oxalic acid is a compound used in cosmetics and paints. A 0.725-g sample of oxalic acid was found to contain 0.194g of carbon, 0.016g of hydrogen, and 0.516g of oxygen. If the molar mass of oxalic acid is 90.04g/ mol, what is the molecular formula?
2006-10-31 10:08:01 · 4 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
0.725g oxalic acid = 0.725/90.04 mol
0.194g C = 0.194/ 12.01 mol ≈ 0.0162 mol
0.016g H = 0.016/ 1.008 mol ≈ 0/0159 mol
0.516g O = 0.516/ 16.00 mol ≈ 0.0323 mol
So C : H : O = 0.0162 : 0/0159 : 0.0323
≈1 : 1 : 2
MW CHO2 = 12.01 + 1.008 + 2 * 16.00= 45.02
So MW Oxalic acid = 2 x MW CHO2
Thus molecular formula of oxalic acid is C2H2O4
2006-10-31 10:28:32 · answer #1 · answered by Wal C 6 · 0⤊ 0⤋
If you divide those weights in grams of C, H, and O by their respective atomic weights, you get 0.0161 for C, 0.016 for H and 0.032 for O, so the ratio of the numbers of C:H:O atoms is 1:1:2. The molar mass of 90.04for oxalic acid tells you that the total atomic mass of H in the molecule is 22.51. So there are 22 H atoms in the molecule. So the molecular formula must be C2H2O4.
2006-10-31 10:36:44 · answer #2 · answered by zee_prime 6 · 0⤊ 0⤋
First, you can find the empirical formula of oxalic acid, by converting the grams of carbon, hydrogen, and oxygen into moles of each of them. Then, divide each number by the lowest number of moles out of the three of them, and you should get whole numbers as your answer for each. This is then the empirical formula for oxalic acid.
Next, you can figure out how much one mole of this empirical formula would weigh. Then, divide 90.04 by this number to see how many times more the molecular formula is than the empirical formula, since you know that the 90.04 is referring to the molecular formula (and it's ok if the answer happens to be 1). Then, multiply each part of your answer in the empirical formula by this number to get the molecular formula. For example, if you got C2H1O3, and got 2 when you divided, then the molecular formula would be C4H2O6. Hope this helps!
2006-10-31 10:19:13 · answer #3 · answered by Spanky M 2 · 0⤊ 1⤋
moles of carbon 0.194 / 12 = 0.016
moles of hydrogen 0.016 / 1 = 0.016
moles of oxygen 0.516 / 16 = 0.032
Divide all the numbers by 0.016 and you get
C : 1
H : 1
O : 2
So the formula should be (CHO2)n
The molecular weight of CHO2 is 12 + 1 + 32 = 45
No you divide the molecular weight of the oxalic acid by 45 and you should find the n
n = 90.04 / 15 ~ 2
So the formula of the oxalic acid is C2H2O4.
2006-10-31 10:24:36 · answer #4 · answered by Dr. J. 6 · 0⤊ 0⤋