## 2005 - Multiple Choice - Various Q's thanks

### mujb

Posted 23 May 2006 - 12:42 PM

hi, it will be handy if you have past papers.

the Qs are 1,3,4,8,11,12,13,14,15,16.

i know, too many questions but any help will be appreciated.

thanks

### Pammy

Posted 23 May 2006 - 01:34 PM

Question 1

Silicon Dioxide and Potassium Fluoride are covalent, therefore do not conduct electricity in any state.
Iodine has a melting point of 114 which is higher than Potassium's (64).

Question 3

For this you need to work out the electron arrangements for each.
Calcium = 2,8,8,2 and sulphur = 2,8,6 Calcium Sulphide = 2,8,2 (which is the same as argon)
If you work out the others you will see that no other arrangements are equal to Argon

Question 4

(power x volume x concentration)
(P x V x C) acid = (P x V x C) alkali
(2 x 0.05 x 0.1) = (1 x V x 0.4)
0.01 = 0.4 V
0.025 cm = V

Question 8

This is kinda hard to explain coz it's a graph but I'll have a go

The energy of the products is greater than the energy of the reactants, the enthalpy change is positive, which is endothermic.

The activation energy is the 'hump' at the top of the graph (activated complex) minus the original energy
so it will be,
120 - 40 = 80

Question 11

You need to use the ionisation energies for this,
Scandium has to lose one electron to obtain a 2 positive charge,
so the energy needed = 637 J (from data book, page 10)

Titanium has to lose two electrons to obtain a 2 positive charge,
so the energy needed = 664 + 1320 = 1984 J

Vanadium has to lose three electrons to obtain a 2 positive charge,
so the energy needed = 656 + 1430 + 2850 = 4936 J

Chromium has to lose four electrons to obtain a 2 positive charge,
so the energy needed = 659 + 1600 + 3000 + 4800 = 10,059 J

Chromium needs the most energy

Question 13

I've done this before, but I've forgotten now so could someone enlighten me ?? Question 14

Work out the number of moles in 128.2 g of Sulphur Dioxide
128.2 g = x moles
64.1 g = 1 mole

cross multiply and you get
128.2 = 64.1 x
2 moles = x

Look at the options, which one has two moles of the element
2g of Hydrogen = 1 mole (diatomic)
8g of He = 2 moles (1 mole = 4g)
32g of Oxygen= 1 mole (diatomic)
80.8g Neon = 4 moles (1 mole = 20.2g)

Question 15

Again could someone show me the path to enlightenment !! Question 16

I'm not sure how to explain this, but if the number of each of the elements is the same on both sides, a smaller compound is formed (as the aim of reforming is to produce smaller, more useful products) and hydrogen is formed it is re-forming.
Sorry about the waffly explanation !!

EDIT: Sooooo sorry !!! But I thought it was 2004 !!!!!

### mujb

Posted 23 May 2006 - 01:38 PM

hi i am being very rude but this is the answers to 2004 not 2005.
thanks

### Pammy

Posted 23 May 2006 - 03:23 PM

Question 1

You just need to know this
Isotopes are the same element with a different mass number.
sorry I can't really give a proper explanation for this

Question 3

I don't know this, because I would have said C

Question 4

no. moles = V x C
= 0.02 x 2
= 0.04 moles

Magnesium chloride will be formed, which is Mg(Cl) Ratio of Mg to Cl is 1:2
So 2Mg = 1Cl
2Mg = 0.04
Mg = 0.02 moles

Question 8

Not too sure why you do this but
To break the bonds in 1 mole H you need 432 kJ/mol
To break the bonds in 1 mole I you need 149 kJ/mol
So 432 + 149 = 581
The formation of 2HI = 2 x -295 (minus because it's the formation)
= -590

So, 581 + (-590) = -9 kJ/mol

Question 11

The substance conducts electricity when molton which automatically rules out the two covalent bonds
The high m and b points tell us that it is ionic

Question 12

Distillation is not a chemical reaction, so NO bonds are broken or formed
Therefore, it must break and form Van Der Walls forces ( these are forces of attraction)

Question 13

There is a large difference in the electronegativities in silicon dioxide
So I am left with a noble gas and a fullerene.....

Question 14

The original metal is molten and as the one you obtain is of a lower mp then it will be a liquid. As it is more dense it appears on the bottom.

Question 15

Work out how many moles are in 100g of each element

F- 2.63 moles
N- 3.57 moles
O- 3.13 moles
H - 50 moles

You could then multiply each one by 6.02 x 10^23
but you could just say F has the least no. of moles

Question 16

No. moles = Volume/ Molar vol.
= 11.5/23
= 0.5 moles

11.5l = 0.5mole = 3x1023 molecules

1 mole = 6x1023 molecules = 12x1023 atoms

0.5 mole = 6x1023 