Practical Booklet Heidi Hanes Central College Nottingham

Topic Separation of Substances Aims  Practical Booklet, building skills for separating substances and estimating purity Level Level 3 Method PowerPoint slides with Experiments: Experiment 1 Separating a sand and salt mixture, Experiment 2 Separating metal salts in water by paper chromatography, Experiment 3 Purification of impure benzoic acid by hot filtration and recrystallization, Experiment 4 Preparation and Purification of paracetamol. Equipment  Please see each experiment for lists of equipment and substances Duration > 30 Minutes

Practical Booklet Separating substances and estimating purity Experiments in this booklet: 1)Separating a sand and salt mixture. 2)Separating metal salts in water by paper chromatography. 3)Purification of impure benzoic acid by hot filtration and recrystallization. 4)The preparation and purification of paracetamol

Experiment 1: Separating a sand and salt mixture Safety Information: Full laboratory rules are in effect, wear your lab coat, gloves and goggles at ALL times. No eating, drinking, texting, speaking on mobile phones or putting on make-up. Avoid ingesting chemicals. Take note of the individual safety notices with all reagents. Aim: The aim of this experiment is to separate sand and salt in a sand and salt mixture. You will need: 250 cm 3 beaker Filter funnel and paper Evaporating dish Tripod gauze Bunsen burner Heat proof mat Glass rod for stirring Method: 1.Mix 5 g of the mixture with 50 cm 3 of water. 2.Filter the mixture into a conical flask and pour the filtrate into an evaporating dish. 3)Heat the salt solution gently until it starts to “spit”. 4)Turn off the Bunsen burner and let the salt dry. 5)Once cool and dry weigh the salt. Experiment 1

Results: Record the mass of the salt and calculate the percentage of recovered salt from the salt and sand mixture. Analysis: Explain the reasons for each of the steps in this practical. Experiment 1

Experiment 2: Separating metal salts in water by paper chromatography Safety Information: Full laboratory rules are in effect, wear your lab coat, gloves and goggles at ALL times. No eating, drinking, texting, speaking on mobile phones or putting on make- up. Avoid ingesting chemicals. Take note of the individual safety notices with all reagents. Aim: The aim of this experiment is to identify and assess the purity of unknown solutions of metal salts or mixtures of metal salts. Since these salts all have similar chemical properties they are difficult to separate, so we will be using a technique called chromatography. You will need: 3 unknown sample bottles containing either pure or mixtures of metal salts in water (these salts could be iron (III) chloride, cobalt (II) chloride, manganese (II) chloride or copper (II) chloride) Pure samples of each of the metal salts in water Chromatography paper Capillary tubes Acetone-hydrochloric acid developing solvent (350 ml acetone ml 6M HCl) – Take care, Corrosive, flammable, harmful Capillary tube for each solution 600 ml beaker Plastic wrap 6 M ammonia solution – Corrosive, harmful Dilute sodium sulphide solution (Na 2 S) Method 1.Obtain a piece of chromatography paper that is at least 9 cm wide and 12 cm long. 2.Draw a line in pencil about 1 cm from the bottom (long edge) of the paper. 3.Place an “X” on the line every 2.5 cm. 4.Label each “X” with the samples you are using. 5.Using a capillary tube, spot a small dot of a solution on the corresponding “X”. Experiment 2

6.Dry the spots. 7.Repeat the procedure in step 5 adding a second drop to each spot on top of the first. 8.Form the paper into a cylinder taking care not to overlap the ends and secure with two staples. 9.Wearing gloves and working in the fume cupboard place about 40 ml of the developing solvent into the beaker. 10.Place the paper cylinder carefully into the beaker with the spots at the bottom. 11.Cover with plastic wrap and observe. 12.When the solvent has almost reached the top remove the paper and place a pencil mark where the solvent stopped. 13.Let the paper dry and observe any spots. 14.Wearing gloves and still working in the fume cupboard spray the paper with 6 M ammonia and observe any spots. 15.Using a dropper full of sodium sulphide solution, streak the dropper across the paper up from each “X” to the top of the paper and observe the spots. 16.Compare your unknown samples to the known metal salts. Experiment 2

SampleNumber of spotsAppearance of spots Unknown 1 Unknown 2 Unknown 3 iron (III) chloride cobalt (II) chloride manganese (II) chloride copper (II) chloride Results: Complete the table below: Experiment 2

Analysis: 1)Which of the unknown solutions were mixtures of salts and which were pure salts? 2)Evaluate the validity of using paper chromatography to establish the purity of a substance Experiment 2

Experiment 3 Experiment 3: Purification of impure benzoic acid by hot filtration and recrystallization Safety Information: Full laboratory rules are in effect, wear your lab coat, gloves and goggles at ALL times. No eating, drinking, texting, speaking on mobile phones or putting on make-up. Avoid ingesting chemicals. Take note of the individual safety notices with all reagents. Part 1: Purification of benzoic acid Aim: To purify benzoic acid by recrystallisation and test the purity of the purified sample by melting point analysis. You will need: Impure benzoic acidGlass funnel Water Filter paper – folded 250 ml beakerConical flask Bunsen burner, mat, tripod and gauzeBuchner set-up Heat proof gloves or tongsVacuum Glass rodDrying cabinet Watch glassThermometer (100 °C) Method: 1.Warm up your gravity filtration setup. Place a 125 cm 3 conical flask on a hotplate. Place a funnel into the neck of the flask. 2.Heat up 100 cm 3 of water in a 250 cm 3 beaker on the hot plate 3.Fold a piece of fluted filter paper as shown by your tutor and place this into the funnel. 4.Weigh 0.8 – 1.0 g of the impure benzoic acid solid (crude sample) onto a clean watch glass and record the exact mass. On a second watch glass save a small amount of the crude sample for a melting point analysis later.

Experiment 3 5.Put the impure solid into a 125 cm 3 conical flask and add 20 cm 3 of near boiling water and stir with a glass rod until dissolved. Keep the temperature at about 100 °C with gentle heating. 6.Filter the hot benzoic acid solution by hot filtration. 7.Rinse the funnel with hot water to remove any crystals that may have formed during the filtration process. 8.Allow the mixture to cool to room temperature. In the mean-time set up the melting point apparatus. 9.Once the mixture has cooled to room temperature place on ice. The crystals should form. 10. Weigh a watch glass and Buchner filter paper and record the mass. 11. Set up the Buchner apparatus and vacuum filter the mixture which should now contain crystals. 12. Wash the crystals with 5 ml of cold water to rinse away any impurities that may be left. 13.Dry with the vacuum to make sure that you have gotten rid of most of the water. 14.Place the crystals and filter paper onto the pre-weighed watch glass. 15.Dry in the drying cabinet then weigh. 16.Calculate the mass of recovered product and then calculate the percentage yield. 17.Test the purity of your product using the melting point apparatus.

Experiment 3 Part 2: Melting Point Analysis Aim: To test the purity of the benzoic acid recovered by assessing its melting point. You will need: Your purified benzoic acid sample Pure benzoic acid Crude benzoic acid sample Melting point apparatus 12 Capillary tubes Method: 1.Once the crystals are dried fill three capillaries with your purified product to a depth of about 4 mm. 2.Place the three capillary tubes and a 250 °C thermometer into the melting point apparatus. Set to maximum. This will give you a rough idea of the melting point because it is not very accurate. 3.As soon as the sample is melted record the temperature and switch off the apparatus so that it can cool. This estimate can be out by up to 15 °C. 4.Repeat the process again with a fresh sample and new capillary tubes but this time turn the machine off or set the temperature to very low once you get to a temperature that is 25 °C below your first estimate for melting point. 5.Record your results. 6.Repeat the process again with the crude and pure samples.

Experiment 3 Results RunStarting melting point Temperature last crystal melts Rough estimate Your recovered product Crude sample Pure sample Mass of crude sample: ___________________ Mass of watch glass and Buchner filter paper: __________________ Mass of watch glass, filter paper and crystals: __________________ Mass of recovered product (benzoic acid): ____________________ Melting Point analysis:

Experiment 3 Analysis 1.Calculate the percentage recovery of purified benzoic acid using the equation below: % recovery = x 100 impure mass purified mass 2.Estimate the purity of your purified sample by melting point analysis. You have the melting point of the pure sample and crude samples to compare to. To estimate purity you can use the equation below: % purity = x 100 Median of melting point range Melting point of pure sample

Experiment 3 Analysis 3.How effective was the separation procedure used and what factors could influence the purity of the sample? 4.Critically evaluate the validity of using melting point to estimate purity in this example

Experiment 4 Experiment 4: Preparation and purification of paracetamol Safety Information: Full laboratory rules are in effect, wear your lab coat, gloves and goggles at ALL times. No eating, drinking, texting, speaking on mobile phones or putting on make- up. Avoid ingesting chemicals. Take note of the individual safety notices with all reagents. Aim: To prepare a sample of paracetamol from 4-aminophenol and assess its purity and yield. You will need: 4-aminophenol 2 small conical flasksAcetic anhydride Buchner set-upWater Vacuum Ice bathGlass rodDrying cabinet Watch glassCold de-ionised waterhot water bath at 80 ºC Melting point apparatus6 Capillary tubesEthyl ethanoate cyclohexane IodineUV light source TLC plateTweezers Commercial sample of paracetamolpencil and ruler4 test-tubes Method: Part 1: Preparation of paracetamol 1.Accurately weigh 1 g of 4-aminophenol in a 125 ml conical flask and record its mass. 2.Add 9 cm 3 of distilled water and stir briskly at room temperature so that you get a suspension of the solid in the water. 3.Add 1.1 cm 3 of acetic anhydride (ethanoic anhydride) in the fume cupboard and swirl the flask to mix. The solid should dissolve in 30 seconds. Continue shaking and a precipitate will form after 2 minutes. 4.After 10 minutes the solid should be filtered off under suction and washed with a little ice cold water. Leave the suction on for a little while longer to dry the solid. 5.Weigh the crude sample and record its mass in the tables below.

Experiment 4 Part 2: Purification of paracetamol by crystallisation from distilled water 1.Dissolve the crude paracetamol in a minimum of distilled water at about 80 ºC. Make sure you do not use more than 15 cm 3 of water. 2.Allow the clear solution to cool slowly to room temperature and collect the recrystallized product by vacuum filtration. 3.Wash the solid with 5 cm 3 of ice cold water 4.Transfer the solid and its filter paper onto a watch glass to dry 5.Weigh the dried and purified paracetamol and record its mass in the tables below. Part 3: Melting point analysis of paracetamol 1.Once the crystals are dried fill three capillaries with your purified product to a depth of about 4 mm. 2.Place the three capillary tubes and a 250 °C thermometer into the melting point apparatus. Set to maximum. This will give you a rough idea of the melting point because it is not very accurate. 3.As soon as the sample is melted record the temperature and switch off the apparatus so that it can cool. This estimate can be out by up to 15 °C. 4.Repeat the process again with a fresh sample and new capillary tubes but this time turn the machine off or set the temperature to very low once you get to a temperature that is 25 °C below your first estimate for melting point. 5.Record your results. 6.Compare your melting point to the melting point of pure paracetamol which is ºC and determine its percentage purity.

Experiment 4 Part 4: Thin Layer Chromatography of paracetamol 1.Make sure you do not touch the surface of the TLC plate with your fingers, use tweezers and hold only on the outside edges. 2.Lightly draw a pencil line about 1 cm from the bottom edge of the plate. The silica gel is very delicate so make sure you do not scrape it off, your experiment will not work if you do. 3.Mark off and label four equally spaced points on the plate. These are for your crude sample, your purified sample, 4-aminophenol and a commercial sample of paracetamol provided. 4.Place about 1/3 of a spatula full of each sample into a separate test-tube and add 1 cm 3 ethyl ethanoate to dissolve. 5.Spot your samples onto the TLC plate using capillary tubes. Allow to dry and repeat again. Your spots should not exceed 1-2 mm in diameter. 6.Once the spots are dry place the plates into a chromatography tank or large beaker containing a small amount of the developing solvent. This should all be in the fume cupboard. Make sure the level of the solvent is below the level of the spots on the plate. The developing solvent is a 2:1 mixture of ethyl ethanoate:cyclohexane. 7.Place a lid or plastic wrap on the tank and leave it in the fume cupboard to develop. 8.Once the solvent from is a few mm from the top of the plate, remove the plate from the tank and quickly mark off the position of the solvent front. Allow to dry. 9.Observe under UV light and lightly mark off any spots that are visible. 10.In the fume cupboard carefully place the plate in a jar or beaker containing a few iodine crystals. Cover the jar and wait for the spots to appear.

Experiment 4 Results: Part 1: Preparation of crude paracetamol Mass of watch glass and Buchner filter paper: __________________ Mass of watch glass, filter paper and crystals: __________________ Mass of crude paracetamol: ___________________ Part 2: Recrystalisation of paracetamol from crude sample Mass of watch glass and Buchner filter paper: __________________ Mass of watch glass, filter paper and crystals: __________________ Mass of recovered paracetamol: ____________________ Work out the percentage yield (%) for your crude and purified samples. What is the percentage recovery of purified paracetamol after recrystallization?

Experiment 4 RunStarting melting point Temperature last crystal melts Rough Purified paracetamol Part 3: Melting Point analysis: Percentage purity of paracetamol: Part 4: TLC of paracetamol (1) Draw a diagram to show which spots appeared under UV light and which spots appeared with iodine. (2) Determine the Rf values of the samples using the expression below: Rf = (distance travelled by spot)/(distance travelled by solvent)

Experiment 4 Distance travelledRf value solvent Crude sample Purified sample 4-aminophenol Commercial sample of paracetamol

Experiment 4 Analysis 1.How effective was the separation procedure used and what factors could influence the purity of the sample? Use the results of your melting point analysis and TLC to answer this question. 2.Critically evaluate the validity of using melting point and TLC to estimate purity in this example.

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