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 Hwa Chong Institution (High School) – Secondary Two LSS Chemistry

Acids, Bases and Salts I

The Characteristic Proerties o! Acids and Bases

 At the end of the lesson, students should know how to:

(a) name some common mineral/inorganic acids eg. hydrochloric acid, nitric acid,sulphuric acid and carbonic acid

(b) name some organic acids eg. citric, malic, lactic, tartaric, tannic and ethanoicacids

(c) state some uses of common acids eg. hydrochloric, nitric, sulphuric, citric andethanoic acid

(d) describe the importance of water for acidity, ie water causes acid molecules toionise and form hydrogen ions.

(e) define acid as a substance that produces hydrogen ions as the only positiveions in water 

(f) describe qualitatively the difference between strong and weak acids in termsof extent of ionisation of acid in water 

(g) state the physical and chemical properties of acids(h) define a base as a metal oxide/metal hydroxide(i) describe an alkali as a soluble metal hydroxide(j) name some common alkalis (sodium hydroxide, potassium hydroxide, calcium

hydroxide and aqueous ammonia)(k) state the uses of common alkalis or bases(l) state the physical and chemical properties of alkalis(m) identify sodium hydroxide and potassium hydroxide as strong alkalis and

aqueous ammonia as weak alkali

(n) classify oxides as acidic, basic, amphoteric or neutral (!", #", $")

H and Indicators

 At the end of the lesson, students should know how to:

(a) state the colour changes of common indicators eg litmus paper, methylorange, phenolphthalein and universal indicator)

(b) state that indicators are substances that change colour when an acidic oralkaline solution is added to them

(c) investigate the use of %niversal &ndicator and p scale to test forconcentration of hydrogen ions and hence relative acidity

"# Acid

$%amles o! acids and their uses

'. Inorganic acids compound composed of hydrogen and a nonmetallicelement or group of atoms.

*xamples are hydrochloric acid, #l, sulphuric acid, !+", and carbonicacid, !#"-.

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$ame %ses

ydrochloric acid, #l &n manufacture of &leach found in the stomach where

it digests proteins

$itric acid, $"- anufacture of nitrate'containing explosives such as

nitroglycerin, trinitrotoluene (0$0) and

cyclotrimethylenetrinitramine (123), as well asfertilizers such as ammonium nitrate.

+ulphuric acid, !+" &n manufacture of detergents, paints, dyes, artificial

fibres and plastics. lso used in &atteries  for road

vehicles such as cars and buses.

#arbonic acid, !#"- 4i55y or car&onated drinks

!. rganic acids  any various acids containing one or more carbon 6containing polyatomic groups.

*xamples are ethanoic acid, citric acid, malic acid, lactic acid etc.

$ame 4ound in %ses

#itric acid

#78"9

Citrus !ruits. *.g

oranges, lemon, lime

• flavouring and preservative in

food  and beverages, especially

soft drinks

• buffering properties of citrates

are used to control pH   in

household cleaners and

 pharmaceuticals

alic acid

#7":

Ale alic acid may be helpful to individuals

suffering from chronic fatigue and

fibromyalgia. +ome athletes consume

malic acid hoping that it will increase

the delivery of oxygen to muscle cells,

thereby improving stamina andendurance. alic acid is also used to

acidi!y &eerages such as wines, acid

drinks, fruit juice, soda water and

various soft drinks. &t is also frequently

used in cosmetic formulations to adjust

the p of the product.

;actic acid

#-7"-

Sour mil*  and

yoghurt

;actic acid is used as a moisturi5er, in

some cosmetics and as a mordant, a

chemical that helps fabrics accept

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dyes, in textiles. &t is also used in

making pickles and sauerkraut, foods

for which a sour taste is desired. ;actic

acid is used in the dairy industry not

only in ma*ing yoghurt but in ma*ing

cheese  as well. &t is also used in

tanning leather.0artaric acid

#7"7

+raes, tartar 0artaric acid is found in cream of tartar,

which is used in cooking candies and

frostings for cakes. 0artaric acid is also

found in baking powder, where it

serves as the source of acid that reacts

with sodium bicarbonate (baking soda).

0his reaction produces carbon dioxide 

gas, and lets products <rise,< but does

so without any <yeasty< taste, that can

result from using active yeast  cultures

as a source of the carbon dioxide gas.

0annic acid

#97:!"7

 Dare to draw that?? 

Tea %se as a powerful astringent

What’s that? 

*thanoic acid

#-#""

inegar , tomato juice %sed as a chemical reagent  for the

production of many chemical

compounds

• major  esters of acetic acid are

commonly used solvents for

inks, paints and coatings

• &n the form of vinegar , ethanoic

acid are used directly as a

condiment , and also in the

 pickling  of vegetables and other

foodstuffs

• 2ilute solutions of acetic acids

are used for their mild acidity .

 Examples in the household  

environment include the use in a

 stop bath during the development

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What are esters? How

are they produced?

What are esters used

 for? Can you find them

occurring naturally? 

of photographic films, and in

descaling agents to remove

limescale  from taps and kettles.

The acidity is also used for treating

the sting of the box jellyfish by

disabling the stinging cells of the

 jellyfish, preventing serious injury

or death if applied immediately,

and for treating outer ear

infections in people in preparations

 such as Vosol . Equivalently, acetic

acid is used as a spray-on

 preservative  for livestock silage , to

discourage bacterial and fungal  

 groth.

Imortance o! -ater !or Acids

•  cids will only show their acidic properties in the presence of water.

• 0he acid molecules dissociate into hydrogen ions (=) and anions in the

presence of water.

• &t is the positive hydrogen ions that are responsible for acidic properties.

.e!inition o! acids

 n acid is a su&stance that produces hydrogen ions as the only positive ions ina/ueous solution (water).

HA 0 H1 H20 0 A'

Examples:

Hydrochloric acid: HCl (aq) →  H  (aq)  Cl ! (aq)

"itric acid: H"#$ (aq) →  H  (aq)  "#$!

(aq)

%thanoic acid: CH $C##H (aq) →  H  (aq)  CH $C##!(aq)

What are those little ‘(aq)’? What other such notations are there in chemical equations?Why do these chemical equations have charges on their chemical formulae? 

Strength o! Acids

• +trong acids> All its molecules comletely dissociate  to become ions in thepresence of water. '??@ of the molecules of strong acids ioni5ecompletely.

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%&ample : ' HCl molecules in the presence of e&cess water would all ionie toform ' H  ions and at the same time releases ' Cl ! ions*

HCl H + # →   H $#  Cl !

• Aeak acids> Some o! the molecules dissociate to form ions in the presence of

water. 0he rest remains as molecules. olecules of weak aciddissociate partially.

*xample > #-#"" molecules in the presence of excess water would have few =

ions formed. Ae say that the reactants and products eventually reachchemical equilibrium.

#-#"" = !"⇔  -"=  = #-#""

What on earth is H  !"? #sn’t it H " in solution? Why is the ionic equation written with H  !"? 

 Chemical Proerties o! .ilute Acid

Aord equations are ital to answering many chemistry questions.

'. 2ilute acids react with metals to produce a salt and hydrogen gas.

Acid 0 3etal Salt 0 Hydrogen

%*g*

+"a (s)  +HCl (aq) →  +"aCl (aq)  H + (g)

g (s)  H + -#. (aq) →  g-#. (aq)  H + (g)

1eactivity +eries>B, $a, #a, g, l, Cn, 4e, Db, (), #u, g, g, uost reactive ;east 1eactive

etals that are less reactie than hydrogen will not be able to produce anyhydrogen from the acid 6 no reaction occurs.

!. cid reacts with carbonate/bicarbonate to form salt, water and carbon dioxide.

  Acid 0 Car&onate4&icar&onate Salt 0 -ater 0 Car&on dio%ide

%*g*gC#$ (s)  H + -#. (aq)  →  g-#. (aq)  H + # (l)  C#+ (g)

CuC#$ (s)  +HCl (aq) →  CuCl + (aq)  H + # (l)  C#+ (g)

-. cid reacts with base to form salt and water in a process calledneutralisation.

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 cid = Ease→ +alt = Aater 

%*g*

HCl (aq)  "a#H (aq) →  "aCl (aq)  H + # (l)

g# (s)  H + -#. (aq) →  g-#. (aq)  H + # (l)

. 0he & asicity of an acid is the num&er o! hydrogen ions roduced whenone molecule o! acid ionises in water .

%*g*

HCl / monobasic (basicity / ') #l = = #l

H + -#. / dibasic (basicity / +) !+"  != = +"!

H $0#. / tribasic (basicity / $) -D"  -= = D"-

:. queous acids are able to conduct electricity due to the resence o! mo&ileions. 0hus they are called electrolytes (solutions that conduct electricity). 0hehigher the concentration o! mo&ile ions, the higher the electrical

conductiity of the aqueous acid.

0herefore, strong acids form better electrolytes than weak acids, in thepresence of water.

7. cids only show their acidic properties in the resence o! water . 0he acidmolecules dissociate into hydrogen ions and anions, in the presence ofwater. 0he positive hydrogen ions are resonsi&le !or the acidicroerties. Aithout water, there will be no free mobile hydrogen ions, andthere are then no acidic properties. 1see the section on 23mportance of water

for acids4 

Can pure water conduct electricity? 

Physical Proerties o! .ilute Acids

'. Sour  taste

!. A/ueous acid conduct electricity due to the abundance of free hydrogenions and anions when the acid molecules ioni5e in water.

-. Acid molecules in other solent do not conduct electricity# *xample > #l molecules in methylben5ene, an organic solvent, which does

not allow #l molecules to ioni5e. 0hey exist as molecules andthus do not conduct electricity.

Why are organic solvents una$le to cause acid molecule ionisation% $ut water is a$le to? 

1# Base and Al*ali

•   base is a substance that reacts with acids to !orm salt and water

only.

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•  n alkali

• is a base that is dissolved in water and reacts with acid to form a salt and

water.

• Al*ali is a solu&le &ase. 0hus not all bases are alkalis but all alkalis are

bases.

•

A solu&le &ase dissoles in water to !orm an al*ali, its moleculesdissociating in the resence o! water to !orm hydro%ide (H ' ) ions#

• Basic o%ide is an oxide that reacts with acid to form a salt and water. &f it

dissolves in water it would form an alkali. ll &asic o%ides are o%ides o!metal.

• Basic hydro%ide is a hydroxide that reacts with acid to form a salt and

water. &f it dissolves in water it would form an alkali. ll &asic hydro%ides arehydro%ides o! metal#

• +ome examples of bases>

Base

Basic %ides Al*ali4Solu&lehydro%ides

Insolu&le hydro%ides

$a!" $a" 4e(")!

4e!"- B" #u(")!

#u" ;i" g(")!

4e" $-

Ea" (watersoluble) Ea(")!

#a(")! (partially soluble)

• %ses of common alkalis

Al*alis 5ses

+odium hydroxide, $a" +oap making, paper making, draincleaning agent for clearing cloggeddrains

Dotassium hydroxide, B" #orrection of the p  of acidic soils , as afungicide , as a herbicide

#alcium hydroxide, #a(")! &n sewage treatment, used in mortar and

plaster &ot mortar and pestle?? 

 queous ammonia, $- Droduction of nitric acid, fertili5er,disinfectant, used in liquids to removegrease and dirt from glass.

Tyes o! %ides

"# Acidic o%ide > carbon dioxide, sulphur dioxide, nitrogen dioxide etc.

1# Basic o%ide > calcium oxide, iron(&&&) oxide, magnesium oxide etc.

2# 6eutral o%ide > carbon monoxide, nitric oxide, water etc.

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• +trong alkali ioni5es or comletely dissociates in water to produce "

ions in the resence o! water . 0he ionic lattice structure of the hydroxidesbreaks down to allow free ions to be formed.

*xample > $a" (s) → $a=  (aq) = " (aq)

• Aeak alkali artially ioni8es or dissociates to produce "  ions in the

presence of water.

*xample > queous ammonia is a weak alkali. &n an aqueous solution ofammonia, it contains ammonia molecules, water molecules,ammonium cations and hydroxide anions. mmonium andhydroxide ions are formed in solution but ammonium hydroxideis not an isolatable compound per se. +ince it is a weak alkali,there would be more ammonia and water molecules ascompared to ammonium and hydroxide ions.

$-  = !" ⇔ $

=

  = "

What is the chemical $ehaviour of $ase molecules in water (eg' &H   $ecomes &H " )? mmonia molecules don’t e*actly dissociate in water + how then is it a $ase? 

Chemical Proerties o! Base

'. Ease/alkali reacts with acid to form salt and water   in a process calledneutralisation.

Ease/lkali = cid G +alt = Aater 

*xamples>

#l (aq) = $a" (aq) → $a#l (aq) = !" (l)

g" (s) = !+" (aq) → g+" (aq) = !" (l)

!. lkali reacts with ammonium salts to form salt, ammonia gas  and water  .

 lkali = mmonium salt G +alt = mmonia gas = water 

*xample>

($)!+" (aq) = !$a" (aq) →  $a!+" (aq) = !$- (g) = !!" (l)

 ll ammonium salts would under gentle warming release ammonia gas in thepresence of a base. mmonia formed dissolves readily in water. eatingallows ammonia to be evolved as a gas. 0his is a chemical test that can beused to confirm the presence of alkali or ammonium salt.

Eases, like acids, are also able to dissociate in water to form mobile ions,which conduct electricity. +uch solutions containing dissociated base or acid

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are called electrolytes. 0he higher the concentration of mobile ions, the higherthe electrical conductivity of the alkali.

Physical Proerties o! Al*ali

'. Bitter  taste and Soay feelWhy does al,ali feel soapy on touch with our oily fingers? 

!. A/ueous al*ali conducts electricity due to its abundance of free "

 anionsand cations when the base dissolves in water.

2# H and Indicator 

• p of a solution is a measurement o! the concentration o! hydrogen

ions  in the solution. 0he higher the concentration o! hydrogen ions, thelower the H alue#

• H 9 ' log :H0;

+o if concentration of = is ?.?:?? mol/dm-, then p H log ?.?:?? H '.-?

• +trong acid> p ?I!  How can we call hydrochloric

acid a strong

Aeak acid> p I7 acid when -'-.-- mol/dm  is diluted to half 

$eutral> p 9 its concentration? How is !H 0 concentration

Aeak alkali> p 8I'? measured? When is 1H " 2 3 1!H 0 2? 

+trong alkali> p '!I'

H Indicators

• &ndicators are substances that change colour in the presence of

acid or alkali.

• #ommon p indicators are litmus aer , methyl orange,

henolhthalein and uniersal indicator . ost of these indicators areorganic compounds. $ote that phenolphthalein is rather insoluble in waterand, when added in large amounts, may result in white precipitate beingformed.

Indicator Acid colour H range o!colour transition

Al*aline colour 

;itmus paper red blue

ethyl orange red -.' 6 . yellow

Dhenolphthalein colourless 8.! 6 '?.? pink

• %niversal indicator 

+imple indicators, such as litmus, tell whether a solution is an acid or an

alkali. owever, other indicators not only indicate an acid or alkali, but alsohow acidic or alkaline a solution is.

p is a measure of the acidity or alkalinity of a solution.

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p ? ' ! - : 7 9 8 J '? '' '! '-

'

  p of a solution is shown as a number on a scale ranging from ? to '. 0hisp scale has the following features>

•   p of 9 is neutral. 0his is the p of pure water.4his is not true most of the time' 5ind out the specific conditions where it istrue that water has a pH of 6 when totally pure'

•   solution with p less than 9 is acidic. 0he solution contains hydrogen

ions. 0he smaller the p, the more acidic the solution is and the morehydrogen ions it contains. solution with p of ! has more hydrogenions than a solution with a p of :.  How much more? 

•   solution with p greater than 9 is alkaline. 0he solution contains

hydroxide ions. 0he larger the p value, the more alkaline the solution is

and the more hydroxide ions it contains. solution with p of '! hasmore hydroxide ions than a solution with a p of J.

<estoration o! H

Ahen there is an acid spillage or p of soil becomes acidic, the p can be restoredby various basic substances>

Chemicalsu&stance

Ionic $/uations Adantage4.isadantage

 lkali, such as

sodiumhydroxide,potassiumhydroxide

=  = " →  !" 2isadvantage>

&f added in excess, alkali causes H togo a&oe =. %nder too alkalineenvironment, aquatic life and crop growthcan be affected.

#alciumhydroxides(partiallyinsoluble)

!=  = #a(")! → 

#a!=  = !"

2isadvantage>

• &f added in excess,

calcium hydroxide can dissolve inwater/rain water and spread outthroughout the environment, causingthe H to go a&oe =. %nder an

alkaline environment, aquatic life andcrop growth can be affected.

•  mmonium salt is added

to plants to provide them with

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 cids

 lkalisNeutral – neither

acidic nor alkaline

More acidic  More alkaline

1ed Dink "range Kellow Lreen 0urquoise Elue Durple

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nitrogen that is needed for plantgrowth. ddition of calcium hydroxidewould result in direct chemicalreaction with ammonium salt causingthe release of ammonia to theenvironment.

#a(")! = !$= → !$- = #a!= 

= !!"

• 1elease of ammonia

would mean the loss of nitrogen thatthe farmer added as fertili5er neededfor plant growth.

#alciumcarbonate

!= = #a#"- → #a!=

= !" = #"!

 dvantage>

• &f added in excess,

calcium carbonate would not dissolvein the water and thus would notcause the H o! the enironment togo a&oe =#

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