1st Term Week 10 Lesson Note: Acids, Bases, and Salts for SS1
Class: Senior Secondary School 1 (SSS 1)
Subject: Chemistry
Topic: Acids, Bases, and Salts
Sub-Topics: Definitions, Properties, Examples, pH Scale, and Neutralization
Duration: 40 Minutes
1. Acids
Definitions
Arrhenius Definition: An acid is a substance which, when dissolved in water, produces hydrogen ions (H+ or hydronium ions, H3O+) as the only positive ions.
Lewis Definition: An acid is an electron-pair acceptor.
Types of Acids
Organic Acids: Weak acids naturally found in plants and animals (e.g., Ethanoic acid in vinegar, Citric acid in lemons, Lactic acid in sour milk).
Inorganic (Mineral) Acids: Strong acids prepared from mineral elements (e.g., Hydrochloric acid [HCl], Tetraoxosulphate(VI) acid [H2SO4], Trioxonitrate(V) acid [HNO3]).
Properties of Acids
They have a sour taste.
They turn blue litmus paper red.
They conduct electricity in aqueous solutions (electrolytes).
They react with reactive metals (like Zinc or Magnesium) to liberate Hydrogen gas (H2).
They react with trioxocarbonate(IV) salts (CO3^2-) to liberate Carbon Dioxide gas (CO2).
2. Bases and Alkalis
Definitions
A Base is a substance (usually a metal oxide or metal hydroxide) which reacts with an acid to form salt and water only.
An Alkali is simply a base that is soluble in water (e.g., Sodium Hydroxide [$NaOH$], Potassium Hydroxide [KOH]). Remember: All alkalis are bases, but not all bases are alkalis.
Examples of Bases
Soluble Bases (Alkalis): NaOH, KOH, Ca(OH)2.
Insoluble Bases: Copper(II) oxide (CuO), Iron(III) hydroxide (Fe(OH)3).
Properties of Bases
They have a bitter taste.
They feel soapy or slippery to the touch.
They turn red litmus paper blue.
They react with acids to form salt and water.
3. The pH Scale
The pH scale (Power of Hydrogen) is a logarithmic scale ranging from 0 to 14 used to measure the degree of acidity or alkalinity of a chemical solution.
<--- Highly Acidic Neutral Highly Alkaline --->
[ 0 --- 1 --- 2 --- 3 --- 4 --- 5 --- 6 ] [ 7 ] [ 8 --- 9 --- 10 --- 11 --- 12 --- 13 --- 14 ]
pH < 7: The solution is Acidic. (The closer to 0, the stronger the acid).
pH = 7: The solution is Neutral. (e.g., Pure distilled water).
pH > 7: The solution is Alkaline/Basic. (The closer to 14, the stronger the base).
4. Neutralization Reaction
Neutralization is a chemical reaction in which an acid reacts completely with a base to produce a salt and water only.
Ionic Representation
In terms of ions in an aqueous solution, neutralization is simply the combination of hydrogen ions (H+) from the acid with hydroxide ions (OH-) from the base to form neutral water molecules (H2O):
Real-life Examples of Neutralization
Hydrochloric acid reacting with Sodium hydroxide:
HCl(aq) + NaOH(aq) = NaCl(aq) + H2O(l)Application: Taking antacid tablets (which are basic, like magnesium hydroxide) to neutralize excess hydrochloric acid causing indigestion in the stomach.
5. Salts
A salt is a chemical compound formed when all or part of the replaceable hydrogen ions of an acid are replaced by a metallic ion or an ammonium ion (NH4+).
Example: Replacing the H in HCl with Na gives Sodium Chloride (NaCl), which is standard table salt.
Evaluation Exercises (For Classwork/Assignment)
Define an acid and an alkali according to the Arrhenius theory.
State three distinct differences between the properties of acids and bases.
A solution has a pH value of 2.5.
a) Is this solution acidic, basic, or neutral?
b) What color change would you observe if blue litmus paper is dipped into it?
Write a balanced chemical equation for the neutralization reaction between Tetraoxosulphate(VI) acid (H2SO4) and Potassium hydroxide (KOH).
No comments