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Unformatted text preview: Topic 9 - Acids and Bases 9.1 Properties of acids and bases 9.1.1 : Properties of acids and bases in aqueous solutions on stuff...nb...the term alkali refers to a base dissolved in water. Indicators...they change color depending on whether they're in acidic or basic conditions...each one's different, so I suppose I'd better list some common ones... Methyl orange Bromophenol blue Methyl red Bromothymol blue Phenolphtalein Acid red yellow red yellow colorless Base yellow blue yellow blue red Each one change color as a different pH, and so there will be cases where one is useful and others are not. (not really necessary is SL?) Reaction of acids with bases...They will often produce water, and the remaining components will combine to form a salt...ie HCl + NaOH -> H 2 O + NaCl. Acids with metals...will produce hydrogen ie 2HCl + Mg -> MgCl 2 + H 2 . Acids with carbonates...will produce water and CO 2 ie 2HCl + CaCO 3-> CO 2 + H 2 O + CaCl 2 . 9.1.2 : Experimental properties of acids and bases...when acids and bases neutralize, the reaction is noticeably exothermic (ie heat can be felt coming from the reaction). Obviously, they will have an effect on the color of indicators as described above. The hydrogen produced in the reaction of acids with metal will produce a 'pop' sound if a match is held to it, and the CO 2 from the carbonate reaction will turn limewater a milky white when bubbled trough it. Examples of some acids : HCl, CH 3 COOH, H 2 SO 4 ,NH 4 + . Examples of bases : NaOH, NH 3 , CH 3 COO- . 9.2 Bronsted-Lowry acids and bases 9.2.1 : According to the bronsted-lowry theory acids are defined as proton (H + ion) donators and bases are defined as proton acceptors. 9.2.2 : For a compound to act as a BL acid, it must have a hydrogen atom in it, which it is capable or losing while remaining fairly stable. A BL base must be capable of accepting a hydrogen ion while remaining relatively stable (or reacting to form a stable compound...ie water and a salt). Some compounds (such as water) may act as both ie (H 2 O-> OH- or H 3 O + ) 9.2.3 : Acid base reactions always involve an acid-base conjugate pair...one is an acid, one is its conjugate base...ie HCl/Cl- , CH 3 COOH/CH 3 COO- , NH 4 + /NH 3 . 9.2.4 : The conjugate base will always have one less H atom that the acid (or the acid one more than the base). In compounds where there are many hydrogen atoms, the one which is held the weakest is generally the one which is lost, and this must be reflected in the writing of the compound...as in the CH 3 COOH example above. 9.3 Strong and weak acids and bases 9.3.1 : Strong and weak acids are defined by their ease of losing (or donating) a proton. A strong acid, when placed in water, will almost fully ionise/dissociate straight away, producing H 3 O + ions from water. a weak acid will, however, only partially do this, leaving some unreacted acid remaining. This is set up as an equilibrium, and so when some of the H 3 O + ions produced by a weak acid are reacted, LCP means that more of the acid will react to form H...
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- Spring '10