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ea' acids

A wea- acid is one that ionises ! dissociates incompletel ! partiall in water to produce !ewhydrogen ions $H ' %. ost o! the acid molecules remain as molecules. &he solution contains a low

concentration o! ions: poor electrical conductor.

CH 3COOH $a)% CH 3COO + $a)% ' H ' $a)%

mportance of *ater for acidit

(ure acids exist as molecules instead o! ions. (ure acids do not behave as acids as theproperties o! acids are due to the presence o! hydrogen ions. /hen acids are mixed with water0ionisation o! acids occurs0 and hydrogen ions are produced. &here!ore0 acids can only behave asacids when they are dissolved in water.

+roperties of Acids

An acid0 when dissolved in water0 !orms a colourless solution. olutions o! acids have the!ollowing properties:

,. so%r taste.". change the colour o! indicators $e.g. turn l%e litmus paper red %.3. contain hydrogen ions and conduct electricity.#. react with metals, car onates and ases .

-eactions *it# metals

Acids react with metals to produce a salt and # dro en

Acid ' metal * salt ' hydrogen

Example: "HCl $a)% ' 1n $s% * 1nCl " $a)% ' H " $g%

Observations: $a% E!!ervescence observed. Colourless0 odourless gas evolved whichextinguished a lighted wooden splint with a 2pop sound.

$b% 4rey solid reduced in si5e $when in excess%. 4rey solid dissolves to !orma colourless solution

$c% Heat liberated.

1inc chloride is called a salt. alts o! nitric acid are called nitrates. alts o! sul!uric acid are calledsul!ates0 and those o! hydrochloric acid are called chlorides. A salt is generally made up a cation$that comes !rom a base% and an anion $that comes !rom an acid%. A salt is the product o! theneutralisation o! an acid and a base

Acid Examples o! alts 6ormula

ul!uric acid 1inc sul!ateodium sul!ate

1n O #Na " O #

Nitric acid (otassium nitrateCopper $77% nitrate

8NO 3Cu$NO 3%"

Hydrochloric acid agnesium chlorideodium chloride

gCl "NaCl

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Exceptions ( ptional)

a% etals which are less reactive than hydrogen is not reactive enough to react with acids.

9eactivity eries:

(otassium ost 9eactiveodium

Calciumagnesium

Aluminium1inc7ron&in

eadHydrogenCopper

ilver

4old east reactive

-eactions *it# car onates

Acids react with carbonate to produce a salt 0car on dioxide and *ater .

Acid ' carbonate * salt ' carbon dioxide ' water

Example: Na " CO 3 $s% ' H " O # $a)% * Na " O # $a)% ' CO " $g% ' H "O $l%

Observations: $a% E!!ervescence occurs. Colourless0 odourless gas evolved which reactswith calcium hydroxide to !orm a white precipitate.

$b% /hite solid dissolves to !orm a colourless solution.

-eactions *it# ases

Acids react with ases (metal oxides and metal # droxides) to produce a salt and *ater.

Acid ' base * salt ' water

Example: gO $s% ' H " O # $a)% * g O # $a)% ' H " O $l%Observation: $a% /hite solid dissolves to !orm a colourless solution.

Example: "8OH $a)% ' H " O # $a)% * 8 " O # $a)% ' "H "O $l%

Observation: $a% Heat is evolved. No visible change.

/ses of acids

ul!uric acid: in ma-ing detergents and !ertilisersin car batteries as battery acid

Ethanoic acid: to preserve !ood

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Colo%r c#an e of indicators

ndicators ser0ation(s)

itmus paper An acid turns l%e litmus paper red .

ethyl Orange ;sed to identi!y strong acids.Colour change at pH #

trong acid turns methyl orange red . Al-ali turn methyl orange ello* .

(henolphthalein ;sed to identi!y strong al-alis.Colour change at pH ases are the oxides or hydroxides o! metal that reacts with an acid to !orm a salt and water only.

Definition of al'ali

An al-ali is a metal hydroxide which is soluble in water and produces hydroxide ions $OH +% inwater.

All al-alis are bases but not all bases are al-alis.

Examples

nsol% le ase

Copper $77% oxide0 aluminium oxide0 5inc oxide0 5inc hydroxide

Sol% le ase ! al'ali

odium oxide0 potassium oxide0 sodium hydroxide0 potassium hydroxide0 calcium hydroxide$slightly soluble%0 ammonium hydroxide

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Stren t# of an al'ali

&he stren t# o! an al-ali depends on its degree o! dissociation ! ionisation in water to !ormhydroxide ions. &he properties o! al-alis are due to the hydroxides ions.

Stron al'ali

A strong al-ali is one that ionises ! dissociates completel in water to produce hydroxide ions$OH+%. &here are no molecules le!t. &he common strong al-alis are sodium hydroxide andpotassium hydroxide.

NaOH $a)% * Na ' $a)% ' OH + $a)%8OH $a)% * 8 ' $a)% ' OH + $a)%

ea' al'ali

A wea- al-ali is one that ionises ! dissociates incompletel ! partiall in water to produce !ewhydroxide ions $OH +%. ost o! the al-ali molecules remain as molecules.

+roperties of ases

,. Al-alis have a soapy !eel and a bitter taste.". Al-alis can change the colour o! indicators $e.g. turn red litmus paper l%e%.3. >ases can react with acids to !orm salt and *ater only ? Ne%tralisation .

>ase ' acid * salt ' water

Example: NaOH $a)% ' HCl $a)% * NaCl $a)% ' H "O $l%

Note: Neutralisation ? &he !ormation o! molecules o! water !rom hydrogen ion o! an acid andhydroxide ion o! an al-ali. H ' $a)% ' OH + $a)% * H "O $l%.

#. >ases can react with ammonium salts to !orm salt 0ammonia and *ater .

>ase ' ammonium salt * salt ' ammonia ' water

Example: NaOH $a)% ' NH #Cl $s% * NaCl $a)% ' NH 3 $g% ' H " O $l%

Observation: $a% A colourless0 pungent gas is evolved.4as turns damp red litmus paper blue.

@. Al-alis can react with a solution o! one metal salt to give metal hydroxide and another metalsalt

Example: Cu O # $a)% ' "NaOH $a)% * Cu$OH% " $s% ' Na " O # $a)%

/ses of Bases and Al'alis

agnesium hydroxide: in toothpaste to neutralise the acids on our teeth produced bybacteria.

Ammonia solution: used !or cleaning glass windows

@