ocr a f325 revision thread

Original post by Tobeadoc

Fe 2+ being oxidised to Fe3+. Then O2 is reduced to O2-so overall -4. So then overall:

4Fe2+ +4H+ +O2> 4Fe3+ + 2H2O

yup !

my turn

Reply 542

Original post by otrivine

yup !

my turn

what is a homogenous equilibrium?

Reply 543

Original post by Tobeadoc

what is a homogenous equilibrium?

is an equilibrium in which the species that make up the reactant and products are in the same physical states.

Reply 544

Original post by otrivine

is an equilibrium in which the species that make up the reactant and products are in the same physical states.

correct my turn

Reply 545

Original post by Tobeadoc

correct my turn

Why is it impossible to measure the lattice enthalpy directly (2)

Reply 546

Original post by otrivine

Why is it impossible to measure the lattice enthalpy directly (2)

It would be impossible to react the gaseous ions together, as formation of them and then causing them to react would require too high energies.

Reply 547

Original post by Tobeadoc

It would be impossible to react the gaseous ions together, as formation of them and then causing them to react would require too high energies.

Not quite, no, its because it is impossible to form 1 mole of an ionic compound from its gaseous ions

my turn

Reply 548

Original post by otrivine

Not quite, no, its because it is impossible to form 1 mole of an ionic compound from its gaseous ions

my turn

when is a dynamic equilibrium established?

Reply 549

Original post by Tobeadoc

when is a dynamic equilibrium established?

In a closed system and that the rate of the forward reaction is the same as the rate of the reverse reaction.

There is a constant concentration of both reactants and products

Reply 550

Original post by otrivine

In a closed system and that the rate of the forward reaction is the same as the rate of the reverse reaction.

There is a constant concentration of both reactants and products

correct! my turn

Reply 551

Original post by Tobeadoc

correct! my turn

Artists between the 13th and the 19th Centuries used a green pigment called verdigris. The artists made the pigment by hanging copper foil over boiling vinegar.
During the preparation of verdigris, copper atoms are oxidised to copper(II) ions.

i) Write the oxidation half equation for the conversion of copper atoms into copper(II) ions.

(ii) The reduction half equation that takes place is as follows.
O2(g) + 4H+(aq) + 4e– ---> 2H2O(l)
Construct the equation for the redox reaction between copper, oxygen and hydrogen ions.

Reply 552

Original post by otrivine

Artists between the 13th and the 19th Centuries used a green pigment called verdigris. The artists made the pigment by hanging copper foil over boiling vinegar.
During the preparation of verdigris, copper atoms are oxidised to copper(II) ions.

i) Write the oxidation half equation for the conversion of copper atoms into copper(II) ions.

(ii) The reduction half equation that takes place is as follows.
O2(g) + 4H+(aq) + 4e– ---> 2H2O(l)
Construct the equation for the redox reaction between copper, oxygen and hydrogen ions.

The equation for the oxidation of copper atoms: Cu->Cu2+ + 2e-
O2(g) + 4H+(aq) + 2Cu <~> 2H2O + 2Cu2+

Reply 553

Original post by Tobeadoc

The equation for the oxidation of copper atoms: Cu->Cu2+ + 2e-
O2(g) + 4H+(aq) + 2Cu <~> 2H2O + 2Cu2+

Good

my turn

Reply 554

Original post by otrivine

Good

my turn

Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation? (6)

Reply 555

Original post by Tobeadoc

Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation? (6)

Okay,

Firstly, in order to carry out the experiment, you would need to use a polystrene cup or a bombcalorimeter. Polystrene cup is quick but can lead to unreliable data.
Using a polysterene cup for example you pour the solution into the cup and add any solid to the solution for a reaction to take place, you put a thermometer in the cup in order to detect the temperature. Also, use known concentration of the solution for example could be water, such as add 100cm3 of water. Record the temperature, if temperature is rising the reaction would be exothermic or if reaction is decreasing it would be endothermic. Then calculate the energy in joules that was released during the experiment

formula is energy= 4.18 (specific heat capacity) x volume x temperature change

then you get the answer in joules, always convert into Kj in order to get accurate results.

Then you calculate the number of moles , it could be the solid that you added into the solution, and formula is moles =mass/Molar mass of that substance/compound

then you work out the enthalpy change of neutralisation= energy in Kj divided by the number of moles and this gives the enthalpy change of neutralisation value. Most cases the value is exothermic for neutralsiation.

Reply 556

uttamo

10

The questions in this paper are so nasty. One of my classmates told me she saw a 20-marker! The max you would get previously was like 12 marks but even that was a juicy NMR question that was satisfying.

Edit: reason for negs?

(edited 10 years ago)

Reply 557