AS Chemistry- helping each other out!

Can someone give me the answer and working to this Q? its weird...


Calculate the mass of 3-methylbutan-2-ol used by the student.

3-methylbutan-2-ol + [O] = 3-methylbutan-2-one + H2O

the 3-methylbutan-2-one weighed 2.15g

The yield was 62.5%​

i will literally give you a rep eevery day forever if you give me a good answer <3

Can someone give me the answer and working to this Q? its weird...


Calculate the mass of 3-methylbutan-2-ol used by the student.

3-methylbutan-2-ol + [O] = 3-methylbutan-2-one + H2O

the 3-methylbutan-2-one weighed 2.15g

The yield was 62.5%​

i will literally give you a rep eevery day forever if you give me a good answer <3

So Percentage yield= actual yield/ theoretical yield x100
so 62.5/100= actual yield/ theoretical yield
so theoretical yield= actual yield/ 0.625
" " " = 2.15/ 0.625
= 3.44g
Number of moles= mass/mr
Number of moles of 3-methylbutan-2-one= 3.44/ 86
Number of moles= 0.0400 (3sf)
1:1 mole ratio
mass of 3methylbutan-2-ol= mr x number of moles
" " " = 88 x 0.0400
= 3.52g (3sf)
( I think )
A2 student atm who got an A at AS

Yesssssss that was my answer thank you so much

any other questions? want to use this thread for my revision haha

Yeah that's a good idea but not right now, I am mentally exhausted after a practical exam in chemistry today! Maybe next week lol :P

good luck for the results

Thank you!! Well done on getting an A at AS, I may need you again!

what exam board are you on?

OCR

OCR

A or B? (Basically Salters or the other one)

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jesus christ unit 2 chemistry is impossible for me, we've been taught it so terribly and i have the mock tomorrow, i know nothing

in the unit 1 mock i got a C, 4 marks off a B, all i want at this point would be a C for both exams because I don't see myself getting above a B in chemistry because of this unit 2

I do AQA, if you do the same as me please feel free to ask me anything.

Don't worry about your U grade. When I did the CHEM2 MOCK in April (not March sorry) there were only topics that I understood completely like Maxwell-Boltzmann and Equilibria but the rest of the content was just mumbo jumbo. It'll take time and practise to get the grade you want, you'll be fine mate

Anyone care to help me with a question.

Use the data from the table above to calculate a value for the enthalpy of formation of ammonia?

Why is it sum of bonds broken - sum of bonds made and not sum of products - sum of reactants?

When you are GIVEN enthalpies of formation, you use PRODUCTS - REACTANTS.

When you are GIVEN mean bond enthalpies, you use REACTANTS - PRODUCTS.

This is sort of because all values given in mean bond enthalpies are positive, i.e. energy is required to break a bond. So in effect you are doing [positive number] - [positive number] right? (since both sums are positive since all values given are positive).

If more energy is released, the sum of the products will be greater right? This makes sense because [small positive number] - [big positive number] = negative answer = exothermic, which makes sense if more energy was released.

You're probably a little confused because it says "formation of ammonia" so you instantly think "must be products - reactants", however, you are GIVEN mean bond enthalpies and not GIVEN formation enthalpies, so you cannot use that formula! You use products - reactants when you are GIVEN enthalpies of formation! (Basically, focus on the values you are GIVEN rather than what reaction is actually happening!)