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ocr a f325 revision thread

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I found comparing the cations with the cations only and the Anions only as a good rule of thumb, with the charge most overruling and the f- ions is smaller than cl

I did that, those were the first two marking points. But the last point was to explain the pattern of lattice enthalpies.

Reply 2441

otrivine

Original post by LegendX

Indeed.

how comes I thought you got an A in Jan

Reply 2442

bluedate

Hi
Can someone explain to me what cathode and anode is with examples, and what it means when writing half equations from the positive/negative cathode/anode (i don't know)

Thank you

Reply 2443

samzurai

Stretch and challenge be nice to tomorrow to me babe

Reply 2444

überambitious_ox

For the following questions, I have done equations for step 1 and step 2, however am confused as to how to formulate an equation for step 4.

Please could somebody explain how to do so. Thank you

(edited 10 years ago)

Reply 2445

master y

Please can someone explain Q8 last part from jan 2013

Reply 2446

LegendX

Original post by otrivine

how comes I thought you got an A in Jan

Nope, i did not :frown:

Reply 2447

User944645

I know it's a little late, but I've got some notes here if anyone wants something concise for last-minute revision :smile:

http://www.thestudentroom.co.uk/showthread.php?t=2378761

Reply 2448

KD35

For a definition of rate, can you say rate of change of concentration?

Anyone doing physics will prefer it like that but the mark schemes seem to like change in concentration per unit time and it kind of annoys me.

Reply 2449

Namod

Original post by master y

please can someone explain q8 last part from jan 2013

no one can its too advance for students!!!

Reply 2450

wl1

Original post by rival_

In the mark scheme where does the "40" come from when working out conc^ in g dm^-3

When you work out the concentration, the volume you divide by is 25cm³. Although you have scaled up to 250cm³, that 250cm³ was originally made up with water from 25cm³.

Reply 2451

X44

Original post by LegendX

Gosh, i hate explaining over a forum but here goes:

You're reacting NaOH ( a base ) with an acid to form a salt, so you must do the moles of the acid - the moles of the naoh to see how many moles of acid are left over.
The mol of NaOH reacted = moles of the salt formed and you should know from your chemistry that the salt is going to decompose to form conjugate base and sodium ( this is where the large conjugate base reservoir comes from ) however the final step is realised that 50cm3 of volume came from each mixture so the total volume of the solution is 100cm3, convert that into dm3 and then work out the concentrations and then basically plug it into the formula :smile:

Thank you

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Reply 2452

georgiaaaxo

Original post by slacky123

http://www.docbrown.info/page07/SSquestions/redox_vol_calcs1.htm

I find these are really good practice!

thankyou!!!

Reply 2453

otrivine

Original post by LegendX

Nope, i did not :frown:

Good Luck

Reply 2454

eggfriedrice

Original post by KD35

I do physics and I find saying "per unit time" is better.

Reply 2455

X44

Original post by Namod

no one can its too advance for students!!!

Lool damn right, it took my teacher 20 mins to figure it out but on the examiners report some geniuses still managed full marks in that question

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Reply 2456

Wheeeto

Original post by überambitious_ox

Quick question:

When you are told to identify acid 1, base 1, acid 2 and base 2, how do you know from the LHS of the equilibrium, which to choose as the acid and which as the base?

Each side has an acid and a base as you know, but in the previous information it should tell you if say you had 2 acids on the LHS which one is strong and which one is weak. The strong acid will completely dissociate making it the acid and the weak will partially dissociate making it the base as it will accept a proton. Another method is to see which is the acid or base on the RHS, i.e. NO3- you label it as a base, then look for HNO3 on the LHS and that will be the acid for that pair. Then you can just fill in the other base/ acid pair 2

Reply 2457

DudeBoy

Just to be 100% sure, we don't need to know the transition element colours?

Reply 2458

Namod

Just to be 100% sure, we don't need to know the indicator range and colour change?

Reply 2459

samzurai

Original post by eggfriedrice

Slightly confused about the mark scheme for question 1 d in the June 2012 paper.

I wrote F- ions are more attracted to Mg2+ ions than Na+ ions hence has a greater lattice enthalpy. And Na+ ions are more attracted to F- than Cl-, and hence NaF has a greater lattice enthalpy than NaCl.

Which would explain the pattern in lattice enthalpies.

However, the mark scheme just says F- has greater attraction for Na+ (but surely it'll have greater attraction for Mg2+).
Also Mg2+ has greater attraction for F- ions, however this doesn't explain why MgF2 is the most exothermic :s

Note; I got the two earlier marking points correct so I've already talked about charge density etc.