Two part Chemistry problem?
The two parts are as follows:
A compound is known to contain 54.95 percent carbon and 24.38 percent oxygen (balance with hydrogen). Each molecule contains two atoms of oxygen. What is the molecular weight of this substance?
How many carbons are there in the molecular formula for this compound?
~~~An explanation of the solving methods would be much appreciated, thank you!
Comments
To answer just the questions as stated:
(2 mol O/mol) x (15.9994 g O/mol) x (100/24.38) = 131.3 g/mol
(2 atoms O) x (15.9994 g O/mol) x (54.95/24.38) / (12.0108 g C/mol) = 6 atoms C
The complete solution goes like this:
100% - 54.95% C - 24.38% O = 20.67% H
Take a hypothetical sample of 100.0 g:
(54.95 g C) / (12.0108 g C/mol) = 4.5750 mol C
(24.38 g O) / (15.9994 g O/mol = 1.5238 mol O
(20.67 g H) / (1.0079 g H/mol) = 20.508 mol H
Divide by the smallest number of moles:
(4.5750 mol C) / 1.5238 = 3.00
(1.5238 mol O) / 1.5238 = 1.00
(20.508 mol H) / 1.5238 = 13.5
In order for these ratios to turn into integers, it is necessary to multiply them all by 2, then round to the nearest whole number to find the empirical formula:
C6O2H27
Since there are two atoms of oxygen as specified, this is also the molecular formula.
The molecular weight of C6O2H27 is 131.2781 g/mol.
Assume you have 100 g of the compound, then you have:
54.95 g C
24.38 g O and
20.67 g H
Moles of each:
54.95 / 12 = 4.58 mol C
24.38 / 16 = 1.52 mol O
20.67 /1 = 20.67 mol H
Divide each of these by the smallest:
C = 4.58 / 1.52 = 3
O = 1.52 / 1.52 = 1
H = 20.67 / 1.52 = 13
Empirical formula = C3H13O. Since the problem states that each molecule has 2 oxygens, the molecular formula will be C6H26O2.
You can figure out the molecular weight from that formula.
one million. moles CO2: 11 g/40 4 g /mole= 0.25 moles 0.25 moles x 6.022E23 molecules/mole*= one million.5E23 molecules 2. moles H2O: 24 g/28 g/mole= one million.33 moles H2O one million.33 moles H2O x 6.022E23 molecules/mole*=one million.07E24 molecules * Avogodro's No.