Practicals

Question 1

Test for carbonates

Answer 1

Add dilute acid
If carbonate is present the carbon dioxide will be released
Use limewater to test gas

Question 2

Test for sulfates

Answer 2

dilute HCl
Add barium chloride solution
White precipitate is barium sulflate, which is insoluble

Question 3

Test for halides

Answer 3

Nitric acid
Silver nitrate solution
Colour of precipitate shows halide

Question 4

Solubility of halide precipitates

Answer 4

Cl dilute
Br conc
I nothing

Question 5

Test for ammonia gas

Answer 5

turns damp red litmus paper blue

Question 6

Test for ammonium ions

Answer 6

NaOH and warm

If theres ammonia given off, ammonium ions are present?

Question 7

Why does litmus paper need to be damp when testing gasses?

Answer 7

so they can dissolve and make the colour change

Question 8

Oder of test for ions

Answer 8

Carbonates
Sulfates
Halides

Question 9

What are false positives when doing tests for different ions?

Answer 9

barium carbonate and barium sulfite are also insoluble

Sulfate ions also produce a precipitate with silver nitrate

Question 10

What do you need to know when measuring enthalpy change?

Answer 10

number of moles of reactants

change in temperature

Question 11

How do you find out enthalpy change of combustion of a flammable liquid using calorimetry?

Answer 11

Mass of water being heated
Temperature change of water
specific heat capacity of water
heat absorbed = enthalpy change of combustion

Question 12

How do you measure enthalpy change of neutralisation?

Answer 12

Combines two quantities of acid and alkali in an insulated container and measure temperature change

Question 13

Different ways of measuring reaction rates?

Answer 13

volume of gas given off
change in mass
changes in pressure
changes in colour
changes in conductivity

Question 14

How do you measure volume of gas given off?

Answer 14

gas syringe

vigorous reactions can blow the plunger out

Question 15

How do you investigate equilibrium position with changing temperature?

Answer 15

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

Question 16

Reversible reaction that is used to investigate effect of changing concentrations on equilibrium?

Answer 16

Iron (III) nitrate (yellow) +potassium thiocyanate (colourless) = iron (III) thiocynate (blood red)

Question 17

Experiment to investigate effect of changing concentration on equilibrium?

Answer 17

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

Question 18

How do you just obtain an aldehyde in distillation?

Answer 18

Gently heating with excess alcohol
controlled amount of oxidising agent
distillation apparatus

Question 19

How do you obtain a carboxylic acid in distillation?

Answer 19

reflux

excess oxidising agent

Question 20

Explain which haloalkanes are hydrolysed the fastest

Answer 20

Iodoalkanes are hydrolysed the fastest as they have the weakest bond enthalpy

Question 21

Haloalkane + water?

Answer 21

alcohol

Question 22

Experiment for hydrolysing haloalkanes?

Answer 22

Three test tubes with different haloalkane, ethanol, silver nitrate solution
Pale yellow forms quickest so Iodoalkanes are most reactive

Question 23

How can volatile materials be purified?

Answer 23

Redistillation separates product and impurities
Collect at boiling point of 1
When temp changing, change flask for different liquid

Question 24

How does separation work?

Answer 24

Pour into separating funnel and add water
Shake and allow to settle
Organic layer floats on top
Remove stopper and allow to flow out

Question 25

How do you dry a mixture that has just been separated?

Answer 25

anhydrous salt as drying agent
first lumpy
know complete when looks like snow globe
filter to remove drying agent

Question 26

What do Na2CO3 and NaHCO3 test for?

Answer 26

usually carboxylic acids

produce CO2, salt and water

Question 27

How to filter under reduced pressure

Answer 27

• 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

Question 28

Steps of recrystallisation

Answer 28

• 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)

Question 29

What do to if no crystals for in recrystallisation?

Answer 29

scratch sides of conical flask with a clean glass rod

Question 30

Two methods of measuring boiling points

Answer 30

melting point apparatus

thiele tube

Question 31

How to use melting point apparatus

Answer 31

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

Question 32

How to use a thiele tube

Answer 32

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