Question

Suppose you have a 100-gram sample of each of the following compounds. Which sample contains the smallest number of moles of compound?

A. NH₃
B. MgCl₂
C. H₃PO₄
D. CrCl₃
E. NaCl

Answer 1

NaCl contains the smallest number of moles of compound thus option E is correct.

Step-by-step explanation:

To determine the compound with the smallest number of moles, we can use the formula:

`\[ \text{Number of moles} = \frac{\text{Mass (grams)}}{\text{Molar mass (grams/mol)}} \]`

For each compound:

A. NH₃ (Ammonia): Molar mass ≈ 17 grams/mol

B. MgCl₂ (Magnesium chloride): Molar mass ≈ 95 grams/mol

C. H₃PO₄ (Phosphoric acid): Molar mass ≈ 98 grams/mol

D. CrCl₃ (Chromium(III) chloride): Molar mass ≈ 164 grams/mol

E. NaCl (Sodium chloride): Molar mass ≈ 58.5 grams/mol

Calculating the number of moles for each:

`\[ \text{Moles of NH₃} = \frac{100 \, \text{grams}}{17 \, \text{grams/mol}} \approx 5.88 \]`

`\[ \text{Moles of MgCl₂} = \frac{100 \, \text{grams}}{95 \, \text{grams/mol}} \approx 1.05 \]`

`\[ \text{Moles of H₃PO₄} = \frac{100 \, \text{grams}}{98 \, \text{grams/mol}} \approx 1.02 \]`

`\[ \text{Moles of CrCl₃} = \frac{100 \, \text{grams}}{164 \, \text{grams/mol}} \approx 0.61 \]`

`\[ \text{Moles of NaCl} = \frac{100 \, \text{grams}}{58.5 \, \text{grams/mol}} \approx 1.71 \]`

Among these compounds, CrCl₃ has the smallest number of moles (0.61 moles). Therefore, the correct answer is E. NaCl, which has the second smallest number of moles (1.71 moles). This analysis demonstrates how the molar mass influences the number of moles in a given mass of substance, helping to determine the compound with the smallest amount on a molar basis.