Question

A +15g sample of a compound is found to contain 58.87% sodium and 41.13% sulfur. Calculate the empirical formula of this compound.

a) Na₂S
b) Na₂S₂
c) Na₂S₃
d) Na₂S₄

Answer 1

To find the empirical formula of a compound with 58.87% sodium and 41.13% sulfur, we convert these percentages to moles, then divide by the smallest number to get a mole ratio, resulting in the empirical formula Na2S, which is option (a).

Step-by-step explanation:

To calculate the empirical formula of the compound containing sodium (Na) and sulfur (S), we first convert the percentages to grams, assuming we have a 100 g sample so that the percentages can be directly considered as grams. We then calculate moles for each element by dividing the mass of each element by its atomic mass (for Na, it is approximately 23 g/mol, and for S, it is approximately 32 g/mol).

For sodium (58.87g):

• Number of moles of Na = 58.87 g / 23 g/mol ≈ 2.56 moles

For sulfur (41.13g):

• Number of moles of S = 41.13 g / 32 g/mol ≈ 1.29 moles

We then divide each mole value by the smallest number of moles to get the ratio:

• Ratio for Na = 2.56 / 1.29 ≈ 2
• Ratio for S = 1.29 / 1.29 ≈ 1

Hence, the empirical formula is Na2S, which is option (a).