6.4 Iron chloride test, Formation of verdigris. Task. How can acetic acid and formic acid be recognized?

Transcription

1 Science - Chemistry - Organic Chemistry - 6 Carboxylic acids (P772900) 6.4 Iron chloride test, Formation of verdigris Experiment by: Anouch Printed: Feb 25, 204 2:3:4 PM intertess (Version 3.2 B24, Export 2000) Task Task How can acetic acid and formic acid be recognized? Examine acetic acid and formic acid for some specific reactions Use the space below for your own notes. Logged in as a teacher you will find a button below for additional information. - -

2 Additional Information Learning objectives Formic acid and acetic acid exhibit some reactions typical for carboxylic acids, and can so be distinguished from other acids. Typical reactions are the red colouration on the addition of iron(iii) chloride and the formation of verdigris. Notes on setup and procedure Preparation: Provide the following solutions: Formic acid, 50% (40 ml) Acetic acid, 0% ( ml) Acetic acid, 50% (32 ml) Sodium carbonate solution, 0% ( g) Sodium formate solution, 0% ( g) Sodium acetate solution, 0% ( g) lron (III) chloride solution, 0% ( g). All of the quantities given refer to the quantity of substance which should be added to 00 ml water. The concentrations stated can be varied slightly. Remarks on the students experiments: The addition of iron(iii) chloride solution should be stopped when a red colouration is shown. Ensure that the test tubes are carefully heated, as the solutions have a tendency towards delayed boiling - 2 -

3 Hazard and precautionary statements Formic acid: H226: Flammable liquid and vapour. H34: Causes severe skin burns and eye damage. P260: Do not breathe dust/fume/gas/mist/vapours/spray. P280: Wear protective gloves/protective clothing/eye protection/face protection. P30+P330+P33:IF SWALLOWED: Rinse mouth. Do NOT induce vomiting. P305+P35+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do continue rinsing. P309+P30: IF exposed or you feel unwell: Immediately call a POISON CENTER or doctor/physician. Acetic acid: H226: Flammable liquid and vapour. H34: Causes severe skin burns and eye damage. P280: Wear protective gloves/protective clothing/eye protection/face protection. P30+P330+P33:IF SWALLOWED: Rinse mouth. Do NOT induce vomiting. P307+P30: IF exposed: Immediately call a POISON CENTER or doctor/physician. P305+P35+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do continue rinsing. Sodium carbonate: H39: Causes serious eye irritation. P260: Do not breathe dust/fume/gas/mist/vapours/spray. P305+P35+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do continue rinsing. Iron(III) chloride H302: Harmful if swallowed. H35: Causes skin irritation. H37: May cause an allergic skin reaction. H38: Causes serious eye damage. P280: Wear protective gloves/protective clothing/eye protection/face protection. P30+P32: IF SWALLOWED: Call a POISON CENTER or doctor/physician if you feel unwell. P302+P352: IF ON SKIN: Wash with soap and water. P305+P35+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do continue rinsing. P30: Immediately call a POISON CENTER or doctor/physician. P50: Dispose of contents/ containers to be collected by a licensed contractor in accordance with national and local regulations

4 Hazards Formic acid and acetic acid are corrosive! Wash splashes off the skin with copious water! Wear protective glasses! Copper compounds are poisonous. Do not swallow them! Notes Short-chain carboxylic acids react with Fe 3+ ions to form red-coloured complexes of the type [Fe 3 (OH - ) 2 (HCOO - ) 6 ] + [HCOO] -, which decompose to brown iron(ii) oxyhydrate on heating. Verdigris is basic copper acetate Cu(CH 3 COO) 2 Cu(OH) 2. Naturally occurring verdigris forms in the presence of CO 2, CO and moisture in the air with basic copper carbonate as intermediate. The verdigris formation is not very specific, as the other short-chain carboxylic acids also form similarly structured copper compounds. Remarks on the method It could be useful to show in a parallel demonstration experiment that pure acetic acid does not give a red-colouration. Working in groups is recommended for this experiment, so that the time until the formation of verdigris can be utilized. One group can carry out the iron chloride test while a second group starts the experiment on verdigris formation. Waste disposal Pour all liquids in the container for acidic and alkali waste. Either recycle copper foil or put strips coated with verdigris in the heavy metals waste

5 Material Material Material from "TESS advanced Chemistry Set Organic Chemistry, CH-4 " (Order No ) Position No. Material Test tube rack for 2 tubes, holes d = 22 mm, wood Order No Quantity 2 Graduated cylinder, 0 ml, plastic Test tube brush w. wool tip, d = 25 mm Glass beaker DURAN, short, 50 ml Test tube, 80x8 mm (3) 6 Test tube, 80x20 mm, DURAN, PN Test tube holder, up to d = 22 mm Tweezers, straight, blunt, 30 mm Glass beaker DURAN, short, 250 ml Crucible tongs, 200 mm, stainl. steel Scissors, straight/blunt pts, 0 mm Pipette with rubber bulb Protecting glasses, clear glass Erlenmeyer flask, narrow neck, 00 ml, PN Chemicals, Additional Material Position No. Material Bunsen burner /DIN/, nat.g., w. cock Order No Quantity Safety gas tubing, DVGW, sold per metre Formic acid 98-00%, 250 ml Iron(III) chloride, 250 g Copper foil, 00 g Sodium acetate trihydrate, 250 g Sodium carbonate, anhyd., 000 g Sodium formate, 250 g Water, distilled, 5 l Acetic acid, 99-00%, pure, l Indicator paper, ph -4, roll Material required for the experiment - 5 -

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7 Action Action Hazards Formic acid and acetic acid are corrosive! Wash splashes off the skin with copious water! Wear protective glasses! Copper compounds are poisonous. Do not swallow them! Procedure Number the test tubes from to 3. Pour 5 ml of 0% acetic acid into an Erlenmeyer flask and add sodium carbonate solution until no further evolution of gas is seen. Check with a strip of indicator paper if the acid has been neutralized, add more sodium carbonate solution if necessary. Fill a test tube one third full with the neutralized solution (Fig. ), add a few drops of iron(iii) chloride solution (Fig. 2) and shake gently to mix the liquids. Heat the solution to boiling (Fig. 3). Fig. Fig

8 Fig. 3 Fill another test tube one third full with sodium acetate solution. Again add a few drops of iron(iii) chloride solution and heat the liquid. Cut 3 strips out from the copper foil, each about cm wide and 5 cm long. Fill 50% formic acid in a beaker to a height of approx. 3 cm, and the same amount of 50% acetic acid in two other beakers (50 ml and 250 ml). Put one strip of copper foil in the beaker containing the formic acid, and another in the 50 ml beaker containing acetic acid (Fig. 4). Fig. 4 Heat the third strip of copper foil to glowing and then put it directly into the 250 ml beaker (Fig. 5). Allow the three beakers to stand somewhere with free access of air for about 2 weeks. Note your observations during this time

9 Fig. 5 Waste disposal Pour all liquids in the container for acidic and alkali waste. Either recycle copper foil or put strips coated with verdigris in the heavy metals waste

10 Results Results Note the observations you make in general form. Also summarize your observations in table. Reaction with iron(iii) chloride: Reaction with copper foil: - 0 -

11 Table reactants reaction neutralized acetic acid + iron(iii) chloride sodium acetate + iron(iii) chloride sodium formate + iron(iii) chloride formic acid + copper foil acetic acid + copper foil Reaction with iron(iii) chloride: On the addition of sodium carbonate solution to acetic acid, a gas is evolved and the solution froths. All three solutions are coloured red on the addition of iron(iii) chloride - -

12 solution. On heating, a rust-brown solid precipitates. Reaction with copper foil: The strips of copper foil are shiny after immersion in the acids. After some days, a green layer forms on the surfaces protruding out of the acids, the liquids also turn green. The oxidized foil forms a green coating quicker than the pure copper foil. reactants neutralized acetic acid + iron(iii) chloride sodium acetate + iron(iii) chloride sodium formate + iron(iii) chloride formic acid + copper foil acetic acid + copper foil reaction red colouration a brown precipitate is formed on heating a brown precipitate is formed on heating a green coating is formed the solution is coloured green - 2 -

13 Evaluation Evaluation Question : Draw conclusions from your observations. Reaction with iron(iii) chloride: Reaction with copper foil: Reaction with iron chloride: The acetic acid is neutralized by the added sodium carbonate, and sodium acetate is formed. On the addition of the iron(iii) chloride solution to the formates and acetates, a red coloured substance is formed which allows these acids to be recognized (as salts). Reaction with copper foil: Verdigris is formed on the copper foil when it is exposed to air and in contact with acetic acid (or formic acid). This reaction is also useable for the recognition of short-chain carboxylic acids

14 Question 2: Formulate the equations for the reactions which took place. 2 CH 3 COOH + Na2CO3 2 CH 3 COONa + H 2 O + CO 2 CuO + 2 HCOOH (HCOO) 2 Cu + H 2 O CuO + 2 CH 3 COOH (CH 3 COO) 2 Cu + H 2 O Question 3: Enter the properties of acetic acid and formic acid which have been observed up to now in the general data sheet, look up missing entries in your text book to fill it in completely. See "General data sheet" - 4 -

15 General data sheet General data sheet - 5 -

16 Name of Formic acid the substance: Chemical nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn formula: Colour: nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn State of nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn aggregation: Melting nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn point: Boiling nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn points: Other properties: Occurrence/ preparation: Use: - 6 -

17 Name of the substance:formic acid Chemical formula: Colour: State of aggregation: Melting point: Boiling points: Other properties: HCOOH colourless liquid 8.4 C 00.5 C biting smell; colours indicators like other acids; reacts with metals formic hydrogen; corrosive; inhibits bacterial growth; the salts (formates) form red-coloured compelexes with iron(iii) chloride Occurrence/ preparation: ants; stinging nettles; fir-needles; is formed by the oxidation of formaldehyde or the thermal decomposition of oxalic acid Use: preservative - 7 -

18 Name of Acetic acid the substance: Chemical nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn formula: Colour: nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn State of nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn aggregation: Melting nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn point: Boiling nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn points: Other properties: Occurrence/ preparation: Use: - 8 -

19 Name of the substance:acetic acid Chemical formula Colour: State of aggregation: Melting point: Boiling points: Other properties: CH 3 COOH colourless liquid 6.6 C 8 C biting smell; colours indicators like other acids; reacts with metals formic hydrogen; corrosive; inhibits bacterial growth; the salts (acetates) form red-coloured compelexes with iron(iii) chloride Occurrence/ preparation: constituent of wood vinegar; formed by the oxidation of acetaldehyde and the dry distillation of wood Use: vinegar - 9 -