问题讨论

但愿清楚地糊涂UID: 2393744

我做Major Field Test in Chemistry Sample Questions时遇到几道题。有的时候干脆就觉得是答案错了。不知道哪里能够找到解释。大家是不是做题都觉得没有疑问？不知道能不能把所有不确定的题都贴到这里。

Measurement Pipet X Pipet Y
1 10.25 mL 9.70 mL
2 9.65 mL 9.69 mL
3 10.10 mL 9.73 mL
4 10.40 mL 9.68 mL
Mean 10.0 mL 9.70 mL
Standard Deviation 0.36 0.02
7. Two students calibrated their 10 mL pipets and
obtained the data shown above. Which of the
following statements about these data is true?
I. Student X has evidence of a significant
indeterminant (random) error.
II. Student X can use the value of 10.00 mL as
the volume of pipet X without introducing
any significant error (less than 4 parts per
thousand) in an analysis.
III. Student Y has evidence of a significant
indeterminant (random) error.
IV. Student Y can use pipet Y without
correction, because the standard deviation is
so small.
V. Student Y can use the value of 9.70 mL as
the volume of pipet Y without introducing
any significant error (less than 4 parts per
thousand) in an analysis.
(A) IV only
(B) V only
(C) I and II only
(D) I and V only
(E) II and IV only

为什么II不对？

[ 本帖最后由 但愿清楚地糊涂 于 2008-10-11 19:39 编辑 ]

yuxueliang_2008UID: 2425006

D吧
  
X组的数据差别很大，s较大；Y组的差别较小，s较小。数据可看得Y只能量9.7的

但愿清楚地糊涂UID: 2393744

谢谢楼上。但是我还是不知道II为什么不对。


A certain monobasic acid is found to be soluble in aqueous sodium carbonate but insoluble in aqueous sodium bicarbonate. If the ionization constants for carbonic acid are 3*10^(-7) and 6*10^(-11), the ionization constant for the acid must be?

我知道答案是 "greater than 6*10^(-11) but smaller than 3*10^(-7)" 但是不知道该怎样算。谢谢

但愿清楚地糊涂UID: 2393744

Ag2SO4(s) <-> 2Ag+    +    sulfate anion (SO4)2-

A sample of solid silver sufate was put into a solution originally 0.020 molar in Na2SO4. After equilibrium was obtained, the concentration of the silver ion in the supernatant liquid was 0.01 molar. If the only significant equilibrium reaction is one above, what is the value of solubility product constant of silver sulfate?

(A)1.6e-3
(B)8.0e-4
(C)2.6e-4
(D)1.3e-4
(E)none of the above

我算出来的是D, 而且我自己觉得很有道理。但是答案是E.

[ 本帖最后由 但愿清楚地糊涂 于 2008-10-11 19:48 编辑 ]

但愿清楚地糊涂UID: 2393744

[HA]CHCl3/[HA]H2O

The value for the distribution constant for an organic acid HA between chloroform and water is 100. The dissociation constant of the acid in water is 10^(-5), and it can be assumed that it does not dissociate or dimerize in the chloroform phase. Increasing the pH of the aqueous phase from 4 to 9 has what effect on the fraction of HA extracted into the chloroform phase?

我觉得此题条件不够。the volume ratio of water phase and organic phase 必须要告诉才行。