A-level Chemistry Revision Squad!

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i was just wondering if we have to learn organic chemistry for paper 1 AS level which is on the 27th may?

Look up your exam's syllabus and they will break down the topics into Unit e.g Unit 1 and Unit 2. and Unit 3 which is the practical paper.

If you mean the practical is on the 27th May, then yes, you need to learn all this year's organic preparations like making an ester for example.

Learn unit 1 for your first exam and unit 2 for your second.

hope this helps! :smile:

Reply 641

n2697

Original post by Junaidc122

10% reacted, so 30cm^3 had been converted in to ozone, leaving 270cm^3 of oxygen. Since there is a 3:2 molar ratio, the volume of ozone produced from 30cm^3 oxygen = 30 x (2/3) = 20
Therefore, the total volume of gas left in the mixture is now 270 + 20 = 290cm^3.

With the second question, 100cm^3 decomposed, so 50cm^3 of nitrogen and 150cm^3 must have been formed, respectively. (Due to the molar ratios). This leaves you with 400 + 150 + 50 =600cm^3.
Hope this made sense, and just remember, the ratio of the volumes in which gases react is the same as how they react in terms of moles!!!

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Thank you so much this really helped !! :biggrin:

Reply 642

Farmerjj

Hey can someone help me with this please?
14.3g of hydrated sodium carbonate, Na2CO3.10H2O is dissolved in water and made up to 250cm3 of solution.
What is the concentration of sodium ions in the solution, in Moldm-3?
The answers 0.400 but I'm not sure why! Thanks 😊

Reply 643

Sandy_Vega30

Can someone help me out with this question? I think the answer is B. What do you think? :

A 27.0 g sample of an unknown hydrocarbon, CxHy, was burned completely in excessoxygen to form 88.0 g of carbon dioxide and 27.0 g of water. [Molar]
Which of the following is a possible formula of the unknown hydrocarbon?

A CH4
B C2H6
C C4H6
D C6H6

Reply 644

boredom07

Original post by Farmerjj

Firstly work out moles of hydrated sodium carbonate which is Mass/Mr = 14.3/286 = 0.05 moles of Na2CO3.10H2O.
When the hydrated sodium carbonate dissolves, the ions dissociate from the compound so 2Na+ ions are in solution.
So the molar ratio of Na2CO3.10H2O to the Na+ ions is 1:2
Thus you multiply your moles by 2:
0.05 x 2 = 0.1 moles of Na+ ions

Then using the formula (C x V)/1000 = moles, you can work out the concentration which is 0.4 mol dm-3

(edited 7 years ago)

Reply 645

TeaAndTextbooks

If 1.45% of 1 dm3 of air is CO2, how many parts per million is CO2?
I'm so stuck on this question so if you know how you do this please could you explain it. Thank you

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Reply 646

TeaAndTextbooks

Also could someone explain how you get the answer for this question. Thanks

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Reply 647

Junaidc122

Original post by TeaAndTextbooks

Also could someone explain how you get the answer for this question. Thanks

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Mole H2O = mass / Mr = 1.8/18 =0.1
Therefore to find the number of molecules of H2O, multiply by Avagadro's:
0.1 x 6.0 x10^23 = 6 x 10^22
Next times by three , because there are 3 atoms per molecule, giving 1.8 x 10^23
Hope this helped 😇

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(edited 7 years ago)

Reply 648

voltz

What marks did you guys get on the Physical and Inorganic spec paper for AS Chemistry? Just want to get an idea as to how difficult it is in reality

Reply 649

n2697

sorry I don't know why you multiply by 2?? I don't remember having to do this in other questions?

Reply 650

n2697

if the carbon carbon double bond is weaker than the c-c bond why does it have a greater bond enthalpy I.e. I don't why the answer to that question is that the carbon double bond is weaker

Reply 651

voltz

For a titration, is the acid always in the burette or is the solution of unknown just always the base (in flask)?

Reply 652

Nelson Barnaby

Original post by n2697

if the carbon carbon double bond is weaker than the c-c bond why does it have a greater bond enthalpy I.e. I don't why the answer to that question is that the carbon double bond is weaker

The C=C bond isn't weaker than the C-C bond, it is just less than twice as strong. This is because the pi bond in the C=C bond isn't as strong as the sigma bond which is present in both C=C bond and C-C bond.
C=C has a higher bond enthalpy because more energy is required to break the bond :smile:

Reply 653

TeaAndTextbooks

Original post by Junaidc122

Mole H2O = mass / Mr = 1.8/18 =0.1
Therefore to find the number of molecules of H2O, multiply Avagadro's:
0.1 x 6.0 x10^23 = 6 x 10^22
Next times by three , because there are 3 atoms per molecule, giving 1.8 x 10^23
Hope this helped 😇

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I forgot to multiply by three. That was very helpful, thank you :biggrin:

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Reply 654

Junaidc122

Original post by TeaAndTextbooks

I forgot to multiply by three. That was very helpful, thank you :biggrin:

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No problem

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(edited 7 years ago)

Reply 655

ayvaak

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Another couple of questions i cant seem

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to get my head around. I was hoping someone could help out. I thought that yellow ppts only form when a carbonyl methyl group is present?
thanks in advance

(edited 7 years ago)

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Reply 656

Enderbat1999

guys question,

in mass spec why do we get different peaks for example Kr+1 and Kr+2

and where are they drew on the mass spec graph

Reply 657

Supermanxxxxxx

ImageUploadedByStudent Room1464295237.711118.jpg

Anyone that can explain question 3

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Reply 658

GracelovesNeuro

With the Hydroxides what are the test you do when its cloudy milky etc?? Quite confused and its not in the textbook.I'm referring to the part of the spec where it states "Students could test the solubility of Group 2 hydroxides by mixing solutions of soluble Group 2 salts with sodium hydroxide and record their results." vice versa for Sulfates.