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ocr a f325 revision thread

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Original post by MathsNerd1


Give 3 properties of transition elements apart from forming coloured compounds (3)
Original post by otrivine
Give 3 properties of transition elements apart from forming coloured compounds (3)


They are all metals so are shiny in appearance and have high densities and high melting and boiling points. They have variable oxidation states. They are able to conduct electricity.


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Original post by MathsNerd1
They are all metals so are shiny in appearance and have high densities and high melting and boiling points. They have variable oxidation states. They are able to conduct electricity.


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I will sadly, have to award you 0 marks , although your answers are correct, in my question I stated 3 and you exceeded 3 so have to penalise you :frown:

my turn
Original post by otrivine
I will sadly, have to award you 0 marks , although your answers are correct, in my question I stated 3 and you exceeded 3 so have to penalise you :frown:

my turn


Surely they wouldn't be allowed to do that in the exam?

What are the 3 main types of electrochemical cells? (3)


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Original post by MathsNerd1
Surely they wouldn't be allowed to do that in the exam?

What are the 3 main types of electrochemical cells? (3)


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Do they penalise you? cause I read an examiner report and they said they would ignore the answer?


1) non rechangeable cell
2) rechargeable cell
3) fuel cells
Original post by otrivine
Do they penalise you? cause I read an examiner report and they said they would ignore the answer?


1) non rechangeable cell
2) rechargeable cell
3) fuel cells


Oh, but you're showing you know more than what they want which surely couldn't be a bad thing? Oh well and that's correct


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Original post by MathsNerd1
Oh, but you're showing you know more than what they want which surely couldn't be a bad thing? Oh well and that's correct


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Ok, ill give you a benefit of doubt because I am generous today from the sunshine,:biggrin:

thanks

Define:coordination number
Original post by otrivine
Ok, ill give you a benefit of doubt because I am generous today from the sunshine,:biggrin:

thanks

Define:coordination number


Oh no, if its not allowed then be as harsh as they would be otherwise it'll be pointless really.

A coordinate number is the total number of coordinate bonds (dative covalent) formed between the central metal ion and its ligands.


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Original post by MathsNerd1
Oh no, if its not allowed then be as harsh as they would be otherwise it'll be pointless really.

A coordinate number is the total number of coordinate bonds (dative covalent) formed between the central metal ion and its ligands.


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Perfect!

my turn
Original post by otrivine
Perfect!

my turn


Explain how the ionic size and charge effects the lattice enthalpy (3)


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Original post by MathsNerd1
Explain how the ionic size and charge effects the lattice enthalpy (3)


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If the ionic sizes of the two (or more) ions are small then the ions pack more closely together and will result in a strong electrostatic attaction between oppositely charged ions and hence, more energy will be needed to break or sepeate the attractive forces between the ions, so more exothermic.

Higher charge density the more exothermic the reaction will be as there is a strong attraction between the ions and more energy needed to break/separate forces.
Original post by otrivine
If the ionic sizes of the two (or more) ions are small then the ions pack more closely together and will result in a strong electrostatic attaction between oppositely charged ions and hence, more energy will be needed to break or sepeate the attractive forces between the ions, so more exothermic.

Higher charge density the more exothermic the reaction will be as there is a strong attraction between the ions and more energy needed to break/separate forces.


Correct


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Original post by MathsNerd1


are you being a harsh marker?


What is the colour of Mn2+(aq)
Original post by otrivine
are you being a harsh marker?


What is the colour of Mn2+(aq)


I've been checking back to the book just to be certain, so I'm marking it fairly and it's pale pink but whenever I do experiments it's always appearing colourless, in solution.


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Original post by MathsNerd1
I've been checking back to the book just to be certain, so I'm marking it fairly and it's pale pink but whenever I do experiments it's always appearing colourless, in solution.


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perfect, well done you really are doing well with extra details :biggrin:

my turn
Original post by otrivine
perfect, well done you really are doing well with extra details :biggrin:

my turn


Okay, explain what types of indicators do we need to know about, what is the starting, ending and change colours and which indicators would you use in these cases. 1) strong base strong acid 2) weak base strong acid 3) weak acid strong base and finally 4) weak base and weak acid. (6)


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Original post by MathsNerd1
Okay, explain what types of indicators do we need to know about, what is the starting, ending and change colours and which indicators would you use in these cases. 1) strong base strong acid 2) weak base strong acid 3) weak acid strong base and finally 4) weak base and weak acid. (6)


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1) strong acid strong base
use methyl orange and phenolphatelin
starting orange, colourless, pink

2) strong acid , weak base

use methyorange
colour changes from colourless to orange

3) strong base, weak acid
pheolphtalien
colourless to pink

4) weak acid, weak base
no indicators used because there is no equivalence point and so PH range does not match vertical section of graph in titration curve
Original post by otrivine
1) strong acid strong base
use methyl orange and phenolphatelin
starting orange, colourless, pink

2) strong acid , weak base

use methyorange
colour changes from colourless to orange

3) strong base, weak acid
pheolphtalien
colourless to pink

4) weak acid, weak base
no indicators used because there is no equivalence point and so PH range does not match vertical section of graph in titration curve


That's all correct although for methyl orange I wouldn't say it goes from colourless to orange but red to orange and then going to yellow in the basic conditions, I don't think I explained it very well, sorry :-/


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Original post by MathsNerd1
That's all correct although for methyl orange I wouldn't say it goes from colourless to orange but red to orange and then going to yellow in the basic conditions, I don't think I explained it very well, sorry :-/


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so for strong acid -strong base

can you tell me the colour changes again please?

why is water ligands repel less than chloride ligands(1)
Original post by otrivine
so for strong acid -strong base

can you tell me the colour changes again please?

why is water ligands repel less than chloride ligands(1)


You got them all correct, I was just asking for phenolphthalein the acidic colour, neutral colour and basic colour, same for methyl orange but you got all the actual combinations correct and such.

Does it have to do with the fact chlorine is more electronegativity than either hydrogen or oxygen so will have a greater charge causing more repelling?


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