chem questions

[synchronise3]

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[b^3]

Well we know that "table salt" is NaCl.

1) Now if we have 100g of salt and pepper, then 40g of that will be Cl.
So n(Cl)=40/35.453=1.128mol
So that means n(NaCl)=n(Cl)=1.128mol
So m(NaCl)=1.128*(35.453+22.989)
=65.94g
So m(pepper)=100-64.94=34.06g
So % by mass of pepper==34% (w/w)

2) m(B)=m(A₂B) (since 25% percentage by mass)
m(A₂B)=4m(B)
m(A)=m(A₂B) (since 75% percentage by mass)
m(A_2B)=m(A)*
So m(A)=4m(B)
i.e. m(A)=m(B)

So % of A in A₅B₃ = *100
= *100
= *100
=71.4% (w/w)

EDIT: completed q2.

[synchronise3]

awesome thanks!

[synchronise3]

btw would you classify these as harder questions or easy?

[pi]

Q2 was harder, Q1 was a medium-ish one

[paulsterio]

btw would you classify these as harder questions or easy?

They're both standard stoichiometry questions which you should be able to do, I agree with pi, Q2 was a little above average, Q1 was average, you'll get better at them about a month into Unit 3, you'll be doing so many of these sorts of questions in the first stages of U3

Moderator action: removed real name, sorry for the inconvenience

[b^3]

btw would you classify these as harder questions or easy?

They're both standard stoichiometry questions which you should be able to do, I agree with pi, Q2 was a little above average, Q1 was average, you'll get better at them about a month into Unit 3, you'll be doing so many of these sorts of questions in the first stages of U3

I wouldn't called them the standard stoich questions (like the ones in the textbook), they make you think in a slightly different way more typical of an exam question. And plus question 2 was more of manipulation using maths than anything else.

Moderator action: removed real name, sorry for the inconvenience

[paulsterio]

Sorry, I meant standard Exam-ish stoichiometry questions (unit 3 was so long ago!), but yeah Q2 is probably too mathematical to be in an exam

[synchronise3]

haha yeah, the questions in the textbook seem far more easier.

Do you guys know where i can find more of these types of questions?

[paulsterio]

Probably Checkpoints

You go to GWSC as well? hi-5

[b^3]

Yeh even the NEAP smart study guides, they have a few good questions in there.

[synchronise3]

You go to GWSC as well? hi-5

yep! year 11 though. Don't think there's many gwsc students on this forum :\

yeah ok checkpoints and neap sounds good

[paulsterio]

There's quite a few who have finished Year 12 this year, I know of at least a handful

[synchronise3]

wow ok! yeah i only recently joined - month ago

[mr.politiks]

If u do checkpoints, it is better for you to only do the non-vcaa (expose yourself to VCAA exam qs in exam conditions, and do VCAA exams twice). Go ahead with NEAP, it is probably the best