Chemistry: Post your doubts here!

[Xaptor16]

2Mg(NO3)2 ----> 2MgO + 4NO2 + O2

The equation shows us that for every 4 moles of NO2 released, 1 mole of O2 is released.
Mass of NO2: (14 + 16x2) x 4 = 46 x 4 = 184 grams
Mass of O2: (16x2)x1 = 32 grams.
184/32 = 5.75 = 1/0.174 = A!

thankyou!

 

[Metanoia]

http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_qp_22.pdf

Question 4 b part i and ii

For part i, to find moles oh H2 you do
n = v/24 = 0.08/24
= 6.67 x 10^-3 mol

Now it asks you to find the moles for hydrogen ATOMS and not H2 ...
so that means a single atom of Hydrogen right?

So then wouldn't you divide 6.67 x 10^-3 mol by 2 to get the moles rather than multiply...
The mark scheme says multiply by 2 but then by doing that aren't you finding the moles for 2H2 instead of H?

Please explain why it's multiplied by 2?!?!?

1 mole of H2 = ? mol of H atoms

 

[nehaoscar]

a molecule of H2 has two hydrogen atoms so:
hydrogen molecule : hydrogen atom
1 : 2
6.67 x 10^-3 : x

x = ( 6.67 x 10^-3 ) x 2

Oh i see! Thankyou!

 

[Lola_sweet]

https://docs.google.com/viewerng/vi...11/9701_May-June-2011-All-Question-Papers.pdf

Qp 22
Qs)2a) hw do we calculate the bond energy

 

[asadalam]

Is So3 connected via PD PD forces or Van Der waals?Shouldnt it be PD PD Due to difference in e-vity of S and O?Or is SO3 symmetrical?.
Also are large scale uses of halogenoalkanes,naoh and other such compounds included.What are included.

Also when HCL is dissolved in water is the bonding changed to form ions of H30 and Cl or due to hydrogen bonds being formed?

Metanoia
The Sarcastic Retard

 

[Xylferion]

https://docs.google.com/viewerng/vi...11/9701_May-June-2011-All-Question-Papers.pdf

Qp 22
Qs)2a) hw do we calculate the bond energy

Delta H = Bonds broken - Bonds formed

You're already told the value of Delta H, so use that as a starting point. Now work out the total energy for bonds broken and the total energy for bonds formed.
Bonds broken:-

1 x C=C
4 x C-H
1 x H-F

Bonds formed :-

1 x C-F
5 x C-H
1 x C-C

Bonds broken = 610 + 4(410) + 562 = 2812 kJmol-1
Bonds formed = X + 5(410) + 350 = 2400 + X kJmol-1

X is the bond energy of C-F which we are going to find.

-73 kJmol-1 = 2812 - ( 2400 + X )
-73 = 2812 - 2400 - X
X = 2812 - 2400 + 73
X = 485 kJmol-1

Hope that helped!

 

[qwertypoiu]

Is So3 connected via PD PD forces or Van Der waals?Shouldnt it be PD PD Due to difference in e-vity of S and O?Or is SO3 symmetrical?.
Also are large scale uses of halogenoalkanes,naoh and other such compounds included.What are included.

Also when HCL is dissolved in water is the bonding changed to form ions of H30 and Cl or due to hydrogen bonds being formed?

Metanoia
The Sarcastic Retard

SO3 is symmetrical, it wouldn't have permanent dipole attraction.

 

[ashcull14]

 

[asadalam]

View attachment 52888

Look closely. Its the CH2OH group that is oxidised not the carbon youvd highlighted.so it can be oxidised

 

[qwertypoiu]

View attachment 52888

This is actually a primary alcohol.
-CH2OH means primary.
OH group is attached to a carbon atom that has two hydrogen atoms bonded to it.
Or, the OH group is attached to a carbon atom that is only bonded to one other carbon atom.

 

[Lola_sweet]

Delta H = Bonds broken - Bonds formed

You're already told the value of Delta H, so use that as a starting point. Now work out the total energy for bonds broken and the total energy for bonds formed.
Bonds broken:-

1 x C=C
4 x C-H
1 x H-F

Bonds formed :-

1 x C-F
5 x C-H
1 x C-C

Bonds broken = 610 + 4(410) + 562 = 2812 kJmol-1
Bonds formed = X + 5(410) + 350 = 2400 + X kJmol-1

X is the bond energy of C-F which we are going to find.

-73 kJmol-1 = 2812 - ( 2400 + X )
-73 = 2812 - 2400 - X
X = 2812 - 2400 + 73
X = 485 kJmol-1

Hope that helped!

THANK U SOOO MUCH!!!!!!!!!!

 

[The Sarcastic Retard]

Is So3 connected via PD PD forces or Van Der waals?Shouldnt it be PD PD Due to difference in e-vity of S and O?Or is SO3 symmetrical?.
Also are large scale uses of halogenoalkanes,naoh and other such compounds included.What are included.

Also when HCL is dissolved in water is the bonding changed to form ions of H30 and Cl or due to hydrogen bonds being formed?

Metanoia
The Sarcastic Retard

•It is a planar molecule with the oxygens spaced at 120 degrees around the central sulfur. Consequently it is perfectly symmetrical and has no dipole moment.
•Included in what, I dont get you. Sorry.
•Look at the image attached below:

 

[robinhoodmustafa]

Here's the mark scheme: http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_22.pdf

My doubt: How do I figure out how many lone pairs are present?

Draw the dot and cross of that compound. Un bonded pairs of electrons on the atom denotes the lone pair present

 

[princess Anu]

what do these terms imply;
monohydric
dibasic

 

[princess Anu]

can somebody explain how do we name this compound ;
(Ch3)2CBrCH3

 

[princess Anu]

can somebody post 2001 J/N question papers & marking scheme ?? pls

 

[princess Anu]

How do shell/ subshell/ orbital mainly differ from each other??

 

[Metanoia]

whats the reason for oxides getting more acidic as we move across the period

The short answer to this is to realize that the types of bonding changes from ionic to covalent across the Period.

The more in-depth answer is found in the paragraph below.



From Understanding Advanced Physical Inorganic Chemistry
http://www.worldscientific.com/worldscibooks/10.1142/7833

 

[qwertypoiu]

what does these terms imply;
monohydric
dibasic

A monohydric alcohol has only one hydroxyl group. (OH)
An example of such an alcohol would be ethanol, CH3CH2OH.

A dibasic acid has two hydrogen atoms that can ionise and form H+ ions.
An example would be H2SO4.

A dibasic salt is one that was formed by replacement of two hydrogen atoms from the acid. An example would be Na2HPO4.
This was obviously formed from H3PO4.

Please note that I just looked these words up, if anyone finds mistakes in what I've written please correct me.

 

[qwertypoiu]

can somebody explain how do we name this compound ;
(Ch3)2CBrCH3

2-bromo-2-methylpropane

The longest chain has 3 carbons.
The second carbon has a bromine atom and a methyl group attached. Perhaps it's easier to understand if the compound is written like this:
CH3C(CH3)BrCH3