Determine the number of moles of the compound and determine the number of moles of each type of atom in each of the following:
(a) 2.12 g of potassium bromide, KBr
(b) 0.1488 g of phosphoric acid, H3PO4
(c) 23 kg of calcium carbonate, CaCO3
(d) 78.452 g of aluminum sulfate, Al2(SO4)3
(e) 0.1250 mg of caffeine, C8H10N4O2

a. 0.0178 moles of KBr

0.0178 moles of K

0.0178 moles of Br

b.  1.52×10⁻³ moles of acid

4.55×10⁻³ moles of H

1.52×10⁻³ moles of P

6.07×10⁻³ moles of O

c. 229.8 moles of calcium carbonate

229.8 moles of Ca

229.8 moles of C

689.4 moles of O

d. 0.229 moles of aluminum sulfate

0.458 moles of Al

0.687 moles of S

2.75 moles of O

e. 6.43×10⁻⁷ moles of C₈H₁₀N₄O₂

5.14×10⁻⁶ moles of C

6.43×10⁻⁶ moles of H

2.57×10⁻⁶ moles of N

1.28×10⁻⁶ moles of O

Explanation:

To determine the moles of each compound we need to know the molar mass of them

Subscripts number of compounds are the number of moles, of each atoms.

For example, H₂O. 1 mol of water has 2 moles of H and 1 mol of O.

a. KBr → 119 g/mol

We convert the mass to moles (mass/molar mass)

2.12 g / 119 g/mol = 0.0178 moles of bromide

1 mol of potassium bromide has 1 mol of K and 1 mol of Br, then 0.0178 moles of salt, will have:

0.0178 moles of K

0.0178 moles of Br

b. H₃PO₄ → 97.97 g/mol

0.1488 g / 97.97 g/mol = 1.52×10⁻³ moles of acid.

1 mol of phosphoric acid has 3 moles of H, 1 mol of P and 4 moles of O

Then 1.52×10⁻³ moles of acid. will have:

(1.52×10⁻³ . 3) / 1 = 4.55×10⁻³ moles of H

1.52×10⁻³ moles of P

(1.52×10⁻³ . 4) / 1 = 6.07×10⁻³ moles of O

c. CaCO₃ → 100.08 g/mol

23000g / 100.08 g/mol = 229.8 moles

(notice, we convert the kg to g, before)

1 mol of calcium carbonate has 1 mol of Ca, 1 mol of C and 3 moles of O

Then 229.8 moles of salt will have

229.8 moles of Ca

229.8 moles of C

(229.8 . 3) / 1 = 689.4 moles of O

d. Al₂(SO₄)₃ → 342.15 g/mol

78.452 g / 342.15 g/mol = 0.229 moles

1 mol of Al₂(SO₄)₃ has 2 moles of Al, 3 moles of S and 12 moles of O

Then  0.229 moles of sulfate will have:

(0.229 . 2) / 1 = 0.458 moles of Al

(0.229 . 3) / 1 = 0.687 moles of S

(0.229 . 12) / 1 = 2.75 moles of O

e. C₈H₁₀N₄O₂  → 194.19 g/mol

0.0001250 g / 194.19 g/mol = 6.43×10⁻⁷ moles

(Notice, we convert mg to g)

1 mol of caffeine has 8 moles of C, 10 moles of H, 4 moles of N and 2 moles of O

Then, 6.43×10⁻⁷ moles of caffeine will have:

(6.43×10⁻⁷ . 5) / 1 = 5.14×10⁻⁶ moles of C

(6.43×10⁻⁷ . 10) / 1 = 6.43×10⁻⁶ moles of H

(6.43×10⁻⁷ . 4)/1 = 2.57×10⁻⁶ moles of N

(6.43×10⁻⁷ . 2)/ 1 = 1.28×10⁻⁶ moles of O

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