Chemistry Test of Ions

[ThatReallyReallyWeirdDude]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s04_qp_6.pdf

Q8)

Alrighty
Measure a mass of 10g of Manganese oxide
Pour 50cm3 of Hydrogen Peroxide into a conical flask, add manganese oxide
It says hydrogen peroxide otherwise decomposes very slowly so if manganese oxide is a catalyst there will be fizzing. The bubbles produced should be oxygen; test if it is with a glowing splint (should relight).
Take out the manganese oxide, dry it and reweigh it. It should still be 10g. If it decreases in mass that means its not a catalyst cause it reacted.
Sorry for being late, was eating

 

[ZainH]

Alrighty
Measure a mass of 10g of Manganese oxide
Pour 50cm3 of Hydrogen Peroxide into a conical flask, add manganese oxide
It says hydrogen peroxide otherwise decomposes very slowly so if manganese oxide is a catalyst there will be fizzing. The bubbles produced should be oxygen; test if it is with a glowing splint (should relight).
Take out the manganese oxide, dry it and reweigh it. It should still be 10g. If it decreases in mass that means its not a catalyst cause it reacted.
Sorry for being late, was eating

Wow your answers make me feel like an idiot. So simple! Thanks again.. for the 10th time.
Just a small question, if in 2 experiments HCL is used. One has double the volume of HCL, what could be the reason
Would you need more HCL if something is more concentrated or less concentrated? Im confused because I solved 2 different past papers with this sort of question and there were two different answers :s

 

[shalala]

Alrighty
Measure a mass of 10g of Manganese oxide
Pour 50cm3 of Hydrogen Peroxide into a conical flask, add manganese oxide
It says hydrogen peroxide otherwise decomposes very slowly so if manganese oxide is a catalyst there will be fizzing. The bubbles produced should be oxygen; test if it is with a glowing splint (should relight).
Take out the manganese oxide, dry it and reweigh it. It should still be 10g. If it decreases in mass that means its not a catalyst cause it reacted.
Sorry for being late, was eating

How do we find the concentration of an acid?

 

[ThatReallyReallyWeirdDude]

Wow your answers make me feel like an idiot. So simple! Thanks again.. for the 10th time.
Just a small question, if in 2 experiments HCL is used. One has double the volume of HCL, what could be the reason
Would you need more HCL if something is more concentrated or less concentrated? Im confused because I solved 2 different past papers with this sort of question and there were two different answers :s

Alright
Let A and B be two solutions of HCl
Let's say they react with 20cm3 of potassium hydroxide
If we need 20cm3 of A to react with 20cm3 of KOH, and 40cm3 of B to react with 20cm3, that means there is the same number of moles of HCL in 20cm3 of A as there is in 40 cm3 of B.
no. of moles = concentration times volume
If the volume is doubled, then if the no. of moles is to stay the same then the concentration is halved
in other words. B has the same number of moles in TWICE the volume, so it's more spread out - it's less concentrated. B is a bigger room containing 20 people and A is a smaller room containing 20 people as well, but in A it's much more crowded (concentrated) because they're packed in a smaller case.
SO the reason you need MORE HCl is because it's LESS concentrated. When it's less concentrated it means there is less moles for a certain volume of HCl than a solution which is more concentrated . Therefore you need MORE HCl to have the same number of moles.
I have a feeling that explanation sucked. If you don't get it i'll try again
EDIT: Summary, you'd need MORE HCl if it's LESS concentrated. P:

 

[ThatReallyReallyWeirdDude]

How do we find the concentration of an acid?

Hmm concentration of an acid
The best method would be to titrate it against an alkali of known concentration
Put 25cm3 of the acid into a beaker, and add some phenolpthalein.
Add the alkali with a burette drop by drop until the end point is reached
We'll then know the volume of alkali needed to neutralize 25cm3 of the acid
You then use calculations to find the concentration of the acid
First you have to write the balanced equation
e.g. HCl + KOH -> KCl + H2O
If we know the volume and concentration of the alkali used we can find the number of moles of alkali right? Then using the mole ratio from the equation (in this case 1:1) we can find the number of moles of acid in 25cm3 of acid.
Then it's easy - concentration = number of moles divided by volume. Just remember the volume should be in dm3 (where 1000cm3 = 1 dm3) so the concentration can be the standard mol/dm3
If you find an example question I'll answer it for you

 

[Babs saad]

Never encountered such questions in my life.
It's mostly test of ions, graphs, basic lab apparatus and titration etc.

theres test for alkene... which is org... add bromine water... from brown to colourless, just sayin

 

[ThatReallyReallyWeirdDude]

Some general ideas for Paper 6.

1. You should know the basic lab apparatus.
2. You should know how to read from the burette/pippette/measuring cylinder images given
3. You should know to draw a graph
4. You should know the identification of ions (test to check the presense of iron(ii) etc)
5. You should know Titration
6. You should know Chomatography
7. You should know Crystallization
8. You should know difference between distillation and fractional distillation
9. You should know the basic filtration methods
10. You should know effect of heat and concentration on reaction

If anyone has any more points, feel free to add to the list

Just thought I'd add.
Solubility Identification of gasses as well.
EDIT: Removed graphing, it's already there.

 

[wooowooowoo]

theres test for alkene... which is org... add bromine water... from brown to colourless, just sayin

Ah! Right.

 

[ThatReallyReallyWeirdDude]

theres test for alkene... which is org... add bromine water... from brown to colourless, just sayin

Also isn't there the test for alcohol/carboxylic acid?
I'm not sure - correct me if i'm wrong wooowooowoo - but if you have alcohol you add carboxylic acid and thin white layer of ester forms?

 

[wooowooowoo]

Also isn't there the test for alcohol/carboxylic acid?
I'm not sure - correct me if i'm wrong wooowooowoo - but if you have alcohol you add carboxylic acid and thin white layer of ester forms?

Haha yess but that's P3, it doesn't come in P6. Alcohol test is lighted split - flame produced

 

[ThatReallyReallyWeirdDude]

Haha yess but that's P3, it doesn't come in P6. Alcohol test is lighted split - flame produced

:O I've never heard that before. Or read it. And when I google test for alcohol, my google-fu fails me.
Some say add potassium dichromate/turns orange to green

 

[wooowooowoo]

:O I've never heard that before. Or read it. And when I google test for alcohol, my google-fu fails me.
Some say add potassium dichromate/turns orange to green

Even that is a test
Check ON 10 62

 

[ZainH]

Hmm concentration of an acid
The best method would be to titrate it against an alkali of known concentration
Put 25cm3 of the acid into a beaker, and add some phenolpthalein.
Add the alkali with a burette drop by drop until the end point is reached
We'll then know the volume of alkali needed to neutralize 25cm3 of the acid
You then use calculations to find the concentration of the acid
First you have to write the balanced equation
e.g. HCl + KOH -> KCl + H2O
If we know the volume and concentration of the alkali used we can find the number of moles of alkali right? Then using the mole ratio from the equation (in this case 1:1) we can find the number of moles of acid in 25cm3 of acid.
Then it's easy - concentration = number of moles divided by volume. Just remember the volume should be in dm3 (where 1000cm3 = 1 dm3) so the concentration can be the standard mol/dm3
If you find an example question I'll answer it for you

Well your explanation helped in the way that I went back and looked at my answer, noticed that was straight forward x)
But thanks anyways, prepare yourself for MOREEE questions.

 

[ThatReallyReallyWeirdDude]

Even that is a test
Check ON 10 62

Ahh thanks

 

[Chucky]

I'm glad I could help.
If you encounter any flaw in it, do let me know. Thanks

i posted some additional points in afraahs thread (its a reply to your post)
add them here too, and let people know!

 

[ZainH]

Paper :http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_6.pdf
This is the mark scheme, just go to question 5)h)

The question itself says what conclusions can you draw about salt E? I get the answer, just need a good way to write it.

 

[wooowooowoo]

Paper :http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_6.pdf
This is the mark scheme, just go to question 5)h)

The question itself says what conclusions can you draw about salt E? I get the answer, just need a good way to write it.

Fe(ii)+ with presence of ammonium and sulphate

 

[ZainH]

Fe(ii)+ with presence of ammonium and sulphate

All right thanks, and another small question. When plotting points on a graph for say the reaction of a catalyst from data on a table, if at 0 seconds the volume of oxygen produced is 0, should I also plot this on the graph? Or leave it?

 

[Sara5396]

how to know when the graph is a curve or a straight line or joined by a scale?

 

[wooowooowoo]

All right thanks, and another small question. When plotting points on a graph for say the reaction of a catalyst from data on a table, if at 0 seconds the volume of oxygen produced is 0, should I also plot this on the graph? Or leave it?

If it is given you will have to plot it. It's good the graph is starting from the origin, anyway I'm off for now. It was nice answering your questions, if weirdude is here he'll answer your further questions.
Good night! Best of luck for your exam