Acid and Bases

A : ACIDS AND BASES

B : THE STRENGTH OF ACIDS AND ALKALIS

C : CONCENTRATION OF ACIDS AND ALKALIS

D : NEUTRALISATION

A : ACIDS AND BASES

• ACIDS

• BASES AND ALKALIS

• USES OF ACIDS, BASES AND ALKALIS

• ROLE OF WATER AND THE PROPERTIES OF ACIDS

• ROLE OF WATER AND THE PROPERTIES OF ALKALIS

• CHEMICAL PROPERTIES OF ACIDS

• CHEMICAL PROPERTIES OF ALKALIS

A : ACIDS AND BASES

Acids is a chemical substance which ionizes in water to produce hydrogen ions, H+

Examples : HCl, HNO3 and H2SO4

HCl + H2O H3O+ + Cl-

Or

H2O HCl H+ + Cl-

ACIDS EQUATION

CH3COOH CH3COO- + H+

CH3COOH – Ethanoic acid

HNO3 H+ + NO3-

HNO3 – Nitric acid

H2SO4 – Sulphuric acid

H2SO4 2H+ + SO42-

ACID

monoprotic diprotic

Basicity – The number of ionisable hydrogen

atoms per molecule of an acid

Bases is a substance that reacts with an acid to form a salt and water only. Examples: metal hydroxides and metal oxides. ( solid )

BASES

Bases Acid Equation

Copper (II) oxideCuO

HClCuO (s) + 2HCl(aq)

CuCl2(aq) + H2O(l)

Potassium oxide, KOH

HClKOH (s) + HCl(aq)

KCl (aq) + H2O(l)

Sodium hydroxide,NaOH

HClNaOH (s) + HCl(aq)

NaCl (aq) + H2O (l)

Iron (III) oxide,Fe2O3

HCl Fe2O3 (s) + 6HCl(aq) 2FeCl3(aq) + 3H2O(l)

What are the product when a base reacts with an acid?

Base + Acid Salt + water

What happen if these bases are mixed with water?

Bases

Cannot dissolves in water

Can dissolves in water

BaseAlkali

Some bases can dissolve in water and some cannot

A base is a substance which ionises in water to produce hydroxide ions, OH-

Examples: Sodium hydroxide, NaOH potassium hydroxide, KOH, ammonium hydroxide or ammonia solution, NH4OH and calcium hydroxide, Ca(OH)2

NaOH (aq) Na+ (aq) + OH- (aq)

NH3(g) + H2O (l) ↔ NH4+ (aq) + OH- (aq)

KOH (aq) K+ (aq) + OH-(aq)

Ca(OH)2 Ca2+ + 2(OH)-

ALKALI

Car battery, detergent and dyes

Jus, carbonic drink, grapes

Dyes, fertiliser, photographic film

Soap and detergent

Antacid and toothpaste

Cement, to neutralise acid soil

THE ROLE OF WATER IN SHOWINGTHE PROPERTIES OF ACIDIC ANDALKALINE

To investigate the role of water in showing the properties of acids

A : Glacial ethanoic acid , CH3COOHB : Glacial ethanoic acid , CH3COOH dissolved in dry propanone, CH3COCH3

C : Glacial ethanoic acid ,CH3COOH dissolved in water

A B C

Without water, an acid still exist as molecules and there are no hydrogen ions, H+ present.

The presence of water, the acid ionizes to form hydrogenions, H+.

To investigate the role of water in showing the properties of alkalis.

A : Dry ammonia gas, NH3

B : Ammonia, NH3 dissolved in dry propanone,CH3COCH3

C : Ammonia, NH3 dissolved in water

Without water, NH3 still exist as molecules and there are no hydroxide ions, OH- present.

The presence of water, the alkalis ionizes to form hydroxideions, OH-.

PHYSICAL AND CHEMICAL PROPERTIES

A. ACIDSB. ALKALIS

Physical properties of acids

Physical properties of an alkalis

Chemical properties of acids

Chemical properties of an alkalis

B : THE STRENGTH OF ACIDS AND ALKALIS

• THE PH SCALE

• STRONG AND WEAK ACIDS

• STRONG AND WEAK ALKALIS

THE PH SCALE

Can you predict what are coloured change if litmus solution is used to each of the test tube?

A : AlkaliB : AcidC : AcidD : AlkaliE : Neutral

Diagram below shows the observation of each of the solution.Could you predict what are the properties of each of the solution?

The litmus test can tell us whether a substance is acidic or alkaline but it does not tell us how acidic or alkaline it is.

• Indicators are substances that give a certain colour in acidic or alkaline environment

• The Universal indicator is a mixture of many indicators. It gives a different colour at different pH values.

• The Universal indicator can be used to measure the pH of solution.

PH SCALE

• pH values are used to express how acidic or alkaline a substance is• The pH value rages from 0 to 14• The lower the pH value, the more acidic it is• The higher the pH value, the more alkaline it is• A neutral solution has a pH of 7

pH

Power of

Hydrogen ions

• The pH scale is used to indicate the degree of acidity or alkalinity of a solution• It is used to measure the concentration of hydrogen ions, H+ and hydroxide ions, OH-

pH indicator

13 7 1 10 7

Could you predict the pH value for each of the solutions?

Strong and weak acids and alkalis

HCl H+ + Cl-

Strong Acids

WEAK ACID : CH3COOH

CH3COOH ↔ CH3COO- + H+

What is the standard solution?

A standard solution is a solution in which its concentration is accurately known. Its concentration is usually given in mol/dm-3

To prepare 100 cm3 of 2.0 mol/dm3 of sodium hydroxide solution

Number of Moles, n1Volume, V1

Number of Moles, n1Volume, V2

Water

Number of moles before dilution = number of moles after dilution

n1 = n2

M1V1 = M2V2

M1V1 = M2V2

M1 = Molarity of solution before water is addedV1 = Volume of solution before water is addedM2 = Molarity of solution after water is addedV2 = Volume of solution after water is added

7.3.2 : Preparation of standard solution.

1. A solution in which its concentration is accurately known iscalled standard solution.

2. Steps involved in the preparation of a standard solution.

a. Calculate the mass of solute neededb. Weigh out the exact mass of solute needed.c. Dissolve the solute in a small amount of distilled waterd. Transfer the dissolved solute into a suitable volumetric

flask.e. Add enough water to the required volume.

7.3.3 : Preparation of a solution by dilution method.

1. Dilution is a process of diluting a concentrated solution by adding a solvent such as water to obtain a more diluted solution.

2. Steps involved in the preparation of a dilute solution.

a. Calculate the volume of stock* requiredb. Use a pipette to draw up the required volume of

stock solutionc. Transfer the stock solution to a volumetric flaskd. Add water to bring the level of solution to calibration

mark.e. Shake well to ensure thorough mixing.

*Stock – Water is added into a concentration standardsolution

Refer practical book pg 98

3. To calculate a new molarity or volume can be determine as follows

Number of moles of solute= Number of moles of solute before dilution after dilution

M1V1 = M2V2

Where,

M1 = Molarity of original solutionV1 = Volume of original solution

M2 = Molarity of new solutionV2 = Volume of new solution

To prepare 100cm3 of 0.20 moldm-3 sodium hydroxide,NaOH solution

M1 = 0.20