What is the empirical formula of a compound that contains 52.7% K and 47.3% Cl?
Understand the Problem
The question asks us to find the empirical formula of a compound given the percentage composition of its elements (K and Cl). To solve this, we'll convert percentages to masses, then to moles, and finally find the simplest whole number ratio of K to Cl.
Answer
$KCl$
Answer for screen readers
KCl
Steps to Solve
- Convert percentages to masses
Assume we have 100g of the compound. This makes the percentages directly equal to grams.Thus we have 52.7 g of K and 47.3 g of Cl.
- Convert masses to moles
To convert grams to moles, divide by the molar mass of each element. The molar mass of K is 39.10 g/mol, and the molar mass of Cl is 35.45 g/mol. $$ \text{Moles of K} = \frac{52.7 \text{ g}}{39.10 \text{ g/mol}} \approx 1.35 \text{ mol} $$ $$ \text{Moles of Cl} = \frac{47.3 \text{ g}}{35.45 \text{ g/mol}} \approx 1.33 \text{ mol} $$ 3. Find the simplest whole number ratio
Divide both mole values by the smallest mole value to get the simplest ratio. In this case, the smallest mole value is approximately 1.33. $$ \text{Ratio of K} = \frac{1.35}{1.33} \approx 1.02 $$ $$ \text{Ratio of Cl} = \frac{1.33}{1.33} = 1 $$
The ratio is approximately 1.02:1, which is very close to 1:1. Therefore, the empirical formula is KCl.
KCl
More Information
The empirical formula represents the simplest whole number ratio of elements in a compound. In this case, potassium and chlorine combine in a 1:1 ratio. Potassium chloride, $KCl$, is commonly known as table salt.
Tips
A common mistake is not dividing by the smallest number of moles. This step is crucial to find the simplest whole number ratio. Another common mistake is incorrectly calculating the number of moles by dividing the molar mass by the mass, instead of the other way around.
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