AQA A-level Chemistry 7405 - Paper 1 (Inorganic & Physical Chem) - 04th June 2019

has anyone got exampro

Does anyone have the links to the specimen set 2 papers and mark schemes (paper 1, 2 and 3)?

Can someone help, I got the first couple steps, but then they divided by three, and I don't really understand

The complex has 3 C2O42- ions. You need to find just one so you divide by 3

how?

So they tell you that the total pressure was 150 kPa.
The mole fraction of NH3 is 0.80 so if you do 0.80 multiplied by 150 you get a partial pressure of 120kPa for nitrogen.
There are still 30 kPa left unaccounted for, and they tell you that the ratio is 1:3. So you divide 30 by 4 (because there are 4 parts in total, 1+3=4) and then you get an answer of 7.5 kPa. This the partial pressure of nitrogen. To get hydrogen you do 7.5 times 3 (because 1:3 ratio) and you get 22.5 kPa for hydrogen.
Hope it helps

i found the question paper, it says (1.01 x 10^5) in the question not (1.01 x 105)

https://www.thestudentroom.co.uk/showthread.php?t=914063&page=2

the same question was asked in this thread.
this is the worked solution from this thread

n = mass / Mr = (1000 x 10^3) / (28 + 16 + 16) = 16666.67 mol

pV = nRT

V = nRT / p = (16666.67 x 8.31 x 298) / (1.01 x 10^5) = 408m3

hope this helps

Can someone help, I got the first couple steps, but then they divided by three, and I don't really understand

do we need to know about fragmentation of molecular ions in mass spectrometers? like the equation for fragmentation

A student added 627 mg of hydrated sodium carbonate (Na2CO3.xH2O) to 200 cm3 of
0.250 mol dm–3 hydrochloric acid in a beaker and stirred the mixture.
After the reaction was complete, the resulting solution was transferred to a volumetric
flask, made up to 250 cm3 with deionised water and mixed thoroughly.
Several 25.0 cm3 portions of the resulting solution were titrated with 0.150 mol dm–3
aqueous sodium hydroxide. The mean titre was 26.60 cm3 of aqueous sodium
hydroxide.
Calculate the value of x in Na2CO3.xH2O
Show your working.
Give your answer as an integer.


I get how to do the question, but why is the 25cm^3 scaled up to 250 and not 200? because there was originally 200cm^3 of HCl, not 250. and the reaction happened with 200.

Anyone understand part b? I did it but got 3cm3, the right answer is 4cm3.