(Original post by PowerPuff)
UNOFFICIAL MARK SCHEME - AQA AS Chemistry 13/01/2011 -
This Mark Scheme is an Unofficial Mark Scheme (simply predictions)
* indicates my side comments.
Some questions are missing, so feel free to add any.
State the type of bond and explain how it is formed:
Covalent, shared pair of electrons. (2marks; 1 for covalent, 1 for shared pair)
Shape of BrF3
(Resembles trigonal bypyramidal) angle between BONDING pairs, 90 degrees, ( 85-90 ) ( 2 marks, 1 for shape, one for angle)
Square planar, 120degrees ( 85-90 ) ( 2 marks; 1 for shape, one for angle )
High melting point of KBrF4-... ??
Giant ionic structure. Strong oppositely charged ions keep structure together, lots of energy required to overcome these forces. (3 marks; 1 for giant ionic structure, 1 for strong forces of opp charged ions, 1 for overcoming forces )
*Myself and others believe that if you said just Ionic bonding instead of Gian Ionic strcuture, you can still get 3 marks since the question asked 'in terms of bonding' so stating the structure wouldnt be needed.
Q) PV= nRT question
0.0175 ( 4marks)
Q) Which element has smallest atomic radii ?
Lithium ( 1 mark )
Q) how does atomic radii change across a period in period 2
*many people are saying they asked why, but I assure you they did not
Q) Label for HCl.
corrosive, toxic, irritant (1 mark)
Q) Nitride ion with same electronic configuration as 1s2 2s2 2p6?
N 3- ion ( 1mark )
Q) Element Q
F- ion ( 1 mark )
Q) question that follows after F- ion question; Li3N ??? (1 mark)
Q) empirical formula of Calcium nitride.
Ca3N2 (3 mark; 2 for appropriate method, 1 for answer)
Q) Balancing lead nitrate equation
2 2 4 1 ( 1 mark ) ( multiples are accepted )
[COLOR="rgb(75, 0, 130)"]*myself and others believe that you can still get full mark if you didnt state a 1 infront of the 02, since it goes without saying[/COLOR]
Q) Environmental dangers of Sulfur compounds
Acid rain ( 1 mark )
Q)Equation of removal of CO or NO ? ( cant remmeber which it was )
2NO + 2CO -> N2 + 2CO2 (1 mark)
Q) Si equation of some sort to form Si3N4
3Si + 2N2 -> 3SiN4 (1 mark )
Q) Calculation questions for Volume of Nitric acid = 0.0524 dm3
[COLOR="rgb(72, 61, 139)"]*my working out:
8.14 / 207.2 = 0.0393
Then to get moles of n02 you times by 8/3 (due to 3:8 ratio)
so 0.0393 x 8/3 = 0.1048 moles of n02
then 0.1048/ 2.00 (conc) to get volumes = 0.0524 dm3[/COLOR]
157/207 x 100 = 76ish % atom economy ? (3marks)
Q) High melting point of Carbon,
Readily forms strong covalent bonds with 4 other carbon atoms, forming giant covalent structure. These strong covalent bonds spread throughout the structure and they MUST be broken. Require a lot of energy to break these strong forces. ( 3 marks; 1 mark for readily forms bonds with 4 other C atoms, 1 for giant covalent structure or macromolecular, 1 for strong bonds must be broken, 1 for require a lot of energy to break )
[COLOR="rgb(75, 0, 130)"]*I also mentioned tetrahedral like structure[/COLOR]
Q) Cross for nitrogen
Nitrogen in the graph should appear lower than all other elements plotted (1 mark)
Q) which raw material is hexane obtained from ?
Crude oil (1 mark )
Q) How to remove sulfur ?
React with CaO, neutralises sulfur. ( 2 marks )
*However some mentioned CaC03 (limestone) and reason because it is easily accesible/high in abundance/can be easily collected
Q) Bonding between two molecules of H-F
F has delta +, H has delta -, F has 3 lone pairs, H atom of another H-F molecule bonded to a lone pair from F atom in other molecule. ( 2 marks ? )
Q) which cracking method produces high % of alkenes and state conditions
Thermal cracking, high temp and pressure ( 2 marks; 1 for thermal cracking, 1 for both conditions )
Q) State a catalyst used in exausht pipes to remove NO and CO and explain the benefit of having honey comb structure ??
Rh/Pt/Pl , Increased surface area for reaction. ( 2 marks )
Q) Number of isomers ?
5 ( 1 mark )
Q) name of compound shown ?
2,2-dichloro,3-methylpentane ( 1mark )
Q) empirical formula of compound shown ?
C3H6Cl ( 1mark )
Q) how is Kr ionised ?
Krypton is ionised by electron gun that fires electron at high speed at gaseous sample of Kr atom knocking an e- out by repulsion. (3marks)
Q) Ar of Kr in sample = 84.0 (4marks)
*needed a .0 as question stated in one decimal place.
Q) why is the value of Ar you obtained different from periodic table ?
Argument for this,
One view: Something about space, so different values
Second view: (which I put) Mass spectrometer used for periodic table may be of high resolution so more precise/accurate
Third view: something about different isotopes
Q) IE change for 1st IE of Krypton.
Kr(g) + e- -> Kr+(g) + e-
Kr(g) -> Kr+(g) + e- (2marks; 1 for states, 1 for correct equation)
Q) which element deviates from general trend of first IE in period 2 ?. Explain why.
Boron, electron in 2p orbital, Beryllium has electron in 2s orbital. 2p is of slightly higher energy than 2s orbital, less shielding, less energy required to remove. ( 3marks )
Q) Explain peak at 42,
I said: Krpton may of been ionisied to form 2+ charge which is rare/occurs less likely so abundance is smaller and also M/Z is smaller/ behaves as a ion half its mass