AQA Chemistry New AS Unofficial Mark Scheme

Original post by GabbytheGreek_48

i hope but even so ill just expect the worst so i get my stuff together and smash paper 2

Indeed. I am usually better at paper 1, due to the maths, but we'll see. Hopefully you, and I, can smash the paper and get that A :biggrin:

Reply 201

GabbytheGreek_48

11

Original post by britishtf2

Indeed. I am usually better at paper 1, due to the maths, but we'll see. Hopefully you, and I, can smash the paper and get that A :biggrin:

yeah good luck to uuu :biggrin:

Reply 202

SM-

6

What was each part of the titration question and how many marks was each part?

Reply 203

britishtf2

16

Original post by SM-

What was each part of the titration question and how many marks was each part?

Find mean and mol HCl in 25cm^3 [3]
Find Mr of MHCO3 [3]
How could you reduce percentage uncertainty? [2?]

I think that was it - maybe another part. I am not sure.
6 Maker was how to make a standard solution, which may have been part of it.

Reply 204

SM-

6

Original post by britishtf2

Find mean and mol HCl in 25cm^3 [3]
Find Mr of MHCO3 [3]
How could you reduce percentage uncertainty? [2?]

I think that was it - maybe another part. I am not sure.
6 Maker was how to make a standard solution, which may have been part of it.

How could the first part be 3 marks?

Reply 205

britishtf2

16

Original post by SM-

How could the first part be 3 marks?

M1 - Find mean using 2 values "9.65cm^3 and 9.75cm^3" (assuming they want you to only use concordant values) to get 9.70cm^3, or (9.70*10^-3)dm^3

M1 - Use n = cv (Moles = Concentration*Volume), using correct data. E.g. Both in either cm^3 or dm^3

A1 - Correct value for moles, likely with ECF on the mean titre.

Obviously not 100%, but that is my guess.

(edited 7 years ago)

Reply 206

saahil0987

3

Original post by DaVinciGirl

You should have multiplied the energy by 2 then divide by the mass. Then you square root it.

Posted from TSR Mobile

Yeah, I rearranged the equation to be v = sqrt 2KE / m
but I got 12 probably put in the wrong values on my calculators

Reply 207

Namita Gurung

16

What compound has a +2 and -3 ions and has the same number electrons as Argon?
Ca3P2

This. How did you guys know that this was the answer. Can't seem to think how to figure it out :s-smilie:

Reply 208

britishtf2

16

Original post by Namita Gurung

What compound has a +2 and -3 ions and has the same number electrons as Argon?
Ca3P2

This. How did you guys know that this was the answer. Can't seem to think how to figure it out :s-smilie:

A 2+ ion means it has lost 2 electrons. Argon has 18 electrons. So it has 20 electrons when unionised (18+2 which were removed when ionised). Calcium has 20 electrons when unionised, so one element is calcium.

Use the same logic with the 3- ion. 3- means it has gained 3 electrons. So it has 15 electrons when unionised (18-3 electrons which were added). Phosphorus has 15 electrons when unionised, so the other element is Phosphorus.

A neutral charge is required, so therefore it must be Ca3P2.

Hope this helped.

Reply 209

Namita Gurung

16

Original post by britishtf2

A 2+ ion means it has lost 2 electrons. Argon has 18 electrons. So it has 20 electrons when unionised (18+2 which were removed when ionised). Calcium has 20 electrons when unionised, so one element is calcium.

Use the same logic with the 3- ion. 3- means it has gained 3 electrons. So it has 15 electrons when unionised (18-3 electrons which were added). Phosphorus has 15 electrons when unionised, so the other element is Phosphorus.

A neutral charge is required, so therefore it must be Ca3P2.

Hope this helped.

Ahhh. Thank you! Looks Like I was needlessly over-complicating things. Makes a lot of sense now :smile:

Reply 210

britishtf2

16

Original post by Namita Gurung

Ahhh. Thank you! Looks Like I was needlessly over-complicating things. Makes a lot of sense now :smile:

Glad I could help!

Reply 211

Al_YG

5

The answer must have been ClF3 and NOT Bf3.... BF3 is a trigonal planar and if we count the dipoles as a vector quantity the dipoles cancel... in ClF3 there are present lone pairs which cause the molecule to have a pyramidal shape... the charges vector quantities cannot cancel wholly.

Reply 212

Al_YG

5

For the last queston which noone seems to be discussing... it was B

Reply 213

britishtf2

16

Original post by Al_YG

For the last queston which noone seems to be discussing... it was B

With the BF3, you are correct thinking of it.
That question I had 1 second to put something, and I think I put B, which is nice lol.

I despise multi-choice.

Reply 214

Schoolgirl99

1

If I got 50% in this paper and get 100% in the next, do you reckon that I can get an A?

Reply 215

username1924691

2

Original post by Schoolgirl99

If I got 50% in this paper and get 100% in the next, do you reckon that I can get an A?

That averages to 75% and some people said they think the grade boundaries will be around there so hopefully! Good luck :smile:

Reply 216

leksj10

Could you talk about metallic bonding for why Mg2+ had a smaller atomic radius, because it had stronger forces between electrons and nucleus??

Reply 217

abxo

Original post by britishtf2

1.052g total in the solid, from memory. BaSO4 is the ppt as it is insoluble in water. Mass of ppt was something around 0.78, I think. (137.3/233.4) is proportion of Ba in BaSO4. So, (137.3/233.4)*0.78 (or whatever it was) is mass of barium in ppt. This is therefore the mass of the barium in the BaCl2.

I used that to find the mass of the Cl in the BaCl2 using the fact that Cl ion is 1- and Ba ion is 2+. Therefore, you can find that the mass of the BaCl2 is 0.681 (from memory) and from that you can find the proportion of the MgCl2 in the solid at the start.

With this you get 35.5%

Oh **** i found the wrong salt omg 😂😂 i got 65.5% for the other BaCl2 LoOL how many marks do u think i would have dropped? Im saying 2 out of the four because all my numbers were right! Hopefully

Reply 218

britishtf2

16

Original post by Schoolgirl99

If I got 50% in this paper and get 100% in the next, do you reckon that I can get an A?

It depends on each of the grade boundaries for the papers. If you get 100% on the next paper, you most likely "waste" marks due to 100 UMS being able to be achieved with a little less than 100 marks, though I could be wrong.

However, it highly depends how low the boundaries are for this paper. If the boundaries are low then you could get an A with a high mark in the next paper, and I wouldn't be surprised if they were low (70-75% for an A). We'll have to see.

Sorry I couldn't be more decisive!

Reply 219

britishtf2

16

Original post by leksj10

Could you talk about metallic bonding for why Mg2+ had a smaller atomic radius, because it had stronger forces between electrons and nucleus??

No. We are only concerned with a single atom, or ion in this case, rather than a lattice of multiple ions. Therefore you want to talk about more protons in the nucleus so that the electrostatic/electromagnetic force is stronger, so the electrons are pulled in closer.

AQA Chemistry New AS Unofficial Mark Scheme

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