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AQA GCSE Chemistry C2/C3 May 15th 2014

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Reply 40
Avatar for kkomde
kkomde
Original post by chronicmusic
I will use silver chloride as an example. Silver chloride is insoluble. You need a soluble silver salt and a soluble chloride salt to make it. Silver nitrate and sodium chloride are both soluble. When you mix their solutions together, you make soluble sodium nitrate and insoluble silver chloride:

•

silver nitrate + sodium chloride → sodium nitrate + silver chloride

•

AgNO3(aq) + NaCl(aq) → NaNO3(aq) +AgCl(s)


The silver chloride appears as tiny particles suspended in the reaction mixture - it forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven.
Remember: if you want to make an insoluble salt XY, mixing X nitrate with sodium Y will always work. In the example above, X is silver and Y is chloride.


I understand it completely now. Thank you! But would I be expected to know if the salt is insoluble, or would they state it in the exam? Would I need to memorise the symbol equations too?
Original post by kkomde
I understand it completely now. Thank you! But would I be expected to know if the salt is insoluble, or would they state it in the exam? Would I need to memorise the symbol equations too?


That's great! I don't think you would need to know either of those because they should give you both in the exam.
Original post by chronicmusic
Yeah alkali is all you need for q1, for q2, although you are not wrong, specifically I was asking for the property changes to ammonia so you could say something like it is cooled until it liquefies - but good job anyway :smile:


Do you want to do some questions?
Original post by chronicmusic
That's great! I don't think you would need to know either of those because they should give you both in the exam.


Describe the structure and bonding in a thermosoftening polymer and explain why thermosoftening polymers melt when heated. (4 marks)
Reply 44
Avatar for izzy610
izzy610
1
Does anyone know whether we have to memorise all the equations for the exam or will we be given the equations on the data sheet??
the particles gain more energy! and so thats why they collide more frequently resulting in successful collisions. the faster the reaction.
Original post by Kevin Paul Beale
Describe the structure and bonding in a thermosoftening polymer and explain why thermosoftening polymers melt when heated. (4 marks)


Thermosoftening polymers have weak intermolecular forces, are malleable and have weak bonds. They melt when heated because the weak intermolecular forces between the polymer chains can be overcome easily.

My question:

What is a hydrogen fuel cell? [3 marks]
Original post by kkomde
I understand it completely now. Thank you! But would I be expected to know if the salt is insoluble, or would they state it in the exam? Would I need to memorise the symbol equations too?

no dont memorise the equation all u need to know is the state symbols and tada u dun!
and u get the data sheet so dont need memorise symbols
(edited 9 years ago)
Original post by kkomde
Can someone please explain to me how to make insoluble salts? I tried CGP and my-gcsescience but I still can't understand. :confused:

By mixing together two solutions of soluble salts :smile:
Original post by chronicmusic
Thermosoftening polymers have weak intermolecular forces, are malleable and have weak bonds. They melt when heated because the weak intermolecular forces between the polymer chains can be overcome easily.

My question:

What is a hydrogen fuel cell? [3 marks]

can answer this?
well....
a hydrogen fuel cell is a cell supplied with a fuel in this case which is hydrogen and oxygen and they react to produce energy this energy is used to generate electricity.
is that it or do i need more info?
oh i forgot to give a question.

on an energy level diagram describe how you would know if its an exothermic reaction or and endothermic reaction?
Original post by famzyjaanxx
can answer this?
well....
a hydrogen fuel cell is a cell supplied with a fuel in this case which is hydrogen and oxygen and they react to produce energy this energy is used to generate electricity.
is that it or do i need more info?


A good start, but to ensure 3 marks:
A hydrogen fuel cell is made from an anode and a cathode with an electrolyte contained between them. The fuel cell generates electricity. It is not the same as an electrolysis cell which needs to be supplied with electricity.

The formula is
hydrogen + oxygen --> water + energy
2H2(g) + O2(g) ---> 2H2O(l)
Original post by famzyjaanxx
oh i forgot to give a question.

on an energy level diagram describe how you would know if its an exothermic reaction or and endothermic reaction?


Exothermic - Reactants have more energy than products

Endothermic - Reactants have less energy than products

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Original post by chronicmusic
A good start, but to ensure 3 marks:
A hydrogen fuel cell is made from an anode and a cathode with an electrolyte contained between them. The fuel cell generates electricity. It is not the same as an electrolysis cell which needs to be supplied with electricity.

The formula is
hydrogen + oxygen --> water + energy
2H2(g) + O2(g) ---> 2H2O(l)


thank you i never knew that the hydrogen fuel cell is made from amode and cathode.
next question!
how does electroplating work?
Original post by chronicmusic
Thermosoftening polymers have weak intermolecular forces, are malleable and have weak bonds. They melt when heated because the weak intermolecular forces between the polymer chains can be overcome easily.

My question:

What is a hydrogen fuel cell? [3 marks]


Can be used in cars
Chemical reaction takes place which creates electricity, heat energy and water.
The electricity is used to power the car.
Original post by famzyjaanxx
oh i forgot to give a question.

on an energy level diagram describe how you would know if its an exothermic reaction or and endothermic reaction?


If the products line is lower than the reactants line (the energy of the products is lower than the energy of the reactants), the reaction is exothermic. It's the opposite for endothermic.

My question:

When do reversible reactions occur?
Original post by chronicmusic
If the products line is lower than the reactants line (the energy of the products is lower than the energy of the reactants), the reaction is exothermic. It's the opposite for endothermic.

My question:

When do reversible reactions occur?


do you mean when they at equilibrium?
if a reversible reaction is happening in a closed system and reaches a equilibrium then the rate of forward reaction is the exact same rate as the backward reaction
Original post by chronicmusic
If the products line is lower than the reactants line (the energy of the products is lower than the energy of the reactants), the reaction is exothermic. It's the opposite for endothermic.

My question:

When do reversible reactions occur?


When the products of a reaction are able to either split up or react to create the original reactants.
Original post by chronicmusic
A good start, but to ensure 3 marks:
A hydrogen fuel cell is made from an anode and a cathode with an electrolyte contained between them. The fuel cell generates electricity. It is not the same as an electrolysis cell which needs to be supplied with electricity.

The formula is
hydrogen + oxygen --> water + energy
2H2(g) + O2(g) ---> 2H2O(l)



Describe the process of making ammonia. (4 marks)

Why do the scientists choose not to use the pressure that produces the highest rate of reaction? (2 marks)
Original post by famzyjaanxx
do you mean when they at equilibrium?
if a reversible reaction is happening in a closed system and reaches a equilibrium then the rate of forward reaction is the exact same rate as the backward reaction


Reversible reactions occur when the backwards reaction (products --> reactants) takes place relatively easily under certain conditions. The products turn back into the reactants

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