on an ideal gas if 0.25 moles of it occupies 3 L at 300 K? 15. What volume does 50 grams of CO 2 occupy if it is at 0 o C and 700 mm Hg? 16. How many grams of CH 4 are present if 300 ml of it is at 120 kpa and -25 o C? 17. What is the density of H 2 gas at STP? 18. What is the density of air (assume 80% N 2 and 20% O 2 ) at STP? 19. What is the density of Xe gas at 22 o C and 740 mm Hg? 20. What is the molecular weight of a gas if 2.3 grams of it occupy 230 ml at a pressure of 750 mm Hg and a temperature of 75 o C? 21. A gas is 11.8% C, 69.6% Cl and 18.6% F. If grams of it fills a 458 ml flask at 25 o C at a pressure of 21.3 mm Hg, what is the molecular formula of the compound? 22. A gas is 25.2% S and 74.8% F. If g are put in an 89 ml flask at 45 o C and a pressure of 83.8 mm Hg, what is the molecular formula of the gas? 23. State Dalton s Law of Partial Pressures. 24. A container has 0.5 atm of H 2, 2.5 atm of He, and 3 atm of O 2. What is the P total in the container? 25. A container has 10 grams of N 2, 100 grams of Xe, and 42 grams of Ar. What is the P tot in the container if the volume is 4 L and the temperature is 50 o C? 26. A container has 20 grams of O 2, 40 grams of CH 4, and 10 grams of He at a P tot of 600 mm Hg. What is the partial pressure of each gas? 27. Which of the following gases would be nearly impossible to collect over water? Why? N 2, HCl, NH 3, Cl 2

3 28. Hydrogen gas is collected over water at 15 o C. If the gas was collected at 800 mm Hg atmospheric pressure, what pressure of H 2 gas was collected? 29. Oxygen gas is collected over water at 22 o C. If the gas was collected in a 250 ml container at 740 mm Hg atmospheric pressure, how many grams of oxygen were collected? Kinetic Molecular Theory 1. What are the four ideas of the kinetic molecular theory? 2. Which two of the ideas in #1 are not technically true? 3. What is the Van der Waal s equation? What does it correct for? 4. Which gas in each pair would deviate most from ideality and why? a. N 2 vs. CO b. CH 3 OH vs. O 2 c. Ne vs. Xe 5. Two equal balloons are made; one with Helium and one with Neon. How much faster does the Helium balloon deflate compared to the Neon? 6. SO 2 diffuses 1.5 times as fast as an unknown gas. What is the molar weight of the unknown gas? 7. If BH 3 is put into one end of a tube marked 0 cm and NF 3 is put into the other end marked 100 cm, at what distance mark on the tube do they meet? 8. What is the RMS speed of O 2 gas at STP? 9. What is the RMS speed of Rn gas at STP? 10. You have four gas samples: a. 1 L H 2 at STP b. 1 L of Ar at STP c. 1 L of H 2 at 27 o C and 760 mm Hg d. 1 L of He at 0 o C and 900 mm Hg i) Which sample has the most atoms or molecules? ii) Which sample has the least atoms or molecules? iii) Which sample has the largest mass? iv) Which sample has the largest KE? 11. Five identical balloons are each filled to the same volume at the same temperature and pressure but are filled with CO 2, O 2, He, N 2, and CH 4. a. Which has the greatest mass? b. Compare the KE avg of the molecules in each of the balloons. Explain. c. Which should deviate most from ideality? Why? d. All of the balloons decrease in size over time. Which balloon will be the smallest? Why? 12. CO and CO 2 are put in separate containers of the same size and the same temperature. The pressure of CO gas is 2 atm while the pressure of the CO 2 gas is 1 atm. a. Compare the KE avg of the 2 samples. Explain. b. Which gas has a greater RMS speed? Explain why. c. Which container contains a greater number of molecules. Justify your answer.

4 Molarity 1. What is the definition of molarity? How do you make a M solution? 2. What is the M of a solution that has 2.5 moles of C 2 H 5 OH dissolved in 2500 ml of solution? 3. What is the M of a solution that has 100 grams of Na 2 CO 3 dissolved in 475 ml of solution? 4. How many grams of K 3 PO 4 must be dissolved in 250 ml total to make a 0.75 M solution? 5. How many ml are needed to dissolve 35 grams of CaCl 2 into a M solution? 6. What is the concentration of each of the ions in each of the following solutions: a M KI b M Li 2 SO 4 c M Na 3 PO 4 d M Al 2 (SO 4 ) 3 7. If 20 ml of 6 M HCl is diluted to a total volume of 100 ml, what is the new concentration? 8. If 127 ml of M H 2 SO 4 needs to be diluted to M, what is the new volume? 9. If 100 ml of 2.5 M solution A is mixed with 100 ml of 1.6 M solution B, what is the new concentration of each solution? 10. If 57.2 ml of M solution A is mixed with 32.9 ml of M solution B, what is the new concentration of each solution?

Saturation Curves 1. What is the solubility of NH 4 Cl at 40 o C? 2. How many grams of KCl will dissolve in 300 g H 2 O at 80 o C? 3. A solution has 50 grams of LiCl dissolved in 100 g H 2 O at 50 o C.

5 Saturation Curves 1. What is the solubility of NH 4 Cl at 40 o C? 2. How many grams of KCl will dissolve in 300 g H 2 O at 80 o C? 3. A solution has 50 grams of LiCl dissolved in 100 g H 2 O at 50 o C. Is it saturated, unsaturated, or supersaturated? grams of H 2 O were made into a saturated solution of NaNO 3 at 80 o C. The solution was then cooled to 20 o C. How many grams of NaNO 3 ppt out of solution? 5. On the graph above, draw in a line which represents the solubility of gases such as CO 2.

6 Colligative Properties 1. List the following solutions in order of increasing melting point: a. 0.1 m sugar b. 0.1 m NaCl c m CaCl 2 d m Na 2 CO 3 2. List the following solutions in order of decreasing freezing point: a m C 2 H 4 (OH) 2 b m K 2 SO 4 c m MgCl 2 d m KBr 3. What happens to the vapor pressure of a solvent when a solute is dissolved in it? Types of Reactions & Balancing 1. For each of the equations below, decide whether the reaction is an example of: synthesis, decomposition, single replacement, double replacement, or combustion a. CaI 2 + Br 2 CaBr 2 + I 2 b. CH O 2 CO H 2 O c. 2 Al + 3 Cl 2 2 AlCl 3 d. 6 K + N 2 2 K 3 N e. 3 MgCl K 3 PO 4 Mg 3 (PO 4 ) KCl f. CaCO 3 CaO + CO 2 g. NH 4 OH NH 3 + H 2 O h. 2 Li + F 2 2 LiF i. CS O 2 CO SO 2 j. Zn + Cu(NO 3 ) 2 Zn(NO 3 ) 2 + Cu 2. Balance the following equations: a. Fe 2 O 3 + Mg MgO + Fe b. SF 4 + H 2 O SO 2 + HF c. BF 3 + H 2 O HF + H 3 BO 3 d. C 6 H 5 CH 3 + O 2 H 2 O + CO 2 e. Fe + H 2 O Fe 3 O 4 + H 2 3. Predict the products and balance the equation: a. Si + Cl 2 b. Na 2 SO 4 + BaCl 2 c. CaO d. Zn + AgNO 3 e. C 8 H 18 + O 2

7 Stoichiometry 1. For the reaction: 4 Al + 3 O 2 2 Al 2 O 3 a. How many moles of Al are needed to react with 9 moles of O 2? b. How many moles of Al 2 O 3 can be made from 3.2 moles of O 2 and excess Al? c. How many grams of O 2 are needed to react with 100 grams of Al? d. How many grams of Al 2 O 3 can be produced from 75 grams of Al and excess O 2? 2. For the reaction: 2 B 4 H O 2 4 B 2 O H 2 O a. How many moles of O 2 are needed to react with 3.7 moles of B 4 H 10? b. How many moles of B 2 O 3 can be made from moles of O 2 and excess B 4 H 10? c. How many grams of B 4 H 10 are needed to react with 0.25 grams of O 2? d. How many grams of water will be made from 0.43 grams of B 4 H 10 and excess O 2? 3. For the reaction: Na 2 SO 4 (s) + 4 C (s) Na 2 S (s) + 4 CO (g) a. If you mix 15 g of Na 2 SO 4 with 7.5 g of C, how many grams of Na 2 S can be made? b. If you mix 10 g of Na 2 SO 4 with 14.2 g of C, how many grams of CO can be made? 4. For the reaction: 2 Al + 3 Cl 2 2 AlCl 3 a. If you mix 2.7 g Al and 4.05 g Cl 2, which reactant is limiting? b. What mass of AlCl 3 can be made? c. What mass of the excess reactant remains? 5. For the reaction: CaO + 2 NH 4 Cl 2 NH 3 + H 2 O + CaCl 2 a. If 112 g of CaO and 224 g of NH 4 Cl are mixed, what is the theoretical yield of NH 3? b. If only 16.3 g of NH 3 is actually made, what is the % yield?

8 6. For the reaction: CuSO NH 3 Cu(NH 3 ) 4 SO 4 a. If you react 25 ml of 1.25 NH 3 with 7.5 grams of CuSO 4, what is the theoretical yield of the product in grams? b. If you only get 0.63 grams of the product, what is the % yield? 7. For the reaction: 2 NaN 3 2 Na + 3 N 2 What mass of NaN 3 is required to give 75 L of N 2 at a pressure of 1.3 atm and 25 o C? 8. For the reaction: 2 C 8 H O 2 16 CO H 2 O a. If g of C 8 H 18 burns in O 2, what will be the pressure of water vapor in a 4.75 L flask at 30 o C? b. If the O 2 gas needed for complete combustion was in the 4.75 L flask at 22 o C, what would its pressure have been? 9. For the reaction: 4 KO CO 2 2 K 2 CO O 2 What mass of KO 2 is required to react with 8.90 L of CO 2 at 30 o C and 780 mm Hg? 10. For the reaction: Na 2 CO HCl 2 NaCl + CO 2 + H 2 O If ml of HCl is needed to titrate g of Na 2 CO 3, what is the M of HCl? 11. For the reaction: H 2 A + 2 NaOH Na 2 A + 2 H 2 O If ml of M NaOH is needed to reach the endpoint of g of H 2 A, what is the molar mass of H 2 A?

9 Chemical Analysis 1. A mixture of CuSO 4 and CuSO 4 *5H 2 O has a mass of g. After heating to drive off the water, the mass is only g. What was the mass % of CuSO 4 and CuSO 4 *5H 2 O in the original mixture? 2. For the reaction: 2 NaHCO 3 Na 2 CO 3 + CO 2 + H 2 O Heating a g sample of impure NaHCO 3 gives g of CO 2. What was the mass percent of NaHCO 3 in the original sample? 3. For the reaction: BeC 2 O 4 *3 H 2 O (s) BeC 2 O 4 (s) + 3 H 2 O (g) a. If 3.21 g of BeC 2 O 4 *3H 2 O is heated, calculate: i) the mass of BeC 2 O 4 (s) formed ii) the volume of H 2 O (g) released at 220 o C and 735 mm Hg b. A g of BeC 2 O 4 which contained an inert impurity was dissolved in enough water to give 100 ml of solution. A 20 ml portion of this was titrated with M KMnO 4 and required ml to reach the endpoint. The equation is as follows: 16 H MnO C 2 O Mn CO H 2 O i) Identify the reducing agent ii) Calculate the number of moles of each of the following at the endpoint of the titration: MnO 4-1 C 2 O 4-2 iii) Calculate the total moles of C 2 O 4-2 that were in the 100 ml sample iv) Calculate the mass % of BeC 2 O 4 in the impure g sample 4. For the following reaction: Fe 2 O 3 (s) + 3 CO (g) 2 Fe (s) + 3 CO 2 (g) A 16.2 L sample of CO (g) at 1.5 atm and 200 o C is combined with g of Fe 2 O 3 a. How many moles of CO are present? b. What is the limiting reagent? Prove it with calculations. c. How many grams of Fe are made? d. How many L of CO 2 are made?

10 5. For the reaction: 3 Ba(NO 3 ) 2 (aq) + 2 H 3 PO 4 (aq) Ba 3 (PO 4 ) 2 (s) + 6 HNO 3 (aq) If 200 ml of 3 M Ba(NO 3 ) 2 are mixed with 300 ml of 1 M H 3 PO 4, calculate the following: a) The mass of Ba 3 (PO 4 ) 2 (s) formed b) The final concentration of the NO 3-1 ion in solution 6. For the reaction: MnO Fe H + Mn Fe H 2 O A g sample of an iron-containing compound was analyzed. It required ml of M KMnO 4 to reach the equivalence point. What is the mass % of iron in the sample?

Stoichiometry. Percent composition Part / whole x 100 = %

Stoichiometry. Percent composition Part / whole x 100 = % Stoichiometry Conversion factors 1 mole = 6.02 x 10 23 atoms (element) 1 mole = 6.02 x 10 23 molecules (covalent compounds) 1 mole = 6.02 x 10 23 formula units (ionic compounds) 1 mole (any gas @ STP)