Lets Solve A's chem MCQ paper together.

[xhizors]

ok our first paper going live
Venue: Skype- muhammad.devdeen
Date/Day: today (sunday) 5pm Pakistan Time
Moto: mastery in 9701/11
MCQ year: 2010 summer.

Lets do it with Allah's help..

 

[wajji345]

i love this idea....

but we don't have enough time now.

 

[xhizors]

we should give it a try atleast

 

[smartangel]

Regarding Question 16

You are right on that Sodium hydroxide IS the main product. Howver, Don't forget that Cl2 and H2 are also given out at the anodes and cathodes respectively. Instead of just throwing the two gases away they are used. H2 can be used in the Haber process. Cl2 can be used in manufacture of paper and other stuff too. As a result, the two gases are considered products of the Electrolysis of Brine.

Hence, the answer is A. It's not B or C because the diaphragm cell prevents Cl- ions to cross the membrane and react with OH- ions to give Sodium Cholorate (NaClO). It's not D because Sodium Hydroxide is the main product and not "among the main products" as the question puts it.

your explanation does make sense but the answer is B as per the marking scheme..

 

[xhizors]

paper is live

 

[smartangel]

so how"d it go guys?

 

[saudha]

but we don't have enough time now.

yup you are right .... so lets just prepare ourselves as much as we can.....

 

[wajji345]

ok our first paper going live
Venue: Skype- muhammad.devdeen
Date/Day: today (sunday) 5pm Pakistan Time
Moto: mastery in 9701/11
MCQ year: 2010 summer.

Lets do it with Allah's help..

OH MAN, on skype.. That would have been really helpful... I thought we have to post our queries here. Shit

 

[donorsolutions]

i really need help with these questions.. 1,4,8,15,16,25,26,29,36.. in some of them i do have an explanation for my answer but apparently they:re wrong so if someone could please correct me!​

in 16 isnt the major product of the electrolysis of brine, NaOH?​

1n 25 (2.76 - 2.07)/2.76 x 100 gives us 75%. so why isnt B the answer?​

in 29..why cant C be the right answer? im getting 3 Ch3 and 3 Ch2..​

in 36..if we consider Sulfur then it doesnt form a basic hydride?​

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf​

i know these are quite a lot of questions but please do help me out because i think this is the 5th time im posting it in this forum but no one answered as yet ​

Here is the theory behind Question 16 : Basically in the electrolysis of brine, we use a diaphgram, so that NaOH and Cl2 do not react together.
However, in this question it says that the products are reacted together, with THE CELL KEPT COLD.
If you remember we have studied disproportionation(where chlorine is oxidised and reduced simultaneously), when it reacts with NaOH. These reactions are in our AS syllabus and can be found and studied in Group 7.
Anyways, there are 2 different products when NaOH reacts with Cl2 .
In Hot Solution : Sodium Chlorate(V) is produced.
In Cold Solution : Sodium Chlorate (I) is produced.
Now we know that the cell is kept cold, so definitely Sodium Chlorate(I) will be the product along with Hydrogen.

Hope that Helps

Regarding 8, you have to notice in the first reaction that water is acting like an acid. Its donating H+ ions so, we will call it acid. So what else remains of the water is OH- ions (which we call the conjugate base). This conjugate base reacts with SO2 (because it reacts with a base SO2 must be an acid), When it reacts as an acid it forms a conjugate base (HSO3). So definitely HSO3 is a base.

 

[smartangel]

Here is the theory behind Question 16 : Basically in the electrolysis of brine, we use a diaphgram, so that NaOH and Cl2 do not react together.
However, in this question it says that the products are reacted together, with THE CELL KEPT COLD.
If you remember we have studied disproportionation(where chlorine is oxidised and reduced simultaneously), when it reacts with NaOH. These reactions are in our AS syllabus and can be found and studied in Group 7.
Anyways, there are 2 different products when NaOH reacts with Cl2 .
In Hot Solution : Sodium Chlorate(V) is produced.
In Cold Solution : Sodium Chlorate (I) is produced.
Now we know that the cell is kept cold, so definitely Sodium Chlorate(I) will be the product along with Hydrogen.

Hope that Helps

Regarding 8, you have to notice in the first reaction that water is acting like an acid. Its donating H+ ions so, we will call it acid. So what else remains of the water is OH- ions (which we call the conjugate base). This conjugate base reacts with SO2 (because it reacts with a base SO2 must be an acid), When it reacts as an acid it forms a conjugate base (HSO3). So definitely HSO3 is a base.

in Q8.. i do understand the first equation.. however in the second one HSO3 is losing H+ so doesnt it make an acid??

 

[xhizors]

ok guys are u interested in second paper (live) ??

 

[leosco1995]

Hey... I am also interested. Why don't we do all past papers live from Nov 2002 to Nov 2011 over the course of the next few days? Some people like me don't have a Skype ID so could we use some online chatroom instead? There are many sites where you can create your own chatrooms so maybe we could use one of those..?

In any case, I would love to have live past paper discussions. It's irritating when there's an MCQ I can't solve and I have to deal with it until I can ask my teacher. But if you guys are busy, nevermind.

 

[xhizors]

Hey... I am also interested. Why don't we do all past papers live from Nov 2002 to Nov 2011 over the course of the next few days? Some people like me don't have a Skype ID so could we use some online chatroom instead? There are many sites where you can create your own chatrooms so maybe we could use one of those..?

In any case, I would love to have live past paper discussions. It's irritating when there's an MCQ I can't solve and I have to deal with it until I can ask my teacher. But if you guys are busy, nevermind.

I am in,, no problem,, so whats the plan ??
which chatroom and what time?? we must start up hurry

 

[robotic94]

How many years have you guys practiced?
2002 to 2011 eh?