CE chem 急問!!! chem高手請進啦～～～～～～

[匿名]

2008-04-29 12:44 am

１） A white solid dissolves in water to give an alkaline solution. The solution
reacts with dilute hydrochloric acid to give a gas. The solid is probably
A. calcium oxide.
B. calcium carbonate.
C. potassium hydroxide.
D. potassium carbonate.
(ans is D, WHY ont the others?)

２） In an experiment, 21.8 g of zinc was treated with 250.0 cm3 of 2.0 M
hydrochloric acid. What volume of hydrogen was liberated at room
temperature and pressure ?
(Relative atomic mass : Zn = 65.4;
molar volume of gas at room temperature and pressure = 24.0 dm3 )
A. 4.0 dm3
B. 6.0 dm3
C. 8.0 dm3
D. 12.0 dm3
(ans is B, WHY?)

2000 39. X is an element in Group VI of the Periodic Table. X can form X2– ions.
Which of the following statements are correct ?

(1) The oxidation number of X decreases when X2– ion is formed.
(2) Both X atom and X2– ion have the same number of electron shells.
(3) Both X atom and X2– ion have the same nuclear charge.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)
(ans is D, WHY?)

4) 點樣的molarity自算係concentrated??1M 的H2SO4係dilute定concentrated??

5) 有咩gas係soluble in water?

ｔｈａｎｋｓ！！

回答 (1)

chan

2008-04-29 4:17 am

✔ 最佳答案

1) Ca will form a protective layer with HCL ( CaCl2 )

so A , B are wrong ,

KOH + HCl will form KCl and H2O , which are both not gases .

so D is the ANS .

2) Zn + 2HCl ------- ZnCl2 + H2

no. of mol of HCl = 0.5mol
by the above eq. , 0.5mol HCl can react with 0.25mol Zn

no. of mol of Zn = 21.8 / 65.4 = 0.33 mol

so HCl is the limiting reagent .

no. of mol of H2 = 0.5 / 2 = 0.25mol

volume of H2 = 0.25 x 24 = 6 dm3

3) (1) correct : from 0 to -2
(2) correct : the no. of e- change but not the electron shell
(3) correct : the nuclear charge means the charge of protrons ,
as the no. of protrons remains , so correct

ANS : D

4) in the case of H2SO4 , maybe more than 7~9 M is concentrate ..
In CE , it will state the solution is concentrate or not clearly

5) many ... such as Cl2 , O2 , SO2 ...

參考: me

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