[Chemistry] - Challenge for 'O' & 'A' Level Students

last SG · 2009-09-29T22:00:56+00:00

Did you consider that some of the SO4 2- ions will LEAVE in the form of Ag2SO4(s) ppt?

UltimaOnline SG

Here’s a chemistry calculations question I wrote just the other day, to let my students (both ‘O’ and ‘A’ levels) enjoy a bit of fun with chemistry calculations.

I challenge all ‘O’ and ‘A’ level students on this forum (including lurkers) to solve this question. If you can, post your worked solution here (as proof you solved it). If you’re unable to upload your solutions, at least you still have the satisfaction of solving it yourself on paper.

~ A BedokFunland JC Original Calculations Challenge ~

50cm3 of aqueous sulfuric(VI) acid of unknown molarity was mixed with 75cm3 of 0.45mol/dm3 of aqueous potassium hydroxide. 55cm3 of the resulting alkaline solution A was mixed with 80cm3 of 0.35mol/dm3 of phosphoric(V) acid. 90cm3 of the new resulting acidic solution B required 39.97cm3 of aqueous sodium carbonate of unknown molarity, for complete neutralization. In a separate experiment, 625cm3 of the same aqueous sulfuric(VI) acid solution required 192.3cm3 of the same aqueous sodium carbonate solution for complete neutralization. Calculate the molarities of the sulfuric(VI) acid solution and the sodium carbonate solution.

Answers :
[H2SO4] = 0.2 mol/dm3
[Na2CO3] = 0.65 mol/dm3

yiha093 SG

*stares at question and resolves to solve it later. xD -

-reserve post-

tmr den do . so freaking complicated need alot time xD

absol SG

wa this looks uber hard....

dkcx SG

wa this looks uber hard....

Just make sure u understand the question 1st. Yihao had a few misconceptions and i dunno about any of the rest who are willing to even try.

Just be prepared to do simultaneous equations i believe and have fun forming your equations which won't be easy.

Since the answers are already given, 1 way to 'cheat' but confirm whether your working is correct is to throw the answers into your equations to ensure you have formed them correctly.

tut4nkh4m3n SG

i'll definitely give it a shot tmr =)

dkcx SG

i'll definitely give it a shot tmr =)

wow what level are you?

Never seen u in homework before

qdtimes2 SG

i give up..i tried from afternoon until now lol...when revealing workings/hints?

tut4nkh4m3n SG

wow what level are you?

Never seen u in homework before

a lvls. taking it this yr. prelims just over. yep, will have time in the forums for a while before i'll have to bury myself in the books all over again.

dkcx SG

i give up..i tried from afternoon until now lol...when revealing workings/hints?

It might be better to show your working etc so ultimaonline can correct your mistake and let everyone learn together.

tut4nkh4m3n SG

YAY i got it. took a while tho, found it rather tedious.

for me the challenge was converting everyth into the right molar ratio cos the mono-, di- and triprotic acid/base really make it troublesome and i had calculation errors in my first 2 attempts. after which it was merely using simultaneous equations to solve.

letting X be [H2SO4] and Y be [Na2CO3], the 2 equations i got were:

0.625X - 0.1923Y = 0
0.02933X - 0.07994Y = -0.0461

yuppers. i had fun

UltimaOnline SG

Congrats tut4nkh4m3n! Glad u had fun! Smile

absol SG

tried it yesterday night, same approach as tut4nk4m3n, solve by simultaneous eqns. only got 0.625x - 0.1923y = 0 right.

the first eqn i tried 2 times, i think i made some errors in between...shall try again when im free.

but its solvable within 10 mins, my friend did it haha.

tut4nkh4m3n SG

Congrats tut4nkh4m3n! Glad u had fun! Smile

thanks for the question. if you've got more in the future do post them, i'll gladly give it a go =)

yiha093 SG

sorry, but isit possible for TS to post chemistry-related-but-not-maths-related.eg-sim-eqn questions ?

really dislike it ? =.='' ?

dun like 2 mix chem with maths.

tut4nkh4m3n SG

sorry, but isit possible for TS to post chemistry-related-but-not-maths-related.eg-sim-eqn questions ?

really dislike it ? =.='' ?

dun like 2 mix chem with maths.

haha. i don't like it either. heck, i don't like a lot of things in the syllabus. but we don't really have a choice. sciences overlap with math A LOT, you should know that by now. maybe more for physics, less for biology, but they still overlap.

moreover, the question above is still more of a chemistry question than a math one. differentiate this, expand this, what's the probabilty of this, find the equation of this plane, does this function have an inverse... those would be math questions.

UltimaOnline SG

—-—-- sorry, but isit possible for TS to post chemistry-related-but-not-maths-related.eg-sim-eqn questions ?
really dislike it ? =.=’’ ?
dun like 2 mix chem with maths. --—-—-

That’s still possible for ‘A’ levels, but not for ‘O’ levels; because ‘O’ levels is way too simplified; only possible interesting (challenging) questions that can still be attempted at ‘O’ levels (eg. this question) are mathematics based questions.

dkcx SG

sorry, but isit possible for TS to post chemistry-related-but-not-maths-related.eg-sim-eqn questions ?

really dislike it ? =.='' ?

dun like 2 mix chem with maths.

I know maths is not your strong point but you still have to practice. Remember what we discuss lsat night

yiha093 SG

—-—-- sorry, but isit possible for TS to post chemistry-related-but-not-maths-related.eg-sim-eqn questions ?
really dislike it ? =.=’’ ?
dun like 2 mix chem with maths. --—-—-

i dun understand ?

dkcx SG

i dun understand ?

What he means is the O's syallabus is too simplified to give much challenging questions and the only type of questions that can offer you guys a challenge will be those that require maths.

tut4nkh4m3n SG

true to some extent. but many of the questions at 'A' lvls, challenging or not, require math.

topic such as stoichiometry, equilibria, energetics all require math. some require simple addition, others require an understand of logarithms, or how to solve simultaneous equations... these topics form a large component of the 'A' lvls syllabus.

my point is, you might not need excellent math skills to be gd in chem, but a decent grasp of the basics (addition, subtraction, multiplication, log, square...) is a must.