Chemical Stoichiometry

1
Chemical Stoichiometry

• The determination of the quantities of materials
  consumed or produced in chemical reactions

2
Mass Spectrometer

• A devise that accurately compares the mass of
  atoms
• Peaks represent the relative abundance of the
  atom.
• P.85

3
The mole

• A quantity that is equal to the number of carbon
  atoms in exactly 12 grams of carbon-12.
• Avogadros number
• 6.022 x 1023
• 1 g. 6.022 x 1023 amu

4

• Determine the mass in grams of 8 atoms of
  Americium.
• 3.2 x 10-21grams

5

• A silicon chip from a microcomputer has a mass of
  5.38 mg. How many silicon atoms does it contain?
• 1.15 x 1020atoms

6
Molar mass

• The mass in grams of one mole of a substance.

7

• Juglone, a dye made from black walnuts, has the
  formula C10H6O3.
• What is its molar mass?
• How many moles are present in a 1.52 x 10-2g
  sample? Molecules?

8

• Calculate the composition of penicillin,
  C14H20N2SO4

9
Determining the Formula of a Compound

• Convert from mass ratios to mole ratios.
• Find the lowest whole number ratio for empirical.
• Compare to molar mass for molecular.

10

• Determine the empirical and molecular formulas
  for a compound that is 71.65 Cl, 24.27C, and
  4.07H. It has a molar mass of 98.96g/mol.

11

• When 0.1156g of a compound made of carbon,
  hydrogen and nitrogen is burned , 0.1638g of CO2,
  and 0.1676g of water are formed. Determine the
  formula.

12
Balanced Chemical Equations

• In a chemical reaction atoms are not created or
  destroyed. All atoms in the reactants must be
  accounted for in the products.

13
Remember

• Subscripts on correctly written chemical
  compounds do not change to balance the equation
• Change only the coefficients.

14
Balance the following

• Ca(OH)2 H3PO4? H2O Ca3(PO4)2
• Al(OH)3 HCl? AlCl3 H2O
• AgNO3 H2SO4? Ag2SO4 HNO3
• Cr S8 ? Cr2S3
• NaHCO3? Na2CO3 CO2 H2O
• KClO3 ? KCl O2
• Eu HF ? EuF3 H2

15
Steps in Reaction Stoichiometry

• Balance equation for the reaction.
• Convert known mass of reactant or product to
  moles.
• Use balanced equation to set up appropriate mole
  ratios.
• Use mole ratios to calculate moles of desired
  reactant or product.
• Convert from moles to mass or volume as required.

16
Solve

• Lithium hydroxide is used in space vehicles. to
  remove exhaled carbon dioxide from the
  environment, forming lithium carbonate and water.
  What mass of carbon dioxide can be absorbed by
  1.00kg of lithium hydroxide?

17
Solve

• Baking soda (NaHCO3) and milk of magnesia
  Mg(OH)2 are both used as antacids to neutralize
  excess HCl in the stomach. Which is more
  effective per gram

18
Limiting Reactant

• The reactant that gets used up first.
• Limits the amount of products that can form.

19

• Nitrogen gas can be prepared by passing ammonia
  gas over solid copper(II) oxide. Solid copper and
  water are also produced. If 18.1g NH3reacts with
  90.4g CuO, what is the limiting reactant? How
  much N2 can be made and how much excess reactant
  is left over?

20
Theoretical yield

• The maximum amount of product that can be made in
  a perfect world.
• The actual yield is always less than the
  theoretical yield.

21
Percent() yield

• yield actual yield x 100
• theoretical yield

22

• Methanol(CH3OH) can be produced by a combination
  reaction between carbon monoxide and hydrogen
  gas. If 68.5kg of CO reacts with 8.60kg H2 35.7
  kg of methanol is produced. Calculate the yield.