Chemistry: Post your doubts here!

[daredevil]

Most modern cars are fitted with airbags. These work by decomposing sodium azide to liberate
nitrogen gas, which inflates the bag.
2NaN3
3N2 + 2Na
A typical driver’s airbag contains 50 g of sodium azide.
Calculate the volume of nitrogen this will produce at room temperature.

A 9.2 dm3 B 13.9 dm3 C 27.7 dm3 D 72.0 dm3

calculate the Mr of NAN3 ...
caculate the moles of NaN3 in 50 g of NaN3 by 50/Mr
use the ratio method to calculate the moles of N2 produced
if 2 mole of NaN3 produces 3 moles of N2 then how many moles will (calculated moles) produce?

calculate the volume using the molar gas volume:
moles * 24 = volume of N2

 

[ahmed abdulla]

My new Thread :
With notes + practical tips ect
Have a look { https://www.xtremepapers.com/commun...al-tips-some-important-notes-dont-miss.31108/ }

 

[salvatore]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_51.pdf
Could someone please help me with qn no. 2(a) of this paper? To calculate the mass of zinc, why do we have to use (B - D) and not (B - A)?
Thanks

I'm re-posting this.. anyone??

 

[thats_me]

Use of the Data Booklet is relevant to this question.
A student mixed 25 cm3 of 0.10 mol dm–3 sodium hydroxide solution with 25 cm3 of 0.10 mol dm–3
hydrochloric acid and noted a temperature rise of 2.5 °C.
What is the enthalpy change of the reaction per mole of NaOH?
A –209 kJ mol–1
B –104.5 kJ mol–1
C –209 J mol–1
D –522.5 J mol–1

 

[daredevil]

I'm re-posting this.. anyone??

we need to know the amount of zinc that was used. To do that we have to subtract the total zinc from that which remained in excess. Thus B-D
Do you get it?

If we do B-A we will only subtract the weight of empty test tube and that will only give us the mass of zinc we took initially and is not any help.

If there is further problem do ask

 

[salvatore]

we need to know the amount of zinc that was used. To do that we have to subtract the total zinc from that which remained in excess. Thus B-D
Do you get it?

If we do B-A we will only subtract the weight of empty test tube and that will only give us the mass of zinc we took initially and is not any help.

If there is further problem do ask

That makes perfect sense.. dunno why I couldn't think of that.
Thanks mate..

 

[abruzzi]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_4.pdf
Someone please help me with question 4b (i & ii). It looks pretty easy but I don't know what to do.
ThankYou

 

[skinnyboyfat]

Somebody explain please
got a test tommorow .....

 

[NaNinG]

well,its not a doubt in particular.
but
http://www.chemguideforcie.co.uk <------------This website,i guess most of us use it,(if u dont,look at it its great)
does ny1 here know where i can get the PDF format or jus word format of the data it contains per topic,cuz copy pasting takes like 4 ever.

 

[mahabaloch]

anyone can help me how to make isomers i always get stuck in that?

 

[hassankhan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w03_qp_4.pdf
Q4 part c anyone??

 

[abruzzi]

I just can't get my head through this question. Please help me understand how to balance such types of questions.
I'll be grateful for any tips/tricks given.

 

[sweetiepie]

i have compiled all necessary stuff here https://www.xtremepapers.com/community/threads/some-different-notes-website-are-available.10423/ i hope it helps evryone

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf.
Question 9 please

 

[asma tareen]

What does mono basic mean :/??

 

[daredevil]

What does mono basic mean :/??

a base which, when it dissociates, releases ONE OH- ion (hydroxyl ion)
e.g. NaOH, CH3COOH, etc.

likewise a monoacidic e.g. HCl, HNO3, etc


there are dibasic : Mg(OH)2 ; Ca(OH)2
diacidic : H2SO4

and so on so forth.... If you dont get it then tell me and I'll explain further

 

[asma tareen]

I got it thnx alot

 

[BreakingBad]

anyone can help me how to make isomers i always get stuck in that?

Isomers of what, exactly?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_4.pdf
Q4 part c anyone??

Q4
c) i) G is strongest. Then E. Then F.
ii)
Here's the concept. Carboxylic acids are stronger than all alcohols because the O=C - O - H group has 2 oxygen atoms causing resonance and making it easier for it to lose the H+ ion. Which means that it's easier for it to dissociate in water, hence carboxylic acids are stronger than alcohols (it would be more accurate to call them phenols as their OH group is attached to the ring) which only have an -OH group. The ring in phenol acts as electron donating group making phenols stronger than aliphatic alcohols (not required for this question). The compound F, however, neither has an OH group nor a O=C - O - H group, making it least acidic.
This is the reasoning behind the reactions that take place and the reactions that don't take place when using the compounds above.
Carboxylic acids (including compound G) react with NaOH (forming salt and water) and Na2CO3 (forming salt, water and CO2)
Phenols (including compound E) react with NaOH (salt and water). However, they don't react with Na2CO3 (being less acidic than carboxylic acids).
Compound F will not react with either one as it is the weakest.

I just can't get my head through this question. Please help me understand how to balance such types of questions.
I'll be grateful for any tips/tricks given.

Edit:
I realized that what i was doing was a waste of time. The right way to do this is to see both the MnO4- equation and the Mn2+ equation from the data booklet, balance the electrons and merge the equations according to reduction and oxidation reactions.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf.
Question 9 please

Moles of metallic salt = vol. * conc. = 5*10^-3
Moles of sodium sulphite = vol. * conc. = 2.5*10^-3

Mole ratio = 1:2
Hence electron ratio = 1:2
The sodium sulphite ion gives 2 electrons. Using the ratio, we can understand that 1 mole of metallic salt would receive 1 electron.
Initially, it was +3. Add an electron and we get +2. Answer is B.

 

[Isaac CKR]

Calculate the pH of the solution formed by mixing 60cm^3 of 0.2 mol dm^-3 of ethanoic acid with 40cm^3 of a 0.10 mol dm^-3 of sodium hydroxide. Ka for ethanoic acid = 1.80 x 10^-5 mol dm^-3 .

Can anyone help me with this? (Calculating the pH during weak acid-strong base titration)

 

[BreakingBad]

Calculate the pH of the solution formed by mixing 60cm^3 of 0.2 mol dm^-3 of ethanoic acid with 40cm^3 of a 0.10 mol dm^-3 of sodium hydroxide. Ka for ethanoic acid = 1.80 x 10^-5 mol dm^-3 .

Can anyone help me with this? (Calculating the pH during weak acid-strong base titration)

I have a method in mind. If you can tell me the answer i might be able to help you (considering it matches my answer)