what is the first-hand investigation on pH of salt solutions? (1 Viewer)

[the-intercepter]

in the 2006 HSC question 21. it says:

you performed a first-hand investigation to identify the pH of a range of salt solutions.

identify the acidic salt used and explain the acidic nature of the salt you selected. include a balanced chemical equation in your answer.

anyone know please help.

 

[danz90]

Certain salts contain ions that will 'hydrolyse' (correct me if this term is wrongly used here), which are either moderately weak conjugate acids or bases.

eg. NH₄Cl is an acidic salt, because NH₄⁺ donate a proton to water molecules, forming an acidic solution:
NH₄⁺ + H₂O ---> NH₃(aq) + H₃O⁺

(For validity purposes, you would also measure the pH, using universal indicator and pH colour chart, of a solution of NaCl of equal concentration, to confirm that the ammonium ion is what is 'causing' the acidity.)

A basic salt would be NaCH₃COO. Ethanoate ions accept a proton from water molecules to form a basic solution:

CH₃COO^- + H₂O ---> CH₃COOH(aq) + OH^-.

Just remember some examples of acidic and basic salts, and the ionic equations associated, and you'll be fine

 

[JasonNg1025]

Remember that acidic salts are where a strong acid and a weak base combine to form a salt and basic salts are where a weak acid and a strong base combine to form a salt. This is because of their conjugates, taking example NH₄Cl:

NH₄⁺ essentially acts as the acid, donating its H⁺ to form the weak conjugate base NH₃. Cl^- accepts this proton forming the strong conjugate acid HCl. See how they link? You can use this method to find out acidity and bascisity (100% I spelt it wrong) of salts. NaCH₃COO works because Na is from strong base NaOH and CH₃COO^- is from weak acid CH₃COOH

 

[the-intercepter]

cheers

you resolved an arguement in my household lol

i won

 

[SkimDawg]

Yeah this has also helped me. Fucken I swear, my teachers must've missed like 10 pracs. That physics Q16 today was gay because we didn't do it, so I just made Hertz's experiment instead (they dont know haha).

 

[Pwnage101]

although it is unfortunate some teachers dont go thru the pracs, it is all in the syllabus - and if u havent covered it by the time teh HSC comes along, well its nobody's fault but your own in the end

 

[SkimDawg]

although it is unfortunate some teachers dont go thru the pracs, it is all in the syllabus - and if u havent covered it by the time teh HSC comes along, well its nobody's fault but your own in the end

Yeah thanks for pointing that out man...heaps appreciated. I dont think I need to elaborate on this, my sarcasm is clear.

 

[Pwnage101]

Yeah thanks for pointing that out man...heaps appreciated. I dont think I need to elaborate on this, my sarcasm is clear.

well, if its in the syllabus, it cna be tested, and to be honest, i know many ppl whose teachers dont do the pracs, but they do something about it - look at the notes uploaded here, look on th einteernet, etc

im not saying its ur fault u havent done them, im just sayin if u get a Q in the exam about a prac in the ysllabus ur teacher hasnt done, u aint gonna get ANY amrks for sayin 'we didnt do it' - in year 12 we take responsibility for our own learning, in MOST of my subjects we did not cover every dot point in class - but any good student would at least read up on it in some textbooks and what not

its unfortunate ur in a position like this (not covered course by teacher), which i have been in as well..

 

[SkimDawg]

well, if its in the syllabus, it cna be tested, and to be honest, i know many ppl whose teachers dont do the pracs, but they do something about it - look at the notes uploaded here, look on th einteernet, etc

im not saying its ur fault u havent done them, im just sayin if u get a Q in the exam about a prac in the ysllabus ur teacher hasnt done, u aint gonna get ANY amrks for sayin 'we didnt do it' - in year 12 we take responsibility for our own learning, in MOST of my subjects we did not cover every dot point in class - but any good student would at least read up on it in some textbooks and what not

its unfortunate ur in a position like this (not covered course by teacher), which i have been in as well..

I know what your trying to say, its just that, its ALOT harder to remember when you havent actually done the prac, hence harder to remember from notes instead of personal experience. Get what im saying?

 

[JasonNg1025]

Yeah that's the reason why you'd rarely choose to do your own option topic outside of class