Acids Bases and Salts

ACIDS, BASES AND SALTSACIDSYou know that acids are sour to taste. You have tasted vinegar, you have also tasted lemonjuice which contain acids namely acetic acid and citric acid respectively. Do you know thatour gastric juice in the stomach contains hydrochloric acid which is required to digest thecarbohydrate food that we eat. Do you know ants contain an acid called formic acid andwhen ants bite us, we get the pain in our skin due to the the corrosive action of this formicacid? In fact any substance which is sour to taste usually contains an acid. The curd thatwe eat contains lactic acid. So acids are very important class of compounds which have wideranging applications. Let us know more about acids. According to Arrehenius theory ofacid, substances which can produce H+ in water are called acids.

TYPES OF ACIDS ON THE BASIS OF ITS ORIGINBased on the source from which acids are obtained, they are of two types.(i) Mineral acids:These acids are prepared from inorganic minerals. Say for example, hydrochloric acid(HCl)is prepared from our common salt(sodium chloride). When NaCl is heated in presence ofconcentrated sulphuric acid, we get hydrogen chloride gas(HCl gas) and when we dissolvethis gas in water, we get hydrochloric acid.

NaCl + H2SO

4 -----heat---->Na

2SO

4 + HCl

Of course, to get one acid(HCl) we took the help of another acid(H2SO

4). We shall know

later how sulphuric acid is prepared.(ii) Organic acids:These types of acids are obtained from organic matters such as plants and animals. Forexample, acetic acid(vinegar) which is an organic acid is prepared from wood. When woodis distilled in the absence of air, we get acetic acid among other substances. We shall discussthe details of the preparations of many organic acids later.

Physical state of acids: The acid in the pure form may remain in the solid state, liquid stateor gaseous state. For example pure acetic acid remains in the liquid state, pure oxalic acidwhich an organic acid remains in the solid state and hydrogen chloride which forms hydrochloricacid remains as a gas at room temperature. Only when the substance is dissolved in water,it forms an acid. Note that all acids are completely soluble in water.Now let us define an acid.Acid is a substance which when dissolved in water produces hydrogen ions(H+). Thisis according to Arrhenius theory of acids. Although naked H+ ion does not exist, it remainsbound to a H

2O molecule and remains as H

3O+(hydronium ion), for all practical purposes,

we shall call it H+ ion for the sake of simplicity. So any acid put in water will undergodissolution which means it will become soluble and produce H+ ions. Note that H+ ions arenot produced until the substance is dissolved in water.How to know that a solution is acidic??(i) First of all it will taste sour.(ii) Secondly blue litmus will turn red. You can either add a little quantity of blue litmussolution to an acid or dip a blue litmus paper in the acid. It will turn red.

Types of acids on the basis of strength:When HCl gas is bubbled in water, it undergoes complete dissociation to produce H+ ions andCl- ions. Nearly all molecules undergo dissociation (ionisation). In other words almost nomolecule remains as HCl in the undissociated form. Hence it is called a strong acid. Theamount of H+ ions in unit volume of solution is more in such an acid.

HCl(gas) -----water------> H+ + Cl - (strongly ionised)(very little) (Very large)

But when you put acetic acid in water, all of them will dissolve no doubt but all of them willnot ionise. A very little of the acid will undergo dissociation to produce very little of H+ ions.Thus the acid is weakly dissociated and hence is called a weak acid.

CH3COOH(l) -------water-----> CH

3COO - + H+ (weakly ionised)

(very large) (very little)Hence there are two types of acids(a) Strong acids:

Acids which are strongly ionised and produce a large number of H+ ions.Examples: HCl(hydrochloric acid) HBr(hydrobromic acid)

HI(hydroiodic acid) H2SO

4(sulphuric acid)

HNO3(nitric acid) HClO

3(chloric acid)

HClO4(perchloric acid)

Relative strength : HI > HBr > HCl = HClO4 > H

2SO

4 > HNO

3 > HClO

3

Do you know which acid is the strongest ? it is flouroantimonic acid; HSbF6.

(b) Weak Acids:Acids which are weakly ionised and produce a small number of H+ ions

Example: HF(hydroflouric acid) HCN(hydrocyanic acid)H

2CO

3(carbonic acid) H

2SO

3(sulphurous acid)

HNO2(nitrous acid)

H3PO

4(phosphoric acid more correctly orthophosphoric acid)

H3PO

3(phosphorous acid or more correctly orthophosphorous acid)

H3PO

2(hypophosphorous acid) HClO(hypochlorous acid)

H3BO

3(boric acid or more correctly orthoboric acid)

All organic acids: such as HCOOH(formic acid)CH

3COOH(acetic acid) H

2C

2O

4(oxalic acid)

citric acid, lactic acid and a large number of acids whose formula are beyondthe scope of this book.

SAQ 1: State TRUE or FALSE. Correct the statement if there is any mistake(i)All acids are not soluble in water.(ii)When an acid dissolves in water, nearly complete ionisation may occur.(iii)Hydroflouric acid is a weak acid.

SAQ 2.Indicate which acid is strong and which acid is weak.Also write their formula.sulphuric acid, carbonic acid, nitrous acid, nitric acid, hypochlorous acid, phosphoric

acid, sulphurous acid

How will you know whether an acid solution is strong acid or weak acid?(i) Electrical conductivity:Since acid solution contains free ions, it conducts electricity. If an electric bulb will be placed

in the electric circuit containing a strong acid solution (say hydrochloric acid), the bulb willglow with intense light as the number of ions produced from strong acid is very large. Onthe other hand, if the electricity is passed through a weak acid solution(say acetic acid), thenthe bulb will glow with dim light. This is because the solution contains a small number of ions.(ii) Action on skin:When a strong acid is poured in our skin, it produces painful blisters. The skin colourchanges. For example when concentrated nitric acid is poured on our skin, it produces yellowcolour colour with painful blister. But when a weak acid is poured in the skin, it is notaffected. We eat acetic acid in many dishes in the name of vinegar. It is also used as apreservative to keep food material for a long time without rancidification. But not all weakacids are eatables. HCN is one of the deadliest poison.

Types of acids according to concentration of acid present (not concentration of H+

ions)We knew that on the basis of concentration of H+ ions present in an acid solution, an acidcan either be a strong acid(like HCl) or a weak acid(acetic acid). But now we have adifferent situation. If we have two hydrochloric acid bottles having different amounts of HClper litre of solution. In one case, say 3.65gm HCl is present in one litre solution and in theother case 36.5gms of HCl is present in one litre solution, then the former is called a dilutedsolution and the latter a concentrated solution. So we can classify the acids in thefollowing ways.(i) Concentrated acid:When the amounts of acid is more in a given volume of solution, it is called a concentratedsolution. The commercial concentrated nitric acid which is supplied to laboratories is 60% byweight. It means that 60gms of pure HNO

3 is present in 100gms of solution, which means

100gms solution contains 60gms pure acid and the remaining 40gms water. Commercialconcentrated H

2SO

4 is 98% by weight, that means in every 100gms of acid, there is 98gms

of pure H2SO

4.

In a strict sense there is no limit for a concentrated solution. It is a relative term. One acidcan be relatively more concentrated than the other. The less concentrated solution can becalled as a dilute solution. Usually a concentrated acid is believed to contain at least 30%by weight of pure acid or more.Concentrated acids are more harmful to human skin.(ii) Dilute acid:When amounts of acid is less in a given volume of solution, it is called a diluted acid.Say 10% H

2SO

4 solution can be regarded as a diluted acid. Such an acid is less harmful to

our skin. If such solution spills over our hand, very little pain will be received. So acid solutionhaving less than 30% pure acid can be taken for all practical purposes as diluted acids.

Solubility of acids: We already know that all mineral acids are completely solublein water. Common organic acids like acetic acid, formic acid, citric acid etc. are also solublein water.SAQ 3: Indicate which is a weak acid, diluted acid, strong acid and concentrated acidsolution.

(i)HCl (ii)5%HCl (iii)CH3COOH (iv)70%CH

3COOH

(v)98%H2SO

4(vi)2% H

3BO

3

SAQ 4: Which of the following acids are soluble in water and which is insoluble.

HCl, HNO3, H

2SO

4, CH

3COOH, H

3PO

4, HCN

Types of acids on the basis of the presence or absence of oxygen:If an acid does not contain oxygen say for example HCl, it is called a hydra acid and if anacid contains oxygen alongwith hydrogen, it is called oxo or oxy acid. H

2SO

4 is and oxoacid.

Hence there are two types of acids on this basis.(i) Hydra acids:Acids which contain only hydrogen alongwith the one more element are called hydra acids.They do not contain oxygen.Examples: HCl, HF, HBr, HI, HCN(ii) Oxoacids:Acids which contain oxygen along with hydrogen are called oxoacids.Examples: H

2SO

4, HNO

3, H

2CO

3, CH

3COOH etc.

Types of acids on the basis of replaceable hydrogen atoms:Take the case of HCl. It has one replaceable hydrogen atom. When HCl reacts withNaOH(a base), it forms salt(NaCl) and water. Thus the H atom of HCl is replaced by Na.The number of replaceable hydrogen atoms present in an acid is called basicity of an acid.The basicity of HCl is one i.e it is a monobasic acid. Take the case of H

2SO

4. It contains

two replaceable hydrogen atoms.H

2SO

4 + 2NaOH--------> Na

2SO

4 + H

2

In this case two H atoms of H2SO

4 can be replaced and is called a dibasic acid. So we can

divide the acid in the following ways.(i) Monobasic or Monoprotic acid:Acids containing one replaceable hydrogen atom are called monobasic acids. They produceone H+ ion per molecule in the acid solution.

HCl ------> H+ + Cl-

Examples: HCl, HBr, HI, HNO3, HClO, HCN, CH

3COOH, H

3PO

2(hypophosphorous acid)

Note that although H3PO

2 contains three hydrogen atoms, only one of them can be replaceable

and hence it is a monobasic acid. In organic acids like acetic acid there is one replaceablehydrogen atom which has been underlined. The other three hydrogen atoms are not replaceable.(ii) Dibasic or diprotic acids:Acids which contain two replaceable hydrogen atoms and which can produce two H+ ionsper molecule in the acid solutions are called dibasic or diprotic acids.

H2SO

4 ------------> 2H+ + SO

42-

Examples: H2SO

4, H

2SO

3, H

2C

2O

4(oxalic acid), H

3PO

3 etc.

Note that although H3PO

3(phosphorous acid) contains three hydrogen atoms, only two hydrogen

atoms are replaceable. Hence it is a dibasic or diprotic acid.(iii) Triprotic or tribasic acids:Acids which contain three replaceable hydrogen atoms and which can produce 3H+ ions permolecule in the solution are called tribasic or triprotic acids.

H3PO

4 --------> 3H+ + PO

43-

Examples: H3PO

4, H

3AsO

4(Arsenic acid)

(iv) Tetrabasic or tetraprotic acid:Any acid which has four replaceable hydrogen atoms is called a tetrabasic acid.

H4P

2O

7(Pyrophosphoric acid) ------> 4H+ + P

2O

74-

Di, tri and tetra protic acids are commonly called polyprotic acids.

SAQ 5: Give two examples with names for each of the following(i)oxo acids of sulphur (ii)hydracid of halogen (iii)oxo acids of phosphorous

SAQ 6:Give one example of each of a strong and weak oxo acid of sulphur.SAQ 7: Among the following hydra acids which are weak.

HCl, HF, HBr, HI, CH3COOH, HCN

SAQ 8: Indicate the basicity of each of the following acidsH

2SO

4, HF, H

3PO

4, HNO

3, H

3PO

3, H

2C

2O

4, H

3PO

2, HBr

SAQ 9: Indicate which of the following are diprotic acids.HCl, H

2CO

3, H

3PO

3, CH

3COOH, H

2C

2O

4

ACID ANHYDRIDES:Oxo acids are produced when a nonmetallic oxide reacts with water. For example, whenSO

3 reacts with water, we get sulphuric acid.

SO3

+ H2O----------> H

2SO

4

Hence nonmetallic oxides are called acidic oxides and also called acid anhydrides. The acidanhydrides of the oxoacids are given in Language of Chemistry section. You may revisethem now.SAQ10: What are the acid anhydrides of the following oxoacids.

H2CO

3, HNO

3, H

3PO

4, HClO, HClO

4

Hint : Remove all H-atoms in the form of water. If required multiply by the lowest factorto do so.

BASESBases are substances which are bitter to taste. Have you tasted raw lime(chuna) whiletaking a betel? Does it not taste bitter?Bases are the oxides or hydroxides of metals. According to Arrhenius theory base is anysubstance which produces OH– ions in water. A base can react with an acid to producesalt and water. This is called neutralisation reaction. When the reaction takes place, thebitterness of the base and the sourness of the acid no more exist. The product tastes saltyand hence is called a salt. Bases are of two types.

(i)Metallic oxides (ii)Metallic hydroxides(i) Metallic Oxides: These are the oxides of metals.Examples: Na

2O, MgO, CaO, K

2O, Al

2O

3, SnO etc.

Note that some of the metallic oxides are amphoteric i.e they can react both with acids andbases to form salt and water. Al

2O

3 and SnO belong to that category. The details of amphoterism

has been discussed in chapter-I. You can revise it now.Some of the metallic oxides are soluble in water. On dissolving in water, they produce theircorresponding hydroxides(Chapter-I)

Na2O + H

2O----------> NaOH

Soluble oxides:Alkali metal oxides(Li

2O, Na

2O, K

2O etc) and three oxides of alkaline earth metals such as

Ca, Sr and Ba(CaO, SrO and BaO) are soluble in water and form their hydroxides. Othersare not. The metal hydroxide solutions are called ALKALI. NaOH and KOH solutions arecalled alkalis.

Alkalis: The soluble bases consisting of the hydroxides of metals are called alkali.How to test an alkali:

(i)It is bitter to taste(ii)It is soapy or slippery to touch.(iii)It turns red litmus blue.

SAQ 11: Indicate which oxides are basic and which are amphoteric.Na

2O, BaO, K

2O, SnO, ZnO, CaO, Al

2O

3

SAQ 12: Indicate which will form alkali solution.MgO, Na

2O, Al

2O

3, CaO, BeO, K

2O, BaO, ZnO

SAQ 13: Write the products of the following reactions and what would the resultingsolution be called.

(i) K2O + H

2O------->? (ii)MgO+H

2O------>?

(iii)BaO + H2O----->? (iv)Fe

2O

3 + H

2O----->?

(ii)Metallic hydroxides:The hydroxides of strong metals are bases while hydroxides of semimetals or metalloids areamphoteric. Say for example, NaOH is a base but Al(OH)3 is amphoteric. The hydroxidesare characterised by their number of replaceable hydroxy(OH) groups. This is called the(ii) Metallic hydroxides:The hydroxides of strong metals are bases while hydroxides of semi metals or metalloids areamphoteric. Say for example, NaOH is a base but Al(OH)

3 is amphoteric. The hydroxides

are characterised by their number of replaceable hydroxy(OH) groups. This is called theacidity of the base. The acidity of NaOH is one as it has one replaceable OH group. Theacidity of Ca(OH)

2 is two and that of Al(OH)

3 is three. Metallic hydroxides are solid

substances at room temperature.Acidity of a hydroxide base: The number of replaceable OH groups is called acidity of abase.

NaOH + HCl -----> NaCl +H2O (here one OH group of NaOH has been replaced

by Cl)Ca(OH)

2 + 2HCl -----> CaCl

2 + 2H

2O(here two OH groups of the base have been

replaced by Cl)Al(OH)

3+ 3HCl -------> AlCl

3 + 3 H

2O (here three OH groups have been replaced)

Solubility: A few hydroxides are soluble in water. These are(i)All alkali metal hydroxides such as NaOH, KOH etc. are soluble in water.(ii)Three alkaline earth metals such as Ca(OH)

2, Sr(OH)

2 and Ba(OH)

2 are soluble

in water. The rest hydroxides are insoluble.

SAQ 14: Indicate which hydroxide is soluble and which is insoluble in water.NaOH, Zn(OH)

2, Ba(OH)

2, RbOH, Mg(OH)

2, KOH, Be(OH)

2, Al(OH)

3

Types of alkali on the basis of strength:Some bases are strong because they produce large number of OH- ions when they dissolvein water. Take the case of NaOH solution. Since the solubility of NaOH is very high theconcentration of OH- is always very high. Remember that only on dissolution a base undergoesdissociation to produce free metal ion(M+) and hydroxide ion(OH-). Hence whether a baseis strong or weak depends on whether it is more soluble or less soluble respectively. Takethe case of Ca(OH)

2. The solubility of this hydroxide is very low. So the OH- concentration

is low and this is a weak base.Examples of Strong bases: LiOH, NaOH, KOH, RbOH, CsOH, Ba(OH)

2 are only regarded

as strong bases. Ba(OH)2

is the least strong and CsOH is the strongest among them. Themost commonly available strong bases are NaOH and KOH. Other than the above sixhydroxides, all metallic hydroxides are weak. The following table gives the solubility of alkaliand alkaline earth metal hydroxides: Note that solubility is measured as the number of gramsof solute dissolved per 100gm of the solvent to make a saturated solution.

Solubility of Some Metallic hydroxides:Hydroxides solubility(gm/100gm) Hydroxides solubility(gm/100gm)LiOH 12.8 Be(OH)

2Nil

NaOH 109 Mg(OH)2

0.0009KOH 112 Ca(OH)

20.156

RbOH 177 Sr(OH)2

0.8CsOH 330 Ba(OH)

28.7

Note from the above table that alkali metal hydroxides are more soluble than alkaline earthmetal hydroxides. Be(OH)

2 and Mg(OH)

2 are almost insoluble. Solubility of hydroxides

increases as we move from lower alkali metal to higher alkali metal and so also the sametrend is noticed for alkaline earth metal hydroxides. Among alkaline earth metal hydroxidesBa(OH)

2 is strongest among alkali metal hydroxides. LiOH is least strong. Alkaline earth

metal hydroxides other than Ba(OH)2 have very low solubility and are regarded as weak

bases.Note that unlike solubility of acids(all acids are completely soluble whether strong or weak),not all bases are soluble and hence the strength or weakness of a base depends on thesolubility. The part of the base which is soluble undergoes ionisation, no doubt, but theweakness results due to poor solubility. The solubility of oxides also follow the same orderas hydroxides, although the numerical values are different.SAQ 15: Indicate which are strong and which are weak bases

Al(OH)3, KOH, Ca(OH)

2, LiOH, Mg(OH)

2, Ba(OH)

2,

SAQ 16: Arrange the following in the order of increasing base strengthKOH, LiOH, NaOH, RbOH, Ba(OH)

2, Ca(OH)

2

SALTYou know that when an acid(sour) reacts with a base or alkali(bitter), we get a salt andwater. The salt is salty to taste. I am sure you have tasted the common salt(table salt). Howdoes it taste? That is the taste of all salts. The reaction of sour acid with a bitter base oralkali to produce a salt is called neutralisation reaction. Whether the base is soluble inwater(alkali) or not, it reacts with an acid to form salt and water.

NaOH + H2SO

4 -------> Na

2SO

4(salt) + H

2O

HCl + CaO -------> CaCl2(salt) + H

2O

Al2O

3 + HNO

3 -------> Al(NO

3)

3(salt) + H

2O

In the above three cases, NaOH is completely soluble, CaO is weakly soluble and Al2O

3 is

insoluble, but all of them reacted with acids to form the corresponding salt and water.SAQ 17: Indicate which salt is produced by the reaction of the following acid and base

(i)NaOH + H3PO

4(ii)FeO + H

2SO

4(iii)Al(OH)

3 + HBr

(iv)Fe(OH)3

+ H3PO

4(v)MgO + HNO

3

Types of Salt: There are two three types of salts namely(i)acidic salt (ii)basic salt (iii)basic salt

Acidic Salt:Look to the following reaction.

H2SO

4 + NaOH -------> NaHSO

4(acidic salt) + H

2O

When one mole of sulphuric acid reacts with one mole of sodium hydroxide we find that onlyone acidic hydrogen atom is replaced from H

2SO

4 to produce sodium hydrogen sulphate

or sodium bisulphate. This salt is an acidic salt because it still contains one acidic hydrogenatom and can react with one extra mole of base(NaOH) to give a normal salt.

NaHSO4 + NaOH ------> Na

2SO

4(normal salt)+ H

2O

Sodium sulphate has no more acidic hydrogen atom and is called normal salt.So any salt which contains one or more replaceable (acidic) hydrogen atoms is calledan acidic salt.Normal Salt:Any salt which does not contain any replaceable(acidic) hydrogen atom is called a normalsalt. e.g: K

3PO

4, MgSO

4 etc.

SAQ 18: Indicate which one is an acidic salt and which is a normal saltNaHCO

3, K

2SO

4, NaNO

3, Na

2HPO

4, Ca(HSO

3)

2, KHSO

4, Ca(H

2PO

4)

2, NaCl

**(i) Note that a monobasic acid always gives a normal salt.

HCl + NaOH -----> NaCl + H2O

HNO3 + NaOH------> NaNO

3 + H

2O

CH3COOH + NaOH -----> NaCH

3COO(CH

3COONa) + H

2O

All the above salts are normal salts. Note that in sodium acetate, the other 3H atoms arenot replaceable.(ii) Dibasic acids form two salts, one acidic salt and the other normal salt.We have seen the case of sulphuric acid in the above example.

H2CO

3 + NaOH ----> NaHCO

3(acidic salt) + H

2O

NaHCO3

+ NaOH -----> Na2CO

3(normal salt) +H

2O

(iii) Tribasic acids give three salts out of which two are acidic and one normal. Take thecase of phosphoric acid.

H3PO

4 + NaOH ------> NaH

2PO

4(acidic salt: sodium dihydrogen phosphate) + H

2O

NaH2PO

4 + NaOH ---> Na

2HPO

4(acidic salt: disodium hydrogen phosphate) + H

2O

Na2HPO

4 + NaOH -------> Na

3PO

4(normal salt: sodium phosphate) + H

2O

In this case you found that phosphoric acid had three replaceable hydrogen atoms whichwere replaced one after the other to give two acidic salts and one normal salt.

SAQ 19: What salt you will get if you react one mole of H2CO

3 with two moles of NaOH?

SAQ 20: What salt you get if one mole of sulphurous acid reacts with one mole of NaOH?Is it an acidic or basic salt? What happens when this salt reacts with one mole more ofNaOH?SAQ 21:Predict the product and indicate the nature of the salt

(a)NaOH(one mole) + H2S(one mole) ----->?

(b)NaOH(one mole) + H3PO

3(one mole)------>?

(c)NaOH(two mole) + H3PO

3(one mole)------->?

(d)NaOH(one mole) + H3PO

2(one mole)------?

(e)NaHSO4 + NaOH ------->?

(f)Na2HPO

4 + NaOH------->?

(g)NaH2PO

2 + NaOH------->?

SAQ 22: Indicate which one among the following are the normal salts.NaHSO

4, Na

2CO

3, NaH

2PO

3, Na

2HPO

3, NaH

2PO

2, Na

2SO

4

SAQ 23: Do Na3PO

3 and Na

2HPO

2 exist? Give reason.

SAQ 24: Predict the products and indicate the nature of the salt.(i)NaOH(two moles) + H

3PO

4(one mole)------->?

(ii)NaOH(three moles) + H3PO

4(one mole)------->?

(iii)Na2HPO

4 + NaOH ------->?

(iv)NaH2PO

4 + NaOH(one mole) ------>?

(v)NaH2PO

4 + NaOH(two moles)------>?

SAQ 25: Indicate which one is acidic salt and which normal salt. Write their formula.calcium nitrate, Aluminium chloride, Magnesium hydrogen sulphate, Potassium bicarbonate,Ferric sulphate, Sodium hypophoshite, calcium dihydrogen phsophate, Sodium dihydrogenphosphate, Potassium bromide, Magnesium bisulphite, Disodium hydrogen phosphateSAQ 26: How many salts H

4P

2O

7 will form? Write all of their sodium salts.

Basic Salt:If a base contains one replaceable OH group it will form a normal salt after reacting withone mole of an acid.

NaOH + HCl ------> NaCl + H2O

But if the base contains more than one OH groups and only one of them is replaced by onemole of an acid and other remains in the salt, such a salt will be called a basic salt. It canfurther react with one mole more of acid to produce the normal salt.

Mg(OH)2

+ HCl ------> Mg(OH)Cl(basic salt) + H2O

Mg(OH)Cl + HCl -------> MgCl2(normal salt) + H

2O

SAQ 27: What salts will be obtained in the following reactions(i)one mole of Fe(OH)

3 + one mole of HCl ------->?

(ii)One mole of Fe(OH)3 + two moles of HCl------->?

(iii)One mole of Fe(OH)3

+ three moles of HCl ------->?SAQ 28: Indicate which one of the following are acidic, normal and basic saltsK

3PO

4, Mn(OH)Br, NaHCO

3, NaH

2PO

2, K

2HPO

3, KHPO

4, Mg(NO

3)

2, NaHS, CH

3COOK

HYDROLYSIS OF SALTIt is a general belief that an acid solution is acidic, a base(or alkali) solution is basic(oralkaline) and a salt solution is neutral. More clearly speaking, an acid turns blue litmus red,an alkali turns red litmus blue while the salt which is produced by the neutralisation reactionof an acid and a base is neutral. This is not really true. A salt solution may or may not beneutral. Let us prepare three salt solutions in three different test tubes, one containing NaCl,other containing NaCN and the third containing NH

4Cl. Let us try with litmus papers. We

shall find that while NaCl solution will be neutral(no litmus paper will change colour), NaCN

solution will be alkaline(red litmus will turn blue) and NH4Cl solution will be acidic(blue litmus

will turn red). This is due to a phenomenon called hydrolysis of salt. The salt reacts withwater to a small extent(partially) and produces either excess of H+ ions or OH- ions andmakes the solution acidic or basic respectively. On the basis of nature of hydrolysis, salts areof four types.(A) Salt of strong base and weak acid:We know that the common strong bases are NaOH and KOH. Almost all other bases areweak. The strong acids are also few in number. They are H

2SO

4, HNO

3, HCl, HBr, HI,

HClO3 and HClO

4. All the remaining acids fall under weak acid category. Salt containing Na+

or K+ as basic radical and any acid radical other than SO42-, NO

3-, Cl-, Br -, I-, ClO

3- and

ClO4

- is called a salt of strong base and weak acid. In other words, they have beenprepared by the reaction of a strong base NaOH or KOH and weak acid other than H

2SO

4,

HNO3, HCl, HBr, HI, HClO

3 and HClO

4. Such a salt when dissolved in water produces basic

or alkaline solution. This is due to partial hydrolysis of the salt.Examples: NaCN, K

3PO

4, KNO

2, NaCH

3COO(CH

3COONa) etc.

NaCN(aq) + H2O(l) NaOH(aq) + HCN(aq)

strong weak

Total ionic equation: Na+ + CN- + H2O(l) Na+ + OH- + HCN

Note that NaOH is a strong electrolyte(strong base) and almost completely dissociates intoions, while HCN is a weak electrolyte(weak acid) and is almost non-ionised. So it has beenkept as such. If we cancel the spectator ions from both the sides(Na+), we get,

Net Ionic equation: CN- + H2O OH- + HCN

Due to presence of excess OH- ions as shown above, the solution becomes alkaline. Notethat salts of this type which has Na+ and K+ as basic radical and any acid radical other thanthe seven given before behave in the same way as NaCN i.e produce alkaline(basic)solution.

SAQ 29: Which of the following solutions will be alkaline to litmus.(i)KNO

2(ii)Na

2CO

3(iii)FeCl

3(iv)CuSO

4

(v)Na2SO

4

(B) Salt of strong acid and weak base:This type of salt contains basic radical other than Na+ and K+ and acid radical one ofSO

42-, NO

3-, Cl-, Br-, I-, ClO

3- and ClO

4-. In other words they have been prepared by the

reaction of a weak base i.e any base other than NaOH and KOH and strong acids, i.e oneof H

2SO

4, HNO

3, HCl, HBr, HI, HClO

3 and HClO

4. Such a salt when dissolved in water

forms an acidic solution due to partial hydrolysis.Examples: MgCl

2, CuSO

4, Zn(NO

3)

2, NH

4Cl etc.

NH4Cl(aq) + H

2O(l) NH

4OH(aq) + HCl(aq)

weak strongWhile NH

4OH is a weak base and remain mostly non-ionised, HCl is a strong acid and will

ionise almost completely to form H+ and Cl- ions. The total ionic equation would be

Total Ionic Equation: NH4

+ + Cl- + H2O NH

4OH + H+ + Cl-

Cancelling the spectator ion(Cl-), we get the net ionic equation,

Net Ionic Equation: NH4

+ + H2O NH

4OH + H+

Due to the presence of excess H+ ions, the solution behaves acidic. Salts of NH4Cl type as

given before behave in the same manner and produce acidic aqueous solution.SAQ 30: Indicate which salt will form acidic solution and why?

(i)K2CO

3(ii)Al(NO

3)

3(iii)MgBr

2(iv)Na

2SO

4

(v)FeSO4

(C) Salt of Weak acid and weak base:Salt which contains basic radical other than Na+ and K+ and acid radical other thanSO

42-, NO

3-, Cl-, Br-, I-, ClO

3- and ClO

4- fall into this category. Such salt solution is nearly

neutral because they produce nearly same quantity of H+ and OH- ions.Example: NH

4CN, Al(NO

2)

3, MgF

2, CuCN,(NH

4)CH

3COO[CH

3COONH

4] etc.

NH4CN(aq) + H

2O(l) NH

4OH(aq) + HCN(aq)

Both NH4OH and HCN are weak electrolytes and remain mostly in non-ionised state.

Total ionic equation: NH4

+ + CN- + H2O NH

4OH + HCN

weak weakSo H+ and OH- ions remain in nearly equal amounts due to their weak dissociation. Thus thesolution is nearly neutral.The salt may be slightly acidic or alkaline depending on whether theweak acid is relatively stronger or the weak base is relatively stronger.SAQ 31: Indicate which of the salt solution is nearly neutral and why?

(i)Na2SO

3(ii)NH

4F (iii)FePO

4(iv)Ca(NO

3)

2

(D) Salt of strong acid and strong base:Salt which contain either Na+ or K+ as basic radical and one of SO

42-, NO

3-, Cl-, Br-, I-, ClO

3-

and ClO4- as acid radical belongs to this category. Aqueous solution of such a salt is neutral

because it produces equal amounts of H+ and OH-.Example: NaCl, KNO

3, Na

2SO

4, KBr etc.

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

strong strongBoth the acid and base formed due to hydrolysis are strong and dissociates completely. ThusH+ and OH- concentrations remain same and the solution is neutral.

Total Ionic equation: Na+ + Cl- + H2O Na+ + OH- + H+ + Cl-

Cancelling the spectator ions, we get

Net Ionic equation: H2O H+ + OH-

SAQ 32: Indicate which one of the following shall give neutral solution.(i)K

2SO

4(ii)CuSO

4(ii)KCN (iv)NaI

(v)NH4Cl

SAQ 33: Indicate which salt will produce neutral(N), nearly neutral(NN), acidic(A) andbasic(B) solutions.

(i)NaBr (ii)MgBr2

(iii)(NH4)

2SO

4(iv)K

2SO

3(v)NH

4NO

2

(vi)CuBr2

(vii)KNO3

(viii)AlF3

(ix)Na2C

2O

4(sodium oxalate)

(x)Potassim acetate

MODERN THEORIES OF ACIDS AND BASES:Arrehenius theory of acids and bases dicussed before is a very old theory and is now outdated .Before we discuss the demerits of the Arrehenius theory, let us discuss the modern theories ofacids and bases.

(a) Bronsted-Lowry Theory(b) Lewis Theory

BRONSTED-LOWRY THEORYAcids : Any substance which can accept a H+ ion is called an acid. (PROTON DONORS)Examples: (i) All inorganic and organic acids discussed before

(ii) NH4

+ (ammonium ion) and H3O+ (hydronium ion)

Bases: Any substance which can accept a H+. (PROTON ACCEPTORS)Bronsted bases are of two types.

(i) all negative ions : e.g Cl–, OH–, SO42–, CH

3COO– , NO

3– etc.

(ii) neutral molecules in which the central atom carries a lone pair. e.g H2O,

NH3, C

2H

5OH etc. One lone pair on N and two lone pairs on O are not shown here.

ACID-BASE REACTION:The acids show their acidic properties in water by reacting with it. Hence the dissolution

of acid in water is not a physical change as suggested by Arrhenius theory rather it a chemicalchange i.e an acid-base reaction.

HCl H 2O H3O C l+ +Acid-1 Base-1 Acid-2 Base-2

In the forward reaction, HCl loses a proton and H2O accepts it hence the former is acid and

latter is base. In the backward reaction, H3O+ loses a proton and Cl– accepts it, hence the former

is the acid and latter is the base. Since HCl is a strong acid the equilibrium lies almost entirely tothe right. In other words, HCl is almost fully ionised and the reactionis virtually irreversible. Ifyou have little idea about reversible reactions and concept of equilibrium then read the chapterchemical equilibrium. Note that we commonly write H+ in stead of H

3O+.

CH3COOH H2O ++Acid-1 Base-1 Acid-2Base-2

CH3COO H3O

In this case, CH3COOH(acetic acid) is a weak acid and the equilbrium lies far to the left. In

other words the acid dissociates into ions to a small extent and most of the acid remains unionised.In both the above examples H

2O acts as base in the forward process and H

3O+ acts as an acid

in the backward process.

NH3 H2O ++Acid-1Base-1 Acid-2 Base-2

OH NH4

In this case, NH3 accepts a proton and H

2O loses it in the forward reaction, hence H

2O acts as

acid and NH3 as base. In the backward reaction, NH4+ loses a proton and OH– accepts it,

hence the former is an acid and latter a base. Note that in the earlier examples H2O acted as a

base while in the above example, it acts as an acid. Therefore water has ampoteric property.Since NH

3 is a weak base, the equilbrium lies far to the left, i.e the dissociation into ions is small.

General Acid-Base Reaction in the light of Bronsted Theory :When HCl(aq.) reacts with NaOH(aq.), we know that NaCl and H

2O are formed. But what

really happens ? H3O+ ion present in the HCl(aq.) reacts with OH– present in NaOH(aq.) to

form two water molecules.H

3O+ + OH– H

2O + H

2O

Commonly we write the net ionic equation as H+ + OH– H2O for neutralisation reaction

instead of the previous one. Note that according Bronsted theory, the base present in NaOH isOH– but according to Arrhenius theory it is NaOH which is the base.SAQ 34: (i) Can HCl solution in acetone or benzene turn blue litmus red ?

(ii) Is the dissolution of NaOH in water is a acid-base reaction like the dissolutionof HCl in water ? Explain.

(iii) In common acids like HCl(aq.), H2SO

4 (aq.)etc. which is the actual acid

that reacts with a base(other than water) like NaOH, Ca(OH)2 etc. ?

(iv) In aq. solution of NH3, which speices exist in large quantity and which in

small quantity ? From this, give your opinion about the existence of NH4OH molecule.

(v) Can NH3 show basic nature in gaseous state ? In other words, is water is

absolutely required for showing basic property ?(vi) Do all bases have to possess OH– ? Explain with examples.

SAQ 35: Indicate which one among the following is a Bronstend Base(BB), which aBronsted Acid(BA) and which is of both type(amphoteric)?

(a) OH– (b) NH4

+ (c) Cl– (d) HCl (e) H2O

(f) NH3

(g) HCO3

– (h) H3PO

4(i) H

2PO

4– (j) H

3O+

SAQ 36 : Explain the reactions : (a) NH3(aq.) + HCl(aq.) NH

4+(aq.) + Cl–(aq)

(b) CH3COOH(aq.) + NH

3(aq.) CH

3COO–(aq.) + NH

4+(aq.)

CONJUGATE ACID-BASE :Two species which differ from each other by a single H+ ion is called a conjugate acid-base pair.Example: HCl/Cl– : HCl is the acid and Cl– is its conjugate base.NH

3/NH

4+ : NH

3 is the base and NH

4+ is its conjugate base. In fact, each is the conjugate of the

other.Other examples : H

2O/H

3O+; H

2O/OH–, NH

3/NH

2–; CH

3COOH/CH

3COO–, H

2SO

4/HSO

4–

SAQ 37 : Give the conjugate bases of the following acids.(a) HSO

4– (b) H

3PO

4(c) HPO

42– (d) NH

4+ (e)H

2O

SAQ 38 : Give the cojugate acids of the following bases.(a) H

2PO

4– (b)CN– (c) HCO

3– (d) NH

2– (d) OH–

RELATIVE STRENGTH OF CONJUGATE ACID-BASE PAIR :If a certain acid is strong, then its conjugate base is weak and vice versa.Example: Acid strength : HF < HCl < HBr < HI,Conjugate base strength : F– > Cl– > Br– > I–

In other words, HF is the weakest acid and HI is the strongest acid. Therefore F– is the strongestbase while I– is the weakest base. Note that this concept is applicable in a relative basis for thesake of comparison. The acid or base may or may not be really strong or weak according to theactual meaning of strong or weak acids.SAQ 39 : If the acid strength order of four acids is HCl > CH

3COOH > H

2CO

3 > HCN, then

what is the base strength order.SAQ 40: (a) Why CO

2 produces H+ when dissolved in water ?

(b) Why Cl–, NO3

-, HSO4

- are weak bases ?

DEMERITS OF ARRHENIUS THEORY OF ACIDS AND BASES:(a) A substace can act as an acid even in the absence of water and a base can react with an acideven without producing OH–.(b) Free H+ ion does not really exist aq. solution of acids. It exists as H

3O+.

(c) NH4OH molecule is a misnomer.

(d) According to Arrehenius theory, acid reacts with base to form a neutral salt. Actually saltsolution can be acidic or basic due to hydrolysis.DISSOCIATION CONSTANTS OF ACIDS AND BASES:Acid Disscociation:You know that strong acids like HCl, H

2SO

4 are almost fully dissociated into ions while weak

acids like HF, HCN are ionised to a small extent. The extent of dissociation is expressed by thedissociation constant(K

A). For simplification, H

2O is deleted from LHS and H+ is written in stead

of H3O+.

HA H+ A

-+

K = H

+A

-

HAA

Where KA is the dissociation constant of the acid. The molarities of H+ and A– ion multiplied in

the numerator while the molarity of undissociated HA is in the denominator.Already it has been told that essentially all reactions reversible but practically many are irreversible.If HA is HCl/HBr/HI, it is irreversible and almost negligible undissociated HA(LHS) remains atequilbrium. Hence in such cases, K

A is very large. In fact if K

A of a acid is above 10, it is

regarded as strong acid. Often this value is more than 105 for strong acids. But if the acid isweak like HF or HCN, then the numerator values are small while the denominator value is large.Hence K

A is very small. For example the K

A for HCN is 4.8 X 10–8. From such a small value you

can well imagine how small would be the concentration of H+ ion in solution.

Base Dissociation:A Bronsted base produces OH– by reacting with water.

+NH3 H2O NH4+ OH

-+

For LHS, we commonly write NH4OH in stead of NH

3 + H

2O. The base dissciation constant,

KB is written as follows.

K = OH

-NH4

+

NH4OHB = 1.8 X 10–5

Since NH3(NH

4OH) is a weak base, the base dissociation constant is too small. You can well

imagine how small is the concentration of OH– .IMPORTANT : OH–, NH

2– and H– are strong bases and the rest of bases are weak. K

B value

of OH– is not written as the cause of basicity of a base is the presence of OH–. Weak baseshave low K

B values while strong bases have high KB values.

SAQ 41 : Give the dissociation equation for CN– in water and write the expression of KB.

SAQ 42 : Indicate which one is strong and which one weak acid or base according to Bronstedtheory.

NH3, OH–, H

2O, Cl–, NH

2–, H

2SO

4, HCl

SAQ 43 : Give the acid dissociation equation for H2SO

4 and write the expression of K

A.

IONIC PRODUCT OF WATER:(KW

)From the previous discussion we knew that H

2O acts both as an acid as well as a base. Hence

reaction between two H2O molecule does occur and that is call the dissocation of water.

H2O H2O H3O+ OH

-++ , Deleting one H

2O from LHS and writing H+

for H3O+, the simple equation for ionic dissociation of water is

+H2O H+ OH

-K = [H+] X [OH-] W

KW

is called the ionic product of water which is constant at a given temperature. Note thatmolarity of H

2O has been deleted from the denominator as it is constant.

KW

= 10–14 (250C)At room temperature, the product of the molarities of H+ and OH– is constant and is so low.From this value, you can well imagine to what small extent water is dissociated into ions. Notethat whether the solution is pure water, or a neutral solution or acid or basic solution, this productis constant. If one increases the other has to decrease.PURE WATER OR NEUTRAL SOLUTION:

In this case, [H+] = [OH–]. So [H+]2 = 10–14; [H+] = [OH–] = 10–7 mol/L(M)In other words, in one litre pure water or a neutral solution, only 10–7 mole of H+ and 10–7 moleof OH– are present.ACIDIC SOLUTION:

If the solution is acidic then [H+] > 10–7 and hence [OH–] < 10–7 ⇒ [H+] > [OH–]Note that the product of two concentration is 10–14.Example: If a certain acid has [H+] = 10–4M, then what is its [OH–] ?Answer : 10–14/10–4 = 10–10

BASIC SOLUTION :If the solution is basic or alkaline then [OH–] > 10–7, hence [H+] < 10–7. [H+] < [OH–]

Example : A certain base has [OH–] = 10–3M, what is its [H+] ?Answer : [H+] = 10–14/10–3 = 10–11

pH SCALE :From the above discuss we knew that every solution, be it acidic, basic or neutral, has [H+] aswell as [OH–]. In stead of expressing hydrogen and hydroxyl concentrations for very dilutesolutions as a -ve power of 10, it can be expressed by a simple numerical like 3, 4, 5.6 etc. P.LSorrensen introduced the pH scale.

pH = – log10

[ H+]pOH = – log

10[OH–]

pH + pOH = 14pH is also called as HYDROGEN ION INDEX. Usually pH of all solutions are measured. pOHis not used much, althouh if we know pH of a solution, its pOH is immediately known.NEUTRAL SOLUTION OR PURE WATER:

pH = pOH = – log 10–7 = 7ACIDIC SOLUTION:

pH <7 while pOH > 7BASIC SOLUTION:

pH > 7 while pOH < 7(Note that the reader should have a knowledge of logarithm before studying pH)

pH OF STRONG ACIDS AND BASES:Strong acids and bases are believed to be nearly 100% dissociated into ions. Hence we canpresume that the acid or base concentration is same as H+ or OH– concentration respectively.

[HCl] = [H+] [NaOH] = [OH–]Example : Find the pH of (i) a 0.001M HCl solution (ii) a 10-5M NaOH solutionAnswer : (i) [H+] = 0.001 mole/L = 10–3; pH = –log 10–3 = 3

(ii) [OH–] = 10–5; We know that [H+] X [OH–]= 10–14;hence [H+]= 10–14/10–5 = 10–9; pH = –log10–9 = 9

Alternatively : pOH = –log10–5 = 5; Hence pH = 14 – 5 = 9SAQ 44: What is relationship between pH and H+ ion concentrationSAQ 45 : Find the [OH–] and pH of the following acids.

(a) 0.003M HNO3

(b) 0.04M H2SO

4

SAQ 46 : Find the [H+] and pH of the following bases.(a) 0.0002M KOH (b) 0.04M Ba(OH)

2

pH of Weak Acids and Bases:Weak acids like HF, HCN etc and weak bases like NH4OH are weakly ionised. So we cannotdetermine the pH of such solutions as we had done for strong acids and bases. We have to findout the actual [H+] or [OH–] of the solution by the help of K

A or K

B then find their pH.

Weak Acids:

HX H+ X

-+

A HA

A-H

+

K = =[H

+]

2

HA ⇒ H+ K [HA]= A

Note that here we have made an assumption that concentration of HA at equilibrium is same asthe initial HA concentration. This is justified becaue the degree of dissocation is very small insuch substances at moderate concentrations. But if the solution is diluted, the degree of dissociationis appreciably large and HA concentration at equilbrium wll be less than the initial HAconcentration. Hence the above method will fail to determine the correct [H+}. We stop furtherdiscussion on this topic and keep it pending for higher study. Same method will be used todetermine OH– concentration of a weak base like NH

4OH.

SAQ 47 : Determine the pH of (i) 0.1M CH3COOH having K

A = 1.8 X 10–5)

Relative Acid Strength for Weak Acids:From the K

A values, the decreasing acid strength of a few weak acids is given below. At a fixed

concentration of acid, the [H+] remain in the decreasing order in this case.

H2SO

3 > H

3PO

4 > HF > HNO

2 > CH

3COOH > H

2CO

3 > H

2S > HCN > H

2O

Determination of pH by pH Paper:The approximate pH of various solutions can be determined by using pH paper. pH paper tinybooklets are availale in chemical stores. The cover page of this booklet gives different colourswith the corresponding pH range. A pH paper is plucked out of the booklet and dipped into asolution. A certain colour develops on the paper. The paper is then dried and colour developedon it is compared with the colour given in the cover page of the booklet to determine theapproximate pH range such as 0–2, 2–4, 8 –10 etc.

Preparation of pH Paper : Red cabbage or red onion or red hibiscus flower is cut into smallpieces and then boiled in water for a long time till the aq. solution gets a deep violet color or bloodred colour. Then the solution is filtered to reject the residue. Small pieces of filterpapers areimpregnated with this coloured solution, then heated and dried. Now the pH paper is ready foruse. It contains a dye named as flavin which gives various colours at different [H+] hence pH. Inacid solutions, the pH paper gives red colours while in basic solution it gives various types of bluecolour. pH range of some common solutions are given below.

Solution pH Solution pHHCl(10M) 1 Tea 5.5Lead Storage Battery 0.5 Skin of healthy man 5.5Gastric juice 1.5–2 Milk 6.5Lemon juice 2.4 Pure Water 7.0Cola(Coca cola/pepsi) 2.5 Saliva of healthy man 6.5–7.4Vinegar 2.9 Blood 7.34–7.45Orange/Apple juice 3.5 Soap(bath) 9-10Beer 4.5 Household ammonia 11.5Acid rain <5 Caustic soda 13.9Human urine 4.5–8Coffee 5

RESPONSE to SAQsSAQ 1:(i)FALSE: All acids are soluble in water.

(ii)FALSE: When an acid dissolved in water partial(for weak acid) or nearlycomplete(for strong acids) dissociation occurs.

(iii)TRUESAQ 2: H

2SO

4: Strong; H

2CO

3: Weak; HNO

2: Weak; HNO

3: Strong;

HOCl: Weak; H3PO

4: Weak; H

2SO

3: Weak.

SAQ 3: (i)Strong (ii)diluted strong (iii)weak(iv)concentrated weak (v)concentrated strong (vi)diluted weakSAQ 4: All of them are soluble in water.SAQ 5: (i) H

2SO

4(sulphuric acid) H

2SO

3(sulphurous acid)

(ii)HCl(hydrochloric acid), HBr (hydrobromic acid)(iii)H

3PO

4(phosphoric acid), H

3PO

3(phosphorous acid)

SAQ 6: Strong: H2SO

4(sulphuric acid); Weak: H

2SO

3(sulphurous acid)

SAQ 7: Weak: HF, HCN (Note that CH3COOH although is weak acid is an oxoacid)

SAQ 8: H2SO

4: 2, HF:1, H

3PO

4:3, HNO

3:1, H

3PO

3: 2, H

2C

2O

4:2, H

3PO

2:1, HBr:1

SAQ 9: H2CO

3, H

3PO

3, H

2C

2O

4

SAQ 10: CO2, N

2O

5, P

2O

5(P

4O

10), Cl

2O, Cl

2O

7

SAQ 11: Basic: Na2O, BaO, K

2O, CaO Amphoteric: SnO, ZnO, Al

2O

3

SAQ 12: Alkali: Na2O, CaO, K

2O, BaO (Other oxides are not soluble in water)

SAQ 13: (i)KOH (ii)Not soluble(no reaction) (iii)Ba(OH)2

( i v ) N o tsoluble

(i) and (iii) solutions are called alkalis as these are soluble hydroxides.SAQ 14: Soluble: NaOH, Ba(OH)

2, KOH, RbOH,

Insoluble: Zn(OH)2, Mg(OH)

2, Be(OH)

2, Al(OH)

3

SAQ 15: Strong: KOH, LiOH, Ba(OH)2, Weak: Al(OH)

3, , Ca(OH)

2, , Mg(OH)

2,

SAQ 16: Ca(OH)2<Ba(OH)

2<LiOH<NaOH<KOH<RbOH (Refer solubility table)

SAQ 17: (i)Na3PO

4(ii)FeSO

4(iii)AlBr

3(iv)FePO

4

(v)Mg(NO3)

2

SAQ 18: Normal: K2SO

4, NaNO

3, NaCl

Acidic salt: NaHCO3, Na

2HPO

4, Ca(HSO

3)

2, KHSO

4, Ca(H

2PO

4)

2

SAQ 19: H2CO

3 + 2NaOH --------> Na

2CO

3(normal salt) +2H

2O

SAQ 20: H2SO

3 + NaOH ---------> NaHSO

3(sodium bisulphite) + H

2O

It is an acidic salt. It forms narmal salt when it reacts with one mole of NaOHNaHSO

3 + NaOH -------> Na

2SO

3(normal) + H

2O

SAQ 21: Predict the product and indicate the nature of the salt(a)NaHS(acidic salt) (b)NaH

2PO

3(acidic salt)

(c)Na2HPO

3(normal salt as H

3PO

3 is dibasic)

(d)NaH2PO

2(normal salt as H

3PO

2 is monobasic)

(e)Na2SO

4(normal) + H

2O (f)Na

3PO

4(normal)+ H

2O

(g)No reaction: as it is a normal saltSAQ 22: Na

2CO

3, Na

2HPO

3, NaH

2PO

2, Na

2SO

4

SAQ 23: No, Na3PO

3 and Na

2HPO

2 do not exist? H

3PO

3 is a dibasic acid and maximum

two H atoms can be replaced while H3PO

2 is a monobasic acid and maximum one H atom

can be replaced.SAQ 24: (i)Na

2HPO

4(acid salt) (ii)Na

3PO

4(normal) (iii)Na

3PO

4(normal)

(iv)Na2HPO

4(acid salt) (v)Na

3PO

4(narmal)

SAQ 25: Ca(NO3)

2: normal; AlCl

3: normal; Mg(HSO

4)

2:acidic; KHCO

3:acid;

Fe2(SO

4)

3:normal; NaH

2PO

2:normal, Ca(H

2PO

4)

2: acidic; NaH

2PO

4:acidic;

KBr:normal; Mg(HSO3)

2:acidic; Na

2HPO

4:acidic.

SAQ 26: Four salts can be formed from H4P

2O

7. They are Na

3HP

2O

7, Na

2H

2P

2O

7, NaH

3P

2O

7

and Na4P

2O

7..

SAQ 27: (i) Fe(OH)2Cl (basic salt), (ii)Fe(OH)Cl

2(basic salt)

(iii)FeCl3(normal salt)

SAQ 28: acidic: NaHCO3, KHPO

4, NaHS, normal: K

3PO

4, NaH

2PO

2, K

2HPO

3,

Mg(NO3)

2, CH

3COOK; basic: Mn(OH)Br

SAQ 29: (i)KNO2(salt of strong base KOH and weak acid, HNO

2)

(ii)Na2CO

3(salt of strong base NaOH and weak acid, H

2CO

3)

SAQ 30: (ii)Al(NO3)

2: It is salt of weak base Al(OH)

3 and strong acid HNO

3

(iii)MgBr2: It is a salt of weak base Mg(OH)

2 and strong acid HBr

(v)FeSO4: It is a salt of weak base Fe(OH)

2 and strong acid H

2SO

4.

SAQ 31:` (ii)NH4F: It is a salt of weak base NH

4OH and weak acid HF

(iii)FePO4: it is a salt of weak base Fe(OH)

3 and weak acid H

3PO

4

SAQ 32: (i)K2SO

4: It is a salt of strong base KOH and strong acid H

2SO

4

(iv)NaI: It is a salt of strong base NaOH and strong acid HISAQ 33: (i)N(salt of strong base NaOH and strong acid HBr)

(ii)A:salt of weak base Mg(OH)2 and strong acid HBr

(iii)A: salt of weak base NH4OH and strong acid H

2SO

4

(iv)B: salt of strong base KOH and weak acid H2SO

3

(v)NN: salt of weak base NH4OH and weak acid HNO

2

(vi)A: salt of weak base Cu(OH)2 and strong acid HBr

(vii)N: salt of strong base KOH and strong acid HNO3

(viii)NN: salt of weak base Al(OH)3 and weak acid HF

(ix)B:salt of strong base NaOH and weak acid, H2C

2O

4(oxalic acid),

(x)KCH3COO(CH

3COOK): B: salt of strong base KOH and weak acid,

CH3COOH(acetic acid).

SAQ 34: (i)No, HCl can not donate H+ ion to acetone or benzene, hence its acid property is notshown.(ii)No, it is not a chemical process. It is a physical change i.e separation into hydrated ions.

NaOH(s) + aq. Na+(aq.) + OH–(aq.)(iii) The actual acid in such case H

3O+.

(iv) Undissociated NH3 molecules exist in large quantity while NH4+ and OH– exist in small

quanitities. Hence there is no existence of NH4OH molecule which we often write as a matterof practice for NH

3+H

2O

(v) Yes, NH3 gas reacts with HCl gas in the vapour state to form dense white fumes of NH

4Cl.

No water is required for this reaction. Proton transfer occurs in the vapour state too. Accordingto Arrhenius theory, NH

3 is a base only in aq. solution, which is not true. Water is not always

required for a base to show its properties.(vi) Common bases like NaOH, Ca(OH)

2 etc. produce free OH– in aq. solution. But a base can

directly react with an acid without producing OH– like the example of NH3 given in the previous

question.SAQ 35 : (a) BB (b) BA (c) BB (d) BA (e) BB/BB(both)

(f) BB/BB(both) (g) BB/BB(both) (h) BA(i) BB/BB(both) (j) H

3O+

SAQ 36 : (a) NH3(aq.) produces small quantity of OH– in water and HCl produces large amount

of H3O+ in water. These two ions react with each other to form two H

2O molecules. Thus the

equilbrium for the NH3 reaction with H

2O giving OH– is driven more and more to the right till the

reaction is complete.(b) Similar to the above reaction.SAQ 37 : (a) SO

42– (b) H

2PO

4– (c) PO

43– (d) NH

3(e) OH–

SAQ 38 :(a) H3PO

4(b) HCN (c) H

2CO

3(d) NH

3(d) H

2O

SAQ 39 : Cl– < CH3COO– < HCO

3– < CN–

SAQ 40 :(a) CO2 forms carbonic acid(H

2CO

3) when dissolved in water. This acid dissociates to

from H+ and HCO3

–.(b) Because HCl, HNO

3 and H

2SO

4 are strong acids.

SAQ 41 :

+CN- H2O HCN OH-+ K = OH

-

B

HCN

CN-

Note that the molarity of H2O is not written as it is a constant quantity.

SAQ 42 Strong acids : H2SO

4 and HCl Weak acids : NH

3, H

2O

Weak bases : NH3, H

2O, Cl– Strong bases : OH–, NH

2–

SAQ 43: + +H2SO4 H2O HSO4- H3O

+ K = H

+

A

HSO4-

H2SO4

SAQ 44 : Less the pH more is the acid strength i.e more is the H+ ion concentration. More thepH more is the base stregnth i.e more is the OH– concentration. For example, an acid havingpH=3 has [H+] = 10–3 has more H+ concentration than another acid having pH = 4 i.e [H+]=

10–4. Similarly a base having pH = 11 has [H+] = 10–11 and [OH–] = 10–3 has more OH–

concentration than another base having pH = 10 i.e [OH–] = 10–4.SAQ 45 : (a) [H+] = 3 X 10–3; pH = – log (3 X 10-3} = -log3 + 3 = –0.477 + 3 = 2.523

[OH–] = 10–14/(3X10–3) = 3.33 X 10–12 M(b) [H+] = 2 [H

2SO

4} = 2 X 0.04 = 0.08; pH = -log(8X10–2) = –log23 +2 = –

3log2 +2 = -3 X 0.301 + 2 = 1.097 (because one H2SO

4 molecule produces 2 H+ ions)

[OH–] = 10–14/(8X10-2) = 1.25 X 10–13MSAQ 46 : (a) [OH–] = 2 X 10–4; pOH = -log(2X10–4) = -0.301+4 = 3.699

Hence pH = 14 – 3.699 = 10.301[H+] = 10–14/(2X10–4) = 5 X 10–11M You can get pH from [H+] as usual also.

(b) [OH–] = 2 X 0.04 = 0.08M. Then find pOH as usual and then pH bysubstracting the pOH from 14. Or else first find [H + ] and then find pH.

SAQ 47 : H+ K [HA]= A = 1.8 X 10-5 X 0.1 = 1.34 X 10-3

pH = -log(1.34 X 10–3) = - log 1.34 +3 = – 0.127 + 3 = 2.873(Note that had the acid been HCl, then the pH would have been –log 10–1 = 1. In this case thepH is geater because [H+] is lower.