Chemistry Unit 3 Flashcards
(56 cards)
How to test if solution of metal compounds are amphoteric
If the solution forms a precipitate on addition of hydroxide, which is then able to redissolve in excess hydroxide, the compound is amphoteric.
Define the inert pair effect
This is the tendency of the outermost s2 pair of electrons in
an atom to remain unshared in compounds, leading to a lower oxidation state.
This occurs in groups 3, 4 and 5. As you go down a group, the tendency increases.
Define octet expansion
This is the ability of some atoms to use d-orbitals to have more than 8 electrons in their valence (outer) shell.
Give one difference between graphite and hexagonal BN
There are no delocalised electrons in BN, (the B – N bonds are polar), whilst there are in graphite. So unlike graphite, BN cannot conduct electricity and is used as an electrical insulator.
Give two similarities between diamond and cubic BN
Both are extremely hard and have high melting points due to strong covalent bonds between the atoms.
Why does the stability of the +2 state increase as you go down group 4
The inert pair effect becomes more significant.
Why does SiCl4 react violently to form a white ppt and steamy fumes with water but CCl4 doesn’t react with water despite them both being covalently bonded tetrachlorides
Silicon tetrachloride can react due to the availability of d-orbitals in the silicon atom. They allow a lone pair from oxygen to bond with the SiCl4. These d-orbitals are not available in the carbon atom, so it cannot react.
Define disproportionation reaction
Atoms of the same element are oxidised and reduced to form different products.
Chlorine and cold NaOH reaction
Sodium chloride and sodium chlorate(I) (NaOCl) and water are formed
Chlorine and hot NaOH reaction
Sodium chloride and sodium chlorate(V) (NaClO3) and water are formed
Define transition metal
An element that possesses a partially filled d sub-shell in its atom or stable ions
Why can transition metals have variable oxidation states
Because the energies of the 4s and 3d orbitals are very similar, so the energy required to remove any of these electrons is similar
Why do transition metals make good homogeneous catalysts
By using their variable oxidation states to oxidise/reduce a reactant which makes it more reactive. Products are released and the metal returns to the original
oxidation state
Why do transition metals make good heterogeneous catalysts
They provide a surface for molecules to be adsorbed and come closer together for reaction.
Molecules can form coordinate bonds to the metal atom because there are empty d orbitals to accept electron pairs due to the d-orbitals only being partially filled
Define ligand
A small molecule or ion with a lone pair of electrons
Give the molecular formula, bond angle and colour of the two tetrahedral complex ions
[CoCl4]2– is blue
[CuCl4]2– is yellow/green
Bond angle of 109.5
What does EMF tell you about the feasibility of a reaction
If EMF is positive, the reaction is feasible
Give the energy in terms of wavelength equation
Energy (in Joules) = Planck constant (h) x speed of light (c) / wavelength (in metres)
Give the energy in terms of frequency equation
Energy (in Joules) = Planck constant x frequency
What does the enthalpy change tell you about stability
If enthalpy change of formation is negative, the compound is more stable than its elements
Give the equation for standard enthalpy of solution
Standard enthalpy of hydration + enthalpy of lattice breaking
Give the equation for Gibbs free energy change
delta G = delta H - (T x delta S)
What does a negative Gibbs free energy change tell you
The reaction occurs spontaneously
What is pH equal to when salt concentration and acid concentration are equal in a buffer solution
pH = pKa
