The following set-up was used to determine the no. of moles of water of crystallization in 1 mole of hydrated cobalt(II) chloride, CoCl2.xH2O
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THE EXPERIMENTAL RESULTS WERE:
[1] MASS OF CRUCIBLE+LID= 20.63g
[2] MASS OF CRUCIBLE+LID+HYDRATED CoCl2 = 22.96g
[3] MASS OF CRUCIBLE+LID+ANHYDROUS CoCl2 AFTER STRONG HEATING = 21.93g
(a) Give two reasons why the crucible should be half covered with the lid during heating, as shown in the diagram.
(b) What was the mass of water of crystallization in the sample of hydrated coblat(II) chloride.
(c) Calculate the value of x in the formula CoCl2.xH2O.
(d) Even after accurate weighing, the experimentally determined value of x is usually smaller than the theoretical value. Suggest a reason for this.
Chemistry
2010-07-27 7:00 am
回答 (1)
2010-07-27 8:49 am
✔ 最佳答案
(a)This is to allow water vapour formed to leave the crucible, and prevent the heat solid from spilling out from the crucible.
(b)
Mass of water of crystallization in the sample
= 22.96 - 21.93
= 1.03 g
(c)
Molar mass of H2O = 1x2 + 16 = 18 g/mol
Molar mass of CoCl2 in the sample = 58.9 + 35.5x2 = 129.9 g/mol
Mass of H2O in the sample = 1.03 g
Mass of CoCl2 in the sample = 21.93 - 20.63 = 1.3 g
Mole ratio CoCl2 : H2O
= 1.3/129.9 : 1.03/18
= 0.01 : 0.057
= 1 : 5.7
≈ 1 : 6
Hence, x = 6
(d)
This is because the water of crystallization is not completely released from hydrated CoCl2, and some water vapour is condensed on the lid.
參考: andrew
收錄日期: 2021-04-13 17:23:32
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