Exam questions Flashcards
What is observed when dilute NaOH is added to separate solutions of magnesium chloride and barium chloride?
MgCl2 - white ppt
BaCl2 - no visible change
Chlorine has a low boiling point because the forces between the molecules are weak.
Explain how these forces arise between molecules of chlorine.
Random movement of electrons in one molecule
creates a temporary dipole which induces a dipole in a neighbouring molecule.
These temporary dipoles attract
Explain why complexes formed from transition metal ions are coloured.
They absorb some energies of visible light to excite electrons in d-orbitals
The remaining energies of visible light reflect/transmit to give a colour
Describe how a calibration graph is produced and used to find the concentration of the iron(III) complex.
Measure the absorbance for a range of known concentrations
Plot a graph of absorbance against concentration
Read value of concentration for the measured absorbance from this graph
Suggest why the iron(III) oxide obtained is pure.
Assume a complete reaction.
4Fe(NO3) (s) —> 2Fe2O3 (s) + 12NO2 (g) + 3O2 (g)
Other products are gases / other products escape easily
What is the name of the shape produced by the atoms in NH3
pyramidal
Explain why branched chain molecules have lower bp than their straight chain counterparts
Because molecule is smaller so has less surface area molecules can’t get as close to one another (to feel the VDW forces)
VDW intermolecular forces or VDW force between molecules are weaker or fewer
Good reducing agent to use
zinc (acidified)
What is electrospray ionisation
When the sample is dissolved and then injected through a nozzle at high voltage so it gains a proton to become XH+
State the meaning of the term periodicity
Repeating trends of chemical or physical properties across periods
Explain why a ppt is white (transition metals topic)
Has a full d-orbital so can’t absorb visible light hence its white
Explain how heterogenous catalysts work
Reactants adsorbed onto catalyst surface
Weakens bonds of reactants and increases their proximity
Then the product desorbs (desorption)
Explain how the salt bridge provides an electrical connection between the two solutions in an electrochemical cell
Has mobile ions
Why do you need to ionise molecules in mass spectrometry
So they can be accelerated by electric field
ions create a current when hitting the the detector which is used to find its abundance
Enthalpy change
Heat change at constant pressure
