Biology; Chemistry; Physics: Post your doubts here!

[Dukeofwin]

Q. when we write a test for a gas (e.g. Hydrogen) then do we also need to write the result of the test (e.g. bring a lighted splint in contact and the gas burns with a pop sound or do we just write bring a lighted splint in contct with the gas and its enugh)??

Depends on the question, but usually they always ask the result with the test. And there would be no mark deduction if you write result with the test!
So just do write it if you know it!

 

[Rimsa]

in the CHEM ATP
to how many decimal places do we h ave to round our answer to?
e.g if the number of moles is 0.000247
sometimes they round off in the markscheme and sometimes they do..so wat should i do?

3 significant figures

 

[daredevil]

Depends on the question, but usually they always ask the result with the test. And there would be no mark deduction if you write result with the test!
So just do write it if you know it!

thx
can u answer my other question too that do we have to extend the graph to the y-acis when its a curve even though we don't have the values for it? see Q.11 from Nov1999 p4 chemistry. thnx in advance

 

[Rimi]

Why are the products of the electrolysis of AQUEOUS (NOT conc.) sodium chloride, Chlorine and Hyrdogen?? Why not Oxygen and Hydrogen?? >.<

 

[Soulgamer]

I'm doing A-levels right now but I had some sweet notes for electrolysis. It was related to the electrochemical series. This might help you.

At cathode​

• In CONCENTRATED solutions of nickel/lead compound, nickel/lead will be discharged instead of hydrogen ions of water which is less reactive than nickel/lead.
• In VERY DILUTE solutions, hydrogen, copper and silver ions are preferable to be discharged, according to its ease to be discharged.
• Reactive ions (potassium, sodium, calcium, magnesium, aluminium) will NEVER BE DISCHARGED in either concentrated or dilute condition. Instead, hydrogen ions from water will be discharged at cathode.
• At anode
  • In CONCENTRATED solutions, iodine/chlorine/bromine ions are preferable to be discharged, although it’s harder to discharged compared to hydroxide ions.
  • In VERY DILUTE solutions containing iodide/chloride/bromide ions, hydroxide ions of water will be discharged instead of iodide/chloride/bromide, according to ease of discharge.
  • Sulphate and nitrate are NEVER DISCHARGED in concentrated/dilute solutions.

 

[Dukeofwin]

thx
can u answer my other question too that do we have to extend the graph to the y-acis when its a curve even though we don't have the values for it? see Q.11 from Nov1999 p4 chemistry. thnx in advance

What do you mean extend?
We have to plot for potassium nitrate, and we have the values for it!
Which curve are you talking about?

 

[Dukeofwin]

thx
can u answer my other question too that do we have to extend the graph to the y-acis when its a curve even though we don't have the values for it? see Q.11 from Nov1999 p4 chemistry. thnx in advance

Oh i get it now!
No extension required! Just plot the graph to the given values! There would be no mark deduction if you do it correct but you may be penalised for doing it wrong!
So its preferred to stick to the requirement, and plot till the VALUES.

 

[Rimsa]

I'm doing A-levels right now but I had some sweet notes for electrolysis. It was related to the electrochemical series. This might help you.
.............

• • Sulphate and nitrate are NEVER DISCHARGED in concentrated/dilute solutions.

wow. that helped. by the wya, when they say aq, it means its conc or dilute?

 

[Soulgamer]

wow. that helped. by the wya, when they say aq, it means its conc or dilute?

https://sites.google.com/site/urban...trolysis#TOC-Electrolysis-of-Aqueous-Solution

 

[Dukeofwin]

wow. that helped. by the wya, when they say aq, it means its conc or dilute?

It means DILUTE!

 

[Dukeofwin]

https://sites.google.com/site/urban...trolysis#TOC-Electrolysis-of-Aqueous-Solution

Awesome Website!
Thanks alot!

 

[Rimsa]

https://sites.google.com/site/urban...trolysis#TOC-Electrolysis-of-Aqueous-Solution

It means DILUTE!

thanks

 

[luckywang]

in the CHEM ATP
to how many decimal places do we h ave to round our answer to?
e.g if the number of moles is 0.000247
sometimes they round off in the markscheme and sometimes they do..so wat should i do?

according to syllabus, we should round up titration to nearest 0.1cm3, temperature to nearest 0.5 degree Celsius, and time to nearest second... nothing about mole... 3 sig.fig?

 

[luckywang]

I'm doing A-levels right now but I had some sweet notes for electrolysis. It was related to the electrochemical series. This might help you.

At cathode​

• In CONCENTRATED solutions of nickel/lead compound, nickel/lead will be discharged instead of hydrogen ions of water which is less reactive than nickel/lead.
• Reactive ions (potassium, sodium, calcium, magnesium, aluminium) will NEVER BE DISCHARGED in either concentrated or dilute condition. Instead, hydrogen ions from water will be discharged at cathode.

if potassium, sodium, calcium, magnesium,aluminium in molten state? what is being discharged? coz no water present in molten state...

 

[Dukeofwin]

Stop confusing yourself with rounding figures!
Just make sure ,if you have the value 0.000287, then rounding it off to 0.0003 would be incorrect instead it could be rounded off to 0.00029!
Otherwise keep the value SAME, *no need to round it off*

 

[a.abid]

group 1 and 2 metals are all grey right?

Are you sure of this? :/

 

[Rimsa]

group 1 and 2 metals are all grey right?

arent they colorless? :O

 

[SALT]

Calculate the moles of both.the moles of Q are double tht of P so it will produce double volume of hydrogen and because e concentration of p is more thn Q so the reaction will go faster!

look at the question again...
it says tht for P we use zinc PIECES
and for Q we use POWDER!
do we hav to look at the speed of reaction according to this or the conc.??

 

[SALT]

It means DILUTE!

nopes, wen its not mentioned, we assume it to be conc.

 

[Dukeofwin]

Please answer the question attached! We had to find the molecular mass of 'T'!
Just tell the method to solve it.
Thanks