STPM 化学问题 马拉松！

huhuxboy

no. of mole of alum=3300/474 mol
thus, no. of mole of Al3+= 3300/474 mol
conc. of Al3+, [Al3+] = 3300/(474 x 5000) mol dm^-3

Al(OH)3 (s) <==> Al3+ (aq)  +  3OH- (aq)

Ksp = [Al3+][OH-]^3
3.70x10^-15 = 3300/(474 x 5000) x [OH-]^3
[OH-]=1.39x10^-4 mol dm^-3

pH = 14 - pOH
     = 14+lg 1.39x10^-4
     = 10.1 (3s.f.)

对吗？？？

再见是为了明天

你可以给我你的msn 吗？？？
我有很多问题想问你。。。

huhuxboy

Which of the following statement about a catalyst is true?
1. It increases the rate constant for a reaction.
2. It may undergo a physical change at the end of the reaction.
3. It does not alter the enthalpy of the reaction.

jeremy3232

1 and 2 are correct

huhuxboy

对了
请jeremy3232出题

huhuxboy

After an oil spillage at sea, a liquid hydrocarbon layer floats on the surface of the water. Which of the following statements help to explain why liquid hydrocarbon both float on and are less dense than water?
1. There are only Van der Waals forces between hydrocarbon molecules.
2. Hydrogen bonding between the molecules in liquid water causes them to pack close together.
3. Hydrocarbon molecules are not solvated by water.

[ 本帖最后由 huhuxboy 于 17-6-2007 06:41 PM 编辑 ]

sylvia_r

1 和 3。。。 对吗？

huhuxboy

不好意思，我写错了。
应该是
2. Hydrogen bonding between the molecules in liquid water causes them to pack close together.

~bb~

原帖由 huhuxboy 于 17-6-2007 02:21 AM 发表
After an oil spillage at sea, a liquid hydrocarbon layer floats on the surface of the water. Which of the following statements help to explain why liquid hydrocarbon both float on and are less de ...

全对吧？

huhuxboy

我的老师去年给的答案是1 和 2
但今年却说是1，2，3
问她这么久了她还没给我答案。。。
所以请大家多多指教
多谢。。。

huhuxboy

我的老师答我了。
答案是全部。。。

huhuxboy

这么那么冷清？？？
就让小弟再出一题。。。

At 1100K, Kp=0.130atm^-1 for the system:

2SO2 + O2 <==> 2SO3

(a) If 2.00mol of SO2 and 2.00mol of O2 are mixed and allowed to react, what must the total pressure be to give a 90% yield of SO3?

(b) The equilibrium constant Kp for the above reaction decreases with temperature. State and explain the effect on the position of equilibrium of
(i) increasing the temperature at constant pressure.
(ii) using a catalyst.

夕熹

请问在写electrochemical cell的时候：
electrode | electrolyte || electrolyte | electrode

书上说：Ions or species with lower oxidation states are written closest to the respective electrode
请问怎样子才是lower oxidation state?

jovene

the lower oxidation state usually is anode (negative electrode) with more negative E value or less positive E value..
(E value can get from data booklet)

ckkwill

A/A+      //    B+/B
oxidation       reduction

/ = different phase
, = same phase    e.g.  Fe2+,Fe3+
Pt = when no metalic electrode e.g. Pt(s)/H2(g)/H+(aq)//

huhuxboy

原帖由 huhuxboy 于 21-6-2007 02:29 PM 发表
这么那么冷清？？？
就让小弟再出一题。。。

At 1100K, Kp=0.130atm^-1 for the system:

2SO2 + O2 <==> 2SO3

(a) If 2.00mol of SO2 and 2.00mol of O2 are mixed and allowed to react, what ...

这题怎么没人试一试呢？？？

jovene

(a) O2 is in excess.
to yield 90% SO3 from 2.00 mol SO2
ie to yield 90% * 2.00 mol

              2 SO2  +   O2  <==>  2SO3
INITIAL:     2.00 mol   2.00mol    0 mol
equlibrium   2.00-1.80 (2.00-0.90) 1.80 mol
            =0.20 mol  1.10 mol

Total number of mol = 0.20+1.10+1.80 =3.10
PSO2 =   (0.20)
        --------- x Ptotal
          (3.10)

PO2 =     (1.10)
        --------- x Ptotal
          (3.10)

PSO3 =    (1.80)
        --------- x Ptotal
          (3.10)

Kp =     (Pso3)^2
       --------------
       (Pso2)^2 (Po2)
   = 0.130
                (1.80)             ^ 2
             --------- x Ptotal
                (3.10)
____________________________________________ = 0.130

(1.10)                   (0.20)           ^2
-------- x Ptotal        -------- x Ptotal
(3.10)                    (3.10)

=>                                    (1.80)^2
    TOTAL PRESSURE =          ------------------------
                               (0.20)^2 * 11     1
                                          --  * ----
                                         31    0.130
                   = 29.7 Nm ^-1

huhuxboy

原帖由 jovene 于 30-6-2007 10:25 PM 发表
(a) O2 is in excess.
to yield 90% SO3 from 2.00 mol SO2
ie to yield 90% * 2.00 mol

              2 SO2  +   O2    2SO3
INITIAL:     2.00 mol   2.00mol    0 mol
equlibrium   2.00-1.80 (2.00 ...

最后的部分做错了。。。
应该是

                                                    (1.80)^2 (3.10)
    TOTAL PRESSURE =          ------------------------
                                                   (0.20)^2 (1.10) (0.130)

                                                   = 1.76 X 10^3 atm

huhuxboy

b)i) The forward reaction is exothermic. An increase in temperature shifts the equilibrium in the endothermic direction so that some of the heat is absorbed. Thus the equilibrium position shifts to the left.
ii) No change in equilibrium position as the catalyst increases the rates of the forward reaction and reverse reaction to the same extent.

huhuxboy

来推动一下这楼。。。
不然那么冷清清的

再一题：
(a) Write the mechanism for the following chlorination reaction.
      CH3CH2CH3 + 2Cl2 ----> CH3CH(Cl)CH2Cl + 2HCl

(b) Explain the formation of (CH3)2CHCH(CH3)2 as a side product in the chlorination reaction above.