Paper 3 corrections Flashcards
why is free radical substitution a poor method for producing a high yield of chloromethane?
Because further substitution occurs
Why are C-C bonds the same length in benzene?
The pi bonds are delocalised
How can the concentration of bromine be monitored?
Measure the reduction of colour of bromine
Why is excess used for 0 order?
The concentration of HCOOH would be constant
What is the name for the reaction of metals with carboxylic acids?
Redox
When are they optical isomers and when are they cis/trans isomerism?
Optical = chiral centre
Cis / trans = anything that isn’t octahedral and bidentate ligands
Why would an excess of something be used?
So all the product is formed
How is pH measured?
With a pH probe on a data logger
How do you go from gdm-3 to moldm-3?
Divide by the molar mass of the compound
Why are salts more soluble than carboxylic acids?
Because they are ionic and are attracted to polar H2O molecules
If theres an impure compound, what would its TLC look like?
Two different spots on each place, not just one in the middle
Purification of an organic LIQUID
- Add impure liquid to a separating funnel
- If < 1 gcm-3 it is less dense than water so is on the top layer
- If > 1 gcm-3 it is more dense than water so is on the bottom layer
- If unknown density then the layer that increases with added distilled water is the water layer
- Run out layers into separate beakers
- Add drying agent of anhydrous CaCl2 to remove water
- Filter into round bottomed flask
- Redistill at boiling point of the organic liquid
What is the first step of purifying organic solvents?
Cool and filter under reduced pressure
How do you work out the percentage of a component in a mixture from gas chromatography?
You do the area under the peak of that compound / total area under the peaks
How do you plot a calibration curve for gas chromatography?
Plot graph of area against concentration for known concentrations of the compound and then compare the values
Which moles do you use which dividing the Q value to get the enthalpy change?
The limiting reagent so the one that isn’t in excess or the one with the least amount of moles
What’s the test for ammonium ions?
Add NaOH and warm gently
Turns damp red litmus paper blue
How do fuel cells work and what do they need?
The fuel reacts with oxygen to produce electrical energy
They need a constant supply of fuel an O2
Is the fuel oxidised or reduced?
Oxidised - loses electrons
When testing for halide ions, what do you add?
AgNO3 and then NH3
What happens to the ppts when NH3 is added to the white/cream/yellow of halide ions?
Chlorine - white is soluble in dilute NH3
Bromine - cream is soluble in CONC NH3
Iodine - yellow is insoluble in NH3
What are the limitations of calorimetry?
Heat loss to surroundings
Non standard conditions
Contents of calorimeter may evaporate
What is there to watch out for when working out the enthalpy change from a calorimeter?
If there are two solutions then the m (mass) is them added together
If the reaction is exothermic then dont forget the minus sign
What is the enthalpy change of neutralisation for strong acids and alkalis?
-57 kJmol-1 because they fully ionise in solution
