Chemical Stoichiometry

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

Mass Spectrometer A devise that

accurately compares the mass of atoms

Peaks represent the relative abundance of the atom.

P.85

The mole A quantity that is equal

to the number of carbon atoms in exactly 12 grams of carbon-12.

Avogadro’s number 6.022 x 1023

1 g. = 6.022 x 1023 amu

Determine the mass in grams of 8 atoms of Americium.

3.2 x 10-21grams

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

1.15 x 1020atoms

Molar mass The mass in grams

of one mole of a substance.

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?

Calculate the % composition of penicillin, C14H20N2SO4

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.

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

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.

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.

Remember Subscripts on correctly

written chemical compounds do not change to balance the equation

Change only the coefficients.

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

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.

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?

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

Limiting Reactant

The reactant that gets used up first.

Limits the amount of products that can form.

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?

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.

Percent(%) yield

%yield= actual yield x 100

theoretical yield

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.