7 Acids and Bases

WAJA F4 Chemistry 2009

Chapter 7: Acids and Bases

CHAPTER 7: ACIDS AND BASES A

ACIDS AND BASES Learning Outcomes You should be able to: State the meaning of acid, base and alkali State uses of acids, bases and alkalis in daily life Explain the role of water of water in the formation of of hydrogen ions to show the properties of acids • • •

•

•

Explain the role of water in the formation of hydroxide ions to show the properties of alkalis Describe chemical properties of acids and alkalis

Activity 1 Meaning of acid ,base ,base and alkali alkali Fill in the blanks with the correct words: 1

An aci acid d is a chemic chemical al subs substan tance ce whic which h ioni ionises ses in…… in…………… …………. …. to produ produce ce ………….ions. The hydrogen ion combines with a water molecule, H 2O to form a ……………………….. ………………………..

2

ion, H3O+. Acid Acid can can be classi classifie fied d as as a……… a……………… ……………… ……….ac .acid id or a ………… ………………… ……….ac .acid id based based

3 4

on its basicity. Basici Basicity ty is the the numb number er of of ionisa ionisabl ble e ……………… …………………. …. atoms atoms per per molec molecule ule of of an acid acid.. A base base is is a sub substa stance nce that that react reacts s with with an an acid acid to to form form a ………….. ………….... and and water water onl only. y. Bases include metal hydroxides and metal oxides which dissolve in water which are

5

known as…………….. Give Give the the names names of fou fourr commo common n acids acids and write write out out thei theirr formu formulae lae and basic basicity ity:: Name of acid Formula of acid Basicity (i) (ii) (iii) (iv)

6

Compl mplete the the equ equa atio tions be below :

a)

HCl (aq)

b)

……… (aq)

c)

H2SO4 (aq)

d)

CH3COOH (aq)

→ → →

. . .…….(aq)

+

Cl-

H+ (aq)

+

NO3 - (aq)

+

………..

……. …… ………….

+

(aq)

CH3COO- (aq)

(Refer to page page 117 117 -118 - F4 Chemistry Chemistry textbook) textbook)

Activity 2 : Fill in the blanks with the correct words: 1

An alka alkalili is a water water-so -solub luble le base base which which ionis ionises es in in water water to prod produce uce……… ………..… ..………. ……..,O .,OH H-

1



2

Give Give the the names names of two two commo common n alkal alkalis is and and writ write e out out their their for formul mulae ae.. Name of alkali Formula of alkali (i) (ii)

3

Compl mplete the the equ equa atio tions be below :

NaOH (aq) ……… (aq) 4

→ +

…….(aq)

+

OH-

NH4+ (aq)

H2O (l)

(aq)

+

…………. (aq)

Uses of aci acid ds, bases ases and alk alkal aliis (a) To use as …………………. …………………. … reagent Example: sodium hydroxide solution, sulphuric acid, hydrochloric acid (b) To manufacture and preserve …………… Example: Ethanoic acid (vinegar), benzoic acid (c)To make various ……………….. Example: Magnesium oxide  antacid medicine, Ascorbic acid (d)To produce …………., detergent and ……………… Example: sodium hydroxide





vitamin C

to make soap and detergent

Magnesium hydroxide  added to tooth-paste (e)To manufacture manufacture dyes,……………………. dyes,……………………. and drugs drugs Example: methylamine (f)Used in rocket fuel Example:………………………………………………………………………………………… (Refer to page page 118 118 - F4 Chemistry Chemistry textbook) textbook)

Activity 3: Role of water and its properties of acids / alkalis Fill in the blanks with the correct words. 1

An acid acid only only shows shows its its …………..…… …………..…… propertie properties s when when dissolv dissolve e in ……………… ………………………. ……….

2 3

In the presence presence of water, water, the the acid acid ionises ionises to form form ………………… …………………………… ………………….. ………..ions ions . + Without Without water, water, an acid acid still still exists exists as………… as…………………a ………and nd there there are are no H ions present.

4

Comp Comple lete te the the foll follow owin ing g tabl table. e. Conditi ition of eth ethano anoic acid cid

Effe ffect on the the blue litmu itmus s paper

Inference

Glacial ethanoic acid, CH3COOH Ethanoic acid , CH3COOH in water Ethanoic acid , CH3COOH in dry propanone, CH3COCH3 5 6

An alkali alkali only only shows shows its …………… ……………….. ….. proper properties ties when when dissol dissolve ve in ……………… ……………………… ……….. .. In the presen presence ce of water water,, the base base dissocia dissociates tes to produce produce ……………… …………………… ………… ……... ... ions

2


7


that are responsible for the ………………… properties Comp Comple lete te the the tab table le belo below. w. Condition of ammonia Effect on the red litmus paper Dry

Inference

Aqueous (dissolved in water) Dissolved in propanone

(Refer to page 118 -119 F4 Chemistry textbook and page 84 – 86 F4 Chemistry Practical Prac tical Book )

Activity 4: Properties of acids and alkalis Place a tick in the box next to each of the following statements statements to indicate which are True and which are False. Statement True False 1. All All acid acids s are are dang danger erou ous s 2. All All alka alkalilis s are are danger dangerou ous s 3. Acid Acids s tast taste e swe sweet et 4. Alka Alkali lis s tas taste te bitt bitter er 5. Acid Acids s tas taste te sour sour 6. Most Most aci acids ds can can burn burn skin skin 7. Alka Alkali lis s feel feel soap soapy y

8. Acids produce H+ ions in solution 9. Acids produce OH- ions in solution 10. Acids Acids can corrode corrode 11. Acids have have a pH above 7 12. Acids have have a pH below 7 13. Alkalis turn moist moist red red litmus paper blue 14. Acids turn moist red litmus paper blue Activity 5 : Chemical properties of acids 1 Acids Acids react react with with bases bases to form form salt salts s and wate waterr only. only.

Write an equation for the reaction between sulphuric sulphuric acid and copper(II) oxide. ……………………………………………………………………………………………………...

3


2


Acids Acids react react with reactive reactive metal metals s to produce produce salts salts and hydrogen hydrogen gas. gas.

Write an equation for the reaction between hydrochloric acid and zinc .

3

……………………………………………………………………………………………………... Acids Acids react react with carbon carbonates ates to produ produce ce salts, salts, water water and carbo carbon n dioxide dioxide gas. gas.

Write an equation for the reaction between nitric acid and calcium carbonate. ……………………………………………………………………………………………………... (Refer to page 119 - F4 Chemistry Chemistry textbook and page page 87 – 90 - F4 Chemistry Practical Book Book )

Activity 6 : Chemical properties of alkalis 1

Alkal Alkalis is react react with with acids acids to form form sal salts ts and and water water only only

Write an equation for the reaction between sodium hydroxide and benzoic acid.

2

……………………………………………………………………………………………………... When When a mixture mixture of an alkali alkali and an an ammoniu ammonium m salt is heated, heated, ammoni ammonia a gas is liberate liberated. d.

4



Write an equation for the reaction sodium hydroxide and ammonium chloride .

3

……………………………………………………………………………………………………... Alkalis Alkalis react react with most most metal ion ion solutio solutions ns to produce produce the insol insoluble uble metal metal hydroxi hydroxides des (precipitation (precipitation reaction)

Write an equation for the reaction between sodium hydroxide and iron(II) sulphate. ……………………………………………………………………………………………………... (Refer to page 120 120 - F4 Chemistry textbook textbook and page page 91- F4 Chemistry Chemistry Practical Book Book )

B: The strength of acids and alkalis Learning Outcomes: You should be able to: State the use of a pH scale Relate pH value with acidic or alkaline properties of a substance Relate concentration of hydrogen ions with pH value Relate concentration of hydroxide ions with pH value Relate strong or weak acid with degree of dissociation Conceptualise qualitatively strong and weak acids • • • • • •

•

Conceptualise qualitatively strong and weak alkalis

Activity 7: The pH scale Fill in the blanks with the correct words 1 2

3

The pH pH scale scale 0 to 14 14 , is is used used to indic indicate ate the the degree degree of …………… ……………… … or ……………. ……………. of a solution. pH value value less than 7 , indicates indicates an……………… an………………………… …………solu solution tion pH value equal to 7 , indicates a…………………………solution pH value more than 7 , indicates an…………………………solution pH value value can be determ determine ined d by using……… using…………..,pH …..,pH paper paper or………… or…………………i ………indi ndicator cator.. Acids Neutral Alkalis

5


4

0

1

2

3


4

5

6

7

8

Very……………….

9

10

11 11

12 12

13 13

14

Very…………….

(Refer to page 121 – Chemistry text book)

Activity 8 : Strong and weak acid 1. Complete the flowchart below.

Strong acid

Weak acid

Degree of dissociation

Ionization in water

Concentration of ions

pH value

Examples 2

Write Write the equati equation on for for the the ionis ionisati ation on of of the the follo followin wing g subst substan ances ces in wate waterr :

(a)

nitric acid

(b)

…………………………………………………………………………………………………….. sulphuric acid

(c)

…………………………………………………………………………………………………….. hydrochoric acid

(d)

……………………………………………………………………………………………………. ethanoic ac acid ……………………………………………………………………………………………………..

Activity 9: Strong and weak alkali 1. Complete the flowchart below.

Strong alkali

Weak alkali

Degree of dissociation

6



Ionization in water

Concentration Concentration of ions

pH value

Examples

2 (a)

Write Write the equati equation on for the ionis ionisati ation on of of the the follo followin wing g subta subtance nces s in in wate waterr : sodium hydroxide

(b) (b)

…………………………………………………………………………………………………….. pota otassi ssium hydr hydro oxid xide

(c)

…………………………………………………………………………………………………….. ammonia …………………………………………………………………………………………………….

(Refer to page page 122 122 - F4 Chemistry Chemistry textbook textbook )

CONCENTRATIONS OF ACIDS AND ALKALIS

C:

Learning Outcomes You should be able to: State the meaning of concentration State the meaning of molarity State the relationship between the number of moles with molarity and volume of a solution Describe the methods for preparing standard solutions Describe the preparation of a solution with a specified concentration using dilution method Relate pH values with the the molarity of acids acids and alkalis alkalis Solve numerical involving molarity of acids and alkalis • • • • • • •

Activity 10 : Concentration of acids and alkalis Fill in the blanks with the correct answers. 1

The The …………… ………………… ………… ………… …….. of a soluti solution on refe refers rs to the quan quanti tity ty of solut solute e in 1dm3 of solution can be defined in two ways :-

(a )

Concentration (g dm -3 )

(b

Conc Concen entr trat atio ion n (mol (mol dm-3) also known known as molarity or or molar molar concentration concentration (M)

=

7



) = 2

The two units units of of concen concentra tratio tion n can can be inte inter-c r-conv onvert erted: ed:

X Molar mass Concentration (………..)

……………... (mol dm-3) ÷ Molar mass

Work this out. 3 5.0 g of of coppe copper(II r(II)) sulp sulphat hate e is is disso dissolve lved d in water water to to form form 500 500 cm3 solution. Calculate the concentration of copper(II) sulphate solution in g dm -3 ?

Answer: 10.0 g dm -3] [ Answer:

4

What is the the mass mass of of sodium sodium carbona carbonate te requir required ed to to dissolve dissolve in water water to prepa prepare re 200 200 cm cm3 solution that contains 50 g dm-3 ?

[ Answer: Answer: 10 g ] (Refer to page page 123 -124 - F4 Chemistry Chemistry textbook textbook )

5

4.0 4.0 g of sod sodiu ium m carb carbon onat ate e powd powder er,, Na2CO3 , is dissolved in water and made up to 250 3 cm . What is the molarity of the sodium carbonate solution? solution? [Relative atomic mass: C, 12; O, 16; Na, 23]

[ Answer: 0.15 mol dm mol dm-3 ] Activity 11 The number of moles of solute in a given volume of solution can be calculated using: n = MV n = Numb umber of mol moles of solu olute M = Molarity of solution (mol dm-3) V = Volume of solution (dm3) If the volume in in cm 3 – convert the volume of solution from cm3 to dm3 n = MV 1000

n = M x

or

V 1000

8


5


Calcu Calculat late e the the numb number er of of mole moles s of ammon ammonia ia in in 150 150 cm3 of 2 mol dm-3 aqueous ammonia.

Answer: 0.3 mol ] [ Answer:

6

A stu stude den nt pi pipett pette ed 20 20.0 cm3 of potassium hydroxide , KOH solution into a conical flask. The concentration of the alkali was 1.5 mol dm -3 . Calculate the number of moles of potassium , KOH in the flask.

Answer: [ Answer: 0.03 mol dm-3]

7

Calc Calcul ulat ate e the numb number er of mole moles s of hydro hydroge gen n ions ions prese present nt in 200 200 cm 3 of 0.5 mol dm -3 sulphuric acid.

[ Answer: Answer: 0.2 mol of H + ions] ions]

Activity 12 : Standard solutions –weighing method 1

What What is is a sta stand ndar ard d sol solut utio ion? n? ……………………………………………………………………………………………………

2

Prepa Preparat ration ion of of standa standard rd solu solutio tions ns can can be carr carrie ied d out out by :Weighing method (mass of of solute) n = mass

Calculate the mass of solute needed mass =

n

=

X

MV 1000

molar mass

molar mass X

molar mass

n = MV 1000

Examples Exam ples:: To prepare prep are 100 cm3 of 2.0 mol dm-3 sodium hydroxide solution Calculate the mass of NaOH needed. [Relative atomic mass: Na, Na, 23 ; O, 16 ; H, 1] mass

=

n

X

molar mass

=

MV X molar mass 1000 = 2.0 X 100 X 40 [23 + 16 + 1]

9



= 3

1000 8g

Try this: this: To prepare 250 cm3 of 1.0 mol dm-3 sodium carbonate solution. Calculate the mass of Na2CO3 needed. [Relative atomic mass: Na, Na, 23 ; O, 16 ; C, 12]

[Answer : 26.50g]

4

-3

0.25 mol dm solution of sodium hydroxide was prepared by dissolving x g x g of sodium 3 hydroxide in 750 cm of water. What is the value of x ? x ? [Relative atomic mass: Na, Na, 23 ; O, 16 ; H, 1]

[Answer : 7.5 g]


5

Match the descripti descriptions ons / procedure procedures s with the correct correct diagram diagram below. below. Wash and rinse the weighing bottle ,smal ,smalll beak beaker er and and filt filter er funn funnel el to ensure ensure no solute solute remains remains in any of the apparatus used. Transfer the dissolved solute into a suitable volumetric flask. Add water slowly by using a dropper to bring the level of the solution to the calibration mark. The volumetric flask is closed tightly and inverted several times to get a uniform or homogenous solution. •

•

•

•

• •

•

Calculate the mass of solute needed. Weigh out the exact mass of solute needed in a weighing bottle. Disso ssolved ved the the sol solute ute in a small all amount of distilled water.

10


•

•


Add Add more more wate waterr care carefu full lly y to the the volumetric flask and swirl gently. Sha Shake well to ens ensure ure tho thoroug rough h mixing.

Activity 13 : Standard solutions – dilution method 1 Dilution method Calculate the volume of stock solution required by using the equation:M1V1 = M2V2 M1 V1 M2 V2

= molarity of solution before dilution = volume of solution before dilution = molarity molarity of solution after dilution dilution = volume of solution after dilution

When using the equation M1V1 = M2V2 , make sure that both V 1 and V2 are of the same unit.

Example: 50 cm3 of 0.1 mol dm-3 sodium hydroxide, NaOH solution from 2.0 mol dm -3 sodium hydroxide,NaOH solution Before dilution After dilution M1 V1 M2 V2 -3 -3 2.0 mol dm ? 0.1 mol dm 50 cm3 2.0 x V1 = V1 =

2

0.1 x 50 0.1 x 50 2.0 = 2.5 cm3 Try this: this: 100 cm3 of 0.5 mol dm-3 potassium manganate(VII) ,KMnO4 solution from 1.0 1. 0 mol mo l dm -3 potassium manganate(VII) ,KMnO4 solution.

[ Answer Answer : 50 cm3] 3 (a)

Matc Match h the the diag diagra ram m with with the the corr correc ectt desc descri ript ptio ions ns bel below ow.. Add water ter slow lowly by usi using a dropper to bring the level of the solution to the calibration mark. The The volu volume metr tric ic flas flask k is clos closed ed tightly and inverted several times to get a uniform or homogenous solution. Transf Transfer er the stock stock soluti solution on to a suitable volumetric flask. •

•

(b)

•

•

(c)

11

Calculate the volume of stock solution required.



(d)

•

Use a pipette to draw up the required volume of stock solution.

Activity 14 : The pH values and molarity of acids and alkalis Fill in the blanks with the correct words .Use the words in the box. Increases decreases dissociation dissociation higher 1

concentration concentration hydrogen hydroxide alkali

The pH pH value value of of an acid acid or or alkali alkali depends depends on three three factor factors, s, that that is (a) degree of……………………………………………………………………………………. (b) molarity or ……………………………………… ………………………………………………………………………………. ………………………………………...

2

(c) ………………….. ………………….. of the acid or ………………………………………………… ………………………………………………………….. ……….. The lowe lowerr the pH value, value, the …………… ……………….. ….. the the concentr concentratio ation n of …………… ……………………i ………ions. ons.

3

The higher higher the pH value, value, the …………….. …………….. the concentra concentration tion of …………………. …………………... .. ions. ions.

4

As the molarity molarity of an acid increases increases , the the pH pH valu value e of of the the acid acid …………………… …………………………. ……. The pH value of an alkali increases when the molarity of the alkali ………………..…….


D:

NEUTRALISATION Learning Outcomes You should be able:•

• • • • •

Explain the meaning of neutralisation. neutralisation. Write equations for neutralisation neutralisation Explain the applications of neutralization in daily life Describe the titration process of acid-base Determine the end-point of titration during neutralization Solve numerical problems involving neutralisation

Activity 15 : Neutralisation

1

What is the meaning of neutralisation? neutralisation?

2

……………………………………………………………………………………………….. What are the only products of neutralisation?

3

…………………………………………………………………………………………………. Write a balanced equation for the neutralisation neutralisation of each of the following:(a) nitric acid and barium barium hydroxide hydroxide …………………………………………………………………………………………… (b) sulphuric acid and sodium hydroxide

12



…………………………………………………………………………………………… (c) phosphoric phosphoric acid and calcium calcium hydroxide …………………………………………………………………………………………… (d) ethanoic acid and potassium hydroxide

4

…………………………………………………………………………………………… Complete the flow chart below:-

(Refer to page 128 – 129 129 - F4 Chemistry textbook )

Activity 16 : Acid;base Titration

1

What is titration?

2

…………………………………………………………………………………………………. What is the function of an indicator?

3

………………………………………………………………………………………………….. Comp Comple lete te the the tabl table e belo below. w. Indicator

Colour in solution of: Acid

Alkali

Red litmus paper Blue litmus paper Phenolphthalein Methyl orange

4

Write out the procedure procedure for carrying out an acid-base acid-base titration to determine determine the -3 molarity of nitric acid (0.5 mol dm ) and label the diagram.

[ Alkali used : 25 cm 3 (0.5 mol dm-3 ) potassium hydroxide]

13



(Refer to page 130 – F4 Chemistry Chemistry textbook and Page Page 103 – F4 - Chemistry Practical Book) Book)

Activity 17 : Numerical problems involving neutralisation Useful equations in solving numerical problems involving neutralisation.: MaVa = MbVb

n = MV

n = mass

a

molar

n = no of moles Ma = molarity of acid Mb = molarity of alkali Va = volume of acid Vb = volume of alkali a and b = mole ratio ratio of acid to alkali (balanced (balanced equation) equation) Example: In an expe experi rime ment nt,, 25 cm3 of sodium sodium hydroxid hydroxide e solution solution of unknown unknown concentra concentration tion 3 -3 required required 26.50 cm of 1.0 mol dm sulphuri sulphuric c acid for complete complete reaction in titration titration.. Calculate the molarity of sodium hydroxide. Write out a balanced chemical equation:

2NaOH 2 mol

MaVa 1 MbVb = 2 , 1.0 X 26.50 = Mb X 25.00

+ H2SO4

Na2SO4 +

1 mol

1 2

14

2H2O


Mb = 2 X 1.0 X 26.50 25.00

1


=

2.12 mol dm-3 (Molarity of sodium hydroxide)

What What is the the volu volume me of 1.5 1.5 mol mol dm-3 aqueous ammmonia required to completely neutralise 30.00 cm 3 of 0.5 mol dm -3 sulphuric acid ? 2NH3 + H2SO4 (NH4)) 2SO4

Answer: 20 cm3] [ Answer:

2

Calcul culate ate the the volu olume in cm3 2.0 mol dm -3 hydrochloric acid that is required to react completely with 2.65 g of sodium carbonate. [Relative atomic mass: Na, 23 ; O, 16 ; C, 12]

Answer: 25 cm3] [ Answer:

3

25 cm3 of sulphuric acid was neutralised with 18.0 cm 3 of sodium hydroxide 1.0 mol dm-3. Calculate (a) the numbe numberr of moles moles of of sulphuri sulphuric c acid acid that is is used used in this this reactio reaction. n. (b) the molarity of sulphuric acid

[Answer (a) 0.009 0.009 mol (b) 0.36 mol mol dm-3 ]

4

24 cm3 of 0.1 mol dm-3 NaOH is required to completely neutralise 20.0 cm 3 of sulphuric acid. Calculate the concentration of sulphuric acid in (a) mol dm-3 (b) g dm-3

15



[Answer (a) 0.06 mol dm-3 (b) 5.88 g dm-3 ]

5

What What is the the mola molarit rity y of phosp phosphor horic ic acid acid if 15 15 cm3 of the acid is neutralized by 38.5 cm 3 of 0.15 mol dm-3 NaOH ?

[Answer (a) 0.218 mol dm -3 ]

Activity 18 1

A student student carri carried ed out an expe experim riment ent to deter determin mine e the end-po end-poin intt for the titrati titration on of 25.0 25.0 3 -3 cm of 1.0 mol dm sodium hydroxide solution with hydrochloric acid. Phenolphthalein Phenolphthalein is used as the acid-base indicator. Table 1 shows the three titrations that were conducted and the magnification of the burette readings. Titration No.

I

II

I II

13 1

hydrochloric acid

hydrochloric acid 14

hydrochloric acid

13

2

Initial burette reading

26

27

……………….

…………………..

13

………………..

38

hydrochloric acid

16

26

hydrochloric acid



14

39

hydrochloric acid

27

Final burette reading

……………………

……………………

…………………….

Table 1

(a) (a)

Reco Record rd the the bure burett tte e read readin ings gs for for the the thr three ee tit titra rati tion ons s in the the spa space ce pro provi vide ded d in Tab Table le 1. 1.

(b)

Const Construc ructt a table table and record record the initia initiall bure burette tte readin reading, g, final final burett burette e read reading ing and the volume of acid used for each titration.

(c) (c)

Calc Calcul ulat ate e the the ave avera rage ge volu volume me of hydr hydroc ochl hlor oric ic acid acid used used in the the exp exper erim imen ent. t.

(d) (d)

Calc Calcul ulat ate e the the conc concen entra trati tion on of hydr hydroc ochl hlor oric ic acid acid used used in the the expe experi rime ment nt..

(e) (e)

If the the expe xperim riment ent is is re repeate eated d by by re repla placin cing 1.0 1.0 mol mol dm dm-3 of hydrochloric acid with 1.0 mol dm-3 of sulphuric acid, predict the end-point of the titration. ………………………………………………………………………………………………….

(f) (f)

Acid Acids s can can be clas classi sifi fied ed int into o stro strong ng acid acid and and weak weak aci acid. d. Cla Class ssif ify y the the foll follow owin ing g acid acids s into strong acids and weak acids.

17



Ethanoic acid, hydrochloric acid, sulphuric acid, carbonic acid, nitric acid,

Strong acids

Weak acids

(g)

State State the the colou colourr chan change ge of the phenol phenolph phtha thalei lein n indi indicat cator or at the end end poin pointt of of titra titratio tion. n.

(h) (h)

………………………………………………………………………………………………… If phen phenol olph phth thal alei ein n is repl replac aced ed wit with h meth methyl yl ora orang nge e as the the acid acid-b -bas ase e indi indica cato tor, r, stat state e the colour change.

(i) (i)

………………………………………………………………………………………………… Writ Write e a chem chemic ical al equa equati tion on for for the the neut neutra rali lisa sati tion on reac reacti tion on betw betwee een n hyd hydro roch chlo lori ric c aci acid d and sodium hydroxide. ………………………………………………………………………………………………….

18

7 Acids and Bases

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