Aqa chem 4/ chem 5 june 2016 thread

Hmmm I see
Does it have anything on the right hand side like "allow just 1 OH-"
Because tbh I've learned just 1 OH in excess and that's what all the books say so I'm gonna stick with that.
Also I guess as long as there's as increase in OH-'s I'm sure they'll mark it correct as it's still an excess

Posted from TSR Mobile

It allows 4OH- but generally speaking when they say something is in excess it means the reaction goes to completion (i.e. All the waters are substituted out for hydroxide ions)

Reply 2221

ahsan_ijaz

4

Hi,

A sample of solid chromium(III) hydroxide displays amphoteric character when treatedseparately with dilute hydrochloric acid and with dilute aqueous sodium hydroxide.Write an ionic equation for each of these reactions. Include the formula of eachcomplex ion formed.Describe the changes that you would observe in each reaction

I lost the two marks as it wanted the ionic equations? i really can't do them any one help urgently pleasE??

Reply 2222

GO97

8

Original post by Boundless_x

Now that I think about it... That was probably the main reason why I struggled too since June 2012 is the one I started off with :tongue:

I only got 70 in that paper but the ones I did after that I got into the 80s, thank god. 2015 paper was really good, hope tomorrow will be the same *prays*

aqa eats hopes and prayers for breakfast.

Reply 2223

Suits101

2

Original post by Humza Ali

guys, how do you figure out which the positive/negative electrode is?

Positive electrode = cathode = where reduction happens

Negative electrode = anode = where oxidation happens

Original post by Sexybadman

Btw guys when calculating emf is it always the reduced one minus the oxidised one ?

Posted from TSR Mobile

Whichever gives you a positive answer, but yes.

Reply 2224

Hopefulmedic15

13

[QUOTE="Ali;65999155" Humza="Humza"]

Original post by Sexybadman

Does anyone no the link between decreasing and increasing temperature on delta s or g ? In one paper it says decreasing temp makes delta g negative but then another says increasing temp delta g becomes negative. I could be way off with these statements. If anyone could simplify this id appreciate it ! :smile:

increasing the temp makes T#S bigger therefore it makes #G smaller

#G = #H -T#S
Posted from TSR Mobile

This isn't correct.

It all depends on whether delta H and delta S are positive or negative.

If #H is negative and #S is positive then #G is always negative

If #H is positive and #S is negative then #G is always positive

If #H is negative and #S is negative then the reaction is only feasible (#G is less than or equal to 0) at low temperatures

If #H is positive and #S is positive then the reaction is only feasible (#G is less than or equal to 0) at high temperatures

Also as temperature increases molecules gain kinetic energy so they move/vibrate more and so have an increase of disorder hence an increase in entropy

(edited 7 years ago)

Reply 2225

Boundless_x

16

Guys if something is insoluble e.g. Mg(OH)2 does it mean that ph will not be affected?

Reply 2226

kieton123

1

I hate AQA. Why have they been so evil this year for chemistry? Piss*s me off.

Reply 2227

Suits101

2

Original post by Boundless_x

Guys if something is insoluble e.g. Mg(OH)2 does it mean that ph will not be affected?

It means pH wouldn't be as high as something that is soluble. Hence Mg(OH)2 has a pH of 10 and NaOH has a pH of 14

Reply 2228

kieton123

1

Original post by Boundless_x

Guys if something is insoluble e.g. Mg(OH)2 does it mean that ph will not be affected?

Sparingly soluble bro. pH= 9 for Mg(OH)2

Reply 2229

Cakey_101

7

GUYS ANY TIPS ON HOW TO DO BORN-HABER CYCLES??
I always seem to get them wrong! Any tips?

Reply 2230

Sexybadman

17

[QUOTE="Hopefulmedic15;65999407"]

Original post by Humza Ali

This isn't correct.

It all depends on whether delta H and delta S are positive or negative.

If #H is negative and #S is positive then #G is always negative

If #H is positive and #S is negative then #G is always positive

If #H is negative and #S is negative then the reaction is only feasible (#G is less than or equal to 0) at low temperatures

If #H is positive and #S is positive then the reaction is only feasible (#G is less than or equal to 0) at high temperatures

Also as temperature increases molecules gain kinetic energy so they move/vibrate more and so have an increase of disorder hence an increase in entropy