Practicals Flashcards
Why do you invert a flask when making a solution?
To ensure a uniform solution
Why might you not be able to fill up to the line with a volumetric flask?
You can’t see the line bc the solution is dark
How can you ensure you’re weighing mass properly?
Subtracting mass of empty weighing bottle to give accurate reading on how much mass is actually added
Why use a volumetric pipettes?
Better than a measuring cylinder because smaller uncertainty
When filling a volumetric flask what should you always do?
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
What is the process for making a solution?
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
What should you ensure when measuring liquids
Full to the bottom of the meniscus
How do you do a dilution?
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
How do you do a titration?
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
What should you do to make sure all the alkali goes into the conical flask?
Touch the solution with the pipette
What should you do before using the burette?
Rinse it out three times with the solution you’re going to use
Why do you use anti bumping granules?
So smaller bubbles are produced and reaction reacts less vigorously
How should you read a burette?
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
Which indicator should I use?
Methyl orange for strong acids or neutralisation reactions
Phenolphthalein for stronger alkalis
Why should you only use a small amount of indicator?
They’re acidic, so they could affect your results
How do you work out titre?
Initial burette reading 0.05 - final burette reading 24.05
= 24cm3
When reacting iron and manganate with iron tablets what should you do first?
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
What should you remember with manganate redox?
Only use dilute Sulphuric acid in excess
What is the equation for the reaction of sodium thiosulphate and HCl?
Na2S2O3 +2HCl to 2NaCl + S02 +S+ H20
What is the method to measure the rate of reaction as temperature changes?
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
What is the method of recrystallisation?
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
Method for separating organic liquids?
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
How do you find melting point?
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
TLC method?
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
How do you work out rf values?
Distance moved by amino acid divided by distance moves by solvent
Test for carboxylic acid?
Add Na2C03
Produces effervescence of co2 bubbles
Aldehydes rest?
Silver mirror and tollens reagent
Tollens= silver nitrate then ammonia Ammonia till clear
Fehlings blue to red
Alkenes test?
Decolourises bromine water
Ammonium ions test?
Red litmus paper to blue with fumes from adding hydroxide ions
Hydroxide ions form nh3 and h20
Test for halides?
Add silver nitrate Add ammonia to redissolve Cl dissolves Br does a bit I doesn’t
Test for group 2?
Hydroxide ions
Magnesium white insoluble ppt
Calcium white ppt partially soluble
Test for lower group two metals?
Add sulphate ions
Strontium and barium form white ppt
What is the test for carbonate ions?
Bubble gas through lime water
Turns it cloudy
What are the observations and products of reacting halides with concentrated sulphuric acid?
Produces hx and hS04
Produces white steamy fumes
Test for chloroalkane?
Warm with silver nitrate
Produces white ppt
Test for acyl chloride?
Silver nitrate
Vigorous reaction steamy HCl fumes
White ppt
When measuring rage by initial method what should you remember?
To log the rate for the y axis
And to log the concentration for the x axis
