old chemistry question

ahmdoda

this question is from the 2000 chemistry higher level paper i couldnt find a marking scheme around for it to answer the question for me hoping to find an answer here.
Question 2 on Titration determining total hardness of water link>> http://www.examinations.ie/archive/exampapers/2000/LC022ALPO00EV.pdf
The question is fine but part two (ii) how would you accurately restore the boiled water to its original volume,why is it necessary.why deionised h2o is used?

AB2013

(ii) Describe how you would accurately restore the boiled water to its original volume and explain why it is
necessary to do so. Why is deionised water used?

If I was answering this I'd say you would place the boiled water in a volumetric flask and add deionised water until the bottom of the meniscus was lying on the calibration mark and it's necessary to do so because water hardness is measured in parts per million so you have to have 1 dm^3. Deionised water was used because tap water may contain dissolved ions such as magnesium sulphate which causes permanent hardness and would therefore affect the accuracy of the experiment.

That's just how I would answer it, could be wrong :P

pajero12

AB2013 has it in one, Deionised doesn't contain any ions, tap water may contains ions which cause harness altering your titration end point!

ahmdoda

thanks AB appreciate your answer but the question about why is it necessary to do so is still a puzle!

outnumbered

ahmdoda wrote: »

thanks AB appreciate your answer but the question about why is it necessary to do so is still a puzle!

why is it necessary?
To make it a fair test. Restoring it will not effect the levels of permanent hardness. So we can restore it thus making it a fair test, with only one variable i.e. minus temporary hardness.
Also maybe write so that we have a know volume of water?

That's what I would write anyway. We do exam and mock papers back to 1972!! The questions were way harder as the years go back.... Are we getting stupider?? :P

ahmdoda

outnumbered wrote: »

why is it necessary?
To make it a fair test. Restoring it will not effect the levels of permanent hardness. So we can restore it thus making it a fair test, with only one variable i.e. minus temporary hardness.
Also maybe write so that we have a know volume of water?

That's what I would write anyway. We do exam and mock papers back to 1972!! The questions were way harder as the years go back.... Are we getting stupider?? :P

Thanks!!!!!!!! spot on it seem to make sense,and lol your dam right some of these old question are some challenge non like the questions from 01-12 some years are ridiculously easy like 2009 lucky bastards got the iron table for q1 and preperation of ethene ethyne for q2 i would kill any one that failed that year!! but i cant complain its all good as long as you can get the A1

outnumbered

ahmdoda wrote: »

Thanks!!!!!!!! spot on it seem to make sense,and lol your dam right some of these old question are some challenge non like the questions from 01-12 some years are ridiculously easy like 2009 lucky bastards got the iron table for q1 and preperation of ethene ethyne for q2 i would kill any one that failed that year!! but i cant complain its all good as long as you can get the A1

no prob
i know, right? oh I do pray we get a lovely year
you want medicine yeah? think i seen you in that forum?

ahmdoda

outnumbered wrote: »

no prob
i know, right? oh I do pray we get a lovely year
you want medicine yeah? think i seen you in that forum?

Keep the prayer up im right behind you ,i just keep getting paranoid of them trying something sneaky like repeat the section A experiment that came up last year again this year and yea i decided to give medicine a go pretty sure it might not work out well for me this year due to hpat but no tears i might give it one more go then its moving on! and may god be with you in your application you seem like some one who deserve it as i dont believe in luck!!some bull**** maybe if an earthquake hits ireland before the leaving cert you can call that luck

outnumbered

ahmdoda wrote: »

Keep the prayer up im right behind you ,i just keep getting paranoid of them trying something sneaky like repeat the section A experiment that came up last year again this year and yea i decided to give medicine a go pretty sure it might not work out well for me this year due to hpat but no tears i might give it one more go then its moving on! and may god be with you in your application you seem like some one who deserve it as i dont believe in luck!!some bull**** maybe if an earthquake hits ireland before the leaving cert you can call that luck

I will!
Yeah that would be fierce sneaky but in reality, if you know all your experiments, acids/water/ph q, quilibrium and rates, fuels and thermochem, radioactivity and the machines, and all the definitions and other basics, that's your 8 questions! not so hard when you put it like that is it?
Same as! The hpat was never my strong point! It's hard to know what to do if i don't get med! repeat LC and hpat, take a year out for hpat, or do another course and the hpat, or try for graduate entry??
thanks so much! And the very same to you too!
hahaha, yes that would be lucky...... well actually, it depends hahaa