Attention geniuses! Higher chemistry please! Watch

missyq
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I'm really stuck with chemistry! Doesn't help that i hate it but i've got to revise it anyway. Less than a week to go. So I'd appreciate it if anyone could help me out with these questions. Remember it'll be revision for yourself aswell =D
Thank you!
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missyq
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Hey, would really appreciate it if someone could help me out:

2000 - Q15 - Explain why it is D please

2002 - Q19 - What does it mean by rise and how to do it?

2003 - Q18 - No clue how to answer that!
2003 - Q21 - Agreed loss of 2d hydrogen but wouldn't it gain 16g oxygen? As oxidation is gain of oxygen (same in 2005 Q23)
2003 - Q25 - A because it has NH2?

2005 - Q20 - What about 2, 2 Dimethylbutan-2-ol?

2007 - Q17 - I chose n to be 2 for example. But it didn't give me the formula i thought was correct!
2007 - Q20 - Please explain how to identify (similiar 2005 Q20 as above)

please quote so i know you've replied! Thanks!
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Charzhino
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(Original post by missyq)
Hey, would really appreciate it if someone could help me out:
What board are you on? Is this GCSE or Alevel?
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missyq
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(Original post by Charzhino)
What board are you on? Is this GCSE or Alevel?
higher (scottish qualifications)
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Charzhino
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(Original post by missyq)
higher (scottish qualifications)
Lol ah. Do you have a link to the actual papers for the questions?
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Zedd
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Here's a link to the past papers (doesn't go as far back as this person is wanting though)

http://www.sqa.org.uk/pastpapers/fin...ject=chemistry
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missyq
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(Original post by Charzhino)
Lol ah. Do you have a link to the actual papers for the questions?
Hey, not sure if you do the same thing at A level but i have a few theory questions:

Ions
How do you know what the overall charge is for eg sulphate ion or nitrate ion? What do you have to look out for? Number of outer electrons?
If so, then if the carbonate ion has 4 outer electrons and 3 oxygens joining, each have 8. How does it work? Says it has an overall neagtive charge of two? Don't get it.

What exactly are discrete covalent molecules? CF4, CO2, PCl3, HI and CH4 - what do they have in common?

Are non-polar and pure covalent bonds the same thing?

In hydrogen bonding, is hydrogen always and the only one with delta positive (slightly positive charge)?

Why is hyrogen bonding present in propanol but not in ethanol? Both have oxygen present!

Thanks!
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Xerophelistica
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(Original post by missyq)
Hey, not sure if you do the same thing at A level but i have a few theory questions:

Ions
1. How do you know what the overall charge is for eg sulphate ion or nitrate ion? What do you have to look out for?

2. In hydrogen bonding, is hydrogen always and the only one with delta positive (slightly positive charge)?

3. Why is hyrogen bonding present in propanol but not in ethanol? Both have oxygen present!

Thanks!
1. For the acid ions, the easiest way to know the charge is by how many H atoms were in the original acid. For example, H2SO4 has 2 H's, so the SO4 group will be -2

2. Yes

3. Hydrogen bonding IS present in ethanol
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shengoc
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Overall charge of sulphate is -2, and nitrate is -1 - these are standard things you should know. carbonate has charge -2.

For example, carbonate, CO3-2. The oxidation number of carbon in this case is -2 = C + 3(-2) so C = -2 + 6 = +4, Carbon is in group 4, it can lose four electrons to give you +4. However, that doesn't mean C won't form C4- as in TiC(titanium carbide) is an example of C in -4 oxidation state.

Covalent bond - sharing electrons, ionic bond - transfer of electrons
covalent bond - usually between elements of similar electronegativity,
ionic bond - usually between elements of very dissimilar electronegativity
(however, no such thing as 100 percent ionic/covalent - one will predominate)

Covalent bonds are quite weak(for these compounds), but for covalent bonds in giant molecular structure like diamond or graphite, there are so many covalent bonds that contributes to their high mp and bp.

Essentially, non polar molecule can be considered covalent - however, i don't really think we can consider them to be pure covalent. The overall charge is zero because the dipole is equal by symmetry,(ie CH4), but since it is tetrahedral, so overall dipole cancels out.

Hydrogen bonding is between atoms like N, O, F with hydrogen, since these are more electronegative than H, then definitely, it is the only one with delta positive.

The lone pair availability of oxygen might be more available in propanol due to electron donating inductive effect, thus making it a better Lewis acid, ie a better H-Bond donor than ethanol - i think.
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missyq
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(Original post by Xerophelistica)
1. For the acid ions, the easiest way to know the charge is by how many H atoms were in the original acid. For example, H2SO4 has 2 H's, so the SO4 group will be -2

2. Yes

3. Hydrogen bonding IS present in ethanol
must be mistake in notes - thanks!
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missyq
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2008 - Q8 - I understand atmoic number is given by the number of protons but why isn't the atomic size dependant on the number of electrons?

2004 - Q11 - Titanium requires 664KJ/mol for ionisation energy wherewas Chromium needs 659. So how can chromium require the most energy? Something to do with converting one mole into ions carrying two positive charge that i'm missing here.

2007 - Q11 -Aren't non-polar bonds easier to overcome than polar? Or other way round?

2003 - Q12 - Answer is ethanoic acid. Because the hydrogen bond is attatched to the carboxyl group, which has strong bonds?
Are the only discrete covalent molecules sulphur and phosphorus?
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missyq
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Reaction rates - what are the main things to remember? Calculating is fine. But what about questions like if 'If 100cm3 calcium carbonate is added, to 2mol/l hydrochloric acid, what will be the same if added to 1mol/l hydrochloric acid. And the other million questions about magnesium, zinc, sulphuric acid etc.

2002 Q5 and 2005 Q6 are exactly the same! But answer is A and D respectively. Can someone explain please?
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Zedd
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(Original post by missyq)
Reaction rates - what are the main things to remember? Calculating is fine. But what about questions like if 'If 100cm3 calcium carbonate is added, to 2mol/l hydrochloric acid, what will be the same if added to 1mol/l hydrochloric acid. And the other million questions about magnesium, zinc, sulphuric acid etc.

2002 Q5 and 2005 Q6 are exactly the same! But answer is A and D respectively. Can someone explain please?
The wording is a bit iffy for that first one but all it seems to be asking is how much calcium carbonate do you add to the hydrocholoric acid to get the same result as the first titration.

If you add 100cm3 calcium carbonate to 2 mol l- hydrochloric acid then that's 50cm3 calcium carbonate for every mole of hydrocholoric acid.

What are the 2002 Q5 and 2005 Q6 question and what are the choices?
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missyq
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There's a graph, so you'd need it to answer the question. ABout activation energy and number of collisions regarding change in temp.
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missyq
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2001 - Q12 - Any quick way of eliminating obvious wrong answers? Or do we have to work them all out to see which has the largest volume?
2001 - Q13 - Volume of products is less than reactants because num of moles on RHS is less than that on LHS?

2002 - Q6 - To solve is it 134 - (-227)? And negative sign infront because exothermic?

2003 - Q7 - How?? First found no. of mol to be 0.04 Then used proportion to find one mole: If 0.04mol gives 134KJ, then 1mol gives 3350KJ - which is obviously wrong
2003 - Q14 - does copper (II) phosphate have 2 neagtive ions? (1-3= -2) Don't know how to work it out anyway.

2004 - Q7 - What does iodine vapour indicate in the Q? How to go about solving it?
2004 - Q13 - Using volume by proportion didn't give me the correct answer:
22 So, 1l: 0.5l: 2l
Oxygen has 2-.05= 1.5 excess
Nitrogen monoxide - remaining oxygen = 2 -0.5 = 1.5
therefore, 2+1.5= 3.5 which is incorrect

2005 - Q16
2005 - Q17 - Is copper oxide solid or gas? If answer is A.50cm3 then what happens to excess CuO??

2006 - Q11 - I got 238.5deg. Answer is 23deg.
If 6g gives 13.6KJ
88g gives 199.46KJ

H=cmT
199.46 = 4.18(0.2)T
T= 238.58deg
Out by a decimal? Or wrong approach (probably)?

2006 - Q15 - If 16g Helium gives 8 atoms, how can 17g ammonia give 8 atoms aswell? It has 10!
2006 - Q16 - How do we know the GFM of diamond?

2007 - Q13 - ?
2007 - Q14 - My working:
n=m/G n=12/720= 0.016
1mol has 1 molecule
0.016 has 0.02 molecule

So 0.02xL= 1.2x10^22
Not correct

2007 - Q15 - ? And how can we represent formula units like molecules, ions and atoms ?

I know there are loads of Q's but even if you can help out with a few it will be of great help. Ta!
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missyq
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2000 - Q15 - Explain D please. Because the 3rd hydrogen would join O and prevent condensation from occuring again?

2002 - Q19 - What does rise mean?

2003 - Q14 - ?

2004 - Q15 - ?

Is lithium hydroxide strong alkali?
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shengoc
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Lithium hydroxide is very strong alkali, as basicity decreases down Gp I and Gp II.
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