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標題: [Chem] 有題mc唔識求解 [打印本頁]

作者: Syuu 時間: 2014-4-19 12:27 AM 標題: 有題mc唔識求解

[attach]48214[/attach]
ans: b

唔知點解係b
我本身認為如果conc.最高~應該就係有fastest rate啦掛~所以揀d 但係錯左
:s

作者: chunchung38 時間: 2014-4-19 12:31 AM

the conc it provides is original conc. calculate new conc. by (XM * original volume)/new volume

作者: Syuu 時間: 2014-4-19 12:34 AM

引用:

原帖由 chunchung38 於 2014-4-19 12:31 AM 發表
the conc it provides is original conc. calculate new conc. by (XM * original volume)/new volume

哦!!
姐係b果個有0.09M所以就最快啦?

作者: chunchung38 時間: 2014-4-19 01:07 AM

b should be 0.1M

作者: CSLO 時間: 2014-4-19 05:41 AM

引用:

原帖由 chunchung38 於 2014-4-19 01:07 AM 發表
b should be 0.1M

0.09M

You forgot 10cm3 HCl

作者: chunchung38 時間: 2014-4-19 10:22 AM

u are right, but I think four solutions of equal volume of different conc. mixing with same volume of same solution yield the same order anyway.

作者: CSLO 時間: 2014-4-19 10:49 AM

引用:

原帖由 chunchung38 於 2014-4-19 10:22 AM 發表
u are right, but I think four solutions of equal volume of different conc. mixing with same volume of same solution yield the same order anyway.

算了吧, 下次望清楚d。

作者: kevinchow928 時間: 2014-4-19 02:06 PM

引用:

原帖由 CSLO 於 2014-4-19 05:41 AM 發表

0.09M

You forgot 10cm3 HCl

求解釋點解會0.09M

1.5(.06)/(0.1) = 0.09???????????

作者: CSLO 時間: 2014-4-19 03:01 PM

引用:

原帖由 kevinchow928 於 2014-4-19 02:06 PM 發表

求解釋點解會0.09M

1.5(.06)/(0.1) = 0.09???????????

0.9M
OH.................

作者: amychu964 時間: 2014-4-19 03:03 PM

why not 1.5x0.06/.09=1M?????????

作者: kevinchow928 時間: 2014-4-19 03:05 PM

引用:

原帖由 amychu964 於 2014-4-19 03:03 PM 發表
why not 1.5x0.06/.09=1M?????????

你要加10cm^-3 HCl 喎

作者: amychu964 時間: 2014-4-19 03:21 PM

But ........
in flask W, the original concentrate of NaS2O3 is 1X 0.08/0.09= 0.89M
in flask X, the original concentrate of NaS2O3 is 1.5X 0.06/0.09= 1M
in flask Y, the original concentrate of NaS2O3 is 2.5X 0.03/0.09=0.83M
in flask Z, the original concentrate of NaS2O3 is 3X 0.02/0.09=0.67M
By comparing the original concentration of NaS2O3, so X has the highest rate
唔係咩

作者: kevinchow928 時間: 2014-4-19 07:42 PM

引用:

原帖由 amychu964 於 2014-4-19 03:21 PM 發表
But ........
in flask W, the original concentrate of NaS2O3 is 1X 0.08/0.09= 0.89M
in flask X, the original concentrate of NaS2O3 is 1.5X 0.06/0.09= 1M
in flask Y, the original concentrate of NaS2O ...

YES, THE ANS IS B
However, your concentration of NaS2O3 is wrongly calculated. the total volume should be 0.1 instead of 0.09

作者: amychu964 時間: 2014-4-19 09:21 PM

HCl is added followed by the NaS2O3
in my view, i think the reation is 2M HCl react with 1M NaS2O3
if you are true, than the reaction become (2X0.01/0.1)M HCl i.e. 0.2M HCL react with 0.9M NaS2O3

作者: kevinchow928 時間: 2014-4-19 10:46 PM

引用:

原帖由 amychu964 於 2014-4-19 09:21 PM 發表
HCl is added followed by the NaS2O3
in my view, i think the reation is 2M HCl react with 1M NaS2O3
if you are true, than the reaction become (2X0.01/0.1)M HCl i.e. 0.2M HCL react with 0.9M NaS2O3 ...

what if u are required to compare the rate of reaction between
1. 10cm^3 2.0M HCl + 20cm^3 1.0M NaOH
2. 10cm^3 2.0M HCl + 20cm^3 1.0M NaOH + 70cm^3 H20 ?
they have same initial concentration , but how about rate of reaction??
the second reaction MUST have a lower rate of reaction
Therefore, u can just compare the original concentration, though u can do so in this question

作者: amychu964 時間: 2014-4-19 11:00 PM

引用:

原帖由 kevinchow928 於 2014-4-19 10:46 PM 發表

what if u are required to compare the rate of reaction between
1. 10cm^3 2.0M HCl + 20cm^3 1.0M NaOH
2. 10cm^3 2.0M HCl + 20cm^3 1.0M NaOH + 70cm^3 H20 ?
they have same initial concentration , ...

but in the question, the water is clearly added to NaS2O3 so i treated it as a kind of diluting process. so the mc is slightly different to your question. ( I think)

作者: kevinchow928 時間: 2014-4-19 11:01 PM

引用:

原帖由 amychu964 於 2014-4-19 11:00 PM 發表

but in the question, the water is clearly added to NaS2O3 so i treated it as a kind of diluting process. so the mc is slightly different to your question. ( I think)

ya of coz u can think as this way in this question but i just want to remind u that when considering rate of reaction, you must consider the concentration right after they mix

作者: amychu964 時間: 2014-4-19 11:05 PM

so my calculation of concentration of X is correct or not

0.9M or 1M?

作者: chunchung38 時間: 2014-4-20 12:14 AM

For safety sake, you should calculate actual conc. in the mixture(0.9M). From the condition of the Q, we can know that HCl is controlled(constant) variable, and the question ask for the effect of independent variable(conc of Na2S2O3) on dependent variable(rxn rate), thus I skip and ignore the controlled variable as I know the result will be the same. But to avoid misconception and for safety sake, please calculate actual conc. in the mixture.

作者: amychu964 時間: 2014-4-20 01:03 PM 標題: 回覆 19# chunchung38 的帖子

wait you mean that the conc of na2s2o3 is 0.9M

in the mc , it is a experiment on compering the reaction rate between diff conc of na2s2o3 with standard hcl
why 10 cm^3 is required to add in the denominator of the equation on calculating conc of na2s2o3. Although the total volume is needed for us to add 10 cm^3. but take an example of 2M HCL (100cm^3)+2M NaOH (100cm^3).

if in your calculation, it may become 2X(100/(100+100))M HCl (1M HCl) reacting with 2X(100/(100+100))M Naoh (1M Naoh)
你唔觉得有D怪咩

作者: amychu964 時間: 2014-4-20 01:11 PM

再簡單D
If the question is :
1) naoh replace the na2s2O3
2) no addtional water
3) other value kept constant
then , in your calculation, the conc of naoh in X is 1.5M X 0.06/ 0.07
in my calculation, the conc is remains as 1.5 M
but it is observed that it is just a simple neutralization of Hcl and Naoh ie 2M HCL reacting with 1.5M Naoh

do you agree?

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