Acids, Bases and PH

BBA2106: Basics in Natural Science

(FBA)

Lecture

Acids, Bases and pH What is an acid? What is a base? Acids •

have sour taste (think of lemon juice!);

•

ability to change the color of litmus from blue to red;

•

react with certain metals to metals to produce hydrogen hydrogen gas;

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react with bases to bases to form a salt and water.

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react with carbonates carbonates and and bicarbonates bicarbonates to to produce carbon dioxide gas.

ases •

have bitter taste;

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slippery" or soapy" feeling when applied to the skin;

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ability to turn red color of litmus to blue;

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ability to react with acids to form salts and water.

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their a#ueous (water) solutions conduct electric current current;;

$xamples of %ommon Acids      

citric acid (from certain fruits and veggies& notably citrus fruits) ascorbic acid (vitamin %& as from certain fruits) vinegar (' acetic acid) carbonic acid (for carbonation of soft drinks) lactic acid (in buttermilk) stomach acid (%l)

$xamples of %ommon ases     

antacid *milk of magnesia& magnesium hydroxide hydroxide +g(,) - antacid *maalux& aluminium hydroxide Al(,) / li#uid soap(0otassium hydroxide& 1,) lye (2odium hydroxide& 3a,) stabili4er for plastics *barium hydroxid hydroxide& e& a(,) -

Neutralization Reaction 



5hen acids and bases are added to each other they react to neutrali4e each other if an e#ual number of hydrogen and hydroxide ions are present. 5hen this reaction occurs 6salt and water are formed.

Acids, Bases & pH (Updated on a! 1", 2011)

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(FBA)

%l 7 3a,

Lecture

3a%l 7 -,

(Acid) (ase)666(2alt) (5ater) What Makes a Strong Acid or Strong Base? 2trong electrolytes are completely dissociated into ions in water. 8he acid or base molecule does not exist in a#ueous solution& only ions. 5eak electrolytes are incompletely dissociated. Strong Acids: Acids that completely ioni4e in water& forming 7 and an anion are called strong acids. 8here are six strong acids. 8he others are considered to be weak acids. %l 6 hydrochloric acid 3,/ 6 nitric acid -2,9 6 sulfuric acid r 6 hydrobromic acid : 6 hydroiodic acid %l,9 6 perchloric acid Weak Acids: A weak acid only partially ioni4es in water t o give  7 and the anion. $xamples of weak acids include hydrofluoric acid ()& acetic acid (% /%,,)& formic acid (%,,) etc. 5eak acids include< ,rganic acids containing one or more carboxyl group& 6%,,. 8he  is ioni4able.

=emon juice is about ' citric acid& a weak acid.

Strong Bases: 2trong bases ioni4e >?? into the cation and , 6 (hydroxide ion). 8he hydroxides of the @roup : and @roup :: metals usually are considered to be strong bases.

=i, 6 lithium hydroxide 3a, 6 sodium hydroxide 1, 6 potassium hydroxide b, 6 rubidium hydroxide %s, 6 cesium hydroxide %a(,) - 6 calcium hydroxide 2r(,)- 6 strontium hydroxide a(,)- 6 barium hydroxide

Weak Bases: $xamples of weak bases include ammonia& 3 /& 3a%,/& +g(,)-& Al(,)/ diethylamine& (%/%-)-3 etc. +ost weak bases are anions of weak acids. 5eak bases do not furnish , 6 ions by dissociation. :nstead& they react with water to generate ,6 ions. What is acid rain?:


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(FBA)

Lecture

Bifferent types of oxides such as 3, x& 2,x and %,x are available in the environment due to combustion which result in the production of acids with rain water<  3, and 3,- react with water to give strong nitric acid (3,/).  2,- and 2,/ react with water to give strong sulphuric acid ( -2,9).  %, and %,- react with water to give carbonic acid (%, /). 8he acids thus produced in the atmosphere are collectively known as acid rain. Why do onions make you cry when you cut onios? :nside the onion cells there are some chemical compounds that contain sulfur . 5hen you cut an onion its cells are broken and those chemical compounds then undergo a reaction that transforms them into a more volatile sulfur products& which are released into the air. 8hese sulfur compounds react with the moisture in your eyes forming sulfuric acid& which produces a burning sensation. So you cry to keep your eyes protected from the acid.

pH concept 

 



8he strength of an acid or base in a solution is measured on a scale called a p scale. 8he p scale is a measure of the hydrogen ion concentration. :t spans from ? to >9 with the middle point (p C) being neutral (neither acidic or basic). Any p number greater than 7 is considered a ase and any pH nu!er less than 7 is considered an acid. ? is the strongest acid and >9 is the strongest base.


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(FBA)

Lecture

8he chart shown above will help to know p level of common substances very much in touch with our daily life. $specially note that most foods are slightly acidic; the principal Dbodily fluidsD are slightly alkaline& as is seawaterE not surprising& since early animal life began in the oceans. the p of freshly6distilled water will go downward as it takes up carbon dioxide from the air; %,- reacts with water to produce carbonic acid&  -%,/. the p of water that occurs in nature varies over a wide range. @roundwaters often pick up additional %, - respired by organisms in the soil& but can also become alkaline if they are in contact with carbonate6containing sediments. DAcidD rain is by definition more acidic than pure water in e#uilibrium with atmospheric %, -& owing mainly to sulfuric and nitric acids that originate from fossil6fuel emissions of nitrogen oxides and 2,-. A neutral solution is one in which the concentrations of  7 and , F ions are identical. • •

•

•

•

pH of So!e "o!!on Sustances: Acids ? 6 ydrochloric Acid (%l) >.? 6 attery Acid ( -2,9 sulfuric acid) -.? 6 =emon Guice -.- 6 Hinegar /.? 6 Apples 9.? 6 5ine and eer 9.' 6 8omatoes I.I 6 +ilk Neutral C.? 6 0ure 5ater Bases C.9 6 uman lood J./ 6 aking 2oda (2odium icarbonate) >?.' 6 +ilk of +agnesia >>.? 6 Ammonia >-.9 6 =ime (%alcium ydroxide) >/.? 6 =ye >9.? 6 2odium ydroxide (3a,)

Worked "he!istr# $role!s %: Which of the follo&ing state!ents is true concerning acids and ases? (a) acids and bases donKt react with each other (b) acids mixed with bases neutrali4e each other (c) acids mixed with bases make stronger bases (d) acids mixed with bases make stronger acids %: 'rue or false: ases are so!eti!es called alkalis( (a) true (b) false Acids, Bases & pH (Updated on a! 1", 2011)

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(FBA)

Lecture

%: Which is the correct set of acid properties? (a) sour taste& corrosive& change litmus from red to blue (b) sour taste& corrosive& change litmus from blue to red (c) sweet taste& slippery& change litmus from blue to red (d) sour taste& slippery& change litmus from blue to red


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Acids, Bases and PH

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