Question

question 2 of 10
how does one determine an empirical formula from a percent composition?

a. convert mass percents to grams and then divide by the smallest gram value to find subscripts

b. convert mass percents to moles and then use the moles as subscripts in the formula

c. convert mass percents to grams and then divide by the smallest mass percent value to find subscripts

d. convert mass percents to moles and then divide by the smallest mole value to get subscripts

Explanation:

To determine the empirical formula from percent composition, the steps involve: 1) Assuming a 100g sample (so mass percents become grams), 2) Converting those grams to moles (using molar mass), 3) Dividing each mole value by the smallest mole value to get the subscripts (which represent the simplest whole - number ratio of atoms).

• Option A is incorrect because we need to convert grams to moles (not just divide gram values) to find the mole ratio for subscripts.
• Option B is incorrect as we can't directly use moles as subscripts; we need to find the simplest ratio by dividing by the smallest mole value.
• Option C is incorrect because we should convert grams to moles (not divide by the smallest mass percent value) and then find the ratio.
• Option D correctly describes the process: convert mass percents (from 100g sample) to moles, then divide each mole value by the smallest mole value to obtain the subscripts for the empirical formula.

Answer:

D. Convert mass percents to moles and then divide by the smallest mole value to get subscripts