Acids In daily-life Ethanoic acid( in vinegar) CH 3 COOH Citric acid ( in fruit) Carbonic acid ( in soft drink) H 2 CO 3

Common acids in lab Hydrochloric acid Sulphuric acid Nitric acid HClH 2 SO 4 HNO 3

Mineral acids (in organic acids) Hydrochloric acid, HCl Sulphuric acid, H 2 SO 4 Nitric acid,HNO 3 Carbonic acid, H 2 CO 3 Others mainly are organic acids Acids – H containing covalent molecules

Pure acids can be in different states (g)/(l)/(s) at different temperatures. e.g HCl is in gas state at room temperature. Citric acid is in solid state at room temperature.

Dilute acidConcentrated acid Acid molecule Acid used in lab are usually aqueous solutions.

Physical Properties of Dilute Acids a) sour b) acidic; it turn blue litmus paper to red c) it conduct electricity only in aqueous state. a) Taste b) pH c) Electrical conductivity

a)Reaction with metal (K  Pb) b)Reaction with oxides/ hydroxides c)Reaction with carbonates/ Hydrogencarbonates Chemical Properties of Dilute Acids

acid + metal  salt + hydrogen H 2 SO 4 (aq) + Mg(s)  MgSO 4 (aq) + H 2 (g) 2HCl(aq) + Zn(s)  ZnCl 2 (aq) + H 2 (g) Reaction with metals For example, They react with metals higher than copper in the reactivity series, liberating hydrogen gas: Dilute acids: Only dilute HCl, H 2 SO 4,very dilute HNO 3

acid + metal oxide  salt + water e.g.H 2 SO 4 (aq) + CuO(s)  CuSO 4 (aq) + H 2 O(l) acid + metal hydroxide  salt + water e.g. H 2 SO 4 (aq) + 2NaOH(aq)  Na 2 SO 4 (aq) + 2H 2 O(l) Action on metal oxides and hydroxides

acid + carbonate  salt + carbon dioxide + water For example, 2HCl(aq) + CaCO 3 (s)  CaCl 2 (aq) + CO 2 (g) + H 2 O(l) For example, HNO 3 (aq) + NaHCO 3 (s)  NaNO 3 (aq) + CO 2 (g) + H 2 O(l) acid + hydrogencarbonate  salt + carbon dioxide + water Action on carbonates and hydrogencarbonates

How to test for the existence of carbon dioxide? Limewater test Limewater test 15.2 Characteristics and chemical properties of acids

Limewater test for carbon dioxide Carbon dioxide is a colourless gas. It turns limewater milky. Ca(OH) 2 (aq) + CO 2 (g)  CaCO 3 (s) + H 2 O(l) lime water colourless solution white solid

Na 2 CO 3 (s) + H 2 SO 4 (aq)Na 2 SO 4 (aq) + ***Soluble in water Na + CO H + SO 4 2- Na 2 SO 4 H 2 CO 3 H 2 O(l) + CO 2 (g)

2NaHCO 3 (s)+H 2 SO 4 (aq)Na 2 SO 4 (aq)+ ***Soluble in water 2Na + 2HCO 3 - 2H + SO 4 2- Na 2 SO 4 2H 2 CO 3 2H 2 O(l)+2CO 2 (g)

All oxides are insoluble, (s) All hydroxides except gp 1 are insoluble, (s) All carbonates except gp 1 are insoluble, (s) AgX and PbX 2 are insoluble, (s) (X= Cl -, Br -, I - ) CaSO 4, PbSO 4, BaSO 4 are insoluble, (s) All hydrogencarbonates are soluble ---(aq) ***Even though some compounds are soluble in water, we may use its solid form for a reaction.

SULPHURIC ACID AND NITRIC ACID IN WATER Pure sulphuric acid and nitric acid are colourless liquids. They both consist of covalent molecules. When they dissolve in water, ions are formed. Acids are also electrolytes. H 2 SO 4 (l) H + (aq) SO 4 2  (aq) H + (aq) water molecules

HNO 3 (l) H + (aq) NO 3  (aq) water molecules

When acid molecules dissolve in water, ions are formed. ionization H + (aq) + Cl - (aq) 2H + (aq) + SO (aq) H + (aq) + NO 3 - (aq) HCl(aq) H 2 SO 4 (aq) HNO 3 (aq) Acid is a H containing covalent compound, when dissolved in water, it forms H+ ions. ＾ only Is NaHSO 4 / NaHCO 3 an acid? (as an only kind of positive ion)

HYDROGEN CHLORIDE IN WATER AND IN METHYLBENZENE HCl in water HCl(aq)  H + (aq) + Cl - (aq) HCl in methlybenzene (non-aqueous solvent)

no gas evolved (no apparent reaction) bubbles of carbon dioxide evolved: Na 2 CO 3 (s) + 2H + (aq)  2Na + (aq) + CO 2 (g) + H 2 O(l) Action on solid sodium carbonate no gas evolved (no apparent reaction) bubbles of hydrogen evolved: Mg(s) + 2H + (aq)  Mg 2+ (aq) + H 2 (g) Action on magnesium nonegood Electrical conductivity no colour changeturns to red colour Effect on dry blue litmus paper Hydrogen chloride in dry methylbenzene Hydrogen chloride in water (hydrochloric acid) Test 15.3 The role of water for acids

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 The role of water for acids

Ingredients: solid acid + solid carbonate/hydrogencarbonate Fizzy drink tablet

CO 3 2- (aq) + 2H + (aq)CO 2 (g) + H 2 O(l) HCO 3 - (aq) + H + (aq)CO 2 (g) + H 2 O(l) H+H+ H+H+ H+H+ HCO 3 - CO Without water, acids do not have acidic properties. Ingredients: solid acid + solid carbonate/hydrogencarbonate

When acid dissolves in water  Ionization H + (aq) + Cl - (aq) 2H + (aq) + SO (aq) H + (aq) + NO 3 - (aq) HCl(aq) H 2 SO 4 (aq) HNO 3 (aq) CH 3 COOH(aq) H + (aq) + CH 3 COO - (aq) H 3 PO 4 (aq)3H + (aq) + PO (aq) Basicity = no.of ionizable H+ in an acid molecule

15.4BASICITY OF AN ACID Different acids may give different numbers of hydrogen ions per molecule in aqueous solution Basicity of an acid The BASICITY of an acid is the number of hydrogen ions produced by one molecule of the acid.

H 2 SO 4 (aq) 2H + (aq) + SO 4 2- (aq) H 2 SO 3 (aq) 2H + (aq) + SO 3 2- (aq) H 2 CO 3 (aq) 2H + (aq) + CO 3 2- (aq) H 2 C 2 O 4 (aq) 2H + (aq) + C 2 O 4 2- (aq) 3 (tribasic) H 3 PO 4 (aq) 3H + (aq) + PO 4 3- (aq)Phosphoric acid 2 (dibasic) 1 (monobasic) HCl(aq)  H + (aq) + Cl - (aq) HNO 3 (aq)  H + (aq) + NO 3 - (aq) HNO 2 (aq) H + (aq) + NO 2 - (aq) CH 3 COOH(aq) H + (aq) + CH 3 COO - (aq) Hydrochloric acid Nitric acid Nitrous acid Ethanoic acid Basicity of acid Ionization in waterAcid Sulphuric acid Sulphurous acid Carbonic acid Oxalic acid Acids in “red” are strong acids Basicity of an acid

only this hydrogen atom (connected with O) can form hydrogen ion, H +. Figure Ethanoic acid (CH 3 COOH) is monobasic because each molecule can only give one hydrogen ion Basicity of an acid

Strong acid exists mainly as ions. It ionizes completely in water. Weak acid exists mainly in molecular forms, it contains less ions since it only slightly ionizes in water.

15.5CORROSIVE NATURE OF CONCENTRATED ACIDS All concentrated mineral acids are highly corrosive. Figure This hazard warning label means ‘corrosive’. Concentrated mineral acids always carry this label Corrosive nature of concentrated acids High acidity (High concentration of H + ions) High acidity (High concentration of H + ions)

Figure Holes appear in clothes in contact with concentrated sulphuric acid Corrosive nature of concentrated acids

Figure Concentrated mineral acids are highly corrosive Corrosive nature of concentrated acids

CONCENTRATED HYDROCHLORIC ACID 15.5 Corrosive nature of concentrated acids  gives out white fumes (acid mist) in air.  a colourless liquid  35% by mass (~11 M)  an aqueous solution of hydrogen chloride gas

 Con HCl reacts with metals, carbonates, oxide in the same way as the dilute acid, but at a faster rate. Corrosiveness explained  The acidity increases as concentration increases.

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 Corrosive nature of concentrated acids 4HNO 3 (aq) 2H 2 O (l) + 2NO 2 (g) + O 2 (g) a yellowish brown gas light

Figure 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 Corrosive nature of concentrated acids

Corrosiveness explained  Conc. nitric acid shows the usual acidic properties, except towards metals Conc. nitric acid is highly corrosive oxidizing properties  Very dilute nitric acid is not corrosive, but concentrated nitric acid is very corrosive.

CONCENTRATED SULPHURIC ACID Ordinary concentrated sulphuric acid (about 18 M) is a colourless oily liquid. Figure Concentrated sulphuric acid is a colourless oily liquid Corrosive nature of concentrated acids

Corrosiveness explained 15.5 Corrosive nature of concentrated acids  Concentrated sulphuric acid has the usual acidic properties, except towards metals.  Dilute sulphuric acid is irritant, but concentrated sulphuric acid is very corrosive. Corrosiveness Dehydratin g property Oxidizing property

15.6IONIC EQUATIONS For writing ionic equations from full equations, the formulae of electrolytes in aqueous solution should be rewritten as separate formulae of cations and anions Ionic equations Formula of cations Formula of anions Formulae of electrolyte

15.6 Ionic equations 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.