Lesson Notes By Weeks and Term - Senior Secondary 1

Term: 2^nd Term

Week: 9

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Chemistry

Topic:-       Acids, Bases and Salts I

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Highlights the characteristics of acids, bases and salts
2. Discuss the preparations, reactions and uses of acids, bases and salts

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION	TEACHER’S ACTIVITY	STUDENT’S ACTIVITY
STEP 1 INTRODUCTION	The teacher reviews the previous lesson on Graham’s, Avogadro’s number and the molar volume of gases	Students pay attention
STEP 2 EXPLANATION	He highlights the characteristics of acids, bases and salts	Students pay attention and participates
STEP 3 DEMONSTRATION	He discusses the preparations, reactions and uses of acids, bases and salts	Students pay attention and participate
STEP 4 NOTE TAKING	The teacher writes a summarized note on the board	The students copy the note in their books

 

NOTE

ACIDS, BASES AND SALTS

ACIDS

Arrhenius defined an acid as a substance which when in water produces Hydrogen ion (H⁺)as the only positive ion. Some common examples of acids are Ethanoic acid found in vinegar and tomato juice, Citric acid found in citrus foods like lemons, oranges and grapefruit, Lactic acid found in sour milk and yoghurt, and in muscle respiration, Tartaric acid found in grapes, Tannic acid found in tea and ant’s body. Formic acid found in bee stings, Hydrochloric acid found in stomach juices etc

 

3 common laboratory acids called Mineral acids includes

1. Hydrochloric acid (HCl)
2. Tetraoxosulphate (VI) acid H₂SO₄
3. Trioxonitrate (V) acid HNO₃

 

DILUTE ACIDS

These are solution containing small amount of acid dissolved in water

 

CONCENTRATED ACIDS

These are solution containing large amount of acid dissolved in water

 

Physical Properties of Dilute Acids

1. Acids have a sour taste
2. Acids are hazardous
3. acids are irritants (they cause skin to redden and blister)
4. They turn blue litmus paper to red

 

CHEMICAL PROPERTIES OF AN ACID

1. Acids react with metals

Acids react with metals to produce hydrogen gas. The gas is tested with a

Burning/glowing splint which shows hydrogen burns with a ‘pop’ sound.

2Na(s) + 2HCl (aq)       2NaCl (aq) + H₂(g)^-

 

2. Acids react with trioxocarbonate (IV) and hydrogentrioxocarbonate (IV)

Carbon(IV)oxide is to be formed. To test this, the gas produced is bubbled into limewater which forms a white precipitate.

trioxocarbonate (IV):

MgCO₃(s) + 2HCl (aq)  MgCl ₂(aq) + CO₂(g) +

H₂O (l)

hydrogentrioxocarbonate (IV):

NaHCO₃(s or aq) + HCl (aq) NaCl (aq) + CO₂ (g) + H₂O(l)

 

3. Acids react with bases to form salt and water only

Metal oxides and hydroxides react slowly with warm dilute acid to form salt+water

Cu(OH)2(s) + H2SO4(aq)     CuSO4(aq) + 2H2O(l)

 

 

USES OF ACIDS

Tetraoxosulphate (VI) Acid –

1. Used in car batteries production
2. Manufacture of ammonium sulphate for fertilizers-
3. Manufacture of detergents, paints, dyes, artificial fibres & plastics
4. Hydrochloric acid can remove rust (iron (III) oxide) which dissolves in acids
5. Acids are used in preservation of foods (e.g. ethanoic acid)

 

Hydrogen Ions

Hydrogen gas is formed by acids as H⁺(aq) ions present in the acid solutions.

This means when acids dissolved in water, they produce H⁺ ions in it .

Chemical equation: HCl(s) + water  --->  HCl(aq)

Ionic Equation: HCl(s) + water  ----> H⁺(aq) + Cl^-(aq)

 

*Note that for ionic equation only aqueous solutions are ionized *However when dissolved in organic solutions, they don’t show acidic properties

When metals react with acids, only the hydrogen ions react with metals,

Chemical equation:

2Na_(s) +2HCl_(aq)à2NaCl(aq) + H2(g)

Ionic equation:                            

2Na(s) + 2H⁺(aq)à2Na⁺(aq) + H₂(g)

Basicity of an acid is the maximum number of H⁺ Ions produced by a molecule of acid in a chemical reaction

Hydrochloric acid                    

HCl (aq)àH⁺(aq)+Cl^-(aq). it is monobasic

Trioxonitrate (V) acid               

HNO₃ (aq)àH⁺(aq)+NO₃^-(aq) it is monobasic

Ethanoic acid                            

CH₃COOH (aq)  ⇌H⁺(aq) + CHCOO^-(aq) it is monobasic

Tetraoxosulphate (VI) acid

H₂SO₄(aq)à2H⁺(aq) + SO₄^2-(aq)it is dibasic

 

 

Strong and Weak Acids

Strong Acids are acids that completely ionize in water. This reaction is irreversible. E.g.The mineral acids (H₂SO₄, HNO₃, HCl)

H₂SO₄(aq) 2H⁺(aq) SO₄^2-(aq)

In the above equation SO₄^2- is completely been ionized in water, forming in 3 kinds of particles:-

i. H⁺ ions ii. SO₄^2- ions iii. H₂O molecules Strong acids react more vigorously with metals than weak acids, hydrogen gas bubbles are produced rapidly.

 

Weak Acids are acids that partially ionize in water. The remaining molecules remain unchanged as acids. Their reactions are reversible. E.g.

CH₃COOH, H₃PO₄

H₃PO_{4 (aq})   ⇌ 3H⁺_(aq) + PO₄^3-_(aq)

Note Weak acids react slowly with metals than strong acids hydrogen gas bubbles are produced slowly.

 

Comparing Strong and Weak Acids with Concentrated and Dilute Acids

CONCENTRATION STRENGTH OF ACIDS

This is the amount of solute (acids) dissolved in 1 dm³ of a solution. i.e how much ions can be dissociated in to from acid or alkali. It can be diluted by adding more water to solution or concentrated by adding more solute to solution. The strength cannot be change. Comparing 10 mol/dm³ and 0.1mol/dm³ of hydrochloric acids and 10 mol/dm³ and0.1 mol/dm³ of ethanoic acids.

10 mol/dm³of ethanoic acid solution is a concentrated solution of weak acid

0.1 mol/dm³of ethanoic acid solution is a dilute solution of weak acid- 10 mol/dm³ of hydrochloric acid solution is a concentrated solution of strong acid-0.1 mol/dm³ of hydrochloric acid solution is a dilute solution of strong acid.

 

BASES

Bases are oxides or hydroxides of metals

Alkalis are bases which are soluble in water

Laboratory Alkalis Potassium Hydroxide, KOH Sodium Hydroxide, NaOH Aqueous Ammonia, NH₄OH Calcium Hydroxide, Ca(OH)₂

All alkalis produce hydroxide ions (OH^-) when dissolved in water.

Hydroxide ions give the properties of alkalis.

They do not behave as bases in the absence of water.

Alkalis are therefore substances that produce hydroxide ions, OH^-(aq) in water.

 

Physical Properties of Alkalis

1. Alkalis have a slippery and soap feel
2. Alkalis are hazardous as well
3. Dilute alkalis are irritants
4. Concentrated alkalis are corrosive and burn skin ( caustic (i.e. burning)alkalis)-
5. Alkalis turn common indicator red litmus to blue

 

Chemical properties of Alkalis

1. Alkalis react with acids. The reaction is called neutralization reaction

 

2. Alkalis react with ammonium compounds

They react with heated solid ammonium compounds to produce ammonia gas

(NH₄)₂SO₄(s) + Ca(OH)₂(aq) CaSO₄(aq) + 2NH₃g) +

2H₂O(l)

3. Alkalis are precipitating agent. Alkalis react with salt solution to precipitate metallic hydroxides

e.g

BaSO₄ (aq), contains Ba²⁺(aq) ions

2NaOH(aq) + CaCl₂(aq) Ca(OH)₂(aq) + 2NaCl(aq) The solid formed is a precipitate

And the reaction is called precipitation reaction

Strong and Weak Alkalis

Strong Alkalis- are base that completely ionizes in water to form OH^-(aq) ions. Their reactions are irreversible. E.g. NaOH, KOH, Ca(OH)₂

Ca(OH)(s)  Ca²⁺(aq) + 2OH^-(aq)

 

Weak Alkalis base that partially ionize in water. The remaining molecules remain unchanged as base. Their reactions are reversible.

E.g. NH₃

NH_{3 (g)} + H_2(l)  ⇌ NH⁴⁺_(aq) + OH^-_(aq)

 

USES OF ALKALIS

1. Alkalis neutralize acids in teeth (toothpaste) and stomach (indigestion)
2. Soap and detergents contain weak alkalis to dissolve grease

3. Floor and oven cleaners contain NaOH (strong alkalis)
4. Ammonia (mild alkalis) is used in liquids to remove dirt and grease from glass

 

INDICATORS AND PH

Indicators are substances that has different colours in acidic and alkaline solutions

Common indicators:

1. Litmus solution from where paper is made
2. Methyl orange
3. Phenolphthalein

 

THE PH SCALE

pH is a measure of acidity or alkalinity of a solution. pH 7 is neutral

Solutions of less than pH 7 are acidic. The solutions contain hydrogen ions. The smaller the pH, the more acidic the solution is and more hydrogen ions it contains.

Solutions of more than pH 7 are alkaline. The solution contains hydroxide ions. The bigger the pH, the more alkaline the solution and more hydroxide ions it contains.

 

Measuring pH of a Solution

1. Universal indicators : It can be in paper or solution form. Universal paper can be dipped into a solution then pH found is matched with the colour chart. It gives approximate pH value.
2. pH meter A hand-held pH probe is dipped into solution and meter will show the pH digitally or by a scale.
3. pH sensor and computer A probe is dipped into solution and will be sent to computer through interface used to measure pH of solution. The pH reading is displayed on computer screen.

 

IONIC EQUATION

This is an equation involving ions in aqueous solution, showing formation and changes of ions during the reaction

 

Rule to develop ionic equations:

Only formulae of ions that changed in oxidation number is included; Aqueous solutions are written as ions; liquids, solids and gases written in full

 

Reaction between Metals and Acids.

For example, reaction of sodium with hydrochloric acid

2Na(s) + 2HCl(aq)	2NaCl(aq) + H2(g)
Its ionic equation is written as:
2Na(s) + 2H+(aq) + 2Cl-(aq)	2Na+(aq) + 2Cl-(aq) + H2(g)

Since 2 Cl^-_(aq) ions did not have a change in its oxidation number, they are not involved in chemical reaction .

 

As ionic equation is used to show changes in reactions, we omit Cl^-_(aq) ions. So we are left with:

2Na_(s) + 2H⁺_(aq)→ 2Na⁺_(aq) + H_2(g)

 

Reaction between Soluble Ionic Compounds and Acids

e.g. Reaction of sodium hydrogentrioxocargbonate (IV) with hydrochloric acid

NaHCO3(aq) + HCl(aq)	NaCl(aq) + CO2(g) + H2O (l)
The ionic equation is:
Na+(aq) + H+(aq) + CO32-(aq)+H+(aq)+Cl-(aq)		Na+(aq) + Cl-
(aq) +CO2(g)+H2O(l)

Since Na⁺_(aq) and Cl^-_(aq) ions do not change, we omit them, leaving

 

 

H+(aq) + Co32-(aq) + H+(aq)	CO2(g) + H2O(l)
CO32-(aq) + 2H+(aq)	CO2(g) + H2O(l)

 

Reaction between Insoluble Ionic Compounds and Acids

e.g. Reaction between iron(II) oxide and Tetraoxosulphate (VI) acid

FeO(s) + H2SO4(aq)	FeSO4(aq) + H2O(g)
Its ionic equation is : FeO(s) + 2H+(aq) + SO42-(aq)		Fe2+(aq)

SO₄^2-_(aq)+H₂O_(g)

Note: FeO is written in full as its solid (although it’s an ionic compound)

Since SO₄^2-_(aq) ions do not change, we omit SO₄^2-ions, leaving:

FeO_(s) + 2H⁺_(aq)    Fe²⁺_(aq) + H₂O_(g)

E.g. Reaction between calcium carbonate and hydrochloric acid

CaCO3(s) + 2HCl (aq) CaCl2(aq) + CO2(g) + H2O(l)

Its ionic equation is:

CaCO_3(s) + 2H⁺_(aq) + 2Cl^-_(aq)    Ca²⁺_(aq) + 2Cl^-_(aq) + CO_2(g)

+H2O(l)

Since 2 Cl^-_(aq) ions do not change, we omit Cl^-ions, leaving:

CaCO_3(s) + 2H⁺_(aq)         Ca²⁺_(aq) + CO_2(g) + H₂O_(l)

 

Reactions Producing Precipitate

E.g. Reaction between calcium hydroxide and barium sulphate

Ca(OH)2(aq) + BaSO4(aq)	Ba(OH)2(s) + CaSO4(aq)
Its ionic equation is written as:
Ca2+(aq) + 2OH-(aq) + Ba2+(aq) + SO42-(aq)		Ba(OH)2(s) +

Ca²⁺_(aq) + SO₄^2-_(aq)

 

Since Ca²⁺_(aq) and SO₄^2-_(aq) ions don’t change, we omit them, leaving:

Ba2+(aq) + 2OH-(aq)	Ba(OH)2(s)
Displacement Reactions
E.g. Reactions between magnesium with zinc sulphate
Mg(s) + ZnSO4(aq)	MgSO4(aq) + Zn(s)
Its ionic equation is written as:
Mg(s) + Zn2+(aq) + SO42 (aq)		Mg2+(aq) + SO42-(aq) + Zn(s)

 

Since SO₄^2-_(aq) ions do not change, we omit them, leaving:

Mg_(s) + Zn²⁺_(aq)     Mg²⁺_(aq) + Zn_(s)

EVALUATION:    1. Define

1. acid
2. base

2. Explain strong and weak acids giving two examples of each

3. Explain strong and weak bases giving two examples of each

4. State three physical and chemical properties each of acids and bases

5. Outline three uses each of acids and bases

6. Define Ionic equations. List three examples of ionic equations

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively