11. acids and bases.ppt

7/27/2019 11. Acids and Bases.ppt

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Properties of acids

have sour taste

are hazardous

change the colour of indicators

Turns blue litmus paper red

reacts with metals to produce hydrogen gas

reacts with carbonates and hydrogen

carbonates reacts with metal oxides and hydroxides

Storage of acids and acidic foods should be in

glass, plastic or clay pots – Why?



Acids and Bases

Reaction with carbonates to produce salt, carbon

dioxide and water.

FeCO3 + 2HCl FeCl2 + H2O + CO2

Reactions of ACIDS



Acids and Bases

Reaction with carbonates to produce salt, carbon dioxide and water. Reactions of ACIDS

Reaction with reactive metals to producesalt and hydrogen gas.

Mg + H2SO4 MgSO4 + H2



Acids and Bases


Reaction with reactive metals to produce salt and hydrogen gas.

•Reaction with base to produce saltand water

CuO + 2HNO3 Cu(NO3)2 + H2O



Acids and Bases


Reaction with metals to produce salt and hydrogen gas.

•Reaction with base to produce salt and water

Reaction of bases with ammonium saltto produce salt, ammonia gas and water.

Reactions of BASES

NaOH + NH4Cl NaCl + NH3 + H2O



Uses of acids

Sulfuric acid in the manufacture of fertilisers

Ammonium sulfate – fertiliser

Detergents, paints, dyes, artificial fibers and plastics

Dilute sulfuric acid is used in batteries – cars,

buses HCl and H2SO4 are used to remove rust

Food preservations – vinegar



Properties of bases

Bases are oxides or hydroxides of metals.

All alkalis are bases and not all bases are

alkalis.

Insoluble metal oxides are bases. CuO



Bases

Alkalis

Bases

Any difference?



Any Difference?

Bases are oxides or hydroxides of metals.

Alkalis are soluble bases – which produces hydroxide ions in water.

All alkalis are bases and not all bases are

alkalis.



Bases

Alkalis

Bases



Alkalis and bases

Metal oxides insoluble in water are bases.

Example – CuO, Fe2O3,PbO2

Metal oxides soluble in water are alkalis –

Na2O, K 2O

Aqueous ammonia?

NH3(aq) -?



What did you observe in the lab?

NH3.H2O ?

NH3 + H2O NH4+(aq) + OH- (aq) ?



NH3OH

-

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3NH4+

A small fraction of ammonia molecules react with water to

form hydroxide ions. Most ammonia molecules remainunchanged that is why you can smell the pungent gas when abottle of aqueous ammonia is opened.



Hazardous

Soapy to touch Change colour with indicators

Reacts with acids

NaOH + HCl → NaCl + H2O Reacts with ammonium compounds

NH4Cl + NaOH → NaCl (aq)+ H2O(l) + NH3(g)

Reacts with metal ions

2NaOH(aq) +Cu2+ (aq)→ Cu(OH)2(s)+ 2Na+ (aq)



Strong and weak alkalis Sodium hydroxide and potassium hydroxide

completely dissociates (strong alkali)

NaOH(aq) → Na+ (aq) + OH- (aq)

weak alkali (aqueous ammonia)

NH3(g) + H2O(l) NH4+(aq) + OH- (aq)

A small fraction of ammonia molecules react

with water to form hydroxide ions.

Most ammonia molecules remain unchanged

that is why you can smell the pungent gas when

a bottle of aqueous ammonia is opened.



Strong alkalis and weak alkalis

Strong alkalis – dissociates completely in

water to produce a high concentration of

hydroxide ions. Example: NaOH, KOH

OH-

Na+

Na+

Na+Na

+

OH-

OH-

OH-

DILUTE CONCENTRATED



Weak alkalis

Weak alkalis – dissociates partially in water to

produce a low concentration of hydroxide ions.

NH3(aq) + H2O(l) NH4+(aq) + OH- (aq)

NH3OH

-

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH4+



Chemical reactions

Reacts with acids – Neutralisation reaction

NaOH (aq) + HCl (aq) → NaCl (aq) + H2O(l)

Reacts with ammonium compounds NH4Cl (aq) + NaOH (aq) → NaCl(aq) + H2O(l) +

NH3(g)

Reacts with metal ions

2NaOH(aq) +Cu2+ (aq)→ Cu(OH)2(s) + 2Na+ (aq)

2NaOH(aq) +Fe2+ (aq)→ Fe(OH)2(s) + 2Na+ (aq)



Strong alkalis react with amphoteric metal oxides

ZnO + 2NaOH + H2O → Na2(Zn(OH)4) SodiumZincate

Al2O3+ 2NaOH + 3H2O → 2NaAl(OH)4Tetrahydroxoaluminate

Electronegativity increases as you go across the period - and the electronegativity difference betweenaluminium and oxygen is smaller. That allows theformation of covalent bonds between the two.



Alkalis and indicators

Change colour with indicators

Methyl orange - yellow

Red litmus paper changes to blue

Phenolphthalein - peach

Universal indicator



OXIDES

METALLIC OXIDES NON-METALLIC OXIDES

BASIC OXIDES

Most

basic

oxides

are

_______ in

water.

Metal

oxides

that are

soluble in

water are

known as

__ _______.

AMPHOTERIC

OXIDES

ACIDIC

OXIDES

Acidic oxides

dissolve in

water to form

acids.

NEUTRAL

OXIDES

Metal oxides

that can react

with both

_________ and

_________ to

form salt and

water.ALKALIS

insoluble

NaOH

KOH

FeO

CuO

acids

alkalis

ZnO

Al 2O3

PbO

SO2

P2O5

NO2

H2O

NO

CO

http://localhost/var/www/apps/conversion/tmp/My%20Documents/s3pp/acid/saltprep/oxides%20map.rtf





























































OXIDES

METALLIC OXIDES NON-METALLIC OXIDES

BASIC OXIDES

Most

basic

oxides

are

Insoluble

in

water.

Metal

oxides

that are

soluble

in water

are

known

as

Alkalis.

AMPHOTERIC

OXIDES

ACIDIC

OXIDES

Acidic oxides

dissolve in water

to form acids.

NEUTRAL

OXIDES

Metal

oxides that

can react

with both

acids and

alkalis to

form salt

and water.

NaOH

KOH

Fe2O3

CuO

ZnO

Al2O3

PbO

SO2

P2O5

NO2

H2O

NO

CO














































Li Be B C N O F

Na Mg Al Si P S Cl

K Ca Ga Ge As Se Br

Rb Sr In Sn Sb Te I

Cs Ba Tl Pb Bi Po At

Basic Oxides Amphoteric Oxides Acidic Oxides

I II III IV V VI VII

Acidic and amphoteric oxides



Uses of alkalis/bases

Window cleaners, oven cleaners, detergents,

soaps – sodium hydroxide. toothpastes – toneutralise the acids in our teeth, medicines for

indigestion - to neutralise stomach acid.

CaO is used to neutralise the acidity of the soil