AS Chemistry- helping each other out!

This is a question from 2014 paper unit 1 I'm confused.

The equation is 4Fe(NO3)3 ---> 2FeO3 + 12NO2 + 3O2

4Fe(NO3)3 mass is 2.16g and Mr is 241.8

it it said to work out moles of iron nitrate I got it as 0.00893n which was right

then it said work out the moles of oxygen gas produced?
I got the mole ratio 4:3 but how do you work out the moles in 3O2 so confused

Looking at the mole ratio - for every 4 moles of iron(III) nitrate, there are 3 moles of oxygen (or if it's easier, you will have 1 mole of iron(III) nitrate for 3/4 mole of oxygen). That means you need to multiply the number of moles of iron(III) nitrate by 3/4 to get the number of moles of oxygen.

Oh I see thank you that makes sense now! I was dividing 4/3 instead of 3/4 lmao

No worries.

So for the nitrogen dioxide 4/12 = 3
3x 0.00893 is moles in nitrogen dioxide

Yup

The carbon which has hydroxyl group attached to it has three carbon atoms so there is no H atom on its own attached to the said carbon. Draw a tertiary alcohol and you will see. But I don't think the explanation is on any syllabus.

The chromium (VI) in dichromate has orange colour and chromium (III) is green. It is reduced in oxidation of alcohol this is where the colour change comes from.

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Stuck on a physics question .

Which?

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I made a thread about it.

Thanks for replying.

No I understand but it says the method for the reaction is to bubble hydrogen halides (gases @ rt) into liquid alkANE, but if this happened no reaction would occur. The hydrogen halide gas should be bubbled into a liquid alkENE....right?

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Pretty straightforward.

First find the moles of NH3 using N = Mass/Mr ---------- 300g/17 gmol-1 = 17.647 mol

Then use the equation C = N/V so 17.647 mol/1 dm3 volume (no convertion of units required = 17.6 mol dm-3 to 3 sig figs.

Make sure you understand that I got the Mr from adding the Ar (or mass number) of Nitrogen which is 14 on the OCR table. With 3 x 1.0 (1.0 is the mass number of hydrogen, since it's Ammonia NH3. We multiply by 3). 14 + 3 = 17 g mol-1

Remember the equations N = Mass/Mr for moles. N = C x V for solutions and N = V/Vm for gas volumes.

Practice loads and you'll get better

How do you know how many lone pair of electrons an element when it's connected to a compound, eg. the Oxygen in Phenol?
without drawing a dot and cross diagram?

Sorry I was having a totally stupid moment and using the Mr of Ammonium instead of Ammonia! Thanks for the help though A-levels are most definitely frazzling my brain!

What I do is find the amount of electrons on the outer shell of the bonding atom.
Then I work out the electrons that the bonding atom wants - eg chlorine wants 1 (as it will be sharing the same as the electron it wants in the bond if you get me)
Then I add these both together to get the total electrons and divide by 2 as there are 2 electrons in a pair. You can work out how many lone pairs after taking away the shared electrons in the compound

Eg NH3 : So nitrogen has 5 outer electrons. Hydrogen wants a total of 3 electrons.
Now add these both together and there are 8 electrons so a total of 4 bonds. As there are 3 hydrogens there are 3 bonds with atoms so lose 6 electrons (2 electrons per pair) and you are left with 2 electrons, which are a lone pair as it doesn't bond with any atoms.

Hope this helps, dunno if I even answered the question properly haha

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