I think you actually saved my chemistry a level, I by chance came across your paper 3 predictions video and am now head down watching all the videos on this playlist and the multiple choice playlist. I wish I had found this channel before, I cant thank you enough for this !
Question 2b. Should we know that Aluminium dissolves in excess NaOH. Has it got something to do with the fact that Al and Mg are both period 3 elements
Aluminum hydroxide dissolves in excess sodium hydroxide (NaOH) because it is an amphoteric substance. Amphoteric substances can act as either acids or bases depending on the conditions. In the presence of excess NaOH, aluminum hydroxide behaves as an acid and reacts with the hydroxide ions from the NaOH to form a soluble aluminate ion, Al(OH)4^-1 Most other metal hydroxides, including Mg(OH)2 can't do this.
for the last q , when adding AgNO3, the carbonate ion would react and form AgCO3(also a white precipitate), instead of adding more acid, can i say bubble through limewater, so effervescence of CO2 is produced?
That would work in theory... adding acidified AgNO3 will give no visible change, effervescence or a silver halide precipitate. That being said, in exam questions, they prefer it if you treat each test as a separate item. If you wanted to be more concise, add the acid first, not the absence/presence of bubbling, then add the AgNO3 and look for a PPT
For silver nitrate you need your halide ion to be in solution, so it's not especially feasible. Usually they also want a test tube reaction, so something fairly straightforward
You write the equations down for the reactions where you've made an observable change, because the observable change (ppt or fizzing) tells you a chemical reaction has occurred. If there is no observable change, then there's no chemical reaction. Which is why you don't write the equation for any of the reactions with fluoride. There have been no observable changes because there hasn't been a reaction. You only write equations when there has been a change. If you were to write an equation, there would be the same chemicals on both sides, which is something we don't do. We delete anything that's on both sides of an equation... so that would be all the chemicals removed... so no equation
Silver nitrate is the test for chloride ions. NaOH gives precipitates with Mg2+ ions and Al3+ ions. Both are white but the aluminium hydroxide precipitate dissolves in excess NaOH
@user-vq4qy2hq5i I think you're thinking of testing for the nitrate ion? Which is NaOH, Aluminium powder and then the damp litmus paper (which turns blue) If chlorine gas is being produced though, it does Bleach litmus paper
@user-vq4qy2hq5i most of it is from group 2 and group 7 topic. Flame test is extra but nothing more really. The fact its an required practical just means it's more likely that this experiment is on exams
at 9:35 you said you would have to add acid separately to the acidified silver nitrate to find the carbonate ion. wouldn't just doing the one test work as there is acid in the first test
You can add them together, but that way you will probably miss the effervescence (as the bubbles are masked by the ppt) So you'll now you've definitely got chloride, but you won't know that you did or didn't have carbonate. You only get that if you add the acid first
For RP4, That's because they are commonly woven in to other topics and so are small bits here and there. Have you seen my other videos about RP2 and 7?
It really isn't obvious I agree. The most likely link is for maybe a precipitation reaction that collects and weighs all of the precipitate. Then you can do a range of calculations using the ionic equation for the reaction, e.g.: *Percentage purity of a reactant *formula of a reactant (using mole ratios)
It's one of the ppt you need to know. Since nitrate doesnt form a ppt, its the magnesium ion making a white precipitate. This means compound Y contained OH- as MgOH)2 is the only white Mg ppt you need
I think you actually saved my chemistry a level, I by chance came across your paper 3 predictions video and am now head down watching all the videos on this playlist and the multiple choice playlist. I wish I had found this channel before, I cant thank you enough for this !
hey girl me too😅 are you doing past papers as well or just the playlist?
@@chinwenduanaegbu Im watching them all, then gonna go and do past papers!
It's really lovely to know they're useful!
Good luck tomorrow 😀
Thank you for this. I never actually understood this before and now I do!!
Brilliant! I'm really pleased it's helped you 😊
Hi will you ever make exam question videos on the other practicals for aqa? Would be great!
Yes, definitely. I'll start making them in September
don’t have to do my hw now. Beautiful.
Glad it was useful!
Thank you it is really helpful!
You're very welcome, glad it's useful! 😃
Question 2b. Should we know that Aluminium dissolves in excess NaOH. Has it got something to do with the fact that Al and Mg are both period 3 elements
Aluminum hydroxide dissolves in excess sodium hydroxide (NaOH) because it is an amphoteric substance. Amphoteric substances can act as either acids or bases depending on the conditions. In the presence of excess NaOH, aluminum hydroxide behaves as an acid and reacts with the hydroxide ions from the NaOH to form a soluble aluminate ion, Al(OH)4^-1
Most other metal hydroxides, including Mg(OH)2 can't do this.
Amazing this is saving my alevels!
Thanks 😊
You've got this!
Hi, since the practical is linked to amount of substance, is it likely you will need to know all the reactions/method? Thank you :)
I think its likely you'll need to know Reagents and conditions and what the result mean, but not more than that I'd think
@@chemistrytutor Thank you!
@@Katie-kz9ui ua-cam.com/video/N71MWJax-_c/v-deo.html
Might be useful
for the last q , when adding AgNO3, the carbonate ion would react and form AgCO3(also a white precipitate), instead of adding more acid, can i say bubble through limewater, so effervescence of CO2 is produced?
That would work in theory... adding acidified AgNO3 will give no visible change, effervescence or a silver halide precipitate. That being said, in exam questions, they prefer it if you treat each test as a separate item. If you wanted to be more concise, add the acid first, not the absence/presence of bubbling, then add the AgNO3 and look for a PPT
Al3+ ions came in paper 3 and I only knew cause I watched this video Thank you so much
That's brilliant! I'm really glad it was useful! 👍
could you react with conc H2SO4 to give misty fumes of HCl and HF and then differentiate those with AgNO3 ?
For silver nitrate you need your halide ion to be in solution, so it's not especially feasible. Usually they also want a test tube reaction, so something fairly straightforward
For question 3, how would you know which equations to write down, and why wouldn't you write the equation for the reaction with fluorine?
You write the equations down for the reactions where you've made an observable change, because the observable change (ppt or fizzing) tells you a chemical reaction has occurred. If there is no observable change, then there's no chemical reaction.
Which is why you don't write the equation for any of the reactions with fluoride. There have been no observable changes because there hasn't been a reaction. You only write equations when there has been a change. If you were to write an equation, there would be the same chemicals on both sides, which is something we don't do. We delete anything that's on both sides of an equation... so that would be all the chemicals removed... so no equation
i really like these exam question walkthrough videos. Glad i found your channel
Thank you 😊
I really appreciate the feedback!
For question 2b, is NaOH not used to test for chlorine rather than Mg or Al? How would it differentiate between metals in 2 different groups?
For question 3, where it says a named acid, could we just say nitric acid added to sodium carbonate would give effervescence?
@user-vq4qy2hq5i yes, any acid will give effervescence with a carbonate
Silver nitrate is the test for chloride ions. NaOH gives precipitates with Mg2+ ions and Al3+ ions. Both are white but the aluminium hydroxide precipitate dissolves in excess NaOH
@@chemistrytutor Is another way to test for chlorine gas not adding NaOH and using litmus paper?
@user-vq4qy2hq5i I think you're thinking of testing for the nitrate ion? Which is NaOH, Aluminium powder and then the damp litmus paper (which turns blue)
If chlorine gas is being produced though, it does Bleach litmus paper
Why would sodium hydroxide differentiate between magnesium and aluminium?
Aluminium hydroxide (white precipitate) is soluble in excess sodium hydroxide
@@chemistrytutor Is this part of one of the tests learnt in the theory section, or is this just a miscellaneous fact to remember?
@user-vq4qy2hq5i most of it is from group 2 and group 7 topic. Flame test is extra but nothing more really. The fact its an required practical just means it's more likely that this experiment is on exams
would i lose marks for saying bacl2 + hcl on second question
Definitely not! That's the correct acid and so you've given correct additional information 😀
at 9:35 you said you would have to add acid separately to the acidified silver nitrate to find the carbonate ion. wouldn't just doing the one test work as there is acid in the first test
Yes, best to add nitric acid first in any case followed by the silver nitrate. Effervescance for the carbonate and white ppt for the chloride.
You can add them together, but that way you will probably miss the effervescence (as the bubbles are masked by the ppt)
So you'll now you've definitely got chloride, but you won't know that you did or didn't have carbonate. You only get that if you add the acid first
Outstanding
Thanks 😊
why do we need to add water for the last question
The samples are in solid form. They need to be solutions before we can do our chemical tests
Where can I find more Rp 2,4 and 7 exam questions? I cant find prac 4 Qs anywhere?
For RP4, That's because they are commonly woven in to other topics and so are small bits here and there.
Have you seen my other videos about RP2 and 7?
sir i don't understand how RP4 is linked with amount of substance?
It really isn't obvious I agree. The most likely link is for maybe a precipitation reaction that collects and weighs all of the precipitate.
Then you can do a range of calculations using the ionic equation for the reaction, e.g.:
*Percentage purity of a reactant
*formula of a reactant (using mole ratios)
Thank you sir, appreciate it!
For question 1, how do you know its mgOH2?
It's one of the ppt you need to know. Since nitrate doesnt form a ppt, its the magnesium ion making a white precipitate. This means compound Y contained OH- as MgOH)2 is the only white Mg ppt you need
x
Good luck 👍