AQA Chem Unit 1 May 22nd 2015 OFFICIAL THREAD

Scroll to see replies

quick question the addition of neutrons means an isotope is created, and i know that chemical properties are to do with electrons, so would a change in neutrons cause any Physical property change ?

the different masses of isotopes means they have different physical properties ie boiling point

Reply 581

purplecloud

Original post by ashiekh

How is this but-1-ene I am confused I thought it was it was just butene

Its asking for a positional isomer of that molecule, so you must say where the double bond is.

Reply 582

lukejoshjames

Original post by Roshany

3.atoms with the same number of protons but a different number of neutrons

That's an isotope.

Reply 583

ScienceGuy121

Anyone got any tips for balancing complex equations?!! :frown:

Reply 584

Roshany

Original post by lukejoshjames

That's an isotope.

whoops :P

Reply 585

AleenaDina8

Original post by Ozy96

C i) Increases because they are bigger molecules so more vdW forces between the molecules requiring more energy to break.

ii) HF has stronger Intermolecular forces (Hydrogen bonding)

make sure to include increase number of electrons :biggrin:

as they get bigger

Reply 586

j5994

hey has anyone got any tips for balancing equations quickly?? it always takes me so long to do it and I waste all my time on the paper on it :frown:

plzzz

Reply 587

djhodnett

looking forward to getting my full UMS tomorrow :colonhash:

Reply 588

Nels98

Original post by ScienceGuy121

Anyone got any tips for balancing complex equations?!! :frown:

leave till the end then just do one element at a time and keep persisting!!

Reply 589

lukejoshjames

Original post by AleenaDina8

the different masses of isotopes means they have different physical properties ie boiling point

No, they don't. Just because they have different masses doesn't change their properties. Their electrons are what create their characteristical properties, and as the electron configuration doesn't change, because they are the same element, there is no change in physical properties.

Reply 590

ScienceGuy121

Original post by Nels98

leave till the end then just do one element at a time and keep persisting!!

It is the only thing that just stumps me! :frown:

Reply 591

Ladymusiclover

I don't get this question.
Which of the following shows the numbers of iodine atoms in 0.025g of I2.
The answer was a) 0.025/126.9 * 6.02*10^23

I don't get why you don't multiply the Ar (126.9) by 2 since there are two atoms.
Anyone know the reason??

(edited 8 years ago)

Reply 592

Charlie1o5

How do you work out molecular formula? My mind is so scrambled for tomorrow :frown:

Reply 593

jackmichaeljmh

I am so ****ed for this exam even after revising and unit 2 is even worse why did I do chemistry?!?!?!

Reply 594

purplecloud

Original post by j5994

hey has anyone got any tips for balancing equations quickly?? it always takes me so long to do it and I waste all my time on the paper on it :frown:

plzzz

for equations with hydrocarbons in them (e.g burning them) start with balancing 1 atom first e.g. Carbon, then move to hydrogen and then finally to oxygen, dont try balance the whole molecule at once. Sale rule applies to other equations.
Also if you wish you could write out all the atoms on each side of equation and figure out common multiples

Reply 595

banker-121

Original post by lukejoshjames

1) Weighted mean mass of an atom of an element compared to 1/12 the mass of one C-12 atom.
2) Mass of a formula unit compared to 1/12 the mass of one C-12 atom.
3) Really depends on what isomer you're talking about. Structural? Stereo?

For the first two can you use the division sign which is underlined?

Reply 596

Super199

Original post by alevelup

January 2011 question 1d)

http://a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20AS%20Chemistry/Unit%201/Unit%201%20Practice%20Papers%20and%20Revision%20Aids/AQA-CHEM1-W-QP-Jan11.pdf

PLEASE HELP :s-smilie:

(the answer is 3, but why??)

Hydroxide ion is OH-.

Oxygen now has 7 electrons around outer shell. One is being used up with the hydrogen....
Meaning there is 6 electrons left over, hence 3 lone pairs.

:smile:

Reply 597

randoms132

Original post by Charlie1o5

How do you work out molecular formula? My mind is so scrambled for tomorrow :frown:

Have you got a question I can see to help you out?

Posted from TSR Mobile

Reply 598

Nels98

Original post by Charlie1o5

How do you work out molecular formula? My mind is so scrambled for tomorrow :frown:

work out the empirical formula and its Mr then it will tell you the Mr of the molecular formula so just multiply the empirical formula until you get the right Mr