Chemistry - Core Practicals: 1-8

CORE PRACTICAL 1

1. measure out fixed volume of hydrochloric acid in conical flask

2. add known mass of sodium carbonate to conical flask

3. connect gas syringe delivery tube

4. allow reaction to go to completion

5. record volume of carbon dioxide produced

6. repeat experiment with different masses of sodium carbonate

7. assumptions made about experiment:

   • amount of gas lost between adding sodium carbonate + connecting delivery tube is minor

   • delivery tube set up is airtight = no gas lost

   • reaction does go to completion

CORE PRACTICAL 1 ANALYSIS + RESULTS

results are plotted onto a graph

• mass of sodium carbonate on x-axis + volume of carbon dioxide produced on y-axis

• anomalous results ignored + one line of best fit added

CORE PRACTICAL 1 APPLICATION

experiment used to determine identity of unknown metal in a metal carbonate, MCO₃ 
- process can be applied to thermal decomposition of metal carbonates + reaction with acid

hazards, risks + precautions core practical 1

hazards associated with acids depend on type + concentration of acid

• dilute acids require no hazard symbol/an irritant = require symbol = harmful to health

  • eye protection worn when handling

• moderately concentrated acids are often corrosive

  • wear eye protection, gloves should be worn

• concentrated acids are oxidising = cause/intensify a fire

  • eye protection + gloves are necessary when handling concentrated acids + the use of a fume cupboard

CORE PRACTICAL 2

1. using a measuring cylinder place 25cm³ of 1.0 mol dm^-3 copper(II) sulphate solution into polystyrene cup

2. weigh about 6g of zinc powder = an excess

3. draw a table to record initial temperature + time every half minute up to 9.5 minutes

4. put thermometer in cup, stir + record temperature every half minute for 2.5 minutes

5. at 3 minutes, add zinc powder to cup (DON’T RECORD TEMPERATURE AT 3 MINUTES)

6. continue stirring + record temperature for an extra 6 minutes

• for calculations, some assumptions are made about the experiment:

  • specific heat capacity + density of solution is same as pure water

  • specific heat capacity of container is ignored

  • reaction is complete + minor heat loss

why is a temperature correction graph used

reactions that aren’t instantaneous = before maximum temperature reached
- during delay = substances themselves lose heat to surroundings = true maximum temperature never reached
- use graphical analysis to determine maximum enthalpy change

how to make a temperature correction graph

1. take temperature reading before adding reactants for a few minutes

2. add second reactant + continue recording temperature + time

3. plot graph + extrapolate cooling part of graph until intersect time at second reactant added

CORE PRACTICAL 3

1. measure known volume of solutions via volumetric pipette + place it into conical flask

2. The other solution is placed in the burette

   • To start with, the burette will usually be filled to 0.00 cm³

3. drops of indicator added to solution in conical flask

4. tap on burette is opened + add solution at a portion to conical flask until indicator change colour

5. getting near to end point, flow of burette should be slow down

• should be able to close tap on burette after 1 drop has caused colour change

7. multiple runs carried out until concordant results are obtained

   • concordant results within 0.1 cm³ of each other

CORE PRACTICAL 4

1. weigh out precise amount of solid

2. add small volume of water + pre-dissolve solid

3. transfer to volumetric flask

4. rinse beaker with distilled water + add rinsings to flask

5. mark up to scratch mark with distilled water + add stopper + mix contents

CORE PRACTICAL 5

1. acidified silver nitrate used to measure rate of hydrolysis of halogenoalkanes

2. set up 3 test tubes in 50C water bath with mixture of ethanol + acidified silver nitrate

3. add a drops of chloroalkane, bromoalkane + iodoalkane to test tube + start stop watch

4. time how long it takes for precipitates to form

• white precipitate = chloroalkane

• cream precipitate = bromoalkane

• yellow precipitate = iodoalkane

  • yellow precipitate form fastest

  • C-I bond = lowest bond enthalpy = easiest to break + I^- ions to form fastest

  • white precipitate form slowest

  • C-Cl bond = highest bond enthalpy = hardest to break + Cl^- ions to form slowest

CORE PRACTICAL 6

1. measure 8cm³ of 2-methylpropan-2-ol in measuring cylinder

2. pour 2-methylpropan-2-ol in separating funnel

3. via fume hood, add 20cm³ concentrated hydrochloric acid to separating funnel in small portions of 2-3cm³ = ensure to release pressure by opening stopper

4. leave separating funnel to stand in fume hood for 20 minutes + gently shake separating funnel at 2 minute intervals 

5. allow layers to separate + dispose lower aqueous layer by opening tap

6. add sodium hydrogen carbonate solution in small portions to funnel + gently shake funnel = release pressure at regular interval = removes acidic impurities

7. layers have separated, open tap again dispose of aqueues layer

8. pour organic layer in clean dry conical flask + add 2 spatulas of magnesium sulfate = remove water 

9. once clear, decant liquid into distillation apparatus 

10. distill liquid + collect distillate in range of 47-53C

oxidation of alcohols core practical 7

primary alcohols oxidised = aldehydes = further oxidation = carboxylic acids
- propan-1-ol oxidised = ethanal’s produced + oxidised further propanoic acid formed

CORE PRACTICAL 7

1. add 20 cm³ of acidified potassium dichromate(VI) solution to 50 cm³ pear-shaped flask + cool flask in iced water bath

2. set up reflux apparatus keeping pear shaped flask cool

3. place anti-bumping granules to pear shaped flask 

4. measure out 1 cm³ of propan-1-ol 

5. via pipette add propan-1-ol drop wise in reflux condenser

6. propan-1-ol added, remove ice bath + warm up to room temperature 

7. position flask over electric heater in a water bath + heat for 20 minutes 

8. purify product using distillation apparatus 

• propan-1-ol is flammable = naked flames shouldn’t be used when heating

hazards, risks + precautions in core practical 7

alcohols are flammable and often harmful to health, e.g, propan‐1‐ol, butan‐1‐ol, pentan‐1‐ol
- alcohols kept away from naked flames
- avoid contact with skin + breathing in vapour
- fume cupboard used for harmful alcohols
- potassium dichromate is strong oxidising agent + handled with care
- spillages should be mopped up

CORE PRACTICAL 8 (AMMONIUM IONS)

1. about 10 drops of solution with ammonium ions added to clean test tube

2. about 10 drops of sodium hydroxide added via pipette

3. test tube swirled carefully to ensure mixed well

4. test tube of solution placed in beaker of water + beaker of water placed above bunsen burner = become water bath

5. solution’s heated, fumes produced

6. tongs used to hold damp piece of red litmus paper near mouth of test tube = test fumes

7. red litmus paper changes colour = turns blue in presence of ammonia gas

CORE PRACTICAL 8 (CARBONATE IONS)

1. small amount of dilute hydrochloric acid added to test tube via pipette

2. equal amount of sodium carbonate solution added to test tube via clean pipette

3. as soon as the sodium carbonate solution is added, bung with delivery tube should be attached to test tube

• delivery tube transfer gas formed to a different test tube which contains small amount of limewater

4. carbonate ions react with hydrogen ions from acid to produce carbon dioxide gas

5. carbon dioxide gas turn limewater milky

CORE PRACTICAL 8 (SULFATE IONS)

1. acidify sample with dilute hydrochloric acid add a few drops of aqueous barium chloride

2. sulfate’s present = white precipitate of barium sulfate is formed

   • Ba²⁺ (aq) + SO₄^2- (aq) → BaSO₄ (s)

CORE PRACTICAL 8 (FLAME TESTS)

1. dip the loop of nichrome metal wire such in concentrated acid + hold it in blue flame of a bunsen burner until no colour change

• cleans wire loop + avoids contamination

2. dip loop into solid sample + place it in edge of the blue Bunsen flame

• avoid letting wire getting hot that it glows red otherwise can be confused with flame colour