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Acids and Bases. Properties of Acids They are corrosive pH range is 0 to 7, lower the pH, more acidic the acid Taste sour Turns litmus paper red Often.

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Presentation on theme: "Acids and Bases. Properties of Acids They are corrosive pH range is 0 to 7, lower the pH, more acidic the acid Taste sour Turns litmus paper red Often."— Presentation transcript:

1 Acids and Bases

2 Properties of Acids They are corrosive pH range is 0 to 7, lower the pH, more acidic the acid Taste sour Turns litmus paper red Often reacts with metals to produce H 2 gas Often produces H+ in water. Example; HCl H + + Cl -

3 Symbol used for acids

4 Properties of Bases pH range is from 7 to 14, higher the pH more alkaline the base They are caustic Taste bitter Turns litmus paper blue Feels slippery Group 1 and 2 metals make common bases. Example: Na + H 2 O NaOH + 1/2H 2

5 The pH of some common acid and bases

6 Common Acids Binary or Halide Acids –HCl, hydrochloric acid: is stomach and pool acid –HF, hydrofluoric acid: used to etch glass

7 Common acids continued Oxyacids: acids with oxygen (more oxygen- stronger the acid) –HNO 3, Nitric acid, used for making explosives, when it reacts with metals it produces NO 2 gas instead of H 2 –H 2 SO 4, sulfuric acid: used in car batteries, used in many industrial process as a dehydrator.

8 Chemical burn from H 2 SO 4 AHHHHHH SATAN!!!!!!! =]

9 Reaction of Cu with HNO 3

10 Oxyacids continued –H 2 CO 3, carbonic acid, found in carbonated sodas, and in rainwater. It is responsible for the sour taste, or sting in sodas. It is also found in blood to a very small extent. –H 3 PO 4, phosphoric acid, used as lime scale remover, and as flavoring in the colorless sodas like Sprite.

11 Acids continued Organic acids –Carbon based acids. –Structure ends in COOH –COOH is called a carboxyl group. –CH 3 COOH, ethanoic acid or vinegar. Used as a preservative and flavoring O C-OH

12 Bases Group 1 bases –Strongest bases –NaOH, sodium hydroxide, and KOH, potassium hydroxide, both of these bases are used to make commercial cleansers and drain cleaners. Group 2 bases –Weak bases, –Ca(OH) 2 calcium hydroxide, make limewater which is used to test for CO 2,, used to make antacids.

13 Bases Amines. –This group has a -NH 2 at the end of a molecule –These are formed from decomposing proteins –They have a fishy smell –NH 3, ammonia, this is used as glass cleaner and to make fertilizers. –Examples CH 3 NH 2, methyl amine, CH 3 CH 2 NH 2 ethyl amine. Etc.


15 Bases Carbonates (they are antacids) –Have CO 3 -2 in them –This group produces CO 2 when they react with acids. –NaHCO 3 sodium bicarbonate, or baking soda –CaCO 3, calcium carbonate, or baking powder. –MgCO 3 and Al 2 (CO 3 ) 3 are used as antacids, for example: MgCO 3 + 2HCl MgCl 2(aq) + H 2 O (l) + CO 2(g)

16 Arrhenius definition of acids and bases Acids produce a hydrogen ion(H+) or hydronium ion (H 3 O+) when they dissolve in water. (An H+ ion is considered too reactive to exist so an H 3 O+ ion is used) Acids dissolving in water producing an H+ –HCl H + + Cl - –HNO 3 H + + NO 3 - –H 2 SO 4 2H + + SO 4 -2 –CH 3 COOH CH 3 COO - + H +

17 Carbonates are in antacids

18 Arrhenius definition continued Acids dissolving in water form a hydronium ion: HCl + H 2 O H 3 O + + Cl - HNO 3 + H 2 O H 3 O + + NO 3 - H 2 SO 4 + 2H 2 O 2H 3 O + + SO 4 -2 CH 3 COOH + H 2 O CH 3 COO - + H 3 O + Note: H 2 O is written in the reaction when H 3 O+ is used, but not when H+ is used.


20 Arrhenius definition of bases Bases dissolve in water to produce an OH - called a hydroxide ion. –NaOH Na + + OH - –Ca(OH) 2 Ca OH - –NH 3 + H 2 O NH OH - –Note: H 2 O is written in the reaction only with amines

21 Bronsted-Lowry def. of Acids/Bases Acids are proton donors Bases are proton acceptors Ex: HNO 2 + H 2 O H 3 O + +NO 2 - Ex: NH 3 + HCO 3 - NH CO 3 -2 Ex: HCO HSO 4 - SO H 2 CO 3

22 Determining the conj. Acid of a base --Add a H+ BaseConj. Acid HCO 3 - H 2 CO 3 H 2 OH 3 O + OH-H 2 O

23 Determining the conjugate base of an acid. --remove an H+ AcidConj. Base H 2 OOH- HSO 4 -SO 4 -2 NH 4 +NH 3

24 Continued Bronsted-Lowry Stronger the acid/ base, the weaker its conjugate base/ acid. Amphoteric or Amphiprotic: A substance which can be either an acid or a base. Example is H 2 O. Water as an acid: H 2 O + Cl - OH - + HCl Water as a base: H 2 O + HCl H 3 O + + Cl -

25 Conjugate acid-base pairs

26 Definition of a Lewis acid and base Acids are electron pair acceptors in a dative covalent bond. Bases are electron pair donors in a dative covalent bond. These acids are reserved for those molecules/ions which make dative covalent bonds but are NOT ALREADY A BRONSTED- LOWRY ACID. Examples: NH 3 is a base because the nitrogen has a pair of electrons which can be used in a dative bond. AlF 3 can be a Lewis acid since Al has a vacant pair of orbitals that can accept e-.

27 Lewis acids will include substances that are not considered typical acids. Examples: –Some metal ions. Ex Group 3, Trans. metals

28 Strong acids and bases completely dissociate in water

29 Strong and weak acids and bases Strong acid/base when it dissolves in H 2 O, nearly 100% dissociates into ions. Ex: HCl H + + Cl - nearly 100% of the molecules break up into ions Ex: NaOH Na + + OH - nearly 100% of the molecules break up (Remember: the H+ and OH- gives the properties associated with Acids and Bases.) For weak acid and bases, when they dissolve in water only a small % will dissociate to form ions. CH 3 COOH (aq) CH 3 COO - (aq) + H + (aq) Very little of the acid forms ions. Same condition for weak bases. Both the strength and the concentration of the acid or base determines its pH and its harmfulness. So when working with acids and bases one needs to be concerned with 1. Is the acid or base strong or weak? 2. Is the acid or base concentrated or dilute?


31 WWCND How burgers are made

32 The pH equation The pH equation is: pH = -log [H+] –Where [H+] is the molar concentration.

33 The pH scale Development of the pH scale –Based upon the dissociation of water: H 2 O H + + OH - –Based upon the equilibrium of water: K w = [H + ] [OH - ] at equilibrium the concentrations of H + and OH - are each 1x10 -7 M (this was experimentally determined) Substitute these concentrations into the K w expression: K w = [1x10 -7 ][1x10 -7 ]; this = 1x10 -14

34 Development of the pH scale cont. According to the rules of equilibrium changing conc does not change the K w constant. So if acid is added to water, the H+ conc goes up, and the OH- goes down, but K equals 1x The same thing happens if a base is added to water. Knowing that K w is always 1x10 -14, then –The largest conc for either an H + or OH – is 1M –The smallest conc H + or OH – is 1x that we work with –the –log of 1M = 0 the low end of the pH scale –the –log of 1x = 14 the high end of the pH scale –Also, pure H 2 O has a conc of H+ = 1x10 -7, the –log = 7, pure H 2 O has a pH of 7 or it is neutral

35 Acid and Base Neutralizations General equation: acid + base salt+ H 2 O + energy Ex: HCl+ NaOH H 2 O + NaCl CH 3 COOH + NaOH HOH + NaCH 3 COO H 2 SO 4 + 2NaOH 2 HOH + Na 2 SO 4 HNO 3 + NaOH NaNO 3 + H 2 O 2HCl+ Ca(OH) 2 CaCl 2 + 2H 2 O

36 Titration Curves for strong acid and bases

37 Titration curve for strong acid and bases

38 Explanation of a titration curve A titration involves an acid base reaction: Example NaOH + HCl NaCl + NaOH All titration curves have the same shape but they do not all start at the same pH Why this shape? –Start with 1M HCl titrated with 1M NaOH –Initial pH=O, titrate 10% of 1MHCl, 90% of HCl remains. [H+]=.9M or pH=.05 –Titrate 50% of 1M HCl, 50% remains [H+]=.5M or pH=.3 (not a great change in pH yet!) –Titrate 90% of 1MHCl, 10% remains, [H+]=.1M or pH=1 –Titrate 100% of HCl, acid and bases are now equal, pH=7 the cure shoots up until excess NaOH is added. Now curve gradually increases again with the addition of more NaOH

39 Tiration curves with weak acids and bases.



42 IB optional material: Equilibrium and weak acids and bases Since weak acids and bases disassociate partially: –They are reversible and have a measurable equilibrium. –Their pH cannot be based upon the initial molarity of the acid or base. An equilibrium equation must be used to measure it.

43 The K a or K b (equilibrium constant) of weak acids or bases

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