• Final Polyatomic Ion Quiz• Due: HW 7B• Percentage Composition

• Lab Report due Wednesday March 5

• Today’s video: Oldest known piece of earth– How old?!– What do you think their “technique” is? – Zirconium silicate - ZrSiO4

February 28, 2014

• Percent composition: Percentage by mass of each element in a compound.

• What percent of gum is sweetener?

Percent Composition

• Mass percentage of an element in a compound is the same regardless of the sample size. This is because the ratio of one element to another in a given compound is the same regardless of sample size.

• H2O = 2 parts H : 1 part O

Percent Composition

• % element in compound =

n(Molar mass of element) x 100 Molar mass of compound

n = how many of that atom in the compound

To calculate % Composition

What are hydrates? Ionic Compounds that include water in the

crystal lattice

ZnSO47H2O

For every one formula unit of zinc sulfate, there are seven water molecules.

If heated, the water will leave

CuSO45H2O v. CuSO4

• Find the percentage composition of:• Carbon dioxide, CO2

– Molar mass of CO2: 12.01 + 2(16.00) = 44.01 g/mol

– % C: 12.01 g/mol x 100 = 27.29% C 44.01 g/mol

– % O: 2(16.00 g/mol) x 100 = 72.71% O 44.01 g/mol

Check by adding the %s: 27.29 + 72.71 = 100.00%

Example: Carbon dioxide

• Find the percentage composition of:• Sodium nitrate

– Molar mass of NaNO3: 22.99 + 14.01 + 3(16.00) = 85.00 g/mol

– % Na: 22.99 g/mol x 100 = 27.05% Na 85.00 g/mol

– % N: 14.01 g/mol x 100 = 16.48% N– 85.00 g/mol

– % O: 3(16.00 g/mol) x 100 = 56.47% O 85.00 g/mol

Check by adding the %s: 27.05 + 16.48 + 56.74 = 100.00%

Example: Sodium nitrate

• Find the percentage composition of:• Lead (II) Chloride– Molar mass of PbCl2: 207.2 + 2(35.453) = 278.106 g/mol

– % Pb: 207.2 g/mol x 100 = 74.50% Pb 278.106 g/mol

– % Cl: 2(35.453 g/mol) x 100 = 25.50% Cl 278.106 g/mol

Check by adding the %s: 74.50 + 25.50 = 100.00%

Practice: PbCl2

• Find the percentage composition of:• Barium chlorate

– Molar mass of Ba(ClO3)2 : – 137.33 + 2(35.453) + 6(15.999) = 304.23 g/mol

– % Ba: 137.33 g/mol x 100 = 45.14% Ba 304.23 g/mol

– % Cl: 2(35.453 g/mol) x 100 = 23.31% Cl 304.23 g/mol

– % O: 6(15.999 g/mol) x 100 = 31.55% O 304.23 g/mol

Check by adding the %s: 47.14 + 23.31 + 31.55 = 100.00%

Practice: Ba(ClO3)2

• Find the percentage composition of hydrogen in methane

– Molar mass of CH4 – 12.011 + 4(1.0079) = 16.0426 g/mol

– % H: 4(1.0079) g/mol x 100 = 25.13 % H 16.0426 g/mol

Practice: CH4

• Find the percentage composition of water in zinc sulfate heptahydrate.

– Molar mass of ZnSO47H2O – 65.39 + 32.066 + 4(15.999) + 14(1.0079) + 7(15.999) = 287.561

g/mol

– % H2O: 14(1.0079) + 7(15.999) g/mol x 100 287.561 g/mol = 43.85 % H2O

Practice: ZnSO47H2O

Wait - What are hydrates? Ionic compounds that include water in the crystal

lattice.

ZnSO47H2O

For every one formula unit of zinc sulfate, there are seven water molecules.

The dot indicates ratio, not “multiply” If heated, the water will leave the compound and

the color will change.