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AS Chemistry- helping each other out!

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Original post by annie79
its saying the INCREASE in mass, not what the final mass of the atoms and chlorine is combined. The INCREASE in mass after the two have REACTED is due to the ADDITION of Cl because that's the only thing that can cause the increase in mass because the ATOMS stay the SAME. so you do 7.1/35.5 = 0.2 moles of cl. ratio of atoms to Cl is: 1:2, so atom has to be +2!

I was also stuck on this Q, but I literally only JUST got it by reading your post!!

Thing i don't understand, is why you divide 7.1g by 35.5 and not by 71 since Cl2 is diatomic O.o maybe Cobalt can explain :smile:


Ahh, I see. I was also thinking the same as you about the diatomic nature of Cl but I just ignored it for the purposes of calculating the answer. I agree, it would be nice to know why it isn't Cl2?
Hi Can you please show me how to work out this question? its from Edexcel 2014 june

Oxygen gas, O2 , can be converted into ozone, O3 , by passing it through an electric discharge.

3O2 (g)=====>2O3 (g)

In an experiment, a volume of 300 cm3 of oxygen was used but only 10% of the oxygen was converted into ozone. All volumes were measured at the same temperature and pressure. The total volume of gas present at the end of the experiment, in cm3 , was

A 200

B 210

C 290

D 300


Thank you!!
Original post by gabby07
Ahh, I see. I was also thinking the same as you about the diatomic nature of Cl but I just ignored it for the purposes of calculating the answer. I agree, it would be nice to know why it isn't Cl2?


Original post by annie79
its saying the INCREASE in mass, not what the final mass of the atoms and chlorine is combined. The INCREASE in mass after the two have REACTED is due to the ADDITION of Cl because that's the only thing that can cause the increase in mass because the ATOMS stay the SAME. so you do 7.1/35.5 = 0.2 moles of cl. ratio of atoms to Cl is: 1:2, so atom has to be +2!

I was also stuck on this Q, but I literally only JUST got it by reading your post!!

Thing i don't understand, is why you divide 7.1g by 35.5 and not by 71 since Cl2 is diatomic O.o maybe Cobalt can explain :smile:
before you know the metal you don't know how many are going to be involved in the product I.e 1 for sodium, 4 for carbon... So you need to just divide by the mass of one chlorine atom which allows you to find the correct ratio
OCR B Salters :smile:
how did my fellow salters do on F333 (skills test)
Original post by cilla_e
Hi Can you please show me how to work out this question? its from Edexcel 2014 june

Oxygen gas, O2 , can be converted into ozone, O3 , by passing it through an electric discharge.

3O2 (g)=====>2O3 (g)

In an experiment, a volume of 300 cm3 of oxygen was used but only 10% of the oxygen was converted into ozone. All volumes were measured at the same temperature and pressure. The total volume of gas present at the end of the experiment, in cm3 , was

A 200

B 210

C 290

D 300
Thank you!!

The volume of each is directly proportional to the number of moles.

since 10% of the oxygen reacts => 30 cm3
(this leaves 270 cm3 unreacted)
3 moles of oxygen gives 2 moles of ozone
So (2/3)*30= 20 cm3

total volume of gas = 20+270=290 cm3 C

:smile:
Reply 2565
Avatar for Azula
Azula
2
Original post by VetVikki
Anyone doing AQA: What do we need to know for this point of the spec .. can't find anything in my notes

"know that early models of atomic structure predicted thatatoms and ions with noble gas electron arrangementsshould be stable"

Theories of atoms basically:
first there was dalton's model (solid spheres), then thomson's model (plum pudding model)
then there was the gold foil experiment by ernest rutherford to show the plum pudding model was wrong and most of atom is just empty space (nuclear model)
then Bohr's model which showed why noble gases are inert,
then refined bohr's model
finally we have the quantum model
its quite detailed if you have a cgp guide or textbook you should probs check that ^^
and yes i am also on aqa by the way
Can anyone help with this
1431858083905-821538503.jpg506.7KB
Yoo was wonderin if you guys could help me by explaining all the trends across and down groups, i think in unit 1 its like group 2,3,1,7? I struggle alot much help would be appreciated. could you also explain which elements deviate from the trend like mg with al and sulphur and phosphorus. Thanks :smile:


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Reply 2568
Avatar for Azula
Azula
2
Original post by Mo_Jo.
Can anyone help with this


you can use algebra but its way easier just thinking logically
10 is 20% 11 is 80% abundance
Original post by gabby07
Ahh, I see. I was also thinking the same as you about the diatomic nature of Cl but I just ignored it for the purposes of calculating the answer. I agree, it would be nice to know why it isn't Cl2?


Original post by annie79
its saying the INCREASE in mass, not what the final mass of the atoms and chlorine is combined. The INCREASE in mass after the two have REACTED is due to the ADDITION of Cl because that's the only thing that can cause the increase in mass because the ATOMS stay the SAME. so you do 7.1/35.5 = 0.2 moles of cl. ratio of atoms to Cl is: 1:2, so atom has to be +2!

I was also stuck on this Q, but I literally only JUST got it by reading your post!!

Thing i don't understand, is why you divide 7.1g by 35.5 and not by 71 since Cl2 is diatomic O.o maybe Cobalt can explain :smile:


When chlorine has reacted with something they are no longer a molecule

Dividing with 71 still works mathematically and in this case it was magnesium? So it would've be been easy, but if it were odd number group you would have a little bit of confusion

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Original post by C0balt
When chlorine has reacted with something they are no longer a molecule

Dividing with 71 still works mathematically and in this case it was magnesium? So it would've be been easy, but if it were odd number group you would have a little bit of confusion

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cool, makes sense!
Original post by annie79
cool, makes sense!


You're welcome...
Original post by langlitz
You're welcome...

i feel for you :frown:
Original post by Azula
Theories of atoms basically:
first there was dalton's model (solid spheres), then thomson's model (plum pudding model)
then there was the gold foil experiment by ernest rutherford to show the plum pudding model was wrong and most of atom is just empty space (nuclear model)
then Bohr's model which showed why noble gases are inert,
then refined bohr's model
finally we have the quantum model
its quite detailed if you have a cgp guide or textbook you should probs check that ^^
and yes i am also on aqa by the way


Thank you so much - CGP was my life at GCSE :tongue:
Do we need to know about the theories? Not seen a question from any past exam papers asking about the theories
Reply 2575
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Azula
2
Original post by VetVikki
Thank you so much - CGP was my life at GCSE :tongue:


same here!! And now i just use the cgp textbooks for biology and chemistry
Is a week enough to revise for UNIT 2 CHEM AQA?
Hi can you show me how to answer this question, i have no clue! (Its multiple choice btw)

1.40 g of an alkene gave 3.77 g of a dichloroalkane on reaction with chlorine.
What is the molecular formula of the alkene?

A C2H4

B C3H6

C C4H8

D C6H12

Thank you!
Reply 2578
Avatar for 76584
76584
8
I need the mark scheme for the f321 ocr A chemistry 2014 paper, does anyone have it please?
Original post by C0balt
When chlorine has reacted with something they are no longer a molecule

Dividing with 71 still works mathematically and in this case it was magnesium? So it would've be been easy, but if it were odd number group you would have a little bit of confusion

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Cobalt can you answer my question please

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