Practicals Flashcards
Test for carbonates
Add dilute acid
If carbonate is present the carbon dioxide will be released
Use limewater to test gas
Test for sulfates
dilute HCl
Add barium chloride solution
White precipitate is barium sulflate, which is insoluble
Test for halides
Nitric acid
Silver nitrate solution
Colour of precipitate shows halide
Solubility of halide precipitates
Cl dilute
Br conc
I nothing
Test for ammonia gas
turns damp red litmus paper blue
Test for ammonium ions
NaOH and warm
If theres ammonia given off, ammonium ions are present?
Why does litmus paper need to be damp when testing gasses?
so they can dissolve and make the colour change
Oder of test for ions
Carbonates
Sulfates
Halides
What are false positives when doing tests for different ions?
barium carbonate and barium sulfite are also insoluble
Sulfate ions also produce a precipitate with silver nitrate
What do you need to know when measuring enthalpy change?
number of moles of reactants
change in temperature
How do you find out enthalpy change of combustion of a flammable liquid using calorimetry?
Mass of water being heated
Temperature change of water
specific heat capacity of water
heat absorbed = enthalpy change of combustion
How do you measure enthalpy change of neutralisation?
Combines two quantities of acid and alkali in an insulated container and measure temperature change
Different ways of measuring reaction rates?
volume of gas given off change in mass changes in pressure changes in colour changes in conductivity
How do you measure volume of gas given off?
gas syringe
vigorous reactions can blow the plunger out
How do you investigate equilibrium position with changing temperature?
NO2 brown and N2O4 colourless
1) two sealed tubes in water baths - one warm one cool and observe colours
2) Tube in warm bath = darker brown as endothermic reaction speeds up
3) cool bath lose colour as exothermic reaction speeds up
Reversible reaction that is used to investigate effect of changing concentrations on equilibrium?
Iron (III) nitrate (yellow) +potassium thiocyanate (colourless) = iron (III) thiocynate (blood red)
Experiment to investigate effect of changing concentration on equilibrium?
equal amount to equilibrium mixture to 4 tubes
1) control
2) iron (III) nitrate added, deep red
3) Add potassium thiocynate, deep red
4) add iron(III) thiocynate, yellow
How do you just obtain an aldehyde in distillation?
Gently heating with excess alcohol
controlled amount of oxidising agent
distillation apparatus
How do you obtain a carboxylic acid in distillation?
reflux
excess oxidising agent
Explain which haloalkanes are hydrolysed the fastest
Iodoalkanes are hydrolysed the fastest as they have the weakest bond enthalpy
Haloalkane + water?
alcohol
Experiment for hydrolysing haloalkanes?
Three test tubes with different haloalkane, ethanol, silver nitrate solution
Pale yellow forms quickest so Iodoalkanes are most reactive
How can volatile materials be purified?
Redistillation separates product and impurities
Collect at boiling point of 1
When temp changing, change flask for different liquid
How does separation work?
Pour into separating funnel and add water
Shake and allow to settle
Organic layer floats on top
Remove stopper and allow to flow out
How do you dry a mixture that has just been separated?
anhydrous salt as drying agent
first lumpy
know complete when looks like snow globe
filter to remove drying agent
What do Na2CO3 and NaHCO3 test for?
usually carboxylic acids
produce CO2, salt and water
How to filter under reduced pressure
- connect thick walled rubber tubing to vacuum pump + check suction
- Buchner funnel on filter flask
- small filter paper on funnel
- use distilled water/solvent from synthesis to dampen
- wash + rinse
- invert funnel into watch glass
Steps of recrystallisation
- dissolve in min amount of hot solvent, if coloured then heated with activated charcoal to remove coloured impurities
- hot solution does gravoty filtration
- allowed to cool
- wash in vacuum filtration (cold solvent)
What do to if no crystals for in recrystallisation?
scratch sides of conical flask with a clean glass rod
Two methods of measuring boiling points
melting point apparatus
thiele tube
How to use melting point apparatus
organic solid in capillary tube
switch on meachine heating dial to about 4
watch crystals
write down when starts and when liquified
this is the melting point range
How to use a thiele tube
organic solid in capillary tube
attach tube to thermometer
submerge thermometer in thiele tube oil
heat side arm of thiele tube and note the temperature
