AQA Chemistry C3 - Unofficial Mark Scheme

That was on our exam too (Unit 3) - with the nine elements - but it wasn't a 6 marker.
We had 'how to carry out a titration' for our 6 marker - which was kinda easy, since they basically gave the answer to us.

Chemical Analysis and Ethanoic Acid
Test tube 1 - effervescence/fizzing as the calcium carbonate reacted the ethanoic acid
Test tube 2 - limewater turns cloudy as calcium carbonate + ethanoic acid -> calcium ethanoate + carbon dioxde. The carbon dioxide makes the limewater cloudy.

Silver nirate in the presence of dilute nitric acid: white precipitate and no change
Barium chloride in the presence of hydrochloric acid: no change and no change

An acid(ic) catalyst is the production of esters

Post your answers below, and we'll get an unofficial mark scheme!

Random answers:
Bond energies: -1276
Explain why: Energy needed making bonds was greater than energy released breaking bonds
Balance equation: 2 and 2 somewhere
Efficiency of Kettle: Hydrogencarbonate ions thermally decompose to carbonate, then react with calcium ions to product a precitipates of calcium carbonate (limescale). Limescale is a bad conductor of electricity - more energy needed to heat water
Hard water cleaner q: Calcium and magnesium ions replaced by sodium and hydrogen ions
Benefits of hard water: contains calcium which strengthens teeth and bones
Element that has low boiling point: F or Rb
What happens in the mixture of gases? Ammonia is liquified, then cooled - Nitrogen and Hydrogen are recycled
Specific heat capacity: 3444J
How is methane obtained: Natural gas
Two boiling tubes: Tube A: fizzing because acid is dissolving calcium carbonate
Tube B: calcium carbonate produced, solution goes cloudy

Yeah, I also had that. Did your paper have a specific heat capacity question? I'm seeing calculations for it however on my paper I don't remember a question asking for specific calculations however to compare the fuel of Methane and Decadane or something (I think).

Specific heat capacity question?

We had a specific heat capacity question (work out energy transferred) and the answer was 3444J.

It asked for the amount of energy released when 0.8g of the alcohol was burned. I found out the amount of energy released by heating up 50g of water. then finding how much energy would be released for each gram of water, then for 01.g of water and then when 0.8g of water was heated

It's flourine, rubidium is solid at room temp flourine is gas at low temp.

For the methane one i put from a bio gas generator aha oh dear

For the energy change I divided 3444 by 0.8 and go 4305? ANYONE ELSE?

For the methane one i put from a bio gas generator aha oh dear

no, if it was one gram of water, you would have 1*4.2*16.4, which is 68.88J, but since it is the heating of 50g of water, then you times this by 50, to get 3444, if they wanted to know how much energy was released by 1 gram of FUEL rather than the 0.8g listed in the question, thenm you wouuld divide by 0.8, but thye didnt ask for this.

So is the final answer ok as 3,444J?


Posted from TSR Mobile

There was also a 6-marker on doing titration reactions. (That wasn't on the unofficial mark scheme). You basically put the steps to carry out the titration:

put alkali in pipette and into conical flask
acid in burette
phenolphthalein or methyl orange indicator in conical flask
add acid slowly until it starts to change colour
add drop by drop until it goes from purple to colourless (phenolphthalein)
do the same for acid B
repeat until you have concordant results
use formulas to work out concentration (like moles = [concentration x volume] / 1000 and concentration = [moles x 1000] / volume)

I'm praying that we've done the different papers and that I haven't missed out a complete question...

how many marks do you think I would lose if I put the acid in the pipette and alkali in the burette?

WOW! How could you remember all that?!
I put the exact same for the SHC question but lots of people are saying that you have to use 50g instead of 0.8g...