Chemistry F325 - 22nd January 2013

Original post by reneetaylor

What is meant by the term sublimination? (Not enthalphy change, the actual meaning)
What is the definition for half life?
Kw is equal to...?
What is equivalance?
In a buffered solution the acid must be in _____?
How to calculate pH
Who is Kevin Bacon? ( Just kidding..)

1) sublimation is where solid turns straight to gas or from gas to solid
2)half life= is the time taken for the concentration of reactant to reduce by half
3) Kw is equal to ionic product of water ( the number of dissociation of water molecules)
4) is a point in a titration where there is the same volume of one solution is used and a second solution is used where the volume is the same as well.
5) aqueous
6) PH=-log(H+)

Reply 82

Original post by otrivine

1) sublimation is where solid turns straight to gas or from gas to solid
2)half life= is the time taken for the concentration of reactant to reduce by half
3) Kw is equal to ionic product of water ( the number of dissociation of water molecules)
4) is a point in a titration where there is the same volume of one solution is used and a second solution is used where the volume is the same as well.
5) aqueous
6) PH=-log(H+)

For five I meant excess, but I know I worded it wrong, so that's my fault!
You'reeeeee gooooooood! :biggrin:

Too good, you sure you're not looking at the book? Keep it up dude, i wish you every best of luck for the exam! :smile:

Reply 83

Original post by reneetaylor

For five I meant excess, but I know I worded it wrong, so that's my fault!
You'reeeeee gooooooood! :biggrin:

Too good, you sure you're not looking at the book? Keep it up dude, i wish you every best of luck for the exam! :smile:

Nope i am not there is no point to look in the book

thank you wait so if it is an excess is it more water molecules will dissociate and increases the concentration of both H+ and OH- ions

is it ok if you can give me one last A* question please

Reply 84

Rubbaduckzilla

10

im doing edexcel chemistry and i have my paper on the 14th jan :frown:

Reply 85

Man-Utd

Original post by otrivine

1) it would increase by 4
2) it would decrease by 0.25
3) it would increase by 16

I'm applying for pharmacy

Soz but first one is It'll increase by 2
It would decrease by 4
It would increase 64 times (4) x (4)2 = 64

:smile:

Reply 86

Original post by Man-Utd

Soz but first one is It'll increase by 2
It would decrease by 4
It would increase 64 times (4) x (4)2 = 64

:smile:

(H+) is first order
(Br- ) is 2nd order

How does doubling the concentration of H+ affect the rate ?
How does halving the concentration of Br- affect the rate?

What if both Br- and H+ were doubled ?

for the last bit dont you do (2) times 2 power 2 to give 4 x 2 =8?

Reply 87

D4rth

9

Quick question guys on Equilibrium moles. Lets say this is the equation:

A + B → C + D
Start moles:
A = 1
B = 2
C = 0
D = 5

Work out Equilibrium Moles.
A = ?
B = ?
C = 0.46
D = ?

I know how to work out A and B, it's just simple just (1-0.46) and (2-0.46)
but no teacher has ever explained how to work out the =m moles of the second product if there is one, and especially if it has start moles.

I've been taught that the equlibrium moles for the products will be the same but what do you do if it has start moles, will it be (5-0.46) or will it just be 0.46?

Thanks!

Reply 88

Original post by otrivine

Nope i am not there is no point to look in the book

thank you wait so if it is an excess is it more water molecules will dissociate and increases the concentration of both H+ and OH- ions

is it ok if you can give me one last A* question please

I knowwww, you're already smarticles.

In terms of an acidic buffer solution, the acid would need to be in excess for the base to completely neutralise the solution, so in other words there needs to be a sufficient number of moles of the weak acid to completely neutralise the strong base, therefore it is in excess. ( I should have noted I was talking about a acidic buffer solution)

Errm more questions? :biggrin:

You ask me some first.

Reply 89

Original post by reneetaylor

I knowwww, you're already smarticles.

In terms of an acidic buffer solution, the acid would need to be in excess for the base to completely neutralise the solution, so in other words there needs to be a sufficient number of moles of the weak acid to completely neutralise the strong base, therefore it is in excess. ( I should have noted I was talking about a acidic buffer solution)

Errm more questions? :biggrin:

You ask me some first.

ok

but wait in the definition it only stated small not excess?

What is lattice enthalpy and suggest which of magnesium chloride or magenisum fluoride is more exothermic and give reasons (6 marks)

Reply 90

Original post by D4rth

Quick question guys on Equilibrium moles. Lets say this is the equation:

A + B → C + D
Start moles:
A = 1
B = 2
C = 0
D = 5

Work out Equilibrium Moles.
A = ?
B = ?
C = 0.46
D = ?

I know how to work out A and B, it's just simple just (1-0.46) and (2-0.46)
but no teacher has ever explained how to work out the =m moles of the second product if there is one, and especially if it has start moles.

I've been taught that the equlibrium moles for the products will be the same but what do you do if it has start moles, will it be (5-0.46) or will it just be 0.46?

Thanks!

You'd have to add on 0.46 to 5...I think...

If so, it should be.

5.46 = D

Reply 91

Original post by otrivine

ok

but wait in the definition it only stated small not excess?

What is lattice enthalpy and suggest which of magnesium chloride or magenisum fluoride is more exothermic and give reasons (6 marks)

I know, but I believe it helps with extra understanding of buffer solutions :smile:

, It's up to you!

Lattice enthalpy is the enthalpy change that accompanies the formation of one mole of an ionic compound from it's gaseous ions under stand cond.

Magnesium flouride is more exothermic because of :
-Charge density, a flouride molecule is smaller than a chloride molecule, therefore there is a higher concentration of charge within the flouride molecule
-When this molecule is hydrated, it releases more energy ( therefore more exothermic)

I don't think that's enough for 6 marks...could you tell me some more points? :smile:

Reply 92

Original post by reneetaylor

I know, but I believe it helps with extra understanding of buffer solutions :smile:

, It's up to you!

Lattice enthalpy is the enthalpy change that accompanies the formation of one mole of an ionic compound from it's gaseous ions under stand cond.

Magnesium flouride is more exothermic because of :
-Charge density, a flouride molecule is smaller than a chloride molecule, therefore there is a higher concentration of charge within the flouride molecule
-When this molecule is hydrated, it releases more energy ( therefore more exothermic)

I don't think that's enough for 6 marks...could you tell me some more points? :smile:

2 marks for definition but lost 1 mark for not stating the standard conditions.
correct
ok you would lose some marks here, you needed to mention higher charge density , and this is from the book Examiner tip= do not mention molecules or atoms always need to state IONS!! rememeber :smile:

No marks for the last bit,

The clear answer for the last 3 marks are
Magnesium ion has a higher charge density , fluoride ion has a smaller atomic radius and therefore there will be a stronger electrostatic attraction between the Mg2+ ion and F- ion and more energy is required to break/separate the bond

Reply 93

Original post by otrivine

2 marks for definition but lost 1 mark for not stating the standard conditions.
correct
ok you would lose some marks here, you needed to mention higher charge density , and this is from the book Examiner tip= do not mention molecules or atoms always need to state IONS!! rememeber :smile:

No marks for the last bit,

The clear answer for the last 3 marks are
Magnesium ion has a higher charge density , fluoride ion has a smaller atomic radius and therefore there will be a stronger electrostatic attraction between the Mg2+ ion and F- ion and more energy is required to break/separate the bond

Thanks so much! We just started this in class today, and I've yet to go over it :biggrin:

You've helped a lot,
Whereabouts are you now in terms of topics?

More questions ^_^

1) Characteristics of a strong acid-weak base titration curve?
2) What does a high pH indicate in terms of H+ concentration?
3) What does a rate equation tell you about a rate determining step?

Reply 94

Original post by reneetaylor

Thanks so much! We just started this in class today, and I've yet to go over it :biggrin:

You've helped a lot,
Whereabouts are you now in terms of topics?

More questions ^_^

1) Characteristics of a strong acid-weak base titration curve?
2) What does a high pH indicate in terms of H+ concentration?
3) What does a rate equation tell you about a rate determining step?

im self studying this unit i just started on transition metals

1) the PH will start from 1 and then there should be a steep at 25cm^3 which from that steep you it would show what indicator to use in this cause because it is strong acid you can use bromothymol blue but no phenolphatelin is needed and then it should level off at PH 9

2) High PH tells that the concentration of H+ is less
3) the rate equation tells you the number of moles present in the equation for example (NO2)^2 means that there should be 2 moles of NO2 so NO2+NO2

Reply 95

Original post by otrivine

im self studying this unit i just started on transition metals

1) the PH will start from 1 and then there should be a steep at 25cm^3 which from that steep you it would show what indicator to use in this cause because it is strong acid you can use bromothymol blue but no phenolphatelin is needed and then it should level off at PH 9

2) High PH tells that the concentration of H+ is less
3) the rate equation tells you the number of moles present in the equation for example (NO2)^2 means that there should be 2 moles of NO2 so NO2+NO2

Woah, cool!

All good, for 1) you could just say strong acid- weak base buffers have a pH lower than 2, equivalence below 7, and end point below 12 :smile:

(edited 11 years ago)

Reply 96

Original post by reneetaylor

Woah, cool!

All good, for 1) you could just say strong acid- weak base buffers have a pH lower than 2, equivalence below 7, and end point below 12 :smile:

thanks

would my explanation for 1 get no marks ? i think i should have used equivalence thanks
ok
Define entropy (1) , and is there a relationship between free energy and entropy when calculating the minimum temperature (2)

Reply 97