Edexcel AS level Unit 3B: Chemistry Laboratory Skills I Alternative May 7 2014

Scroll to see replies

Reply 20

ahd303

Original post by Paras Agarwal

okay cool thank you guys! we shall all pass :biggrin:

never came across that anti bumping granules thing, where did you see it?

Reply 21

Ripper Phoenix

Original post by ahd303

never came across that anti bumping granules thing, where did you see it?

its not there in a paper..its always used during distillation and reflux and i wondered why so i decided to ask y'áll

Reply 22

ahd303

how do you know what cation it is when they only mention ''red'' ? there is crimson red, brick red and carmine red.

Reply 23

Ripper Phoenix

Original post by ahd303

how do you know what cation it is when they only mention ''red'' ? there is crimson red, brick red and carmine red.

its always calcium as the "red" unless otherwise.. i remember in jan/june 10 they said clearly that a red flame is observed for a group 1 cation so in that case it was lithium

Reply 24

ahd303

Original post by Paras Agarwal

its not there in a paper..its always used during distillation and reflux and i wondered why so i decided to ask y'áll

which one of the three halogenoalkane form ppt faster? primary, secondary or tertiary?

Reply 25

hhalai96

Only red can only mean lithium or strontium

Reply 26

Ripper Phoenix

Original post by hhalai96

Only red can only mean lithium or strontium

u forgot calcium too

Reply 27

Ripper Phoenix

Original post by ahd303

which one of the three halogenoalkane form ppt faster? primary, secondary or tertiary?

om gosh i just called up my teacher to ask him this question.. its tertiary alcohol because the methyl groups weaken the C-X bond..the more the methyl groups the faster the reaction

(edited 9 years ago)

Reply 28

ahd303

Original post by Paras Agarwal

om gosh i just called up my teacher to ask him this question.. its tertiary alcohol because the methyl groups weaken the C-X bond..the more the methyl groups the faster the reaction

hahaha XD thanx alot :biggrin:

Reply 29

ahd303

Original post by Paras Agarwal

om gosh i just called up my teacher to ask him this question.. its tertiary alcohol because the methyl groups weaken the C-X bond..the more the methyl groups the faster the reaction

CAN YOU PLEASE CHECK OUT JUNE 2010 Q2 A(iii) THE MARK SCEHME GAVE THE ANSWER AS A SECONDARY H.A IF IM NOT MISTAKEN.

Reply 30

Ripper Phoenix

Original post by ahd303

CAN YOU PLEASE CHECK OUT JUNE 2010 Q2 A(iii) THE MARK SCEHME GAVE THE ANSWER AS A SECONDARY H.A IF IM NOT MISTAKEN.

yeah because in that case the only 2 HA are primary and secondary.. lol because C3H7I cannot form tertiary halogenoalkane hence the only options are primary and secondary ...so secondary...

if u had a halogenoalkane with -but then its possible so you would say tertiary...

Reply 31

ahd303

Original post by paras agarwal

yeah because in that case the only 2 ha are primary and secondary.. Lol because c3h7i cannot form tertiary halogenoalkane hence the only options are primary and secondary ...so secondary...

If u had a halogenoalkane with -but then its possible so you would say tertiary...

ohhh okay. Excuse me for my stupidness :tongue:

thank you again

Reply 32

sorabackwards

Original post by ahd303

which one of the three halogenoalkane form ppt faster? primary, secondary or tertiary?

Obviously, the time taken for a precipitate of silver halide to appear will depend on how much of everything you use and the temperature at which the reaction is carried out. But the pattern of results is always the same.
For example:

•

A primary iodo compound produces a precipitate quite quickly.

•

A primary bromo compound takes longer to give a precipitate.

•

A primary chloro compound probably won't give any precipitate until well after you have lost interest in the whole thing!

The order of reactivity reflects the strengths of the carbon-halogen bonds. The carbon-iodine bond is the weakest and the carbon-chlorine the strongest of the three bonds. In order for a halide ion to be produced, the carbon-halogen bond has to be broken. The weaker the bond, the easier that is.

Reply 33

sorabackwards

Original post by ahd303

which one of the three halogenoalkane form ppt faster? primary, secondary or tertiary?

im not sure bout the primary, secondary and tertiary though :/

Reply 34

sorabackwards

Here's a more detailed explanation bout why tertiary halogenoalkanes produces ppt. the quickest

Comparing the reaction rates of primary, secondary and tertiary halogenoalkanes

You would need to keep the halogen atom constant. It is common to use bromides because they have moderate reaction rates. You could, for example, compare the reactivity of these compounds:

Again, the actual times taken will vary with reaction conditions, but the pattern will always be the same.
For example:

•

The tertiary halide produces a precipitate almost instantly.

•

The secondary halide gives a slight precipitate after a few seconds. The precipitate thickens up with time.

•

The primary halide may take considerably longer to produce a precipitate.

It is more difficult to explain the reason for this, because it needs a fairly intimate knowledge of the mechanisms involved in the reactions. It reflects the change in the way that the halide ion is produced as you go from primary to secondary to tertiary halogenoalkanes.

Reply 35

hhalai96

Tertiary than secondary Than primary
That order

Reply 36

Ripper Phoenix

GUUUYS! another quick question ... in the graph for extrapolation in jan 12 the q reads: why does this method give a more accurate result than the original procedure.. the answer states to correct for loss of heat during cooling... now what does that even mean??

Reply 37

hhalai96

The dilute nitric acid was measured per minute for 3 minutes... This ensures that the solution is in equilibrium to the surrounding... Giving an accurate results... I think so... Is this right?