Original post by PowerPuffUNOFFICIAL 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.
1)State the type of bond and explain how it is formed:
Covalent, shared pair of electrons. (2marks; 1 for covalent, 1 for shared pair)
Q) 2 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 )
3 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
Decreases
*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 )
*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
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
(3marks)
*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
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 )
*I also mentioned tetrahedral like structure
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-
Or
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
(2marks)
Anymore people?