Empirical Formula Chemistry Question
1) An organic compound X, which contains carbon, hydrogen and oxygen only, has an Mr of 85. When 0.43g of X are burned in excess oxygen, 1.10g of carbon dioxide and 0.45g of water are formed. Find the empirical and molecular formulae of compound X.
2) When ammonium dichromate (VI) is added gradually to molten ammonium thiocyanate, Reinecke's salt is formed. It has the formula NH4[Cr(SCN)x(NH3)y] ** and the following composition by mass: Cr = 15.15%, S = 38.15%, N=29.2%. Calculate the values of x and y in the above formula
It's alright if you just give me the steps and not the answers, I don't mind. I've done the rest of the sheet, these questions just stand out a little.
**note that the numbers in the formula should be subscript.
1 Answer | Add Yours
Moles of C, H and O can be calculated as:
Moles of C = moles of CO2 = 1.1 gm/44 gm = 0.025 moles C = 0.025 x 12 gm = 0.3 gm C
Moles of H = 2 x moles of water = 2 x 0.45/18 moles = 0.05 moles H = 0.05 gm H
Mass of oxygen = total mass - mass of C - mass of H = 0.43 - 0.3 - 0.05 = 0.08 gm oxygen
= 0.08/16 moles O = 0.005 moles O
Thus the empirical formula of the compound is `C_(0.025)O_(0.005)H_(0.05)`
and the molecular formula can be obtained by dividing these moles by the smallest number, i.e. 0.005.
Molecular formula is `C_5H_(10)O`
The molecular weight of this compound is 5x12+10x1+16 = 86 gm/mole
Hope this helps.
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