Edexcel GCE AS Chemistry Unit 1: 22nd May 2015 + Unit 2: 02nd June 2015

Original post by TheLegalDealer

Anyone know how to do this Q (ocr salters btw)

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Please tell me if the mark scheme concurs with my answer?

Reply 782

KingThomas

https://twitter.com/AlevelExaminer Follow me for comments Cheers guys

Reply 783

Coolsmiles123

I've revised everything but I'm still doing really bad in the past papers! :frown:

Reply 784

Sadiariya

Trends in ionic and atomic radii across a period and down a group???? and explanations of why??

Reply 785

jshep000

15

Original post by Sadiariya

Trends in ionic and atomic radii across a period and down a group???? and explanations of why??

Ionic radius decreases across a period, as number of protons increase so nuclear charge becomes more positive. Pulls the electrons in closer more therefore gets smaller. Down a group it will increase because you're getting extra electron shells

Reply 786

samb1234

Original post by jshep000

Ionic radius decreases across a period, as number of protons increase so nuclear charge becomes more positive. Pulls the electrons in closer more therefore gets smaller. Down a group it will increase because you're getting extra electron shells

Remember the increase as you move from +ve to -ve ions

Posted from TSR Mobile

Reply 787

jshep000

15

Original post by samb1234

Remember the increase as you move from +ve to -ve ions

Posted from TSR Mobile

yeah my bad! Remember the drops from P and S, N and O, B and E and B, Mg and Al. (for ionisation energy)

(edited 8 years ago)

Reply 788

Some Guidance with this quesiton would be great...

Reply 789

HopefulDentist..

Can anyone help me with these? Do you approach the questions differently :frown:

Consider the reaction below.2NO(g) + O2(g) ĺ 2NO2(g) What is the maximum volume, in dm3, of nitrogen dioxide that could be obtainedin the reaction occurring when 1 dm3 of nitrogen monoxide is mixed with 2 dm3 ofoxygen, under suitable conditions? All measurements are made at the same temperature and pressure.

A 1
B 2
C 3
D 4

Ammonia gas decomposes when heated.2NH3(g) o N2(g) + 3H2(g) In an experiment, a sample of 500 cm3 of ammonia was heated and 20% decomposed. The total volume of gas present at the end of the experiment, in cm3, was A 200 B 400 C 600 D 1000

(edited 8 years ago)

Reply 790

Feraligatr

OP

20

Original post by lordoftheties

Some Guidance with this quesiton would be great...

Avagadro's Law suggests that the volume of gases in an equation is proportional to moles. So since there is 50cm3 of hydrogen (2 moles), there should be 50cm3 of water (2 moles)

Reply 791

Original post by Feraligatr

Avagadro's Law suggests that the volume of gases in an equation is proportional to moles. So since there is 50cm3 of hydrogen (2 moles), there should be 50cm3 of water (2 moles)

That makes a lot of sense, but I don't remember coming across 'Avogadro's Law' in my revision, would you mind expanding a bit on what it is more precisely?

Reply 792

Feraligatr

OP

20

Original post by lordoftheties

That makes a lot of sense, but I don't remember coming across 'Avogadro's Law' in my revision, would you mind expanding a bit on what it is more precisely?

You just need to be aware that according to the law, the volume of gases in a chemical equation is proportional to moles. That's all :smile:

Reply 793

emmmms

Original post by lordoftheties

Some Guidance with this quesiton would be great...

i might be wrong but i think it is B. this is because the molar ratio is 2:1:2. as gases occupy the same volume at the same atm and temp. 2 moles of hydrogen gas would be the same volume as 2 moles of water vapour.

Reply 794

Milo AS

Original post by Feraligatr

You just need to be aware that according to the law, the volume of gases in a chemical equation is proportional to moles. That's all :smile:

Can't you only produce something with the minimum amount of reactant? Eg. there's 25cm3 of one, so surely only 25cm3 of product can form?

Reply 795

Feraligatr

OP

20

Original post by Milo AS

Can't you only produce something with the minimum amount of reactant? Eg. there's 25cm3 of one, so surely only 25cm3 of product can form?

I'm not sure exactly what you mean since even if you did the equation vol/24 you'd be given the same answer and the number of moles is the same for both hydrogen and water :redface:

Reply 796

Original post by emmmms

i might be wrong but i think it is B. this is because the molar ratio is 2:1:2. as gases occupy the same volume at the same atm and temp. 2 moles of hydrogen gas would be the same volume as 2 moles of water vapour.

That's right!

Reply 797

Milo AS

Original post by Milo AS

Can't you only produce something with the minimum amount of reactant? Eg. there's 25cm3 of one, so surely only 25cm3 of product can form?

Okay i'm confused now. I'm not saying you're wrong, i just need help.So you've got 2 mol of hydrogen reacting with 1 mol of oxygen to produce 2 mol of water.surely, the amount of oxygen (25) is the 'limiting factor' if you will? Or am I being thick, given that there are 2 hydrogen atoms for every oxygen atom, which means it balances out.Pretty sure i answered my own question there.

Reply 798

Sadiariya