Empirical Formula Worksheet 1 Answers
Empirical formulas are a fundamental concept in chemistry, representing the simplest whole-number ratio of atoms in a compound. In this worksheet, we will explore the concept of empirical formulas through a series of problems and provide answers to help solidify your understanding.
What is an Empirical Formula?
Before diving into the problems, let’s quickly review what an empirical formula is. An empirical formula is the simplest whole-number ratio of atoms of each element in a compound. It does not necessarily represent the actual number of atoms in a molecule of the compound.
Calculating Empirical Formulas
To calculate an empirical formula, you need to know the percentage composition of the compound by mass. From there, you can convert the percentages to grams, then to moles, and finally to a whole-number ratio of atoms.
Problems and Answers
Here are some problems and answers to help you practice calculating empirical formulas:
Problem 1:
A compound is composed of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of the compound?
Answer:
To calculate the empirical formula, we first convert the percentages to grams, then to moles:
| Element | Percentage | Grams | Moles |
|---|---|---|---|
| C | 40.0 | 40.0 g | 3.33 mol |
| H | 6.7 | 6.7 g | 6.67 mol |
| O | 53.3 | 53.3 g | 3.33 mol |
Next, we divide each number of moles by the smallest number of moles (3.33):
| Element | Moles | Ratio |
|---|---|---|
| C | 3.33 | 1 |
| H | 6.67 | 2 |
| O | 3.33 | 1 |
The empirical formula is therefore CH2O.
Problem 2:
A compound is composed of 60.0% nitrogen, 20.0% oxygen, and 20.0% sulfur by mass. What is the empirical formula of the compound?
Answer:
To calculate the empirical formula, we first convert the percentages to grams, then to moles:
| Element | Percentage | Grams | Moles |
|---|---|---|---|
| N | 60.0 | 60.0 g | 4.29 mol |
| O | 20.0 | 20.0 g | 1.25 mol |
| S | 20.0 | 20.0 g | 0.63 mol |
Next, we divide each number of moles by the smallest number of moles (0.63):
| Element | Moles | Ratio |
|---|---|---|
| N | 4.29 | 6.8 |
| O | 1.25 | 2 |
| S | 0.63 | 1 |
We can simplify the ratio by dividing all numbers by 2:
| Element | Ratio |
|---|---|
| N | 3.4 |
| O | 1 |
| S | 0.5 |
We can further simplify the ratio by multiplying all numbers by 2 to get whole numbers:
| Element | Ratio |
|---|---|
| N | 7 |
| O | 2 |
| S | 1 |
The empirical formula is therefore N7O2S.
Problem 3:
A compound is composed of 50.0% sodium, 25.0% chlorine, and 25.0% oxygen by mass. What is the empirical formula of the compound?
Answer:
To calculate the empirical formula, we first convert the percentages to grams, then to moles:
| Element | Percentage | Grams | Moles |
|---|---|---|---|
| Na | 50.0 | 50.0 g | 2.17 mol |
| Cl | 25.0 | 25.0 g | 0.70 mol |
| O | 25.0 | 25.0 g | 1.56 mol |
Next, we divide each number of moles by the smallest number of moles (0.70):
| Element | Moles | Ratio |
|---|---|---|
| Na | 2.17 | 3.1 |
| Cl | 0.70 | 1 |
| O | 1.56 | 2.2 |
We can simplify the ratio by dividing all numbers by 1.1:
| Element | Ratio |
|---|---|
| Na | 2.8 |
| Cl | 0.9 |
| O | 2 |
We can further simplify the ratio by multiplying all numbers by 10 to get whole numbers:
| Element | Ratio |
|---|---|
| Na | 28 |
| Cl | 9 |
| O | 20 |
The empirical formula is therefore Na28Cl9O20.
However, this is not the simplest ratio. We can simplify the ratio by dividing all numbers by their greatest common divisor, which is 1:
| Element | Ratio |
|---|---|
| Na | 28 |
| Cl | 9 |
| O | 20 |
The empirical formula is therefore Na28Cl9O20.
But we can simplify this further by realizing that Na28 is the same as Na14 × 2 and Cl9 is the same as Cl3 × 3 and O20 is the same as O4 × 5.
The simplified empirical formula is therefore Na14Cl3O4.
However, the ratio is still not the simplest, as Na14Cl3O4 = Na2ClO4 × 7. Therefore, the empirical formula is Na2ClO4.
Notes
- When calculating empirical formulas, make sure to simplify the ratio of atoms to the simplest whole-number ratio.
- If the ratio is not whole numbers, try multiplying or dividing all numbers by a common factor to get whole numbers.
- Make sure to check the empirical formula for accuracy.
📝 Note: These problems and answers are meant to serve as a guide and may not be comprehensive. Always consult a reliable chemistry textbook or online resource for more information and practice problems.
In Conclusion
Empirical formulas are a fundamental concept in chemistry, representing the simplest whole-number ratio of atoms in a compound. By understanding how to calculate empirical formulas, you can better understand the composition of compounds and how to write their chemical formulas. Remember to always simplify the ratio of atoms to the simplest whole-number ratio and check the empirical formula for accuracy.
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