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Version 1.0 SOP: Diluting concentrated acetic acid Written by: Science ASSIST
STANDARD OPERATING PROCEDURE:
Diluting concentrated acetic acid
Note: To be undertaken only by trained personnel in conjunction with a current Safety Data Sheet (SDS) and site-specific risk assessment.
1. Introduction
Acetic acid is an organic acid with chemical formula CH 3 COOH. Acetic acid containing less than 1% water is commonly referred to as ‘glacial acetic acid’, so-called as it resembles ice crystals when it freezes, which it does at just under 17°C. The concentrated acid is a colourless, corrosive liquid with a pungent odour, and should be handled with care. The name ‘acetic’ is derived from the Latin acetum meaning ‘sour wine’. The production of acetic acid dates back to at least 10000 BC with the emergence of the practice of winemaking. While industrial-grade acetic acid is synthesised from fossil fuels, food-grade vinegar, which typically contains 4-8% acetic acid, is still made through the fermentation of sugars by yeast to give ethanol, which is then oxidised to acetic acid by bacteria of the genus Acetobacter. In senior school chemistry, concentrated acetic acid is used in the preparation of acetate esters. In dilute form in junior and senior school science, acetic acid is used as an example of a weak organic acid. The concentrated acid is flammable and combustible and should be handled away from flames or sparks; it is also hygroscopic, which means that it absorbs water from the air. Synonyms: ethanoic acid, glacial acetic acid, vinegar acid, methanecarboxylic acid, ethylic acid
2. Context
These instructions are for the use of experienced teachers and technicians only. Do not make up a dilution for the first time without seeking practical advice from an experienced colleague. Students must not be asked to make up dilutions from concentrated acetic acid.
3. Safety notes
This activity may only be carried out with appropriate facilities available i.e. running water, fume cupboard, chemical safety/eyewash station and relevant Personal Protective Equipment (PPE). Avoid contact with skin and eyes, and avoid breathing fumes. Concentrated and high molarity acetic acid liquid can cause severe burns and eye damage. Fumes of concentrated acetic acid cause irritation to the eyes and respiratory system. Always carry large bottles of concentrated acid either in an approved carrier or by firmly grasping the body of the bottle with one hand and placing the other hand underneath the bottle. Do not carry by the neck or lid. Do not rush. Always make up dilutions in a fume cupboard.
Version 1.0 SOP: Diluting concentrated acetic acid Written by: Science ASSIST
Ensure that glassware is free from chips and cracks before use. For first aid, accident and spill procedures refer to SDS before performing the dilution. Note that the concentrated acid should be stored in bunding (secondary containment), segregated from strong bases and oxidising agents, including nitric acid, and segregated from other acids. See the SDS for further details of incompatibilities. Pure (glacial) acetic acid has a melting point of 16.7°C and may freeze in cool weather. The frozen acid can be melted by placing the bottle in a plastic bag in a bath of warm water. Always add concentrated acid to water (never water to acid).
4. Regulations, licences and permits
Not applicable.
5. Equipment
Fume cupboard PPE (lab coat, safety glasses or face shield, acetic acid resistant gloves (butyl-rubber gloves are well-suited for the handling of concentrated acetic acid; nitrile, neoprene/latex or latex gloves also provide good splash protection against the concentrated acid), closed-in shoes. Concentrated acetic acid Distilled/de-ionised water and wash bottle Large (2L) borosilicate glass beaker for diluting the acid Small glass measuring cylinder Large (1L) glass measuring cylinder or volumetric flask Glass stirring rod Pre-labelled storage bottle
Note: For laboratory `Stock’ solutions use measuring cylinders. For greater accuracy use volumetric flasks and pipettes.
6. Operating procedure
To make 1 litre of stock solution:
- Wear PPE and work at a fume cupboard.
- Into the large beaker place about 650mL of distilled water (or an amount such that the volume of water combined with the volume of concentrated acid to be added does not exceed about 850mL).
- Carefully measure the required volume of concentrated acid in the small measuring cylinder; see table below. (If your concentrated acid is stored in a large 2.5L Winchester bottle, firstly pour some into a smaller bottle or beaker to be able to safely pour into the measuring cylinder as handling liquids in smaller containers is safer and easier.) Hint: keep the label of the acid bottle uppermost when pouring and clean up any spilt liquid from the outside of the bottle. (Operating procedure cont….)
Version 1.0 SOP: Diluting concentrated acetic acid Written by: Science ASSIST
8. Waste disposal
Clean up any small spillages immediately with plenty of water (larger spills should be neutralised). When fuming stops, sweep/mop up. Spills that are too large to neutralise safely should be absorbed with non-combustible material such as dry sand or vermiculite and placed in a labelled container for collection and disposal by a registered hazardous waste disposal company. To neutralise concentrated acid, first dilute the acid by adding it carefully to a larger volume of water. Neutralise the solution with sodium bicarbonate, sodium carbonate or a 50: mixture of sodium carbonate and calcium hydroxide so that the pH is in the range pH 6-8. Exercise care as heat and corrosive fumes are produced. Use an indicator such as Universal Indicator to determine the pH. Wash the neutralised diluted solution to waste down the sink with excess cold water. Large quantities of waste acetic acid need to be collected and disposed of by a registered hazardous waste disposal company.
9. Related material
Manufacturer’s Safety Data Sheet Risk Assessment
References:
‘Chemical Glove Guide’, Ansell website http://ppe.ansell.com.au/chemical-glove-guide (Accessed June 2015)
Chemwatch GoldFFX, 2013, Material Safety Data Sheet 2789-3 Version 8.1.1.1, Acetic acid glacial https://jr.chemwatch.net/ (Subscription required. June 2015)
Cheryan, M. Acetic Acid Production, in Encyclopedia of Microbiology, (M. Schaechter, Editor-in- Chief) 3rd^ Edition, Elsevier Inc. (2009), Academic Press, pp. 145-149.
CLEAPSS, 2014, Hazcard 38A Ethanoic acid, methanoic acid and their salts, http://www.cleapss.org.uk/attachments/article/0/HC-038A.pdf?Secondary/Science/Hazcards/ (Subscription required. Accessed June 2015)
CLEAPSS, 2014, The CLEAPSS Recipe Book,39 Ethanoic acid and propanoic acid solutions, http://www.cleapss.org.uk/attachments/article/0/RB_039_Ethanoic%20&%20propanoic%20acidsO Oct2014.pdf?Secondary/Science/Recipe%20Book/ (Subscription required. Accessed June 2015)
‘Material Safety Data Sheet – Acetic acid 89-100%’, January 2011, Chem-supply website https://www.chemsupply.com.au/documents/AA0091CH0J.pdf (Accessed June 2015)
