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Chemistry SOL Review— Molar Relationships

Chemistry SOL Review— Molar Relationships. The Mole and Mole Calculations. The molar mass = the sum of all the atomic masses. Example Ca(NO 3 ) 2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams You try one: What is the gram formula mass (molar mass) of Mg 3 (PO 4 ) 2 ?.

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Chemistry SOL Review— Molar Relationships

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  1. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams You try one: What is the gram formula mass (molar mass) of Mg3(PO4)2? http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca7thermite.html

  2. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams You try one: What is the gram formula mass (molar mass) of Mg3(PO4)2? 3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams

  3. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams What is the gram formula mass (molar mass) of Mg3(PO4)2? 3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams What is the percent Magnesium in Mg3(PO4)2? Answer: 3(24.305) x 100 = 27.7% 262.86 What is the percent Lithium in Li2SiO3? molar mass = 2(6.941) + 28.0855 + 3(15.9994) = 89.9657 g % Li = 2(6.941) x 100 = 15.4% 89.9657

  4. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams What is the gram formula mass (molar mass) of Mg3(PO4)2? 3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams What is the percent Magnesium in Mg3(PO4)2? Answer: 3(24.305) x 100 = 27.7% 262.86 What is the percent Lithium in Li2SiO3?

  5. Chemistry SOL Review— Molar Relationships A Brief Return to Empirical Formulas Empirical Formulas are the reduced form of Molecular formulas. For example: The empirical formula for C5H10 is CH2. A favorite SOL type question: What is the empirical formula of a compound that contains 30% Nitrogen and 70% Oxygen? This is really a percent composition problem. Figure out which compound contains 30% nitrogen. a) N2O b) NO2 c) N2O5 d) NO

  6. Nitrogen gas is a diatomic molecule. What is the mass of one mole of nitrogen gas? A 7 g B 14 g C 28 g D 6 x 1023 g • How many grams of nitrogen are present in 2 moles of HNO3? A 1 B 2 C 14 D 28 • What is the mass in grams of one mole of sulfur dioxide (SO2)? A 48.1 g B 64.1 g C 80.1 g D 96.1 g

  7. What is the molar mass of Al(NO3)3? A 57 g/mol B 103 g/mol C 165 g/mol D 213 g/mol • What is the percentage of aluminum in aluminum oxide (Al2O3)? A 47% B 48% C 53% D 54% • A compound is composed of 85.64% carbon and 14.36% hydrogen. The compound has a formula mass of 42.08 grams. What is the molecular formula? A CH2 B C3H6 C C2H4 D C2H18

  8. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations • At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L • You can use this to calculate the density of a gas in g/Liter at STP. • Example: What is the density of CO2 gas at STP? • The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g • Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L

  9. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations • At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L • You can use this to calculate the density of a gas in g/Liter at STP. • Example: What is the density of CO2 gas at STP? • The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g • Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L • What is the density of Cl2 gas at STP?

  10. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations • At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L • You can use this to calculate the density of a gas in g/Liter at STP. • Example: What is the density of CO2 gas at STP? • The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g • Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L • What is the density of Cl2 gas at STP? • Answer: molar mass = 2(35.453) = 70.906 g • 70.906 g/22.4 L = 3.165 g/L

  11. What is the density of carbon dioxide at STP? A 1.96 g/L B 22.0 g/L C 46.0 g/L D 5.09 x 10-1 g/L

  12. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations One mole = 6.02 x 1023 representative particles One mole = 22.4 Liters of gas at 0°C and one atmosphere of pressure One mole = the atomic mass listed on the periodic table. For example: one mole of Helium contains 6.02 x 1023 atoms of Helium and it has a mass of 4.00260 grams. At 0°C and one atmosphere of pressure, it would occupy 22.4 Liters.

  13. GivenUnknown 1 X Known Unknown Given How many liters would 2.0 moles of Neon occupy? • Sample problem: How many liters would 2.0 moles of Neon occupy? • Answer: • 2.0 moles Ne x 22.4 Liters Ne = 44.8 Liters Ne • 1.0 moles Ne

  14. Sample problem: How many moles are in 15.2 grams of Lithium? • Answer: • 15.2 g Li x 1 mole Li = 2.19 mole Li • 6.941 g Li

  15. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations One mole = 6.02 x 1023 representative particles One mole = 22.4 Liters of gas at 0°C and one atmosphere of pressure One mole = the atomic mass listed on the periodic table. • Sample problem: How many liters would 14 grams of Helium occupy? • Answer: • 14 g He x 22.4 L He = 78 Liters He • 4.0026 g He

  16. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations One mole = 6.02 x 1023 representative particles One mole = 22.4 Liters of gas at 0°C and one atmosphere of pressure One mole = the atomic mass listed on the periodic table. You try one: What is the mass of 9.0 Liters of Argon gas at 0°C and one atmosphere of pressure?

  17. Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations One mole = 6.02 x 1023 representative particles One mole = 22.4 Liters of gas at 0°C and one atmosphere of pressure One mole = the atomic mass listed on the periodic table. What is the mass of 9.0 Liters of Argon gas at 0°C and one atmosphere of pressure? 9.0 L Ar x 39.948 g Ar = 16 g Ar 22.4 L Ar

  18. Which volume will be occupied by a gas containing 6.02 x 1023 atoms at STP? A 1.0 L B 11.2 L C 22.4 L D 44.8 L • Which of these is about 2 moles? A 2.0 liters (dm3) of H2 B 4.0 grams of H2 C 2.0 x 1023 molecules of H2 D 4.0 kilograms of H2 • The gas with the largest volume at STP is — A 10.0 g He B 10.0 g Ne C 10.0 g Ar D 10.0 g Kr • How many moles of copper are equivalent to 3.44 x 1023 atoms of copper? A 0.571 moles B 1.75 moles C 5.41 x 1021 moles D 5.71 x 1022 moles

  19. Chemistry SOL Review— Molar Relationships Mole ratio Stoichiometry For reaction calculations, the molar ratio is used. Example: How many moles of nitrogen will react with 9 moles of hydrogen to produce ammonia according to this equation? 2N2(g) +3 H2(g) → 3NH3(g) Given: 9 moles H2, Find moles N2

  20. Chemistry SOL Review— Molar Relationships Stoichiometry For reaction calculations, the molar ratio is used. Example 2: How many grams of nitrogen are needed to react with 2.0 grams of hydrogen using this equation? 2N2(g) +3 H2(g) → 3NH3(g) 2 moles 3 moles 28.02 g 2.02 g Given: 2.0 grams H2, Find grams N2

  21. Formaldehyde (H2CO) reacts with oxygen to form CO2 and H2O. How many moles of CO2 will be produced from reacting 2 moles of H2CO with oxygen? A 1 B 2 C 4 D 8 • N2 + 3H2→ 2NH3 If 6 liters of hydrogen gas are used,how many liters of nitrogen gas will be needed for the above reaction at STP? A 2 liters B 3 liters C 4 liters D 12 liters • 2KOH + H2SO4→ 2H2O + K2SO4 What mass of potassium hydroxide is required to react completely with 2.70 g of sulfuric acid to produce potassium sulfate and water? A 4.73 g B 3.09 g C 2.36 g D 1.54 g

  22. Chemistry SOL Review— Molar Relationships Solution Concentrations • Calculating molarity: • Memorize this equation: Molarity = moles/liters or M = mol • L • Memorize conversion factor: 1000 mL = 1 L • Some example of using this equation: • Example 1: the molarity of 2.0 moles of HCl in a 0.50 L solution of water is: • molarity = 2.0 mole HCl/0.50 L = 4.0 Molar or 4 M • Example 2: The molarity of 0.40 moles of HCl in a 300. mL L solution of water is: • molarity = 0.40 moles HCl/0.300. L = = 1.3 M

  23. Chemistry SOL Review— Molar Relationships Solution Concentrations • Example 3: • The molarity of 72.9 g of HCl in 5.0 liters of aqueous solution is: • Answer: first calculate the moles of HCl Then calculate molarity of solution: 2.00 mol HCl/5.0 L = 0.40 M HCl

  24. Chemistry SOL Review— Molar Relationships Solution Concentrations • You try one: • What is the molarity of 1.2 grams LiF in a 50. mL aqeous solution? • Answer: first calculate the moles of LiF Then calculate molarity of solution (remember convert mL to Liters): 0.046 mol LiF/0.050 L = 0.95 M LiF

  25. Chemistry SOL Review— Molar Relationships Solution Concentrations • Diluting concentrated solutions • Memorize: C1V1 = C2V2 • C1 and V1 are the beginning molarities and volumes • C2 and V2 are the ending molarities and volumes • V1 and V2 can be in Liters or mLs, but must be the same units for both • Example: • What is the molarity of a 10. mL sample of 2.0 M aqueous HCl diluted to 40. mL • Answer: • (2.0)(10.) = (M2)(40.) so M2 = 0.5 Molar HCl

  26. Chemistry SOL Review— Molar Relationships Solution Concentrations • Diluting concentrated solutions • Memorize: C1V1 = C2V2 • C1 and V1 are the beginning molarities and volumes • C2 and V2 are the ending molarities and volumes • V1 and V2 can be in Liters or mLs, but must be the same units for both • You try one: • How many milliliters of 6.0 Molar HCl are required to prepare 240 mL of 2.0 Molar HCl? • Answer: • (6.0)(V1) = (2.0)(240) so V1 = 80. mL HCl

  27. How many milliliters of 2.00 M H2SO4 are needed to provide 0.250 mole of H2SO4? A 125 mL B 1.25 x 101 mL C 8.00 x 103 mL D 8.00 mL • What is the molarity of a solution prepared by dissolving 27.2 g of sodium chloride in enough water to prepare 500.0 mL of solution? A 0.186 M B 0.465 M C 0.930 M D 1.860 M • A solution contains 225 g of glucose, C6H12O6, dissolved in enough water to make 0.825 L of solution. What is the molarity of the solution? A 0.66 M B 0.97 M C 1.03 M D 1.52 M

  28. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Exothermic and Endothermic Reactions Catalysts lower the Activation energy barrier, making reactions faster. http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca6hotglass.html

  29. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Reversible Reactions Some reactions are REVERSIBLE, which means that they can go backwards (from product to reactant) Example: The reaction between nitrogen and hydrogen, where a “” indicates a reversible reaction N2(g) + 3H2(g)  2 NH3(g) + heat The forward reaction takes place at the same rate as the reverse reaction. The equilibrium position of products and reactants depends on the conditions of the reaction. If we change the reaction conditions, the equilibrium changes. “UP UP AND AWAY!”

  30. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Reversible Reactions Le Chatelier’s Principle: If a system at equilibrium is stressed, the equilibrium will shift in a direction that relieves that stress. Equilibrium will shift AWAY from what is added. Here, N2 is added. N2 More “product” made N2(g) + 3H2(g)  2 NH3(g) + heat “UP UP AND AWAY!”

  31. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Reversible Reactions Le Chatelier’s Principle: If a system at equilibrium is stressed, the equilibrium will shift in a direction that relieves that stress. Equilibrium will shift AWAY from what is added. Here, NH3 is added. More “reactants” made NH3 N2(g) + 3H2(g)  2 NH3(g) + heat “UP UP AND AWAY!”

  32. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Reversible Reactions Le Chatelier’s Principle: If a system at equilibrium is stressed, the equilibrium will shift in a direction that relieves that stress. Equilibrium will shift TOWARDS what is removed. Here H2 is removed. H2 N2(g) + 3H2(g)  2 NH3(g) + heat More “reactants” made

  33. Chemistry SOL Review--Molar Relationships Chemical Equilibrium Reversible Reactions Le Chatelier’s Principle: If a system at equilibrium is stressed, the equilibrium will shift in a direction that relieves that stress. Equilibrium will shift TOWARDS what is removed. Here heat is removed. heat N2(g) + 3H2(g)  2 NH3(g) + heat More “product” made

  34. Chemistry SOL Review--Molar Relationships Chemical Equilibrium • Methods to Speed up Reactions: • Use a catalyst • Reduce the particle size • Increase the heat • Increase reactant concentration http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca2icebomb.html

  35. In the reaction 2SO2 (g) + O2 (g) 2SO3 (g), which change would cause the greatest increase in the concentration of SO3? A Decrease the concentration of SO2 B Decrease the concentration of O2 C Increase the concentration of SO2 D Increase the concentration of O2 • Which condition will cause a shift in the equilibrium of the above reaction? A Double the concentration of reactants and products B Increase the reaction temperature C Reduce the concentration of products and reactants by 10% D Keep the reaction temperature constant

  36. Chemistry SOL Review--Molar Relationships Acid/Base Theory http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca5denature1.html Acids and Bases Generic formula for acids = HX (HCl, HNO3, H2SO4) Generic formula for bases = MOH where M is any metal (NaOH, KOH, Ca(OH)2 Ammonia, NH3, is also a base. Acid solutions have a pH less than 7 Basic solutions have a pH more than 7 Arrhenius acids: Taste _______ turn litmus paper red. Arrhenius bases Taste _______ Feel __________ Turn litmus paper blue. SAFETY NOTES Always add acid to water when diluting (AAA) If you spill acid or base on yourself, rinse with lots of water. sour bitter slippery

  37. Chemistry SOL Review--Molar Relationships Acid/Base Theory • What is pH? • pH indicates the hydrogen ion molarity [H+] in a solution • pH = -log[H+] • pOH indicates the hydroxide ion molarity [OH-] in a solution. • pOH = -log[OH-] • Example: A 1.0 x 10-3 molar solution of HCl would have a pH of ___ • Example: A 1.0 x 10-4 molar solution of KOH would have a pOH of ___ • Memorize: pH + pOH = 14. • Example: A solution with a pH of 8 will have a pOH of: ____. 3 4 6

  38. Which pair of solutions would be acidic if mixed in equal quantities? A A and B B B and C C B and D D C and D • What is represented by the pH of a solution? A Partial pressure of hydrogen ions in the solution B Electronegativity of dissociated hydrogen ions in the solution C Concentration of hydrogen ions in the solution D Temperature of hydrogen ions in the solution • The hydrogen ion concentration is 1 x 10-7. What is the pH of this solution? A 1 B 7 C 10 D 14

  39. Ulcers are often caused by an excess of stomach acid. Milk of magnesia is often used to soothe the irritation. Milk of magnesia is probably — A an acid B a base C an indicator D a colloid • The pH of a 0.1 molar aqueous solution of HCl would equal — A -1 B 1 C 11 D 13

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