AQA GCSE Chemistry - C2 & C3 (14th May 2015)

I've been revising these all day so hopefully this is right!

Making salts from acid + metal or insoluble base
1. Add the metal/metal oxide/metal hydroxide to the acid
2. The reaction will have finished when the excess solid sinks to the bottom of the conical flask.
3. Filter out the excess metal/metal oxide/metal hydroxide and you will have the salt solution left.
4. Evaporate some of the water to concentrate the solution.
5. Leave the rest to evaporate slowly. This is known as crystallisation.

I've got to go but if no one else does the rest, I'll explain later

Thanks. But do you not heat the first one you posted to start the crystallisation?

An electrostatic force is the force of attraction in all directions between oppositely charged ions in an ionic compound like NaCl. (This is what holds the ions in a regular structure, hence ionic substances have high mp and bp, and tend to be of regular shape.)

Intermolecular forces are forces of attraction between molecules in a substance (not found in ionic compounds). These are usually found in substances which have covalent bonds holding atoms together in molecules, but the intermolecular forces hold the MOLECULES together.

Thanks a lot

Do you mind me asking where you found this method? I can't seem to find it anywhere in my revision book

OMG your a life saver! Thank you so much!!!!! I think I know how to do calculations I just struggle on the actual writing up a Titration Calculation (in a 6 marker)

Oh okay, that's come up recently if I'm not mistaken so I wouldn't worry too much, but I'll explain anyway!

1. Use a pipette to add (e.g 250cm^3) of the solution of known concentration into conical flask. A conical flask is used to reduce risk of spillage when swirling.

2. Add indicator (phenolphthalein or methyl orange, but I don't think you need to know this) to the conical flask, and place on a white tile so that a colour change can be easily observed when neutralisation occurs.

3. Fill the burette with the other solution, which you don't know the volume of. Clamp burette above flask.

4. Dispense the solution in the burette into the flask, dropwise (particularly near neutralisation).

5. When a colour change is observed, record the volume of the substance in the burette that was required for neutralisation.

6. Repeat the whole thing for more readings to find a mean average. Ensure the same person judges colour change as result can be subjective.

I think that's everything!

Just to add: you need to use phenolphthalein or methyl orange so that the colour changes instantly so you know exactly when neutralisation has occurred (universal indicator would change colour too slowly) and also when you're adding drops into the flask from the burette make sure to say that you swirl the flask at the same time to make sure it's all mixed in!

Good luck tomorrow everyone!

Just to add: you need to use phenolphthalein or methyl orange so that the colour changes instantly so you know exactly when neutralisation has occurred (universal indicator would change colour too slowly) and also when you're adding drops into the flask from the burette make sure to say that you swirl the flask at the same time to make sure it's all mixed in!

Good luck tomorrow everyone!

For the other two:

Making soluble salt from acid + alkali

1. Add indicator to acid
2. Add alkali until indicator changes colour and record how much alkali was used
3. Repeat this using exactly same volumes of alkali and acid but without the indicator so that the salt isn't contaminated
4. Then evaporate the water to concetrate the solution
5. Leave the rest to evaporate slowly (crystallisation)

Making insoluble salt - Precipitation reaction

1. Mix two solutions containing ions you need (i.e. for lead chloride you could mix lead nitrate solution and sodium chloride solution)
2. Once precipitation has occurred (it will leave a solid), you just filter the solution
3. Wash and dry precipitate on filter paper

If anyone has any corrections for those please tell me cause I find this stuff really hard to remember!

best method for doing titration calculations?

Thank you. So for clarification, this works as long as the moles reacted are equal and all you have to do is divide or multiply this answer (depending on the balanced equation - mole ratio) to get the final answer?

please can someone simplify exactly what I have to learn for Acids, Bases & Salts because I'm really really struggling

I used my CGP guide, I can send you a picture of the page if you want?

Guys can Equilibrium come up on C2 or is that old spec?

I used my CGP guide, I can send you a picture of the page if you want?