Official AQA AS Chemistry Unit 1 - 23Rd May 2013

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What definitions can we be asked on chem 1?

Define:
Mass number
Relative Atomic Mass
Relative Molecular Mass
Structural/Positional/Functional/Chain isomer
Electronegativity
Covalent bond
Metallic bond
Ionic bond
First Ionisation Energy
Hydrocarbon
Saturated/Unsaturated
Fraction
Mixture(s)
Co-ordinate bond (Maybe)
Cracking

I think that's it - some are ones my teacher said could come up.

Reply 181

addzyx

Exams tomorrow and im completely lost on bond shapes i dont know how to determine the shape, any help?

Reply 182

Stephie Davis

Original post by heatherdukes

Basically it's rubbish either way :frown:

and unit 2 is even worse, I genuinely will be surprised to pass AS chemistry

i have almost given up with unit 2... luckily it is after half term.... because in these last 3 days iv had 4 exams....

Reply 183

Manni

Original post by lucasluke

Moles equation is moles = mass/Mr
so the mass we know, and the Mr we just add up the atoms.

Yeah I knew that, think revision is taking its toll lool

Reply 184

The Lawful T.J

Original post by med123

hey can someone help me on this question, it is 3biii on moles from jan 2011 paper
http://filestore.aqa.org.uk/subjects/AQA-CHEM1-W-QP-JAN11.PDF
mark scheme aswell http://filestore.aqa.org.uk/subjects/AQA-CHEM1-W-MS-JAN11.PDF
Thanks

I think this is where you times the number of moles from the previous question by ten (because it says in the above paragraph that 3.44g was dissolved in a 250cm something solution, and 25cm was used for HCl - which is the amount of moles you know etc :smile:

Follow my advice - underline the question for key points - Could save you :smile:

Reply 185

lucasluke

Original post by annaelizabet

Ok this kinda makes sense! Thanks. What happens if it asked for the third ionisation energy? which element would it be then?

It would be Magnesium.
Magnesium electron structure is 1s2 2st 2p6 3s2, so you remove the outer 2 in 1st and second I.E and then the 3rd one is removed from a full shell. It would just go from left ro right along the group, e.g. 4th IE highest would be Al, 5th would be Si and so on

Reply 186

marleyxd

Original post by Manni

Someone show me how to do this please

Ca(NO3)2 H2O
Mass(g) :4.20 1.84
Mr: 164 18
Moles: 0.0256 0.102

Divide by the smallest amount of moles, in this case 0.0256.

0.0256/0.0256=1
0.102/0.0256=3.98... rounding up to 4

Therefore x=4

It essentially an empirical formula calculation.

Reply 187

The.Joker

any tips on how to do well on mole calculations?
The wording of some questions throw me off and I end up losing tons of marks :/

Reply 188

Satanel

Chemistry is far and away the most difficult subject at AS, in my opinion. :eek:

Let's all just fail together. :biggrin:

But seriously, good luck for tomorrow everyone! I'm hoping A LOT of calculations come up... legit the only thing I can do. :tongue:

(No shapes, please!)

Reply 189

Farhat16

Original post by maryamnc

I think I know what you're talking about, if it is basically they will give you an unsaturated molecule (an alkene) and ask you for a functional group isomer. Well the functional group in an alkene is the double bond and in a functional group isomer you need to change the functional group (but keep Mr), so you open it up to form an alkane. But a normal alkane has two more hydrogens than an alkene so you draw a cycloalkane as they have less hydrogens.

That was really rambled sorry haha

OMG i get it now! youre amazing thank you sooooooo much :biggrin:

Reply 190

elliannagibbs

Original post by The.Joker

any tips on how to do well on mole calculations?
The wording of some questions throw me off and I end up losing tons of marks :/

remember to check the mole ratio!

Reply 191

ChloelovesChem

Original post by annaelizabet

How do you work out the shape and name of a CL3 + ion? Would you do 3 +1/2 i don't understand!

ImageUploadedByStudent Room1369243834.966663.jpg

Hope this helps!

Posted from TSR Mobile

Reply 192

jscockburn

Original post by addzyx

Exams tomorrow and im completely lost on bond shapes i dont know how to determine the shape, any help?

This is basically a matter of learning some numbers. You will be presented with a molecule and you need to determine two things. The number of bonded pairs and the number of lone pairs on the centeral atom. Here's the learn and churn bit:

If there are 2 bonded pairs on the central atom then the angle is 180˚
If there are 3 bonded pairs on the central atom then the angle is 120˚
If there are 4 bonded pairs on the central atom then the angle is 109.5˚
If there are 6 bonded pairs on the central atom then the angle is 90˚

Now, lone pairs act the same as bonded pairs except the angle is reduced by 2.5˚. For example:

4 pairs on the central atom but one is a lone pair reduce the normal angle of 109.5 to 107˚ because the lone pair reduces the angle by 2.5˚

Thats all you need to know except the names of all of them which can be found easily in your textbook or the internet somewhere. The key to it is just drawing a good diagram and clearly stating the number of lone and bonded pairs.. :biggrin:

Reply 193

Farhat16

Original post by mynameisntbobk

Basically, the functional group isomer of an ALKENE is a CYCLOALKANE.

For instance, think about Butane (C4H8). If you draw this as a cycloalkane, you'd get cyclobutane (C4H8). Same molecular formular, different structural formula

This is because the functional group of an alkene is it's double bond. Changing the functional group forms a cyclic compund (imagine you removed one of the double bonds, and used it connect the first and last carbons in an alkane), each carbon will only be able to hold 2 Hs.

Hope that makes sense, I know its a bit, hard to read/understand