Ethanoic Acid is the slowest de-scaler of the three acids, and is therefore the least effective. It also may cause an unpleasant smell, and can have a negative effect on the taste of coffee  meaning one would need to spend longer time rinsing and cleaning the machine thoroughly to ensure that the taste of the coffee is not affected. Citric Acid
Citric acid leaves behind zero toxic residues and has just enough acidic concentration to descale without etching or damaging household surfaces in any way and there are no volatile compounds or products that harm the environment. Disadvantages:
Because citric acid is a weak acid, it won’t remove heavy build-up of scale very quickly. It is also a powder hence it must be dissolved for use. It also works best with hot water meaning there will be higher energy consumption. Even when used with hot water, citric acid is not as effective at descaling as Sulfamic acid. Sulfamic Acid
Sulfamic acid is the fastest de-scaler – It dissociates into hydroxonium ions more readily in aqueous solution than the others, therefore giving a greater concentration of atoms that are able to react with the calcium in lime scale. It is safe to use because it does not produce chlorine gas , which can be toxic. Sulfamic acid also has a low volatility. Disadvantages:
Sulfamic Acid can be an irritant to eyes or skin and is the most expensive of the de-scalers. Q2) How these de-scalers remove limescale
Limescale forms when hard water is heated above 61°C or when it is left to evaporate on surfaces such as taps and showerheads. Hard water is water that contains high quantities of calcium and magnesium ions. These hardness minerals, in the form of calcium carbonate and magnesium carbonate, precipitate out of hard water to form limescale .
Therefore, to clean or remove limescale, something needs to dissolve or soften calcium carbonate and/or magnesium carbonate, so it can easily wash away. Acids cause mineral deposits such as rust to oxidise, thereby weakening them and making it possible to simply wash them away. Lime scale removers work by chemically reacting with the lime scale to form safe chemicals and ions.
Lime scale is Calcium Carbonate, and when broken down by strong acids, produces Calcium Chloride, Water and CO2. These are much safer, and can be washed away with water, to remove the CaCl from the area. Bibliography
 http://www.coffeehomedirect.com/how/to/clean/a/coffee/maker/with/vinegar  http://www.ehow.co.uk/how_7404899_delime-coffee-maker.html  http://incarinsurance.org/advantages/advantages-and-disadvantages-of-using-ethanoic-acid-as-a-descaler-.html  http://uk.answers.yahoo.com/question/index?qid=20130123013345AA71LkB  http://www.p4c.philips.com/cgi-bin/dcbint/cpindex.pl?scy=ZA;slg=ENG;ctn=HD5405/60;dct=FAQ;refnr=0092154;view=aa12_view_partial.html;session=20120502004843_184.108.40.206;faqview=1