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Chemistry A2 > Required Practicals > Flashcards

Required Practicals Flashcards

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1
Q

How do you make up a volumetric solution?

A
  • Weight out a solid by difference in a clean, dry beaker
  • Add enough distilled water to dissolve the solid
  • Stir with a glass rod
  • Transfer the solution into a 250cm³ volumetric flask using a funnel
  • Rinse the beaker and glass rod with distilled water into the flask
  • Make up to the mark by adding distilled water until the bottom of the meniscus is on the mark
  • Add a stopper to the flask and invert it
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2
Q

How do you carry out a titration?

A
  • Rinse the burette with the solution you’re filling it with
  • Fill the burette
  • Rinse a pipette with distilled water and use it to transfer 25cm³ of solution 2 into a conical flask
  • Add 2-3 drops of suitable indicator into the flask
  • Add solution from burette drop-wise to solution in conical flask with constant swirling
  • Repeat the titration to achieve 2-3 concordant results and calculate a mean from these
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3
Q

How do you calculate % uncertainty?

A

instrument uncertainty/ quantity measured (x number of measurements) x 100

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4
Q

How would you carry out a calorimetry experiment?

A
  • Place a polystyrene cup in a glass beaker
  • Measure 25 cm³ of HCl into the beaker
  • Stir and let sit for 4 minutes and record temp every minute
  • Add 25cm³ of NaOH to the polystyrene cup and record temp every min for 10 more minutes
  • Record results in a graph and extrapolate backwards from the 5th minute to find the temp change
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5
Q

How do you test for ammonium?

A
  • Warm sample with NaOH solution in a test tube
  • Test gas with moist red litmus paper
  • Litmus turns blue
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6
Q

How do you test for magnesium?

A
  • Make up a solution of a magnesium compound and add a few drops of NaOH solution, then excess NaOH solution
  • White ppt formed
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7
Q

How do you test for calcium?

A
  • Nichrome wire into HCl then calcium sample

- Place in blue bunsen flame and it will show a brick red flame

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8
Q

How do you test for barium and strontium?

A
  • Flame test
  • Green flame for Ba
  • Red flame for Sr
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9
Q

How do you test for chloride ions?

A
  • Acidified silver nitrate, followed by dilute ammonia

- White ppt which then dissolves to give colourless solution

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10
Q

How do you test for bromide ions?

A
  • Acidified silver nitrate followed by dilute ammonia, then conc. ammonia
  • Cream ppt, no visible change in dilute NH₃, dissolves in conc NH₃
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11
Q

How do you test for iodide ions?

A
  • Acidified silver nitrate, dilute NH₃, then conc. NH₃

- Yellow ppt insoluble in both dilute and conc. NH₃

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12
Q

How do you test for sulphate ions?

A
  • Add nitric acid to remove carbonates or hydroxides
  • Add barium chloride
  • White ppt
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13
Q

How do you test for hydroxide ions?

A
  • Warm some solid ammonium salt and test gas produced with red litmus
  • Turns litmus blue
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14
Q

How do you test for carbonate ions?

A
  • Nitric acid
  • Fizzing and test gas with limewater
  • Limewater goes cloudy
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15
Q

What is reflux?

A

The continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry

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16
Q

Why would a percentage yield be less than 100?

A

Theoretical: Side reactions, impure reagents, incomplete reaction
Practical: Product lost in purification (filtration), product lost in distillation

17
Q

How do you test for a C=C?

A
  • Shake with bromine water

- Orange solution goes colourless

18
Q

How do you distinguish between a primary/secondary alcohol and a tertiary alcohol?

A
  • Add warm acidified potassium diochromate
  • Orange to green if primary or secondary
  • Stays orange if tertiary
19
Q

How can you distinguish between an aldehyde and a ketone?

A
  • Add Tollens, aldehyde produces silver mirror

- Add Fehling’s, aldehyde turns blue to red

20
Q

How do you test for a carboxylic acid?

A
  • Add sodium carbonate

- Effervescence

21
Q

How do you test for an ester?

A
  • Warm with ethanol and add a few drops of conc. sulphuric acid
  • Sweet smell- ester
22
Q

How do you purify a solid?

A
  • Dissolve in hot solvent
  • Of minimum volume
  • Filter to remove insoluble impurities
  • Cool to recrystallise
  • Filter under reduces pressure
  • Wash AND dry
23
Q

Why would a yield not be 100% after purification?

A

There may be impurities present in the product

24
Q

Describe what happens when a reaction mixture is refluxed and why it is necessary.

A
  • A mixture of liquids is heated to bpt for a long time
  • Vapour is formed which escapes from liquid mixture, is changed back into liquid and returned to liquid mixture
  • Any aldehyde and alcohol that initially evaporates can then be oxidised
25
Q

How you would obtain a sample of aldehyde (low bpt) from a mixture of an alcohol, carboxylic acid and the aldehyde?

A
  • Mixture heated in a suitable flask
  • With still head containing a thermometer
  • Water cooled condenser connected to the still head and suitable cooled collecting vessel
  • Collect sample at the bpt of aldehyde
  • Cooled collection vessel necessary to reduce evaporation of aldehyde
26
Q

How could you reduce % uncertainty in titrations?

A
  • Use a lower conc. of what you are adding so that you will get a larger titre and a lower uncertainty.
27
Q

Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values

A

Use UV
Measure distances from start line to spots (x)
Measure distance from start line to solvent front line (y)
Rf value = x / y

28
Q

What is the purpose of anti-bumping granules?

A
  • Provide a rough surface for small bubbles

- Prevents the formation of large bubbles that could cause hazardous splashing

29
Q

What method is used to heat organic compounds?

A

Electric heating as opposed to Bunsen burners because they are flammable.

30
Q

How can you remove impurities from an organic liquid product?

A
  • Add aqueous solution (sodium hydrogen carbonate) in a separating funnel
  • Stopper and shake the mixture
  • Impurities will dissolve in the aqueous solution
  • Open the tap and allow the bottom layer to run off and run off the second layer into the beaker
  • Repeat
31
Q

What methods can be used to maximise the yield obtained by distillation? (alocohol and aldehyde)

A
  • Use a temperature between the two substances in the mixture
  • Cool the distillate in a beaker with ice
32
Q

Describe a method for determining the melting point of a sample and state how to evaluate its purity.

A
  • Melting point apparatus and heat slowly
  • Check the data book value for the melting point and compare with obtained value
  • If there is a range of melting points its most likely impure
33
Q

State and explain what must be done to each sample before they are titrated with alkali

A

Quench by cooling or dilution

34
Q

How would you determine the rate of reaction of a sample?

A
  • Measure known volumes of the sample and a reagent that will cause a colour change into separate containers
  • Place a cross underneath a conical flask containing the sample
  • Add the reagent to a sample and and start a timer
  • Stop the timer once the cross disappears
  • Do 1/time taken to find the rate
  • Repeat with different concentrations if you want to find the order of reaction
35
Q

Measuring the rate of reaction by an initial rate method

A
  • All concentrations known
  • Series of experiments carried out where the initial conc. of one of the reactants is varied and the other stay the same
  • Concentration time graph is plotted
  • Tangent drawn at t=0 to determine the initial rate
36
Q

Measuring the EMF of an electrochemical cell

A
  • Set up two beakers with two different metal solutions and place a strip of their corresponding metals in each beaker
  • Soak a strip of filter paper in potassium nitrate solution and place each end in each beaker
  • Clip crocodile clip wires onto the metal strips and join them to a voltmeter to complete the circuit
  • A Pt electrode can be used for systems that contain two ions
37
Q

Outline a procedure for setting up a TLC plate

A
  1. Wearing plastic gloves, hold a TLC plate, draw a pencil line 1.5 cm from the bottom.
  2. Use a capillary tube to apply a small drop of the solution at the mid-point of the pencil line.
  3. Allow the spot to dry completely.
  4. In the developing tank, add developing solvent to a depth of not more than 1 cm.
  5. Place your TLC plate in the developing tank.
  6. Allow the developing solvent to rise up the plate to the top.
  7. Remove the plate and quickly mark position of the solvent front with a pencil.
  8. Allow the plate to dry in a fume cupboard.

Chemistry A2 (16 decks)

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