Welcome Back!!

1. Welcome Back!! • New Year’s Resolution—sit in your seat as you read the board. • Make sure you start going to the blog on a nightly basis. I am thinking about getting rid of journals if you start going to the blog. ?? or ?? • Read the information about Honors Chem and post a comment to me tonight. • Today we will be reviewing stoichiometry. • Tomorrow we will be taking our stoichiometry quest—not a partner quest.

2. Stoichiometry Review • Silver sulfide (Ag2S) is the common tarnish on silver objects.  What weight of silver sulfide can be made from 1.23 mg of hydrogen sulfide (H2S) obtained from a rotten egg?  The reaction of formation of silver sulfide is given below: • 4Ag +  2H2S + O2 2Ag2S + 2H2O • 0.00897 g silver sulfide

3. Stoichiometry Review • A somewhat antiquated method for preparing chlorine gas involves heating hydrochloric acid with pyrolusite (manganese dioxide), a common manganese ore.  (Reaction given below.)  How many kg of HCl react with 5.69 kg of manganese dioxide? • 4HCl + MnO2    2H2O +  MnCl2 + Cl2 • 9.56 kg HCl

4. Stoichiometry Review • A typical automobile gets 30 miles per gallon of gas and drives 12,000 miles every year. Assuming that octane (C8H18, density 0.7025 g/mL—3.78L = gal) is a principal component of gasoline; • How much oxygen is required for a car to run for 1 year? (Start with 12,000 miles and step by step go to grams octane—then normal stoich) • How much CO2 is produced by the car in 1 year? • How many trees are required to remove the CO2 produced by the car in 1 year? (Avg tree removes 50 lb CO2 per year—2.2lb = 1 kg)

5. Stoichiometry Review • The Kingston Steam Plant burns 14,000 tons of coal each day and generates 1010 kilowatt - hours of electricity each year (enough for 700,000 homes). Coal is primarily carbon which undergoes combustion in the following reaction: • C (s) + O2(g) CO2 (g) • How many grams of oxygen is required for the combustion of 1 day's coal? (2000 lb = 1 ton, 2.2lb = 1kg) • How much carbon dioxide is produced each day? • How many trees are required to remove the CO2 produced by the KSP in 1 year? (Avg tree removes 50 lb CO2 per year—2.2lb = 1 kg)

6. Stoichiometry Review • CO2 is removed from the atmosphere by trees & converted into cellulose. The basic reaction for this is: • 6 CO2 + 5 H2O  C6H10O5 + 6 O2 • How many grams of water are required to process the CO2 from one day's electrical production at the Kingston Steam Plant? • How much oxygen is produced by this process? • How much cellulose is produced?

7. Stoichiometry Review • An organic chemist reacted 10g CH4 with excess Cl2 and obtained 10g of CH3Cl.  (Hydrogen gas is also produced.) • What should have been the theoretical yield.  • What was their percentage yield?

8. AP Review • 1. 5.12 g of Mg(NO3)2 is dissolved in 800.2g of water. The kb for water is 0.512°C/m. Assume complete dissociation of the salt. What is the boiling point elevation in K? • 2. What is the vapor pressure of an ideal solution containing 61.1g of, CHCl3, and 70.9g of carbon tetrachloride, CCl4 at 25°C? The vapor pressures at 25 °C are 172.0 torr for pure CHCl3 and 98.3 torr for pure CCl4.

9. AP Review • 3. How many grams of ethanol, CH3CH2OH, are needed to raise the boiling point of 500mL of water by 2.5°C? The boiling point elevation constant kb = 0.512 °C/molality. • 4. What is the molecular weight of a covalent compound containing 101g/L if it has an osmotic pressure of 0.711 torr at 25°C? • 5. Assuming the van’t Hoff factor for NaCl to be 2, calculate the freezing point of an aqueous 0.500 molal NaCl solution? For water, Kf = 1.86oC/m.

10. AP Review • 6. A non-volatile liquid with formula C2H6O2 and molar mass 62g/mol, is added to 2102g of water. At 89oC, the vapor pressure of this resulting solution is found to be 460 torr. How many grams of the non-volatile liquid were added to the water? (The vapor pressure of pure water is 526 torr at 89oC). • 7. Find the boiling point of a solution containing 14.59g NaCl in 84.0g water? Kb for water is 0.512oC/m.