Chemical Composition - Moles

Avogadro's Number

100

What is Avogadro's Number (a mole)?

6.02 x 10²³

200

What does 6.02 x 10²³ represent?

The atoms or molecules in 1 mole of an element.

Example: 1 mole He = 6.02 x 10²³ atoms

300

What does this mean?

grams <--> moles <--> atoms

Moles are the heart of chemistry

400

What's wrong with this final answer? Identify what's wrong and fix it.

51.22 x 10²³ atoms K

There can't be more than one number infront of the decimal point.

Correct Answer: 5.122 x 10²⁴ atoms K

500

Solve this mole conversion problem.

Given - 7.75g Ne

Looking for - atoms Ne

Given - 7.75g Ne

Looking for - atoms Ne

Know - 20.1797g Ne = 1 mol Ne, 6.02 x 10²³=1mol

Answer: 2.31 x 10²³ atoms Ne

Molar Mass

100

What is the molar mass of oxygen?

15.999g

200

What is the molar mass of lead?

207.2g

300

What is the molar mass of K₃?

117.294g

400

What is the molar mass of Mg₃N₂?

100.929g

500

What is the molar mass of Al₂(SO₄)₃?

53.964 + 96.18 + 191.988 = 342.132g

Mole Calculations

100

How many atoms are in 7.68 moles of sulfur?

4.62 x 10²⁴ atoms 

200

How many moles are in 531g of potassium?

13.6 moles 

300

How many atoms are in 68.7g of krypton?

4.94 x 10²³ atoms

400

How many molecules are contained in 2.5 moles of sulfur trioxide?

1.5 x 10²⁴ molecules

500

How many atoms are in 510.3g of calcium sulfate?

1.354 x 10²⁵ atoms

Percent Composition

100

What's the percent composition of H₂O?

O - 15.999g/18.015g x 100% = 88.81%

H - 2.016g/18.015g x 100% = 11.19%

200

What's the percent composition of K₂S?

K - 70.92%

S - 29.08%

300

What's the percent composition aluminum sulfide?

Al - 35.94%

S - 64.06%

400

What's the percent composition of aluminum acetate?

Al - 13.22%

C - 35.31%

H - 4.445%

O - 47.03%

500

What's the percent composition of ammonium phosphate? 

(NH₄)₃PO₄ - 149.087

N - 28.186%

H - 8.1134%

P - 20.776%

O - 42.925%

Molecular and Empirical Formulas

100

A compound contains 38.7% K, 13.9% C, and 47.4% O by mass. Find the empirical formula.

K: 38.7g K x 1 mol K/39.098g K = 0.990 mols K

C: 13.9g C x 1 mol C/1.1573g C = 1.16 mols C

O: 47.4g O x 1 mol O/15.999g O = 2.96 mols O

K_0.990/0.990C_1.16/0.990O_2.96/0.990

Empirical Formula: KCO₃

200

A compound contains 4.8g C, 0.8g H, and 4.4g O. Find the empirical formula.

Empirical Formula: C₃H₆O₂

300

A compound's empirical formula is CH₂O. If its molar mass is 180.0g, find the molecular formula.

CH₂O - 30.026g

180.0g/30.026g = 6

Molecular Formula: C₆H₁₂O₆

400

A compound's empirical formula is HgCl. If its molar mass is 472.2 g/mol, find the molecular formula.

Molecular Formula: Hg₂Cl₂

500

A compound contains 42.9% C, 2.4% H, and 54.7% Cl by mass. The molar mass of the compound is 84.0g/mol. Find the empirical and molecular formula.

Empirical Formula: C₂H₂Cl

Molecular Formula: C₂H₂Cl