Welcome Back!!

1
Welcome Back!!

• New Years Resolutionsit 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
  questnot 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/mL3.78L
  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 octanethen 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 year2.2lb 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 year2.2lb 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 0.512C/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 25C? 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 2.5C? 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 25C?
• 5. Assuming the vant 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.