ya..it's A

pH 1 is the measurement for strong acid.

For SPM, 0.1moldm^-3 is considered as strong acid
D could be right, but it is ethanoic acid (a week acid), even though its molarity is 0.1moldm^-3, its pH still higher than 1.

This post has been edited by work_tgr: Oct 27 2008, 09:04 AM

So, in SPM SYLLABUS, WEAK ACID impossible to have pH value less than 2?

This post has been edited by vick5821: Oct 27 2008, 09:07 AM

Not necessary.

There is no obvious statement to tell SPM students about what exactly makes the value of pH. Of course, it must be related with the content of OH- and H+.

So, week acid such as ethanoic acid of 0.1moldm^-3 could be higher than 1 because it doesn't dissociate completely.

But, if the molarity increase to 1moldm^-3 or higher, it could be pH1.

This post has been edited by work_tgr: Oct 27 2008, 09:12 AM

so if weak acid is concentrated, the ph value could be less than 1 la? how abt dilute sulphuric acid..ph 2?

yes, pH 1. But less than 1 ?
It's based on experiment and we can not tell by the concentration to get the exact value of pH. But, we can make a rough guess. pH2 is still under the group of concentrate acid.

This post has been edited by work_tgr: Oct 27 2008, 09:16 AM

oh..so a ques here

when 0.1 mol dm-3 solution L is tested wiuth pH paper, the colour change shows that solution L has a pH of 3.Which of the following is possibly solution L?
A. WEAK ETHANOIC ACID
B. DILUTE SULPHURIC ACID
C. AMMONIA AQUEOUS SOLUTION
D. SODIUM HYDROXIDE SOLUTION.

i know C and D is out already..

yes, C&D are alkali and B is better answer than A because pH of WEAK ETHANOIC ACID around 5 or 6.

if strong ethanoic acid? btw..the book ans is A leh

Got any tips for physics? That's my weakest subject besides addmath of course. The only chapter in physics that I understand is Radioactivity. The rest go kelaut already.

answer is C

Mostly is B...why A?..if its weak CH3COOH then the pH value is around 4.5~5.5...why 3?

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Added on October 27, 2008, 11:00 amMaybe because pH value of sulphuric acid is 2. SO, the pH value of dilute sulphuric acid > 2.
pH value of ethanoic acid is 3. So, pH value of weak ethanoic acid > 3.

C and D is out. SO the best answer is A : Sulphuric acid.

pH value is Reference from revision book.

This post has been edited by macamtakada: Oct 27 2008, 11:07 AM

Vick, that question is from what book? Some workbooks are not good, the questions they give are ridiculous with wrong answers, I had such a book once.

from longman.

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Added on October 27, 2008, 1:34 pmtis correct? but other ppl told me that no wor

This post has been edited by vick5821: Oct 27 2008, 01:34 PM

Guys, since there's so many experiments in Bio,Chem and Physics. How do you guys memorize all of them since the questions in SPM experiments will be randomly out.

This post has been edited by ilovecookies92: Oct 27 2008, 03:26 PM

Only Peka? Isn't it all experiments?

Oops. Sorry. Experiments. *Edited*

All the tita will be substituted with x because I can't type tita out.

2)
2 tan2x = square root x
tan2x = (square root x)/2
2x = 40.8934, 220.8934
x = 20.4467, 110.4467

3)
Translate them into a diagram.
Hope you'll understand.
[attachmentid=646442]

a)sin (P+Q)
=sin P cos Q + cos P sin Q
=3/5(-12/13) + 4/5(-5/13)
=-56/65

b)tan (P-Q)
=(tan P - tan Q) / (1 + tan P tan Q)
=(4/3 - 12/5) / [1 + (4/3)(-12/-5)]
=-16/63

4)Where are the symbols?

Hey , I came across this question . It's something similar with the question about the concentration of hydrogen ions .

Which of the following has the highest concentration of hydrogen ion ?
A . 20cm3 of 0.5mol dm-3 ethanoic acid
B . 10cm3 of 1.0mol dm-3 sulphuric acid
C . 5cm3 of 2.0 moldm-3 hydrochloric acid
D . 1cm3 of 10.0mol dm-3 methanoic acid

How to do ?

From the looks of it, I will pick B.

A and D is out because they are weak acids that only dissociate partially.
Both B and C has the same number of moles, but B is a diprotic acid, which means it has two hydrogen atoms.