a compound with the molecular weight of 276 grams was determined to be 39.10% carbon, 8.77% hydrogen, and 52.13% oxygen. what is the empiricial formula and the molecular formula for the compound? i do not know where to start!
Start by taking a 100 gram sample. That will give you
39.10 g C
8.77 g H
52.13 g O.
Convert each to moles. moles = grams/molar mass.
Then fin the ratio of each with small whole numbers. The easiest way to do that is to divide the smallest number of moles by itself. That will give you 1.00 for that element, then divide all of the other moles by that same small number. That will give you the empirical formula. To fin the molecular formula, find the empirical formula mass by adding the atomic masses of the elements. The molecular formula will be a multiple of that number. Post your work if you get stuck.
To determine the empirical and molecular formulas for a compound, you need to know the percentages of each element by mass or their molar ratios. The first step is to assume that you have 100 grams of the compound, so the masses of each element correspond to those percentages.
Let's start by calculating the mass of each element in the compound based on the given percentages:
Mass of carbon = (39.10/100) * 100g = 39.10g
Mass of hydrogen = (8.77/100) * 100g = 8.77g
Mass of oxygen = (52.13/100) * 100g = 52.13g
Next, convert these masses into moles using their respective atomic masses:
Moles of carbon = Mass of carbon / Atomic mass of carbon
Moles of hydrogen = Mass of hydrogen / Atomic mass of hydrogen
Moles of oxygen = Mass of oxygen / Atomic mass of oxygen
The atomic masses of carbon, hydrogen, and oxygen are approximately 12.01 g/mol, 1.01 g/mol, and 16.00 g/mol, respectively.
Now, divide each mole value by the smallest number of moles among the elements to get the simplest whole number ratio of the elements. In this case, the number of moles of hydrogen is the smallest:
Moles of carbon / Moles of hydrogen = a (a is a whole number)
Moles of hydrogen / Moles of hydrogen = 1
Moles of oxygen / Moles of hydrogen = b (b is a whole number)
Let's assume the number of moles of hydrogen is 1, so:
Moles of carbon = a
Moles of oxygen = b
Now, determine the empirical formula by writing the simplest whole number ratio of elements using these values. We have:
C:a H:1 O:b
Finally, determine the empirical formula by providing the actual subscripts using the calculated values of a and b, and find the molecular formula by knowing the molecular weight of the compound:
Empirical formula: CHOb
Molecular formula: Use the molecular weight of the compound to find how many times the empirical formula is repeated in the actual compound.
To do this, divide the molecular weight of the compound by the empirical formula weight. Calculate this as follows:
Molecular formula weight = 276g/mol
Empirical formula weight = (12.01 + 1.01 + 16.00) g/mol = 29.02 g/mol
Repeat the empirical formula in the molecular formula this many times:
Number of repetitions = Molecular formula weight / Empirical formula weight
Substitute this value into the molecular formula:
Molecular formula: C12H12O12 (if the number of repetitions is 12, for example)
Thus, the empirical formula is CHOb, and the molecular formula depends on the number of repetitions of the empirical formula in the actual compound, which can be calculated using the molecular weight.