求一個未知化合物

設有 100 g 的該化合物, 則:
K 有 26.59 g, 即 26.59/39.1 = 0.680 摩爾
Cr 有 35.36 g, 即 35.36/52 = 0.680 摩爾
O 有 38.02 g, 即 38.02/16 = 2.376 摩爾
所以它們的摩爾比例為:
K : Cr : O = 2 : 2 : 7
因此其方程式為 K2Cr2O7, 即重鉻酸鉀.

mass in K: 26.59
mass in Cr: 35.36
mass in O: 38.02
no. of mole of K: 26.59 / 39.1 = 0.680
no. of mole of Cr: 35.36 / 52 = 0.68
no. of mole of O: 38.02 / 16 = 2.38
relative no. of moles of K: 0.680 / 0.680 = 1
relative no. of moles of Cr: 0.68 / 0.680 = 1
relative no. of moles of O: 2.38 / 0.680 = 3.5
therefore the ratio of K:Cr:O = 1:1:3.5 = 2:2:7
Therefore the empirical formula is K2Cr2O7
(correct to 3 significant figures)
K2Cr2O7, Potassium dicromate, an orange compound which is toxic.
For further information, please search wikipedia yourself.

2008-01-19 17:50:42 補充：
correction:relative no. of moles of K: 0.680 / 0.68 = 1relative no. of moles of Cr: 0.68 / 0.68 = 1relative no. of moles of O: 2.38 / 0.68 = 3.50.680>0.68!!!

K2Cr2O7
Potassium Cromate