A compound that is composed of only carbon and hydrogen contains 80.0% C and 20.0% H by mass. What is the empirical formula of the compound?
Take a 100 g sample. That contains 80 g C and 20 g H. Convert to mols.
mols = g/molar mass or g/atomic mass
mols C = 80/12 = 6.67
mols H = 20/1 = 20
Now you want to find the ratio of these two elements to each other in small whole numbers with the smallest number being no less than 1. The easy way to do that is to divide everything by the smaller number.
C = 6.67/6.67 = 1.00 for C
H = 20/6.67 = 2.998 for H which rounds to 3.0
Empirical formula is CH3
Well, it sounds like this compound is trying to keep it simple with just carbon and hydrogen. With 80% carbon and 20% hydrogen, it's like saying it's 4 parts carbon to 1 part hydrogen.
So, based on those ratios, we can say that the empirical formula of this compound is CH4, which is methane. Just like the saying goes, "Keep it simple, keep it gassy!"
To find the empirical formula of a compound, we need to determine the ratio of the elements present in the compound. In this case, we know that the compound is composed of 80.0% carbon (C) and 20.0% hydrogen (H) by mass.
Step 1: Convert to grams.
Assume that we have 100 grams of the compound, which means we have 80 grams of carbon and 20 grams of hydrogen.
Step 2: Convert to moles.
To convert grams to moles, we need to divide the mass of each element by their respective atomic masses.
The atomic mass of carbon (C) is approximately 12.01 g/mol, so we have:
80 grams C * 1 mol/12.01 g = 6.66 mol C
The atomic mass of hydrogen (H) is approximately 1.01 g/mol, so we have:
20 grams H * 1 mol/1.01 g = 19.8 mol H
Step 3: Simplify the ratio.
Divide the number of moles of each element by the smallest value to get the simplest whole number ratio.
6.66 mol C / 6.66 ≈ 1 mol C
19.8 mol H / 6.66 ≈ 2.97 mol H
To obtain the simplest whole number ratio, we can multiply both values by a factor that would result in whole numbers. In this case, approximately multiplying by 3 would give us whole numbers.
Multiplying by 3 gives us:
1 mol C * 3 = 3 mol C
2.97 mol H * 3 = 8.91 mol H
Therefore, the empirical formula for the compound is CH3.
Note: The empirical formula represents the simplest ratio of atoms in a compound. However, it does not provide the exact number of atoms in the compound. The molecular formula may provide the exact number of atoms by using additional information, such as the molar mass of the compound.
To determine the empirical formula of a compound, we need to find the ratio of the elements present in the compound.
Given that the compound is composed of only carbon and hydrogen and contains 80.0% carbon and 20.0% hydrogen by mass, we can assume a 100g sample of the compound. This means that in a 100g sample, we have:
- 80.0g of carbon (80.0% of 100g)
- 20.0g of hydrogen (20.0% of 100g)
Next, we need to convert the mass of each element to moles using their respective atomic masses:
- The atomic mass of carbon (C) is approximately 12.01 g/mol.
- The atomic mass of hydrogen (H) is approximately 1.01 g/mol.
Converting the masses to moles:
- Moles of carbon (C) = 80.0g / 12.01 g/mol ≈ 6.66 mol
- Moles of hydrogen (H) = 20.0g / 1.01 g/mol ≈ 19.8 mol
The next step is to find the simplest whole-number ratio between the moles of carbon and hydrogen. To do this, we divide both of the moles by the smallest number of moles (in this case, the moles of carbon):
- Moles of carbon (C) = 6.66 mol / 6.66 mol ≈ 1 mol
- Moles of hydrogen (H) = 19.8 mol / 6.66 mol ≈ 2.98 mol
Rounding the moles to the nearest whole number gives us a ratio of approximately 1 carbon atom to 3 hydrogen atoms. Therefore, the empirical formula of the compound is CH3.