Chemistry Core Practicals

• Simple distillation method


  method:1- add a small volume of ink to a flask and connect the flask to a condenser (thermometer may be added) connect the condenser to a tap and place a beaker at the end of the opening.2- using a buses burner heat the flask slowly so that the ink timers. Be careful not to heat the flask too strongly. Move the bunsen burner away if it starts boiling vigorously.3- collect sample of the distilled solvent. Turn the bunsen burner off when finished.

  Equipment list:- 250cm cubed beaker-thermometer-cold water tap-clamp and stand-bunsen burner-round-bottomed or pear shaped flask-quick fit apparatus (condenser, rubber tubing, fractionating column and connectors)

  extra key points/info:- condenser should be horizontal with water entering and leaving at the top.- the flask should NOT be heated too strongly- as it can cause the water yo boil over into the beaker collecting the distillate.

  
• paper chromatography method

  method:1- use a pencil to draw a line across the chromatography paper, 2cm from the bottom.2- use the pipette or capillary tube to add small dots of different inks to the line on the chromatography paper. Make sure they are not placed too close together.3- place the paper in a beaker containing 1cm cubed of solvent reached by drawing a horizontal line across the chromatography paper at this point.4- remove the chromatogram from the solvent. mark where solvent reached by drawing a horizontal line across the chromatography paper at this point.5- leave the chromatography paper at this point.6- measure the distance travelled by the solvent front and the spots from the pencil line.

  chemicals required:1- distilled water2- ink mixture

  equipment:1- 250cm cubed beaker2- ruler and pencil3-distilled water or suitable solvent4- chromatography paper5-pipette or capillary tube

  
• EXTRA FOR CHROMATOGRAPHY:

  calculation often required:

  RF value=

  distance moved by substance divided by moved by solvent

  other key points:- pencil is used to draw the line as it is insoluble so won't travel up the paper.- ink spots place above the line prevent them from dissolving and being washed away.
• investigating ph


  methodmethod:1- using the measuring cylinder or volumetric pipette, add 25cm cubed of dilute hydrochloric acid to a beaker.2- add a few drops of universal indicator. compare the initial colour of the solution to a pH colour chat and record pH. ( can use ph probe)3- add calcium hydroxide or calcium oxide (one spatula at a time) to the beaker, stirring and recording the pH between additions.4-stop adding calcium hydroxide when pH remains constant.

  chemicals required:-hydrochloric acid-powdered calcium hydroxide or calcium oxide

  equipment list:- 25 cm cubed measuring cylinder or volumetric pipette-beaker-glass rod-universal indicator or pH probe-spatula

  key points:- equation for experiment= CaO+2HCL-CaCl2+H20-pH probe is more accurate then a universal indicator
• preparing copper sulfate


  method:1- using a measuring cylinder, measure 25cm cubed of sulphuric acid into a beaker. place the beaker in a water bath to warm the sulphuric acid.2- add copper oxide to the acid, 1 spatula at a time, stirring with a glass rod. Continue adding it until it is In excess and the solid doesn't disappear when stirred.3- put a piece of filter paper in a funnel over a beaker. put the solution through the funnel to remove excess copper oxide.4- pour the filtrate into an evaporating basin. place on a tripod with gauze and heat with a bunsen burner to start evaporation.5- when almost all the water has evaporated, turn off the heat and leave to dry. Blue copper sulphate crystals will remain in the basin.

  chemicals required:- sulfuric acid-copper oxide

  equipment list:-25cm cubed measuring cylinder- two 250cm cubed beakers-glass rod-evaporating basin-spatula-funnel and filter paper-water bath-bunsen burner-tripod and gauze

  key points:- equation= CuO+H2SO4-CuSO4+H2O

  common equations needed=

  percentage yield+ yield dived by theoretical yield x 100
• electrolysis of copper sulphate solution method


  method:1- pour copper sulfate solution into a beaker so that it is half full.2-place two inert graphite electrodes into the beaker and attach to a power supply using crocodile clips and wires.3- fill 2 test tubes with copper sulfate solution and place over each electrode4- turn on the power and record any observations5- use a glowing splint to test any gas that has collected in the test tubes. record any observations.chemicals required:-copper sulfate solution-propanone-distilled water

  
• acid-alkali titration method


  Method:1-Add exactly 25 cm3​ ​of sodium hydroxide to a conical flask using a pipette and pipette filler. Add a few drops of phenolphthalein indicator to the conical flask then place the conical flask on a white tile.2-Setup the burette in the clamp and stand. Close the tap and use a funnel to pour about 10 cm3​ ​of hydrochloric acid into the burette.3-Place a beaker under the burette and open the tap, allowing the tip of the burette to fill with acid and displace any air bubbles.4-Close the tap before the burette empties then use a funnel to fill the burette with acid. Record the initial burette reading to the nearest 0.05 cm3​ .​5-Place the burette above the conical flask. Carry out a rough trial titration, adding the acid 1-2 cm3​ ​at a time, swirling the conical flask constantly.6-Close the burette tap as soon as the solution decolourises. Record the final burette volume and calculate the volume of acid that has been added from the burette.7-Rinse the conical flask with deionised water then add 25 cm3​ ​of sodium hydroxide. Refill the burette if necessary and record the initial volume of acid in the burette.8-Using the rough titre as guidance, add the acid to the conical flask until within about 4 cm3​ of the rough titre volume. Add the acid drop by drop after this, swirling constantly until the endpoint is reached. Record the final burette reading and use this value to calculate the titre volume.9.Repeat steps 7 and 8 until concordant titres are obtained (results within 0.1cm3​)​.10- Use the concordant results to calculate the mean titre.

  
• acid-alkali titration method continued


  Equipment list- 50 cm3​ ​burette- 25 cm3​ ​pipette with pipette filler- 250 cm3​ ​conical flask- 100 cm3​ ​beaker- Funnel- White tile- Burette clamp and standChemicals required-Phenolphthalein indicator- 0.4 mol/dm3​ h​ ydrochloric acid-Sodium hydroxide solution (unknown concentration)- Deionised water
• measuring the production of gas method


  Equipment list- Gas syringe and clamp stand/ measuring cylinder and water trough- Delivery tube and bung- 100 cm3​ ​conical flask- 25 cm3​ ​measuring cylinder- Timer- Digital balance and weighing boat- Pestle and mortarChemicals required- Hydrochloric acid (variety of concentrations)- Marble chipsMethod:1-Set up the apparatus as shown in figure 1 or figure 2. If using a gas syringe, support it horizontally in a clamp stand and attach the delivery tube. If using a measuring cylinder, fill a trough and measuring cylinder with water then turn the measuring cylinder upside-down in the trough. Insert the delivery tube into the measuring cylinder.2-Add 50 cm3​ o​ f dilute hydrochloric acid to the conical flask.3-Add 0.4 g of marble chips to the conical flask. Immediately attach the bung - this should beconnected to the gas collection vessel via the delivery tube. Start the timer.4-For every 10 cm3​ o​ f gas produced, record the time in a results table.5-Repeat steps 1-4 for different concentrations of acid.6-The experiment may be repeated, changing the size of the marble chips instead of theconcentration of acid. The marble chips can be made smaller by crushing them in a pestle and mortar. For this to be a fair test, the concentration and volume of HCl and the mass of marble chips must be controlled.Key points:- The equation for this reactionis: 2HCl(aq)+CaCO3​(​s)⟶H2​O​ (l)+CaCl2​(​aq)+CO2​(​g)

  
• observing colour change method


  Equipment list- 50cm3​m​ easuringcylinder- 10cm3​m​ easuringcylinder- 250 cm3​ c​ onical flask- Piece of paper- Black marker pen- Timer- Thermometer- Water bath- Test tubeChemicals required-Sodium thiosulfate solution- Hydrochloric acidMethod:1-Using a 50 cm3​ ​measuring cylinder, measure 50 cm3​ ​of dilute sodium thiosulfate and pour into the conical flask.2-Draw a cross on the paper using the marker pen then place the conical flask over this cross.3-Use the 10 cm3​ m​ easuring cylinder to measure 10 cm3​ ​of dilute hydrochloric acid. Add this to the conical flask, immediately swirl the flask to mix the reactants and start the timer.4-Record the initial temperature of the mixture using the thermometer.5-Observe the reaction mixture, stopping the timer as soon as the black cross is no longervisible.7-Repeat steps 1 to 4 with different starting temperatures of reactants. This can be achievedby placing a conical flask of sodium thiosulfate and a test tube containing hydrochloric acid into a water bath and leaving them to reach the desired temperature. Remember to use a thermometer in step 4 to record the initial temperature.Key points- The equation is:Na2​S​ 2​O​ 3​(​ s)+2HCl(aq)→2NaCl(aq)+H2​O​ (l)+SO2​(​ g)+S(s)

  
• identifying ions method part 1


  Equipment list- Distilled water- Test tubes- Wire loop- Bunsen burner- Heatproof mat- Tongs- Red litmus paper- Boiling tube- Bung and delivery tube

  Chemicals required- Unknown samples of salts- Hydrochloric acid- Dilute sodium hydroxide- Limewater- Barium chloride- Nitric acid- Silver nitrate
• identifying ions method part 2


  Flame test:1-Clean a wire loop by dipping it in HCl then holding it in a blue flame until it burns without altering the colour of the flame.2-Dip the clean wire loop into the unknown salt and then hold the loop in the blue flame of a bunsen burner. Record the colour.3-Repeat for the other unknown samples.Hydroxide precipitates test:1-Place a little of the unknown solution in a test tube and add a few drops of dilute sodium hydroxide solution. Record any observations.2-If a white precipitate forms, add an excess of sodium hydroxide solution and record any observations.Test for ammonium ions:1- Place a little of the unknown solution in a test tube and add a few drops of dilute sodium hydroxide solution. Warm the solution gently with a bunsen burner, holding the test tube with tongs.2-Place a piece of damp red litmus paper over the end of the test tube and record any observations.
• identifying ions method part 3


  Test for carbonate ions:1- Add a few drops of dilute hydrochloric acid to a boiling tube containing the unknown solution.2- Place a bung and delivery tube onto the boiling tube and place the other end of the delivery tube into a test tube of limewater. Record any observations.Test for sulfate ions:1- Add a few drops of hydrochloric acid to a test tube of the unknown substance followed by a few drops of barium chloride. Record any observations.Test for halide ions:1- Add a few drops of nitric acid to the unknown solution followed by a few drops of silver nitrate. Record any observations.
• combustion of alcohols method


  Equipment list- Copper can- Clamp stand- 100 cm3​ m​ easuring cylinder- Thermometer- Digital balance- Wooden splint and matches- Heatproof mat- Access to a tapChemicals required- Ethanol- Propanol- Butanol- PentanolMethod:1- Place a copper can in a clamp stand. Adjust the height so that the copper can will sit just above the flame of the spirit burner.2- Using a measuring cylinder, pour 100 cm3​ ​of water into the copper can. Record the initial temperature.3- Measure the initial mass of the spirit burner and lid containing the first alcohol.4- Place the spirit burner under the copper can. Take off the lid and light with a wooden splint.5- Replace the lid of the spirit burner when the temperature has risen about 20°C. Make sureto stir the water constantly. Record the final temperature.7- Measure the final mass if the spirit burner and lid.8- Repeat steps 2 to 6 with the other alcohols. Make sure fresh water is used in each