Chemistry Test Stoichiometry 3

Question 1

In the reaction 2Al + 3Cl₂ → 2AlCl₃, if you start with 3 mol Al and 3 mol Cl₂, which is the limiting reagent?

Accepted Answer

Cl₂

Answer

3 mol Al needs 4.5 mol Cl₂, but only 3 mol Cl₂ is available, so Cl₂ is limiting.

Question 2

What is the molar mass of glucose (C₆H₁₂O₆)? (C=12, H=1, O=16)

Accepted Answer

180 g/mol

Answer

6(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180 g/mol.

Question 3

A reaction produces 25.0 g of NaCl but the theoretical yield was 30.0 g. What is the percent yield?

Accepted Answer

83.3%

Answer

Percent yield = (25.0/30.0) × 100 = 83.3%.

Question 4

How many molecules are in 0.5 mol of oxygen gas (O₂)? (Avogadro's number = 6.02 × 10²³)

Accepted Answer

3.01 × 10²³

Answer

0.5 mol × 6.02 × 10²³ molecules/mol = 3.01 × 10²³ molecules.

Question 5

The empirical formula of a compound is CH₂. If the molar mass is 56 g/mol, what is the molecular formula? (C=12, H=1)

Accepted Answer

C₄H₈

Answer

Empirical formula mass of CH₂ = 14 g/mol; 56/14 = 4, so molecular formula is C₄H₈.

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