Chemistry and Physics some Keypoints/Notepoints (onDemandOnly) !! :)

[Wanderer]

Does structural formula mean we have to draw the skeletal formula....for eg can't we write CNCH2CH2CH2CN instead of drawing it in a skeletal form...please please reply
In ms they usually give the skeletal..but isnt the formula i wrote also structural?

 

[knowitall10]

Does structural formula mean we have to draw the skeletal formula....for eg can't we write CNCH2CH2CH2CN instead of drawing it in a skeletal form...please please reply
In ms they usually give the skeletal..but isnt the formula i wrote also structural?

The mark scheme uses short cuts cz it's made 4 teachers YOu draw what u wer tot...it'll be right inshAllah.Yes, that's the structural formula..

 

[Wanderer]

The mark scheme uses short cuts cz it's made 4 teachers YOu draw what u wer tot...it'll be right inshAllah.Yes, that's the structural formula..

Thanks.Do you write it in a similar way or do you draw the skeletal formula too???

 

[knowitall10]

Thanks.Do you write it in a similar way or do you draw the skeletal formula too???

Draw the skeletal if they don't specify, and if you find it easier otherwise, they'll always specify, so draw what the question's asking you to

 

[Wanderer]

Can you help me in J10/42 Q3 part d??

 

[knowitall10]

Important:
Retardation Factor (Rf value)= dist. moved by solute/ dist. moved by solvent front

 

[knowitall10]

Can you help me in J10/42 Q3 part d??

can u please post the link? I have too many tabs open I'll get confused..please...or if u insist, i'll just look for it myself...

 

[PhyZac]

Can you help me in J10/42 Q3 part d??

Here,
I literally played with my calculator. But play it smartly, Si has 4 valency so least times, O has 2 and Cl has 1 so most.

I kept trying some 28 and 16 and 35 adding them etc, to get the following numbers, and main aim was to find 396, because since it is largest peak, so it must be the Mr. (others are fragment)

While playing with numbers I was able to find 133, 247 and 263 and knew how many of each element
Then try to make them in order of the valencies.

Then you can make out the shape.

I am sorry I wasn't able to give nice explanation, but that is what I did.

 

[knowitall10]

Here,
I literally played with my calculator. But play it smartly, Si has 4 valency so least times, O has 2 and Cl has 1 so most.

I kept trying some 28 and 16 and 35 adding them etc, to get the following numbers, and main aim was to find 396, because since it is largest peak, so it must be the Mr. (others are fragment)

While playing with numbers I was able to find 133, 247 and 263 and knew how many of each element
Then try to make them in order of the valencies.

Then you can make out the shape.

I am sorry I wasn't able to give nice explanation, but that is what I did.

I don't just like, i love MashAllah! Awesome explanation!

 

[1357913579]

I don't just like, i love MashAllah! Awesome explanation!

can u or anyone please help me at this problem
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w07_qp_4.pdf
number-6(a)(iii) and (Iv) please help

 

[Ariel Robert]

Wa iyyak PhyZac !
Thank you so much for your sweet prayers, May Allah Grant you twice of what you have prayed for me InshAllah!
And to iKhaled and Ariel Robert :
The GLC: Gas Liquid Chromatography.
-Principle: Partition
Mobile Phase: carrier gas- an inert gas that carries the components of the sample along.
Stationary Phase: non-polar, non-volatile liquid
Limitations: If a new compound is detected, then it will not have a mtch in the computer's database of retention times.
The area under each peak obtained is = 1/2 x base x height (the area of a triangle in other words)
If the peaks are very narrow or have similar base widths, then peak height may be used instead of peak area to estimate the proportion of components ina mixture.
for this method:

• the chromatogram must show peaks for tall the components in the mixture
• all tthe components of the mixture must be separated
• the detector must respond equally to the different components so that the peak area is directly proportional to the component concentration.

For a mixture of three esters, A, B, and C, the amount of each component would be:

(approx.) % of ester A= peak area (or height) of A/ sum of areas (or heights) of A, B, and C x 100
Uses:
> for testing steroids
>testing fuels in F1 motor racing.
>medical diagnosis in analysing blood samples
>possible to determine the %'s of dissolved oxygen, nitrogen, CO2, and CO in blood samples as small as 1.0 cm^3.
Note: Both HPLC and GLC have a detector which records retention times: how long it takes for each component to pass through the column.
iKhaled and all those who have the Chem Coursebook: The CD has excellent animations of GLC. Try them. For those who don't, please let me know, I'll explain it in a much more simple manner inshAllah
and please, no need for thank you's We're all here to help one another. Please do correct me if I am wrong anywhere at all.
Jazakum Allahu Khair!!!

Then which one is the glass chromatography?

 

[knowitall10]

Then which one is the glass chromatography?

Thin layer chromatography is glass chromatography

 

[PhyZac]

can u or anyone please help me at this problem
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_4.pdf
number-6(a)(iii) and (Iv) please help

Hydrolysis mainly means the break down of ester and amide bond (in our chemistry)
So as you see in carbaryl, it has amide and ester bonds.
And amide break between NH and CO
while ester between CO and O
so we will get [dont forget to add H]

CH3NH2
NaOCOONa [reason is it forms, carboxylic acid when breaks from both amide and ester, and since NaOH so Na is added not H]
2 benzene rings and OH

Reagents and conditions; learn this
NaOH (aq) heat and reflux

 

[knowitall10]

can u or anyone please help me at this problem
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_4.pdf
number-6(a)(iii) and (Iv) please help

For part iii, I'm getting benzanoic acid and methylamine...I don't know if it's right, and i can't get the third product.
for part iv, it's the typical hydrolysis reagents, right? Either: dilute HCl Or: NaOH.
If i'm wrong please tell me...

 

[knowitall10]

Hydrolysis mainly means the break down of ester and amide bond (in our chemistry)
So as you see in carbaryl, it has amide and ester bonds.
And amide break between NH and CO
while ester between CO and O
so we will get [dont forget to add H]

CH3NH2
NaOCOONa [reason is it forms, carboxylic acid when breaks from both amide and ester, and since NaOH so Na is added not H]
2 benzene rings and OH

Reagents and conditions; learn this
NaOH (aq) heat and reflux

Excellent! Jazak Allahu Khair!

 

[anishniroula]

No..not a soft copy..that's the problem... maybe you'll just have to go through the book: I don't take Phy so i dont know if the book is the best source out there...
Sorry i can't help..

Okay! you did your best. Recently i found study guide. Thank you.

 

[knowitall10]

Okay! you did your best. Recently i found study guide. Thank you.

No problem I can always try to help!

 

[knowitall10]

ASSALAMU 'ALAYKUM WA RA7MATULLAH GUYS!!!
I'm posting this in the main three chem threads, please inform everyone: The Hydrolysis of the Diazonium Salt is not mentioned in our books; although some of us know it, there're those who probably don't. I uploaded a photo. Please make a note of it. I don't want any one of us to miss out on any important concepts so I'm uploading it as a full image so that we're all able to view it.

 

[knowitall10]

Another important concept not mentioned in our books:

For Diazotization and coupling reactions:
Step 1 is the reaction between phenylamine and nitrous acid (nitric (III) acid), HNO2, to give a diazonium salt. This is what we know.
But nitrous acid is unstable and has to be made in a test tube, then the phenyl amine is added:
Nitrous Acid is made using sodium nitrite (sodium nitrate(III)) and dilute HCl:
NaNO2 + HCl ------> HNO2 + NaCl and then, the production of benezene diazonium chloride takes place (which we all know about)

 

[knowitall10]

Ring Activating groups (Substitute in the 2,4 and 6 positions): -alkyl, -OH, -NH3
Ring De-activating groups (substitute at the 3 and 5 positions): -COOH, -NO2, -carbonyl, -Cl2

If there're any more anyone wants to add to the list, or if I'm wrong, please do mention it
Your help is appreciated!!!