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ocr a f325 revision thread

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IQ Test
17
Original post by otrivine
Want to revise with me and MathsNerd:biggrin:

Sounds like a plan!
Original post by IQ Test
Sounds like a plan!


Describe how you would carry out an experiment in order to determine if the reaction is first order for rate aganist concentration (4)
Original post by IQ Test
Sounds like a plan!


Can I ask you one too? Or would it be too many people asking questions at the same time? If its fine then:

Explain the effects of ionic size and ionic charge on the size of lattice enthalpy. (4)


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Original post by mathsnerd1
okay, identify the acid base pairs in the acid base equilibria:
Ch3cooh + h2o ------> ch3coo- + h3o+
acid 1 base 1 base 2 acid 2
ch3cooh + hcl ---> ch3cooh2- + cl-
base 2 acid 1 acid 2 base 2
write the full and ionic equations for the following acid-base reactions:
Hydrochloric acid and solid calcium carbonate
nitric acid and magnesium oxide
ethanoic acid and aqueous calcium hydroxide (7)


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for the labelling of acid and base see, i quoted

2hcl + caco3 ---> cacl2 + co2 + h2o
ionic = 2h+ + co3 2- ---> co2 + h2o

2hno3 + mgo --> mg(no3)2 + h2o
ionic = 2h+ + o2- --> h2o

2ch3cooh + ca(oh)2 ---> (ch3coo)2ca + 2h2o

ionic = 2h+ + o2- ---> h2o
Original post by MathsNerd1
Can I ask you one too? Or would it be too many people asking questions at the same time? If its fine then:

Explain the effects of ionic size and ionic charge on the size of lattice enthalpy. (4)


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Greater the charge density results in a stronger attraction between ions and so hence more energy needed to sepeate ions. Greater ionic size the smaller the lattice enthalpy as ion is large and hence less electrostatic attraction between ion and less energy needed to separate bonds and value of lattice enthalpy decreases.
Original post by otrivine
for the labelling of acid and base see, i quoted

2hcl + caco3 ---> cacl2 + co2 + h2o
ionic = 2h+ + co3 2- ---> co2 + h2o

2hno3 + mgo --> mg(no3)2 + h2o
ionic = 2h+ + o2- --> h2o

2ch3cooh + ca(oh)2 ---> (ch3coo)2ca + 2h2o

ionic = 2h+ + o2- ---> h2o


Okay that was all correct although I'm not sure your ionic equations are correct.
The first should be 2H+ + CaCO3 --> CaCl2 + CO2 + H2O
The second being:
2H+ + MgO --> Mg2+ + H2O
The last being:
H+ + OH- ---> H2O

Other than those you were completely correct. :smile:


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Original post by otrivine
Greater the charge density results in a stronger attraction between ions and so hence more energy needed to sepeate ions. Greater ionic size the smaller the lattice enthalpy as ion is large and hence less electrostatic attraction between ion and less energy needed to separate bonds and value of lattice enthalpy decreases.


That's correct!


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Reply 147
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H0ls
18
Anyone know of any decent websites online for our chemistry syllabus? I've been using the textbook but it's not been too much help. Thanks.
Original post by MathsNerd1
Okay that was all correct although I'm not sure your ionic equations are correct.
The first should be 2H+ + CaCO3 --> CaCl2 + CO2 + H2O
The second being:
2H+ + MgO --> Mg2+ + H2O
The last being:
H+ + OH- ---> H2O

Other than those you were completely correct. :smile:


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For the second one you did not mention that magnesium oxide was solid, I thought aqueous? In the first one you mentioned it?
Original post by MathsNerd1
That's correct!


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State Hess Law (2)


Why is it difficult in measure the lattice enthalpy directly (2)
Original post by otrivine
For the second one you did not mention that magnesium oxide was solid, I thought aqueous? In the first one you mentioned it?


Oh well that's because it wasn't mentioned in the question at all, sorry for the confusion though.


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Original post by MathsNerd1
Oh well that's because it wasn't mentioned in the question at all, sorry for the confusion though.


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I see , that was sneaky from the question, have to watch out :colone:
Original post by otrivine
State Hess Law (2)


Why is it difficult in measure the lattice enthalpy directly (2)


Hess' law states that if a reaction can take place by more than one route and the initial and final conditions are the same then the total enthalpy change is the same for each route taken.

They can't be measured directly as its impossible to form one mole of an ionic lattice from gaseous ions.


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Original post by otrivine
I see , that was sneaky from the question, have to watch out :colone:


Indeed! They always seem to be trying to catch us out in all or most of the questions.


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Original post by MathsNerd1
Hess' law states that if a reaction can take place by more than one route and the initial and final conditions are the same then the total enthalpy change is the same for each route taken.

They can't be measured directly as its impossible to form one mole of an ionic lattice from gaseous ions.


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Yup!Nicely said ! :smile: my turn
Original post by otrivine
Yup!Nicely said ! :smile: my turn


How do you measure a standard electrode potential. (4)


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Original post by MathsNerd1
How do you measure a standard electrode potential. (4)


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Conditions are 298K,100KPA and 1 mol dm-3

Between half cells depends but between metal and metal

there has to be 2 solutions in a beaker with a salt bridge and voltmeter connected between the solution. Salt bridge allows the ions to move from one half cell to the next and the voltmeter measures the electrode potential resistance. Each solution has to be 1 mol dm-3.
If a half cell is compared with hydrogen half cell then in the hydrogen half cell there should be a platinum electrode that allows the transfers of ions and there and there should be 1 mol dm-3 of aqueous HCL(aq)
Original post by otrivine
Conditions are 298K,100KPA and 1 mol dm-3

Between half cells depends but between metal and metal

there has to be 2 solutions in a beaker with a salt bridge and voltmeter connected between the solution. Salt bridge allows the ions to move from one half cell to the next and the voltmeter measures the electrode potential resistance. Each solution has to be 1 mol dm-3.
If a half cell is compared with hydrogen half cell then in the hydrogen half cell there should be a platinum electrode that allows the transfers of ions and there and there should be 1 mol dm-3 of aqueous HCL(aq)


That's correct!


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Original post by MathsNerd1
That's correct!


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Define:colone:ntropy (2)
Original post by otrivine
Define:colone:ntropy (2)


Just a warning, at 9 I'll do some unit 1 stuff again.

Entropy is the quantitative measure of the degree if disorder in a system.


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