Elemental analysis of a compound, once used as a pesticide, was found to be 74.2% carbon, 8.64% hydrogen, and 17.2% nitrogen.
This compound has a molecular mass of 162.23g/mol, what is the molecular formula for this compound?
Didn't I do this for you a couple days ago?
http://www.jiskha.com/display.cgi?id=1479076160
That was part A this is part B the actual question is different
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To determine the molecular formula for the compound, we need to determine the empirical formula first. The empirical formula represents the simplest whole-number ratio of atoms in a compound.
Step 1: Convert the percentages to grams.
Given that the compound is 74.2% carbon, 8.64% hydrogen, and 17.2% nitrogen, we can assume we have 100g of the compound.
Mass of carbon = 74.2g
Mass of hydrogen = 8.64g
Mass of nitrogen = 17.2g
Step 2: Convert the masses to moles.
To convert the mass of each element to moles, we need to divide each mass by the molar mass of the respective element.
Molar mass of carbon (C) = 12.01 g/mol
Molar mass of hydrogen (H) = 1.008 g/mol
Molar mass of nitrogen (N) = 14.01 g/mol
Number of moles of carbon = mass of carbon / molar mass of carbon
= 74.2g / 12.01 g/mol
≈ 6.18 mol
Number of moles of hydrogen = mass of hydrogen / molar mass of hydrogen
= 8.64g / 1.008 g/mol
≈ 8.57 mol
Number of moles of nitrogen = mass of nitrogen / molar mass of nitrogen
= 17.2g / 14.01 g/mol
≈ 1.23 mol
Step 3: Find the mole ratio.
We need to divide the number of moles of each element by the smallest number of moles obtained. In this case, the smallest number is 1.23 mol (the number of moles of nitrogen).
So, the mole ratio is approximately:
C: 6.18 mol / 1.23 mol = 5
H: 8.57 mol / 1.23 mol ≈ 7
N: 1.23 mol / 1.23 mol = 1
Step 4: Write the empirical formula.
Based on the mole ratio obtained, the empirical formula for the compound is C5H7N.
Step 5: Find the molecular formula.
To determine the molecular formula, we need to find the ratio between the empirical formula mass and the given molecular mass.
Empirical formula mass = (C5H7N) = (5 * 12.01 g/mol) + (7 * 1.008 g/mol) + (1 * 14.01 g/mol)
≈ 71.08 g/mol
To get the ratio: molecular mass / empirical formula mass
= 162.23 g/mol / 71.08 g/mol
≈ 2.28
Round the ratio to the nearest whole number:
2.28 ≈ 2
The molecular formula is obtained by multiplying the empirical formula by the ratio:
(C5H7N)2 = C10H14N2
Therefore, the molecular formula for the compound is C10H14N2.