1.The oxide of an element X with formula X2O5 contains 34.78% oxygen by mass. Find the atomic mass of X.
2.A compound has formula MSO4．xH2O. 14.35g of the compound is heated until all the water of crystallisation is removed. The mass remaining is 8.05g.
(a)Calculate the percentage by mass of water of crystallisation.
(b)Calculate the value of x and the atomic mass of M. (The formula mass of MSO4 is 161.)
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2008-02-18 5:20 am
回答 (1)
2008-02-18 5:43 am
✔ 最佳答案
1.Let the atomic mass of X be x[(16 x 5)/(2x+16 x 5)] x 100% = 34.78%
80/(2x+80) = 0.3478
x = 75.0
Therefore,the atomic mass of X is 75.0
2a/
% by mass of water of crystallisation
=[(14.35 - 8.05) / 14.35] x 100%
=43.9%
2b/
No. of mol of MSO4‧H2O = No. of mol of MSO4
14.35/ [161+ x(2+16)] = 8.05/161
14.35/(161+18x) = 0.05
8.05 + 0.9x = 14.35
x = 7
The atomic mass of M
=161 - 32.1 - (16 x 4)
=64.9
參考: 自己
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