A compound on analysis as 87:8% c,12:2%h determine its empirical formular&molecular formular given mass=56gmol
To determine the empirical formula of the compound, we first need to calculate the moles of each element present.
Given:
Percentage composition of carbon (C): 87.8%
Percentage composition of hydrogen (H): 12.2%
Total mass of the compound: 56 g/mol
Step 1: Calculate the moles of carbon (C)
Molar mass of carbon (C) = 12 g/mol
➜ Moles of carbon (C) = (Percentage composition of C / 100) x (Total mass of compound / Molar mass of C)
= (87.8 / 100) x (56 g/mol / 12 g/mol)
≈ 7.29 mol
Step 2: Calculate the moles of hydrogen (H)
Molar mass of hydrogen (H) = 1 g/mol
➜ Moles of hydrogen (H) = (Percentage composition of H / 100) x (Total mass of compound / Molar mass of H)
= (12.2 / 100) x (56 g/mol / 1 g/mol)
≈ 0.68 mol
Step 3: Find the ratio of moles
Divide the moles of each element by the smallest number of moles to obtain the simplest, whole number ratio.
Moles of carbon (C) ≈ 7.29 mol
Moles of hydrogen (H) ≈ 0.68 mol
Dividing both values by 0.68 (the smallest number of moles):
C ≈ 7.29 mol / 0.68 mol ≈ 10.72 ≈ 11
H ≈ 0.68 mol / 0.68 mol ≈ 1
The empirical formula of the compound is CH11.
To find the molecular formula, we need to know the molar mass of the compound. Given that the molar mass is 56 g/mol, we can calculate the ratio of the molecular mass to the empirical formula mass.
Molar mass of empirical formula (CH11):
Mass of carbon (C) ≈ 11 x 12 g/mol ≈ 132 g/mol
Mass of hydrogen (H) ≈ 1 x 1 g/mol ≈ 1 g/mol
Molar mass of empirical formula (CH11) ≈ 132 g/mol + 1 g/mol ≈ 133 g/mol
Now we can find the ratio of the molar mass of the compound (56 g/mol) to the molar mass of the empirical formula (133 g/mol):
➜ Ratio = molar mass of compound / molar mass of empirical formula
= 56 g/mol / 133 g/mol
≈ 0.4211
Therefore, the molecular formula is the same as the empirical formula, CH11, because the ratio is approximately 1 (0.4211 rounded to 1).
To determine the empirical formula and molecular formula of a compound, you need the percentage composition and molar mass.
Given that the compound consists of 87.8% carbon (C) and 12.2% hydrogen (H), we can assume these are the only two elements in the compound.
Step 1: Calculate the number of moles for each element.
To calculate the number of moles, divide the mass percentage of each element by its atomic mass.
For carbon (C):
Number of moles = (87.8 g ÷ 12.01 g/mol) ≈ 7.31 moles
For hydrogen (H):
Number of moles = (12.2 g ÷ 1.01 g/mol) ≈ 12.08 moles
Step 2: Determine the ratio of the moles.
Divide the number of moles of each element by the smaller number of moles to get the simplest whole number ratio.
For carbon (C): 7.31 ÷ 7.31 ≈ 1
For hydrogen (H): 12.08 ÷ 7.31 ≈ 1.65 (approximately)
Step 3: Adjust the ratio to whole numbers.
Multiply the ratio by a small whole number to obtain whole number values. In this case, multiply by 2 to get the nearest whole number.
For carbon (C): 1 × 2 = 2
For hydrogen (H): 1.65 × 2 = 3.3 (approximately)
The empirical formula is therefore C2H3.
Step 4: Determine the molecular formula using the molar mass.
The empirical formula mass is calculated by adding the atomic masses of the empirical formula elements.
Empirical formula mass of C2H3:
(2 × 12.01 g/mol) + (3 × 1.01 g/mol) = 26.06 g/mol
Given the molar mass of the compound is 56 g/mol, divide the molar mass by the empirical formula mass.
Molecular formula = (56 g/mol) ÷ (26.06 g/mol) ≈ 2.15
Since the molecular formula should be a whole number, round the value to the nearest whole number.
Rounded to the nearest whole number, the molecular formula is 2.
Therefore, the empirical formula of the compound is C2H3, and the molecular formula is C2H3.