Higher chemistry 2014-2015

Can anyone help me? I'm just not getting the right answer but I think I'm using the correct method


Posted from TSR Mobile

The one circled in blue is the correct answer but I don't understand why. An isoprene unit is C5H8 and none of them add up to it.


Posted from TSR Mobile

do any of you guys have a link to every calculation formula in chemistry as this http://www.hsn.uk.net/forum/index.php?/topic/243-higher-chemistry-formulae/ hasnt covered it all,
Thanks alot

Can someone work out 5a on specimen for me please, I think they got numbers wrong


Posted from TSR Mobile

Hi! Which specimen paper is it? cfe Higher?

Yes


Posted from TSR Mobile

Can someone work out 5a on specimen for me please, I think they got numbers wrong


Posted from TSR Mobile

Unit 1

Average rate=change in quantity/change in time

Rate of reaction=1/time
R=1/t

Number of moles=mass/gram formula mass
n=m/gfm

Number of moles=concentration x volume
n=CV

Number of moles=Volume of gas/molar volume(molar volume is usually given)
n=V/Vmol

Heat energy=specific heat capacity of water x mass x change in temperature of water
Eh=c m deltaT

Density=mass/volume
rho=m/V

Unit 2
Percentage yield=actual yield/theoretical yield x 100%

Unit 3
Hess's law: delta H1=delta H2+ delta H3

Acids and Bases: pH=-log10[H+]
(log10[H+] is the power of [H+], e.g. 1/10 mol l-1=10^-1 M, the power is -1, so the log10[H+] os -1, substitute into -log10[H+] gives you 1)

Ionic product of water=10^-14 mol^2 l^-2

Charge=Current x time
Q=It

Avogadro Constant, L=total charge on one mole of electron/charge on one electron
(charge on one electron=1.6 x 10^-19)

Alpha particle is 4 2 He
Beta particle is 0 -1e

Half life=(1/2)^n

I think that's all!

Just realized I probably didn't answer you question~
I had a look at the marking instruction, it says the answer is 12.15 litres?
I'm pretty sure that 1L= 1000 cm^3, which means 1 cm^3=1x10^-3 litres...
What did you get?

The marking scheme used the 1g Kj value as 36.1 where as on the question it says 3.61 so I think their answer is wrong


Posted from TSR Mobile

I think theres only one missing which is change of heat = Kj/mol
im not sure if this is the right order or formula but theres something like this missing
Thanks for your response nevertheless

You mean the heat energy released per mole? (enthalpy?)

Yes


Posted from TSR Mobile

Oops! Sorry~ I use a slightly different way to calculate the enthalpy(mass of one mole over the mass given in the question multiply by the heat energy)

Enthalpy(delta H)=Eh/n
Eh=heat energy
n=number of moles

feel free to add any others that I've missed~

I'm doing the old higher so there could be mistakes~But here is how I would do it.

5a) Burning ethanol produces 351,000kJ energy
Burning 1g of 2-methylpropan-1-ol gives you 3.61kJ energy
So 351,000/3.61=97229.9169
Multiply this number by 1.25 x 10^-3 and that should give you 121.54 litres


5b) Oxygen can form hydrogen bond with Hydrogen because oxygen has a lone pair of electrons. So just do dotted lines between the hydroxyl group O and a hydrogen on water.

Thanks
I think it all relies on how the teacher taught us it tbh