how to count moles?

1.
Each mole of (NH4)3PO4 contains how many moles of hydrogen atoms?

No. of moles of NH4+ ions in each mole of (NH4)3PO4 = 3

No. of moles of H atoms in each mole of NH4+ ion = 4

No. of moles of H atoms in each mole of (NH4)3PO4 = 3 x 4 = 12

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2.
Which of the following would contain the largest number of moles?
1. 5.00 grams of chlorine (Cl)
2. All the answers contain the same number of moles.
3. 5.00 grams of copper (Cu)
4. 5.00 grams of lithium (Li)
5. 5.00 grams of calcium (Ca)

The answer is 4 (5.00 grams of lithium (Li)).

Molar mass of Cl = 35.5 g mol-1
No. of moles of 5 g of Cl = 5/35.5

Molar mass of Cu = 63.5 g mol-1
No. of moles of 5 g of Cu = 5/63.5

Molar mass of Li = 6.9 g mol-1
No. of moles of 5 g of Li = 5/6.9

Molar mass of Ca = 40 g mol-1
No. of moles of 5 g of Ca = 5/40

5 g of Li has the greatest number of moles (smaller denominator).

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How many structural isomers of butylchloride (C4H9Cl) are possible?
1. four
2. one
3. seven
4. three

The answer is 1 (four).

The four structural isomers are :
CH3-CH2-CH2-CH2Cl CH3-CH2-CHCl-CH3
CH3-CH(CH3)-CH2Cl CH3-CCl(CH3)-CH3
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