7 acids and bases
TRANSCRIPT
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
CHAPTER 7: ACIDS AND BASES
A ACIDS AND BASES
Learning OutcomesYou 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 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 and alkali
Fill in the blanks with the correct words:
1 An acid is a chemical substance which ionises in………………. to produce
………….ions.
The hydrogen ion combines with a water molecule, H2O to form a ………………………..
ion, H3O+.
2 Acid can be classified as a……………………….acid or a ………………….acid based
on its basicity.
3 Basicity is the number of ionisable …………………. atoms per molecule of an acid.
4 A base is a substance that reacts with an acid to form a …………... and water only.
Bases include metal hydroxides and metal oxides which dissolve in water which are
known as……………..
5 Give the names of four common acids and write out their formulae and basicity:Name of acid Formula of acid Basicity
(i)
(ii)
(iii)
(iv)
6 Complete the equations below :
a)
b)
c)
d)
HCl (aq) → . . .…….(aq) + Cl- (aq)
……… (aq) → H+ (aq) + NO3 - (aq)
H2SO4 (aq) → ……. …… + ………..
CH3COOH (aq) …………. + CH3COO- (aq)
(Refer to page 117 -118 - F4 Chemistry textbook)
1
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Activity 2 : Fill in the blanks with the correct words:
1 An alkali is a water-soluble base which ionises in water to produce………..………..,OH-
2 Give the names of two common alkalis and write out their formulae.
Name of alkali Formula of alkali
(i)
(ii)
3 Complete the equations below :
NaOH (aq) → …….(aq) + OH- (aq)
……… (aq) + H2O (l) NH4+ (aq) + …………. (aq)
4 Uses of acids, bases and alkalis
(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 vitamin C
(d)To produce …………., detergent and ………………
Example: sodium hydroxide to make soap and detergent
Magnesium hydroxide added to tooth-paste
(e)To manufacture dyes,……………………. and drugs
Example: methylamine
(f)Used in rocket fuel
Example:…………………………………………………………………………………………
(Refer to page 118 - F4 Chemistry textbook)
Activity 3: Role of water and its properties of acids / alkalis
Fill in the blanks with the correct words.
1 An acid only shows its …………..…… properties when dissolve in ……………………….
2 In the presence of water, the acid ionises to form ……………………………………..ions .
3 Without water, an acid still exists as…………………and there are no H+ ions present.
2
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
4 Complete the following table.
Condition of ethanoic acid Effect on the blue litmus paper
Inference
Glacial ethanoic acid, CH3COOHEthanoic acid , CH3COOH in waterEthanoic acid , CH3COOH in dry propanone, CH3COCH3
5 An alkali only shows its ……………….. properties when dissolve in ………………………..
6 In the presence of water, the base dissociates to produce …………………………... ions
that are responsible for the ………………… properties
7 Complete the table below.
Condition of ammonia Effect on the red litmus paper InferenceDry
Aqueous (dissolved in water)Dissolved in propanone
(Refer to page 118 -119 F4 Chemistry textbook and page 84 – 86 F4 Chemistry Practical Book )
Activity 4: Properties of acids and alkalis
Place a tick in the box next to each of the following statements to indicate which are True and which are False.
Statement True False1. All acids are dangerous
2. All alkalis are dangerous
3. Acids taste sweet
4. Alkalis taste bitter
5. Acids taste sour
6. Most acids can burn skin
7. Alkalis feel soapy
8. Acids produce H+ ions in solution
9. Acids produce OH- ions in solution
10. Acids can corrode
11. Acids have a pH above 7
12. Acids have a pH below 7
13. Alkalis turn moist red litmus paper blue
14. Acids turn moist red litmus paper blue
3
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Activity 5 : Chemical properties of acids
1 Acids react with bases to form salts and water only.
Write an equation for the reaction between sulphuric acid and copper(II) oxide.
……………………………………………………………………………………………………...
2 Acids react with reactive metals to produce salts and hydrogen gas.
Write an equation for the reaction between hydrochloric acid and zinc .
……………………………………………………………………………………………………...
3 Acids react with carbonates to produce salts, water and carbon dioxide gas.
Write an equation for the reaction between nitric acid and calcium carbonate.
……………………………………………………………………………………………………...
(Refer to page 119 - F4 Chemistry textbook and page 87 – 90 - F4 Chemistry Practical Book )
4
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Activity 6 : Chemical properties of alkalis
1 Alkalis react with acids to form salts and water only
Write an equation for the reaction between sodium hydroxide and benzoic acid.
……………………………………………………………………………………………………...
2 When a mixture of an alkali and an ammonium salt is heated, ammonia gas is liberated.
Write an equation for the reaction sodium hydroxide and ammonium chloride .
……………………………………………………………………………………………………...
3 Alkalis react with most metal ion solutions to produce the insoluble metal hydroxides (precipitation reaction)
Write an equation for the reaction between sodium hydroxide and iron(II) sulphate.
……………………………………………………………………………………………………...
(Refer to page 120 - F4 Chemistry textbook and page 91- F4 Chemistry Practical Book )
5
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
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 The pH scale 0 to 14 , is used to indicate the degree of ……………… or ……………. of a solution.
2 pH value less than 7 , indicates an…………………………solution
pH value equal to 7 , indicates a…………………………solution
pH value more than 7 , indicates an…………………………solution
3 pH value can be determined by using…………..,pH paper or…………………indicator.
4
Acids Neutral Alkalis0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Very………………. Very…………….(Refer to page 121 – Chemistry text book)
Activity 8 : Strong and weak acid1. Complete the flowchart below.
Strong acid Weak acid
Degree of dissociation
Ionization in water
Concentration of ions
pH value
Examples
6
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
2 Write the equation for the ionisation of the following substances in water :
(a) nitric acid
……………………………………………………………………………………………………..(b) sulphuric acid
……………………………………………………………………………………………………..(c) hydrochoric acid
…………………………………………………………………………………………………….(d) ethanoic acid
……………………………………………………………………………………………………..
Activity 9: Strong and weak alkali
1. Complete the flowchart below.
Strong alkali Weak alkali
Degree of dissociation
Ionization in water
Concentration of ions
pH value
Examples
2 Write the equation for the ionisation of the following subtances in water :
(a) sodium hydroxide
……………………………………………………………………………………………………..(b) potassium hydroxide
……………………………………………………………………………………………………..(c) ammonia
…………………………………………………………………………………………………….(Refer to page 122 - F4 Chemistry textbook )
7
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
C: CONCENTRATIONS OF ACIDS AND ALKALIS
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 molarity of acids and 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 ……………………………. of a solution refers to the quantity of solute in 1dm 3 of solution can be defined in two ways :-
(a) Concentration (g dm-3 ) =
(b) Concentration (mol dm-3) also known as molarity or molar concentration (M) =
2 The two units of concentration can be inter-converted:
Work this out.3 5.0 g of copper(II) sulphate is dissolved in water to form 500 cm3 solution. Calculate the
concentration of copper(II) sulphate solution in g dm-3 ?
[Answer: 10.0 g dm-3]
4 What is the mass of sodium carbonate required to dissolve in water to prepare 200 cm3
solution that contains 50 g dm-3 ?
[Answer: 10 g]
(Refer to page 123 -124 - F4 Chemistry textbook )
8
……………... (mol dm-3) Concentration (………..)
X Molar mass
÷ Molar mass
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
5 4.0 g of sodium carbonate powder, Na2CO3 , is dissolved in water and made up to 250 cm3. What is the molarity of the sodium carbonate solution?[Relative atomic mass: C, 12; O, 16; Na, 23]
[Answer: 0.15 mol dm-3]
Activity 11The number of moles of solute in a given volume of solution can be calculated using:
n = Number of moles of soluteM = Molarity of solution (mol dm-3)V = Volume of solution (dm3)
If the volume in in cm3 – convert the volume of solution from cm3 to dm3
5 Calculate the number of moles of ammonia in 150 cm3 of 2 mol dm-3 aqueous ammonia.
[Answer: 0.3 mol]
6 A student pipetted 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: 0.03 mol dm-3]
7 Calculate the number of moles of hydrogen ions present in 200 cm3 of 0.5 mol dm-3
sulphuric acid.
[Answer: 0.2 mol of H+ ions]
9
n = MV
n = M x V 1000
n = MV 1000 or
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Activity 12 : Standard solutions –weighing method
1 What is a standard solution?
……………………………………………………………………………………………………
2 Preparation of standard solutions can be carried out by :-Weighing method (mass of solute)
3
Calculate the mass of solute needed
mass = n X molar mass
= MV X molar mass 1000
Examples: To prepare 100 cm 3 of 2.0 mol dm -3 sodium hydroxide solution Calculate the mass of NaOH needed.[Relative atomic mass: 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] 1000 = 8 g
Try this: To prepare 250 cm 3 of 1.0 mol dm -3 sodium carbonate solution. Calculate the mass of Na2CO3 needed.[Relative atomic mass: Na, 23 ; O, 16 ; C, 12]
[Answer : 26.50g]4 0.25 mol dm-3 solution of sodium hydroxide was prepared by dissolving x g of sodium
hydroxide in 750 cm3 of water. What is the value of x ?[Relative atomic mass: Na, 23 ; O, 16 ; H, 1]
[Answer : 7.5 g](Refer to page 126 - F4 Chemistry textbook )
10
n = mass molar mass
n = MV 1000
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
5 Match the descriptions / procedures with the correct diagram below. Wash and rinse the weighing
bottle ,small beaker and filter funnel to ensure no solute 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. Dissolved the solute in a small
amount of distilled water.
Add more water carefully to the volumetric flask and swirl gently.
Shake well to ensure thorough mixing.
Activity 13 : Standard solutions – dilution method1 Dilution method
Calculate the volume of stock solution required by using the equation:-
M1 = molarity of solution before dilution V1 = volume of solution before dilution M2 = molarity of solution after dilution V2 = volume of solution after dilution
Example: 50 cm3 of 0.1 mol dm-3 sodium hydroxide, NaOH solution from 2.0 mol dm-3
sodium hydroxide,NaOH solutionBefore dilution After dilution
M1 V1 M2 V2
2.0 mol dm-3 ? 0.1 mol dm-3 50 cm3
2.0 x V1 = 0.1 x 50 V1 = 0.1 x 50 2.0 = 2.5 cm3
2 Try this: 100 cm 3 of 0.5 mol dm -3 potassium manganate(VII) ,KMnO 4 solution from 1.0 mol dm -3 potassium manganate(VII) ,KMnO 4 solution.
[Answer : 50 cm3]
11
M1V1 = M2V2
When using the equation M1V1 = M2V2 ,make sure that both V1 and V2 are of the same unit.
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
3 Match the diagram with the correct descriptions below.(a)
(b)
(c)
(d)
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.
Transfer the stock solution to a suitable volumetric flask.
Calculate the volume of stock solution required.
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 concentration hydrogen dissociation higher hydroxide alkali
1 The pH value of an acid or alkali depends on three factors, that is
(a) degree of…………………………………………………………………………………….
(b) molarity or ………………………………………………………………………………..
(c) ………………….. of the acid or …………………………………………………………..
2 The lower the pH value, the ……………….. the concentration of ……………………ions.
3 The higher the pH value, the …………….. the concentration of …………………... ions.
4 As the molarity of an acid increases , the pH value of the acid ………………………….
The pH value of an alkali increases when the molarity of the alkali ………………..…….
(Refer to page 128 - F4 Chemistry textbook )
D : NEUTRALISATION
12
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Learning OutcomesYou should be able:-
Explain the meaning of neutralisation. Write equations for 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?
………………………………………………………………………………………………..2 What are the only products of neutralisation?
………………………………………………………………………………………………….3 Write a balanced equation for the neutralisation of each of the following:-
(a) nitric acid and barium hydroxide
……………………………………………………………………………………………(b) sulphuric acid and sodium hydroxide
……………………………………………………………………………………………(c) phosphoric acid and calcium hydroxide
……………………………………………………………………………………………(d) ethanoic acid and potassium hydroxide
……………………………………………………………………………………………4 Complete the flow chart below:-
(Refer to page 128 – 129 - F4 Chemistry textbook )Activity 16 : Acid;base Titration
1 What is titration?
13
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
………………………………………………………………………………………………….
2 What is the function of an indicator?
…………………………………………………………………………………………………..
3 Complete the table below.
IndicatorColour in solution of:
Acid AlkaliRed litmus paperBlue litmus paperPhenolphthaleinMethyl orange
4 Write out the procedure for carrying out an acid-base titration to determine the molarity of nitric acid (0.5 mol dm-3) and label the diagram.[ Alkali used : 25 cm3 (0.5 mol dm-3 ) potassium hydroxide]
(Refer to page 130 – F4 Chemistry textbook and Page 103 – F4 - Chemistry Practical Book)
Activity 17 : Numerical problems involving neutralisation
14
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Useful equations in solving numerical problems involving neutralisation.:
15
MaVa = a MbVb
b
n = MVn = mass molar mass
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
n = no of moles Ma = molarity of acidMb = molarity of alkaliVa = volume of acidVb = volume of alkali
a and b = mole ratio of acid to alkali (balanced equation)
Example:In an experiment, 25 cm3 of sodium hydroxide solution of unknown concentration required 26.50 cm3 of 1.0 mol dm-3 sulphuric acid for complete reaction in titration. Calculate the molarity of sodium hydroxide.
Write out a balanced chemical equation:2NaOH + H2SO4 Na2SO4 + 2H2O
2 mol 1 mol
MaVa 1 MbVb = 2 , 1.0 X 26.50 = 1Mb X 25.00 2
Mb = 2 X 1.0 X 26.50 = 2.12 mol dm-3 (Molarity of sodium hydroxide) 25.00
1 What is the volume of 1.5 mol dm-3 aqueous ammmonia required to completely neutralise 30.00 cm3 of 0.5 mol dm-3 sulphuric acid ?
2NH3 + H2SO4 (NH4)) 2SO4
[Answer: 20 cm3]
2 Calculate the volume 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]
3 25 cm3 of sulphuric acid was neutralised with 18.0 cm3 of sodium hydroxide 1.0 moldm-3. Calculate
(a) the number of moles of sulphuric acid that is used in this reaction.(b) the molarity of sulphuric acid
16
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
[Answer (a) 0.009 mol (b) 0.36 mol dm-3]4 24 cm3 of 0.1 mol dm-3 NaOH is required to completely neutralise 20.0 cm3 of sulphuric
acid. Calculate the concentration of sulphuric acid in(a) mol dm-3
(b) g dm-3
[Answer (a) 0.06 mol dm-3 (b) 5.88 g dm-3]5 What is the molarity of phosphoric acid if 15 cm3 of the acid is neutralized by 38.5 cm3 of
0.15 mol dm-3 NaOH ?
[Answer (a) 0.218 mol dm-3]
Activity 18
1 A student carried out an experiment to determine the end-point for the titration of 25.0 cm3 of 1.0 mol dm-3 sodium hydroxide solution with hydrochloric acid. Phenolphthalein is used as the acid-base indicator. Table 1 shows the three titrations that were conducted and the magnification of the burette readings.
17
1
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
Titration No. I II III
Initial burette reading
1 2
…………………..
13
14
……………….
26
27
………………..
Final burette reading
13
14
……………………
26
27
……………………
38
39
…………………….
Table 1
(a) Record the burette readings for the three titrations in the space provided in Table 1.
(b) Construct a table and record the initial burette reading, final burette reading and thevolume of acid used for each titration.
(c) Calculate the average volume of hydrochloric acid used in the experiment.
18
hydrochloric acid
hydrochloric acid hydrochloric
acid hydrochloric acid
hydrochloric acid
hydrochloric acid
WAJA F4 Chemistry 2009 Chapter 7: Acids and Bases
(d) Calculate the concentration of hydrochloric acid used in the experiment.
(e) If the experiment is repeated by replacing 1.0 mol dm-3 of hydrochloric acid with 1.0 mol dm-3 of sulphuric acid, predict the end-point of the titration.
………………………………………………………………………………………………….
(f) Acids can be classified into strong acid and weak acid. Classify the following acids into strong acids and weak acids.
(g) State the colour change of the phenolphthalein indicator at the end point of titration.
…………………………………………………………………………………………………(h) If phenolphthalein is replaced with methyl orange as the acid-base indicator, state
the colour change.
…………………………………………………………………………………………………(i) Write a chemical equation for the neutralisation reaction between hydrochloric acid
and sodium hydroxide.
………………………………………………………………………………………………….
19
Ethanoic acid, hydrochloric acid, sulphuric acid,
carbonic acid, nitric acid,
Strong acids Weak acids