Chemistry Doubts: IGCSE Paper 3

[Maz]

but why is it different? seems like the same monomers in both but its just reversing or something....ok to make it clearer can you tell me the monomers of both of those?

I am sorry i don't know the monomers.
However notice here that in the protein, there is NH and CO on either side of all kinds of boxes.-NH-[]-CO-
In nylon there are 2 types of boxes, one having CO on either side and the other having NH on either side.(-NH-[]-CO-)and(-CO-[]-CO-)

 

[Mozmozil]

Hello,,can u help me with this pleease,,

CH4 + 2O2 → CO2 + 2H2O

Energy needed to break bonds: 4 (C-H): 435 x 4 = 1740 KJ/Mol 2 (O=O): 497 x 1 = 994 KJ/Mol Total energy in: 1740 + 994 = 2734 KJ/Mol Energy needed to form bonds: 2 (C=O): 803 x 2 = 1606 KJ/Mol 4 (H-O): 464 x 4 = 1856 KJ/Mol Total energy out: 1606 + 1856 = 3462 KJ/Mol ΔH= 2734 – 3462 = -728 KJ/Mol r Therefore reaction is Exothermic

Now my question is ,,why didnt we time 2O2 by 4 like we did with CH4 ? does this mean that we only consider the number on the right hand side only ? if yes,, then why did we time 2H2O by 4 :/

thanks..

 

[Beedo]

question 5-(e) in http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s03_qp_3.pdf

 

[salvatore]

Hello,,can u help me with this pleease,,

CH4 + 2O2 → CO2 + 2H2O

Energy needed to break bonds: 4 (C-H): 435 x 4 = 1740 KJ/Mol 2 (O=O): 497 x 1 = 994 KJ/Mol Total energy in: 1740 + 994 = 2734 KJ/Mol Energy needed to form bonds: 2 (C=O): 803 x 2 = 1606 KJ/Mol 4 (H-O): 464 x 4 = 1856 KJ/Mol Total energy out: 1606 + 1856 = 3462 KJ/Mol ΔH= 2734 – 3462 = -728 KJ/Mol r Therefore reaction is Exothermic

Now my question is ,,why didnt we time 2O2 by 4 like we did with CH4 ? does this mean that we only consider the number on the right hand side only ? if yes,, then why did we time 2H2O by 4 :/

thanks..

One H2O is H-O-H. If u break that up, u get (H-O)(H-O). So one H2O = 2(H-O).. and 2H2O = 4(H-O). CH4 is just 4(C-H). Hope this helped!

 

[Jspake]

Can someone please tell me the difference between giant molecular (macromolecular) structures, giant metallic lattice & giant ionic lattice. I'm super confused!

 

[kboss]

can anyone help on question 7bii of paper below pls. ???
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w10_qp_33.pdf
thanks

 

[salvatore]

can anyone help on question 7bii of paper below pls. ???
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w10_qp_33.pdf
thanks

Make sure u break the double bond, show a repeating unit & include 'n' outside the brackets..

 

[ThatReallyReallyWeirdDude]

Can someone please tell me the difference between giant molecular (macromolecular) structures, giant metallic lattice & giant ionic lattice. I'm super confused!

Giant Molecular/Macromolecular structure:
This is a massive structure consisting purely of covalently bonded atoms. The large amount of strong bonds results in a hard structure with high m.p./b.p., and since it's covalent bonded it has some covalent properties e.g. doesn't conduct electricity.
Examples: Silicon (iv) Dioxide, Carbon (Diamond), Germanium.
The structure of diamond and SiO2 is the same. You should be able to draw it and describe it.
For description: SiO2: Each Oxygen molecule is bonded to two silicons and each silicon is bonded to four oxygens in a covalent, tetrahedral structure.
Diamond: Each Carbon is bonded to four other carbons in a covalent, tetrahedral structure.
Drawings:
Silicon Dioxide:

Diamond:

 

[ThatReallyReallyWeirdDude]

Can someone please tell me the difference between giant molecular (macromolecular) structures, giant metallic lattice & giant ionic lattice. I'm super confused!

Metallic Lattice: This is the structure of alloys/metals.
You should be able to describe it, draw it and explain things about the structure which causes properties.
Description: Layers of positive ions embedded in a sea of electrons.
Drawing:

Properties:
Ability to conduct electricity: It has free moving electrons which allow the passing on of electricity
Malleability: When forced, the metal ions can slide over each other while still touching.
( wooowooowoo do we need to be able to explain high m.p./b.p.? Even then isn't it because the electrons form strong electromagnetic bonds keeping the structure together, needs a lot of energy to break this structure? Not sure)
If it's an alloy, the only difference (IMPORTANT WHEN YOU DRAW) is that the positive ions will have different sizes, so regular arrangement of like OoOoOoOo...etc.

 

[ThatReallyReallyWeirdDude]

Can someone please tell me the difference between giant molecular (macromolecular) structures, giant metallic lattice & giant ionic lattice. I'm super confused!

As for ionic lattice...
Sorry I can't be bothered to explain this so:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/differentsubrev1.shtml

 

[Jspake]

Sorry I can't be bothered to explain this so:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/differentsubrev1.shtml

I understand.. its a pain! Thanks a lot bro.. u r awesome!

 

[Tekno-M]

For this you cannot just draw brackets and n, you need to show at least 3 continuous bonds, as stated again and again in the ms.

 

[wooowooowoo]

Metallic Lattice: This is the structure of alloys/metals.
You should be able to describe it, draw it and explain things about the structure which causes properties.
Description: Layers of positive ions embedded in a sea of electrons.
Drawing:
Properties:
Ability to conduct electricity: It has free moving electrons which allow the passing on of electricity
Malleability: When forced, the metal ions can slide over each other while still touching.
( wooowooowoo do we need to be able to explain high m.p./b.p.? Even then isn't it because the electrons form strong electromagnetic bonds keeping the structure together, needs a lot of energy to break this structure? Not sure)
If it's an alloy, the only difference (IMPORTANT WHEN YOU DRAW) is that the positive ions will have different sizes, so regular arrangement of like OoOoOoOo...etc.

No, I don't think it's required but there is no harm in mentioning it.
Mettallic bonding mainly talks about the strong attraction between positive ions and sea of electrons. (i've never seen any question which goes much in detail about it - if you encountered any, please post it here)

 

[salvatore]

For this you cannot just draw brackets and n, you need to show at least 3 continuous bonds, as stated again and again in the ms.

The ms says:
correct repeat unit (one or more whole repeat units must be given) [1]
cond continuation

The repeat unit is the bond after each carbon atom.. the continuation part is the 'n' outside the bracket

 

[omglaigcse]

what do you think is the hardest topic? and what do you think i should do cause i finished all the past year papers

 

[Jaxine]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w10_qp_31.pdf

Last question!
& also

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s11_qp_31.pdf

Q 5d (iii)

I can't solve anything with numbers!

 

[Alla' Abu-Sultaneh]

Can someone help me with equilibrium? I don't know how to tell when it's moving forward or backward

 

[wooowooowoo]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w10_qp_31.pdf

Last question!
& also

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s11_qp_31.pdf

Q 5d (iii)

I can't solve anything with numbers!

W10 QP 31

Moles of HCL = 40/1000 (convert cm^3 to dm^3)
0.04 * 2 as it says 2 Mol/dm^3, so 2 * 0.04 = 0.08 moles

Moles of CoCl2 = 0.08 / 2 = 0.04 [The ratio between HCl and CoCl2]
Number of moles of CoCl 2.6H2O formed = 0.04 [Same as above ^]
Maximum yield = 0.04 * 238 = 9.52

HCl = 0.08
Moles in 6g of CoCO3 = 6/119 = 0.050

Cobalt (II) Carbonate is in excess because the ratio was 1:2 (Between Cobalt and HCl)
And according to ratio cobalt's mole was 0.050 whereas HCl's was 2x0.04 (0.08)
As 0.05 is more than 0.04, Cobalt carbonate is in excess​

​

I'll post your next one in a minute​

 

[ThatReallyReallyWeirdDude]

Can someone help me with equilibrium? I don't know how to tell when it's moving forward or backward

Check the link to the chemistry notes in my signature. There's an awesome chapter about reversible reactions. Not sure which page so you may have to search (Just use Control+F in your .pdf reader and search for the word 'reversible' or 'equilibrium')

 

[Alla' Abu-Sultaneh]

Check the link to the chemistry notes in my signature. There's an awesome chapter about reversible reactions. Not sure which page so you may have to search (Just use Control+F in your .pdf reader and search for the word 'reversible' or 'equilibrium')

Alriigghhtt, Thank youu very much I appreciate it!