Paper 3B Part 2
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Molecular formula of sodium carbonate
Na2CO3
Molecular formula of sodium hydroxide
NaOH
Molecular formula of pottasium hydroxide
KOH
Molecular formula of phosphoric acid
H3PO4
Define hydrogen ion
An ion with no electrons and 1 proton
Define acid
In water an acid releases hydrogen ions into the solution
Define strong acid
Releases all of its hydrogen ions into the solution and completely disassociates, this is irreversible
Define weak acid
Only releases a small number of its hydrogen ions into the solution and partially disassociates, this is reversible
How is sulphuric acid both a strong and weak acid?
Sulphuric acid is both strong and weak, it can form 2H+ and SO42- or H+ and HSO4-
Define a base
A compound that neutralises an acid, by accepting a hydrogen ion to form a salt – for example ammonias, hydroxides, carbonates and metal oxides
Define an alkali
A type of base that dissolves in water to form hydroxide ions
Define a salt
The product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions
Describe and explain the conductivity of sodium Na, chlorine Cl2, and sodium chloride NaCl (6 marks)
.Sodium is a metal and conducts as both a solid and liquid.Free moving delocalised electrons to carry the charge.Chlorine is a small simple molecule that does not conduct.No free moving delocalised electrons to carry the charge.Ionic bond between sodium and chlorine to form sodium chloride, conducts as molten or aqueous but not when solid.Free moving ions when molten and aqueous so can conduct as they carry the charge
Why is the shape of PCl5 special?
Trigonal bi-pyramidBond angles of 120’ and 90’
Describe and explain the shape of a NH3 molecule
3 bonding pairs + 1 lone pair = 4 electron pairsSo repels to corners of tetrahedronDon’t see the lone pair so therefore the shape is pyramidal
Bond angle of NH3
107’
Why do lone pairs of electrons have greater repulsion
not attracted by nuclei unlike bonding pairs
What is the order of repulsion?
LP:LP > LP:BP > BP:BP
By how much does one LP in a tetrahedron reduce the bond angle by?
2.5’
Bond angle of H2O and why?
109.5 – 2.5 – 2.5 = 104.5’2 x LP’s so (– 2.5’) 2 times to the bond angle on a tetrahedron (109.5)
Why is CO2 linear?
C has 2 electron regions (2 BP’s) so it is linear
Define electronegativity
a measure of the tendency of an atom to attract a bonding pair of electrons within a covalent bond.
Where are the electrons positioned when both atoms in a bond are identical?
When the 2 atoms are identical, the electrons are shared equally and stay in the middle
What did Linus Pauling invent and when?
Linus Pauling – invented the Pauling scale in 1932 which measures electronegativity on an atom