February 28, 2014

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# February 28, 2014 - PowerPoint PPT Presentation

February 28, 2014. 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? Z irconium silicate -  ZrSiO 4. Percent Composition.

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Presentation Transcript
February 28, 2014
• 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?
• Zirconiumsilicate - ZrSiO4
Percent Composition
• 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
To calculate % Composition
• % element in compound =

n(Molar mass of element) x 100

Molar mass of compound

n = how many of that atom in the compound

What are hydrates?
• Ionic Compounds that include water in the crystal lattice
• ZnSO47H2O
• For every one formula unit of zinc sulfate, there are seven water molecules.
• If heated, the water will leave
Example: Carbon dioxide
• 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: Sodium nitrate
• 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/molx 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%

Practice: PbCl2
• Find the percentage composition of:
• 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: Ba(ClO3)2
• 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: CH4
• 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: ZnSO47H2O
• Find the percentage composition of water in zinc sulfate heptahydrate.
• Molar mass of ZnSO47H2O
• 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/molx 100

287.561 g/mol

= 43.85 % H2O

Wait - What are hydrates?
• Ionic compounds that include water in the crystal lattice.
• ZnSO47H2O
• 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.