Practicals

Question 1

Why do you invert a flask when making a solution?

Answer 1

To ensure a uniform solution

Question 2

Why might you not be able to fill up to the line with a volumetric flask?

Answer 2

You can’t see the line bc the solution is dark

Question 3

How can you ensure you’re weighing mass properly?

Answer 3

Subtracting mass of empty weighing bottle to give accurate reading on how much mass is actually added

Question 4

Why use a volumetric pipettes?

Answer 4

Better than a measuring cylinder because smaller uncertainty

Question 5

When filling a volumetric flask what should you always do?

Answer 5

Use a test pipette to mark up the volumetric flask line as it ensures the volume of solution is accurately measured and doesn’t go over the line

Question 6

What is the process for making a solution?

Answer 6

Weigh the sample in the the weighing boat containing the sample
Transfer sample to a beaker
Re weight empty weighing boat and record difference in mass
Add 100cm3 distilled water to the beaker
Heat gentle if needed to dissolve and stir with glass rod
Pour into 250cm3 graduated flask using a funnel
Rinse beaker and funnel with cold water and add to volumetric flask
Make up the solution with distilled water to the 250cm3 line
Invert to combine the solution

Question 7

What should you ensure when measuring liquids

Answer 7

Full to the bottom of the meniscus

Question 8

How do you do a dilution?

Answer 8

Pipette 25cm3 using a volumetric pipette into 259cm3 volumetric flask
Make up to the line with distilled water
Use a pipette for the last drops
Invert flask for a uniform solution

Question 9

How do you do a titration?

Answer 9

Rinse equipment (burette with acid, Pipette with acid,conical flask with distilled water)
Pipette 25cm3 of alkali into conical flask
Add acid to the burette, ensure not air bubbles
Add a few drops of indicator to the alkali in the conical flask
Use a white tile below the conical flask to better record the colour change
Add acid dropwise to the alkali whilst swirling the conical flask
Note burette reading before and after adding the acid
Repeat the titration to create a mean or till two readings are obtained within 0.1 of each other

Question 10

What should you do to make sure all the alkali goes into the conical flask?

Answer 10

Touch the solution with the pipette

Question 11

What should you do before using the burette?

Answer 11

Rinse it out three times with the solution you’re going to use

Question 12

Why do you use anti bumping granules?

Answer 12

So smaller bubbles are produced and reaction reacts less vigorously

Question 13

How should you read a burette?

Answer 13

You should always record your results to 2dp

Eg 0.05 because although burettes only measure 0.1cm3 you can see a hallway between each measurements

Question 14

Which indicator should I use?

Answer 14

Methyl orange for strong acids or neutralisation reactions

Phenolphthalein for stronger alkalis

Question 15

Why should you only use a small amount of indicator?

Answer 15

They’re acidic, so they could affect your results

Question 16

How do you work out titre?

Answer 16

Initial burette reading 0.05 - final burette reading 24.05

= 24cm3

Question 17

When reacting iron and manganate with iron tablets what should you do first?

Answer 17

Work out how much iron in a tablet
Weigh two ferrous tablets
Grind up with 1M sulphuric acid and mortal and pestle
Transfer paste to 100cm3 volumetric flask
Rinse pestle and funnel with sulphuric acid
Add sulphuric acid to make up to 100cm3 line
Stopped and shake flask to ensure even mixture
Titrate 10cm3 at a time with 0.005M solution of potassium manganate
End point is permanent purple colour

Question 18

What should you remember with manganate redox?

Answer 18

Only use dilute Sulphuric acid in excess

Question 19

What is the equation for the reaction of sodium thiosulphate and HCl?

Answer 19

Na2S2O3 +2HCl to 2NaCl + S02 +S+ H20

Question 20

What is the method to measure the rate of reaction as temperature changes?

Answer 20

Measure 10cm3 of 0.2M HCl and 10cm3 of sodium thiosulphate in a separate clean measuring cylinder and put in separate boiling tubes
Choose a temp to investigate and heat each tube to this temperature in a water bath
Add first the sodium thiosulphate then HCl ensuring is the apparatus is set up with the conical flask on a white tile with a black cross on it
As soon as the HCl is added, start the timer
Stop it when the cross disappears and record
Then repeat 4 times

Question 21

What is the method of recrystallisation?

Answer 21

Dissolve impure compound in a minimum value of hot solvent
Hot filter solution through filter paper
Cool filtered solution by adding beaker to ice
Then use negative pressure by suctioning filtrate through a Büchner flask to separate crystals
Wash with distilled water
Dry between two sheets of absorbent paper

Question 22

Method for separating organic liquids?

Answer 22

Put distillate of impure product into a separating funnel and add water
Wash product adding either sodium hydrogen carbonate solution and shaking and releasing pressure of co2 bubbles
Or add sodium hydrogen carbonate to neutralise remaining acid
Shake funnel and allow to settle then discard aqueous layer
Run organic layer into a dry conical flask
Add drying agent CaCl2 to remove water
When completely dried liquid should be clear
Filter solid drying agent on to paper

Question 23

How do you find melting point?

Answer 23

Pack small sample of solid into capillary tube and place inside the heating element
Increase temperature until turns solid to liquid
Measure MP range
Pure sample will have sharp MP
Check values in data book

Question 24

TLC method?

Answer 24

Wearing gloves draw a pencil line 1cm above tlc plate bottom
Mark an equally spaced spot for each sample
Use capillary tube to add a tiny drop of each solution to a different spot
Add solvent to beaker at no more than 1cm depth
Add tlc plate putting lid on top
When solvent about 1cm from top of tlc plate, remove it
Dry in a fume cupboard
Place under uv light and mark the spots lightly with a pencil
Calculate rf

Question 25

How do you work out rf values?

Answer 25

Distance moved by amino acid divided by distance moves by solvent

Question 26

Test for carboxylic acid?

Answer 26

Add Na2C03

Produces effervescence of co2 bubbles

Question 27

Aldehydes rest?

Answer 27

Silver mirror and tollens reagent
Tollens= silver nitrate then ammonia Ammonia till clear
Fehlings blue to red

Question 28

Alkenes test?

Answer 28

Decolourises bromine water

Question 29

Ammonium ions test?

Answer 29

Red litmus paper to blue with fumes from adding hydroxide ions
Hydroxide ions form nh3 and h20

Question 30

Test for halides?

Answer 30

Add silver nitrate 
Add ammonia to redissolve 
Cl dissolves
Br does a bit
I doesn’t

Question 31

Test for group 2?

Answer 31

Hydroxide ions
Magnesium white insoluble ppt
Calcium white ppt partially soluble

Question 32

Test for lower group two metals?

Answer 32

Add sulphate ions

Strontium and barium form white ppt

Question 33

What is the test for carbonate ions?

Answer 33

Bubble gas through lime water

Turns it cloudy

Question 34

What are the observations and products of reacting halides with concentrated sulphuric acid?

Answer 34

Produces hx and hS04

Produces white steamy fumes

Question 35

Test for chloroalkane?

Answer 35

Warm with silver nitrate

Produces white ppt

Question 36

Test for acyl chloride?

Answer 36

Silver nitrate
Vigorous reaction steamy HCl fumes
White ppt

Question 37

When measuring rage by initial method what should you remember?

Answer 37

To log the rate for the y axis

And to log the concentration for the x axis