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8/13/2019 Acids, Bases and Salts I Notes
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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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%&le : ' 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 $/uations Adantage4.isadantage
lkali, such as
sodiumhydroxide,potassiumhydroxide
= = " → !" 2isadvantage>
&f added in excess, alkali causes H togo a&oe =. %nder too alkalineenvironment, aquatic life and crop growthcan be affected.
#alciumhydroxides(partiallyinsoluble)
!= = #a(")! →
#a!= = !"
2isadvantage>
• &f added in excess,
calcium hydroxide can dissolve inwater/rain water and spread outthroughout the environment, causingthe H to go a&oe =. %nder an
alkaline environment, aquatic life andcrop growth can be affected.
• mmonium salt is added
to plants to provide them with
11
cids
lkalisNeutral – neither
acidic nor alkaline
More acidic More alkaline
1ed Dink "range Kellow Lreen 0urquoise Elue Durple
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nitrogen that is needed for plantgrowth. ddition of calcium hydroxidewould result in direct chemicalreaction with ammonium salt causingthe release of ammonia to theenvironment.
#a(")! = !$= → !$- = #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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