Transcript Acids

• Insoluble (in general):
•
•
•
•
•
1. all oxides
2. CaSO4, PbSO4
3. PbCl2
4. all carbonates (except: K2CO3 and Na2CO3)
5. all hydroxides, (except: Ca(OH)2 is slightly
soluble, group I hydroxides )
***Even though some compounds are
soluble in water, we may use its solid
form for a reaction.
Acids
In daily-life
• Ethanoic acid( in vinegar) CH3COOH
• Citric acid ( in fruit)
• Carbonic acid ( in soft drink) H2CO3
Common acids in lab
HCl
Hydrochloric
acid
H2SO4
HNO3
Sulphuric
acid
Nitric
acid
1.CH3COOH
2. H2CO3
3. HCl
4. H2SO4
5. HNO3
Acid is a H atom containing covalent
compound, when dissolved in water, it
forms ions.
Physical Properties of
Dilute Acids
a) Taste
b) Electrical conductivity
c) pH
a) sour
b)it conducts electricity only in aqueous
state.
c) acidic; it turn blue litmus paper to red
Chemical Properties of
Dilute Acids
a) Reaction with metal (KPb)
b) Reaction with carbonates/
Hydrogencarbonates
c) Reaction with oxides/ hydroxides
(base)
Reaction with metals
They react with metals higher than copper in the reactivity series,
liberating hydrogen gas:
acid + metal

salt + hydrogen
For example,
H2SO4(aq) + Mg(s)  MgSO4(aq) + H2(g)
2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g)
Action on carbonates and hydrogencarbonates
acid + carbonate  salt + carbon dioxide + water
For example,
2HCl(aq) + CaCO3(s)  CaCl2(aq) + CO2(g) + H2O(l)
acid + hydrogencarbonate  salt + carbon dioxide + water
For example,
HNO3(aq) + NaHCO3(s) 
NaNO3(aq) + CO2(g) + H2O(l)
***Soluble in water
K2CO3(s) + 2HCl(aq)
2K+
CO32-
2KCl
2H+
2KCl (aq) + H2O(l) + CO2(g)
2Cl-
H2CO3
***Soluble in water
2NaHCO3(s)+H2SO4(aq)
2Na+
2HCO3-
Na2SO4
2H+
Na2SO4(aq)+ 2H2O(l)+2CO2(g)
SO42-
2H2CO3
Action on metal oxides and hydroxides (BASE)
acid + metal oxide
e.g.

H2SO4(aq) + CuO(s)  CuSO4(aq) + H2O(l)
acid + metal hydroxide 
e.g.
salt + water
salt + water
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
1.CH3COOH – ethanoic acid
2. H2CO3 – carbonoic acid
3. HCl – hydrochloric acid
4. H2SO4 – sulphuric acid
5. HNO3 – nitric acid
Acid is a H containing covalent
compound, when it dissolves in
water, it forms ions.
Chemical Properties of
Dilute Acids
a) Reaction with metals (KPb)
b) Reaction with carbonates/
Hydrogencarbonates
c) Reaction with oxides/ hydroxides
(base)
***Soluble in water
K2CO3(s) + 2HCl(aq)
2K+
CO32-
2KCl
2H+
2KCl (aq) + H2O(l) + CO2(g)
2Cl-
H2CO3
***Soluble in water
2NaHCO3(aq)+H2SO4(aq) Na2SO4(aq)+ 2H2O(l)+2CO2(g)
2Na+
2HCO3-
Na2SO4
2H+
SO42-
2H2CO3
Limewater test for carbon dioxide
Carbon dioxide is a colourless gas. It turns limewater milky.
lime water(base)
acidic gas
Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l)
colourless solution
white solid
Acid is a H containing covalent
compound, when it dissolves in
water, it forms ions.
15.2 Characteristics and chemical properties of acids
Pure acid
---acid molecules not dissolving in water
At room temp:
HCl(g)
Citric acid(s)
H2SO4(l)
HNO3(l)
H2SO4(aq)
H+(aq)
H2SO4(l)
H+(aq)
SO42-(aq)
water molecules
HNO3(l)
HNO3(aq)
+
H (aq)
-
NO3 (aq)
water molecules
HCl(g)
HCl(aq)
+
H (aq)
-
water molecules
Cl (aq)
When acid molecules dissolve in water, ions are formed.
HCl(aq)
H2SO4 (aq)
HNO3 (aq)
H+ (aq) + Cl- (aq)
2H+ (aq) + SO42- (aq)
H+ (aq) + NO3- (aq)
ionization
Hydrogen ions (H+(aq)) are responsible for all the acidic
properties. Without water, acids cannot ionize to form H+(aq) and
hence do not have acidic properties.
15.3 The role of water for acids
HYDROGEN CHLORIDE IN WATER AND IN
METHYLBENZENE
HCl in water
HCl(aq)  H+(aq) + Cl-(aq)
HCl in methlybenzene
(non-aqueous solvent)
Test
Hydrogen chloride in water
(hydrochloric acid)
Hydrogen chloride in
dry methylbenzene
Effect on dry blue
turns to red colour
litmus paper
no colour change
Electrical
conductivity
good
none
Action on
magnesium
bubbles of hydrogen
evolved:
Mg(s) + 2H+(aq) 
Mg2+(aq) + H2(g)
no gas evolved
(no apparent
reaction)
Action on solid
sodium
carbonate
bubbles of carbon dioxide
no gas evolved
evolved:
(no apparent
Na2CO3(s) + 2H+(aq) 
reaction)
2Na+(aq) + CO2(g) + H2O(l)
So to test acidity of HCl(g)
-Wet litmus paper is used
 H+ can be released by dissolving in the water on
the litmus paper.
Fizzy drink tablet
Ingredients: solid citric acid
+ solid sodium hydrogencarbonate
Ingredients: solid acid
+ solid sodium hydrogencarbonate
water
citric acid (s) + NaHCO3 (s)  Salt + CO2 (g) + H2O (l)
H+(aq)
+ NaHCO3 (s)  Na+(aq) +CO2 (g) + H2O (l)
Without water, acids do not have acidic properties.
Baking Powder
Ingredients: solid acid
+ solid sodium hydrogencarbonate
Heating:
NaHCO33(s)
2NaHCO
(s) 
 Na
Na22CO
CO33++HH22OO(l)
(l)++CO
CO22(g)
(g)
Adding water:
H+(aq)
+ HCO3- (aq) 
CO2 (g) + H2O (l)
Without water, acids do not have acidic properties.
When acid molecules dissolve in water, ions are formed.
ionization
HCl(aq)
H2SO4 (aq)
HNO3 (aq)
H+ (aq) + Cl- (aq)
2H+ (aq) + SO42- (aq)
H+ (aq) + NO3- (aq)
Acid is a H containing covalent
compound, when it dissolves in
water, it forms H+ ions. (as the only
positive ions)
only this hydrogen atom (connected with O)
can form hydrogen ion, H+.
Ionization of Ethanoic acid
CH3COOH(aq)  CH3COO- (aq)+H+ (aq)
SO2 (g) + H2O(l)H2SO3(aq)  2H+ (aq)+ SO32-(aq)
Sulphurous acid
Is NaHSO4 / NaHCO3 an acid?
When acid dissolves in water
Ionization
HCl(aq)
H2SO4(aq)
H+ (aq) + Cl- (aq)
2H+ (aq) + SO42- (aq)
HNO3(aq)
H+ (aq) + NO3- (aq)
CH3COOH(aq)
H+ (aq) + CH3COO- (aq)
H3PO4(aq)
Basicity
3H+ (aq) + PO43- (aq)
BASICITY OF AN ACID
Different acids may give different numbers of hydrogen ions per
molecule in aqueous solution.
The BASICITY of an acid is the maximum number of H+ ions
produced by one molecule of the acid.
15.4 Basicity of an acid
only this hydrogen
atom (connected with
O) can form
hydrogen ion, H+.
Figure 15.12 Ethanoic acid (CH3COOH) is monobasic because each molecule can
only give one hydrogen ion.
15.4 Basicity of an acid
Acid
Ionization in water
Hydrochloric acid
HCl(aq)  H+(aq) + Cl-(aq)
Nitric acid
HNO3(aq)  H+(aq) + NO3-(aq)
Nitrous acid
HNO2(aq)
Ethanoic acid
Sulphuric acid
CH3COOH(aq)
H+(aq) + NO2-(aq)
Basicity
of acid
1
(monobasic)
H+(aq) + CH3COO-(aq)
H2SO4(aq)  2H+(aq) + SO42-(aq)
Sulphurous acid
H2SO3(aq)
2H+(aq) + SO32-(aq)
2
Carbonic acid
H2CO3(aq)
2H+(aq) + CO32-(aq)
(dibasic)
Oxalic acid
H2C2O4(aq)
2H+(aq) + C2O42-(aq)
Phosphoric acid
H3PO4(aq)  3H+(aq) + PO43-(aq)
3
(tribasic)
Acids in “red” are strong acids.

Acid used in lab are usually aqueous solutions.
Acid molecule
Dilute acid
Concentrated acid
15.5
CORROSIVE NATURE OF CONCENTRATED
ACIDS
Concentrated mineral acids are highly corrosive.
High acidity
(High
concentration
of H+ ions)
Figure 15.13 This hazard warning label
means ‘corrosive’. Concentrated mineral
acids always carry this label.
15.5 Corrosive nature of concentrated acids
Figure 15.14 Holes appear in clothes in contact with concentrated sulphuric acid.
15.5 Corrosive nature of concentrated acids
CONCENTRATED HYDROCHLORIC ACID
 an aqueous solution of hydrogen chloride gas
 35% by mass (~11 M)
 a colourless liquid
 gives out white fumes (acid mist) in air.
15.5 Corrosive nature of concentrated acids
Corrosiveness explained

Con HCl reacts with metals, carbonates, oxide in the
same way as the dilute acid, but at a faster rate.

The acidity increases as concentration increases.
High conc
of H+
CONCENTRATED NITRIC ACID
Ordinary concentrated nitric acid (about 16 M) contains about
70 % nitric acid by mass. It is a colourless liquid, but often
turns yellow on storage.
4HNO3 (aq)
light
2H2O (l) + 2NO2 (g) + O2 (g)
a yellowish
brown gas
15.5 Corrosive nature of concentrated acids
Figure 15.17 Concentrated nitric acid is a colourless or pale yellow liquid. It is kept
in a brown bottle since it would decompose much more quickly in light.
15.5 Corrosive nature of concentrated acids
Corrosiveness explained

Conc. nitric acid shows the usual acidic properties, except
towards metals ( not producing salt and H2)

Con HNO3 + metal  other reactions( due to its oxidizing
property)

Very dilute nitric acid is not corrosive, but concentrated nitric
acid is very corrosive.
oxidizing
properties
Conc. nitric
acid is highly
corrosive
High conc
of H+
15.5 Corrosive nature of concentrated acids
CONCENTRATED SULPHURIC ACID
Ordinary concentrated sulphuric acid (about 18 M) is a colourless
oily liquid.
Figure 15.18 Concentrated sulphuric acid is a colourless oily liquid.
15.5 Corrosive nature of concentrated acids
Corrosiveness explained

Concentrated sulphuric acid has the usual acidic properties,
except towards metals. ( not producing salt and H2)

Con H2SO4 + metal  other reactions( due to its oxidizing
property)

Dilute sulphuric acid is irritant, but concentrated sulphuric
acid is very corrosive.
Conc.
sulphuric acid
is highly
corrosive
oxidizing
properties
Dehydrating
properties
15.5 Corrosive nature of concentrated acids
High conc
of H+
Figure 15.15 Concentrated mineral acids are highly corrosive.
http://www.youtube.com/watch?v=nqDHwd9rG0s
15.5 Corrosive nature of concentrated acids
Corrosiveness
Conc HCl < Conc HNO3 < Conc H2SO4
High Conc of H+
High Conc of H+
High Conc of H+
Oxidizing properties
Oxidizing properties
Dehydrating properties
Effects on reactions:Effects on reactions: Effects on reactions:
React much faster
React differently with React differently with
metals( not salt and H2 metals( not salt and H2
are formed)
are formed)
Absorbing water in a
compound, or for drying
a gas
http://www.youtube.com/watch?v=nqDHwd9rG0s
Ionic compounds are electrolytes. Most of them are soluble in
water, but some are insoluble (e.g. lead(II) sulphate).
Acids are usually soluble electrolytes.
15.6 Ionic equations
A BASE is a compound which reacts with an acid to form a salt
and water only.
acid + carbonate  salt + carbon dioxide + water
acid + hydrogencarbonate  salt + carbon dioxide + water
Carbonate and hydrogencarbonates are not bases !!!
Examples of base:
Metal
oxides
16.1 Introducing bases and alkalis
Ammonia
(NH3)
Metal
hydroxides
Only a few bases are soluble in water.
Soluble
Bases
Alkali
This means that all alkalis are bases, but not all bases are
alkalis.
16.1 Introducing bases and alkalis
Bases
e.g. CuO,
Cu(OH)2
Alkalis
e.g. NaOH
Figure 16.1 All alkalis are bases, but not all bases are alkalis.
16.1 Introducing bases and alkalis
COMMON ALKALIS IN DAILY LIFE
ammonia
sodium
hydroxide
Figure 16.2 These household cleaners contain alkalis.
16.1 Introducing bases and alkalis
sodium
hydroxide
COMMON ALKALIS IN LABORATORY
Figure 16.3 Alkalis commonly used in a laboratory.
16.1 Introducing bases and alkalis
CHARACTERISTICS AND CHEMICAL
PROPERTIES OF AQUEOUS ALKALIS
Taste
Aqueous solutions of alkalis usually taste bitter.
(Never try to check this yourself!)
Feel
Dilute solutions of alkalis have a soapy feel.
Electrical conductivity
Like acids, alkalis are electrolytes. They dissolve in water to
form solutions that conduct electricity.
Effect on litmus
They change red litmus paper to blue colour.
A.
Chemical properties of
alkalis
alkali + acidic  salt + H O(l) (neutralization)
(no heating)
2
e.g1. KOH (aq) + HCl (aq)  KCl (aq) + H2O (l)
e.g2. NH3 (aq) + HCl (aq)  NH4Cl (aq)
e.g3. 2NaOH (aq) + CO2 (g)  Na2CO3 (aq) + H2O (l)
e.g4. Ca(OH)2 (aq) + CO2 (g)  CaCO3 (s) + H2O (l)
limewater test
All ammonium compounds (NH4+) are soluble in water
Chemical properties of
alkalis
B. alkali + NH4+ compound  salt + NH3(g) + H2O(l)
(heating)
e.g. KOH (aq) + NH4Cl (aq)  KCl(aq) + NH3(g) + H2O(l)
NH3(g) can turn red litmus
wet limus
paper
paper
blue.
blue.
KOH (aq) + NH4Cl (aq)  KCl(aq) + NH3(g) + H2O(l)
ionic: OH- (aq) + NH4+ (aq)  K+ (aq) + NH3(g) + H2O(l)
.
Chemical properties of alkalis
C. alkali + metal ions (aq)  hydroxides (insoluble ppt)+ salt
(no heating)
e.g1. 2NaOH (aq) + CuSO4 (aq)  Cu(OH)2(s) + Na2SO4(aq)
e.g2. 2NaOH(aq) + Cu(NO3)2 (aq) Cu(OH)2(s) + 2NaNO3(aq)
2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)
NH3(aq)+ CuSO4(aq) 
e.g3. 2H2O(l)+ 2NH3(aq)+ CuSO4(aq) Cu(OH)2(s)+ (NH4)2SO4(aq)
2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)
Remove heavy metal ions from the electroplating industry
-- as the sewage with heavy metal ions is treated with alkali(e,g
NaOH) to form insoluble solid metal hydroxides(ppt), which can
be filtered and collected, so the sewage with heavy metal ions can
be removed before discharging to the sea
e.g4. NaOH(aq) + KNO3(aq) KOH(aq) + NaNO3(aq)
No ppt formed.
•
Gp 1, Ca hydroxides can dissolve in water(no ppt formed).
•
Hydroixdes of main group metals are white, while those are
transition metals are coloured.
•
In excess NaOH:
Pb(OH)2 (s) , Al(OH)3 (s), Zn(OH)2 (s), are soluble in excess NaOH.
( reason: the ppt eg. Zn(OH)2 continues to react with NaOH and
form a product which is soluble)
•
In excess NH3:
Cu(OH)2 (s) , Zn(OH)2 (s), Ag2O (s) are soluble in excess NH3.
( reason: the ppt eg. Zn(OH)2 continues to react with NH3 and
form a product which is soluble)
• Conc Alkalis are also corrosive
• THINGS NEVER FORGET
• (BACKBONE OF THE CHAPTER)
• Example of Acids:
• H2SO4,HCl, HNO3, CH3COOH, H2CO3,
H3PO4
• Citric acid
• Acidic gases:
• SO2 +H2O H2SO3 2H+ + SO32• CO2 +H2O H2CO3 2H+ + CO32-
• Example of Bases:
• Any oxides and hydroxides.(KOH,
Ca(OH)2, ZnO, Mg(OH)2, PbO, Ag2O,
NH3
• Example of Alkalis:
• KOH, NaOH, Ca(OH)2, NH3
•
•
•
•
•
•
•
•
Properties of acids (H+)
Sour
Conduct electricity(mobile ions)
Wet litmus blue  red
Properties of alkalis (OH-) (NOT BASE)
Bitter
Conduct electricity(mobile ions)
Wet litmus red  blue
• Presence of H+ by ionization of acids
(aq)
basicity
• Presence of OH- by dissociation
/ ionization of alkalis
•
•
•
•
D: KOH (aq) K+ (aq) + OH- (aq)
D: NaOH (aq)  Na+ (aq) + OH- (aq)
D: Ca(OH)2 (aq)  Ca2+ (aq) + 2OH- (aq)
NH3 (aq) + H2O(l) <-> NH4+ + OH- (aq)
5 reactions
1.acid + metal (KPb)
 salt + H2
2. acid + carbonate/hydrogencarbonate
 salt + CO2 + H2O
3. acid + base(all oxides+ hydroxides+ ammonia)
 Salt + H2O
4. alkali(soluble base: KOH, NaOH, Ca(OH)2)
+ ammonium cpd
 Salt + NH3 + H2O
5. alkali(soluble base: NaOH, NH3)
+ metal ions solution (except K+, Na+, Ca2+ )
 ppt + salt (by product)
(some ppt redissolve –
continues to react with NH3 or NaOH and form
a product which is soluble)
Ag2O (s)
• Baking powder
• Fizzy drink
• The presence of H+ for acidic
properties
Class practice 14.8
1. Given: potassium hydroxide, magnesium oxide,
zinc hydroxide, copper(II) oxide
(a) (i) Which of the above substances is/are
alkali(s)?
(ii) Write ionic equation(s) for the reaction of
hydrochloric acid and the substance(s)
mentioned in (a)(i).
(b) (i) Which of the above substances is/are
insoluble base(s)?
(ii) Write ionic equation(s) for the reaction of
dilute sulphuric acid and the insoluble
P. 66 / 4
base(s) mentioned in (b)(i).
2. Write (i) a full equation and (ii) an ionic equation
for the reaction of the following pairs of aqueous
solutions.
(a) lead(II) nitrate + limewater
(b) copper(II) sulphate + potassium hydroxide
P. 67 / 4
A 14.8
1. (a) (i) Potassium hydroxide
−
+
(ii) OH (aq) + H (aq)  H2O(l)
(b) (i) Magnesium oxide, zinc hydroxide and
copper(II) oxide
+
2+
(ii) MgO(s) + 2H (aq)  Mg (aq) + H2O(l)
+
2+
Zn(OH)2(s) + 2H (aq)  Zn (aq) + 2H2O(l)
+
2+
CuO(s) + 2H (aq)  Cu (aq) + H2O(l)
2. (a) (i) Pb(NO3)2(aq) + Ca(OH)2(aq)  Pb(OH)2(s) +
Ca(NO3)2(aq)
2+
−
(ii) Pb (aq) + 2OH (aq)  Pb(OH)2(s)
P. 68 / 4
(b) (i) CuSO4(aq) + 2KOH(aq)  Cu(OH)2(s) +
K2SO4(aq)
2+
(ii) Cu (aq) + 2OH (aq)  Cu(OH)2(s)
P. 69 / 4
A 14.2
1. (a) Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
(b) ZnO(s) + H2SO4(aq)  ZnSO4(aq) + H2O(l)
(c) Fe(OH)2(s) + 2HCl(aq)  FeCl2(aq) + 2H2O(l)
(d) CuCO3(s) + H2SO4(aq)  CuSO4(aq) + CO2(g)
+ H2O(l)
(e) Ca(HCO3)2(s) + 2HCl(aq)  CaCl2(aq) +
2CO2(g) + 2H2O(l)
2. (a) Magnesium dissolves./Effervescence occurs.
(Colourless gas bubbles evolve.)/The solution
becomes warm./The resultant solution is
colourless.
P. 70 / 3
(b) Zinc oxide dissolves./The resultant solution is
colourless.
(c) Iron(II) hydroxide dissolves./The resultant
solution is green.
(d) Copper(II) carbonate dissolves./Effervescence
occurs. (Colourless gas bubbles evolve.)/The
resultant solution is blue.
(e) Calcium hydrogencarbonate
dissolves./Effervescence occurs. (Colourless
gas bubbles evolve.)/The resultant solution is
colourless.
P. 71 / 3
Strong acid
Weak acid