TOPIC: ACIDS, BASES, AND SALTS
SUBJECT: CHEMISTRY
CONTENTS:
ACIDS
1. DEFINITION AND CHARACTERISTICS OF ACIDS
2. PREPARATION OF ACIDS
3. REACTIONS OF ACIDS
4. USES OF ACIDS PERIOD
1: DEFINITION AND CHARACTERISTICS OF ACID
Acids are associated with the sour taste we feel when we take fruits such as lemons, lime, and oranges especially when they are not ripe. Palm wine left open in the air becomes sour because of the formation of acid.
Definition of acid: An acid is a substance that produces hydrogen ions (or protons) as the only positive ion when dissolved in water. For example, hydrochloric acid (HCl) dissolves in water to form hydrogen ions (H+) and hydroxyl ions (OH-). This process is known as ionization.
There are two main classes of acids:
Organic acids and mineral or inorganic acids. The former occurs as natural products in plants or animal materials while the latter can be prepared from mineral elements or inorganic matter.
Acids can also be grouped into Strong acids (ionizes completely) and Weak acids (ionizes partially).
Some organic and Inorganic acids Organic acids Source Inorganic acids Constituents
Ethanoic acids Vinegar Hydrochloric acid Hydrogen, Chlorine Citric acids Lime, Lemon Tetraoxosulphate
(vi) acid Hydrogen, Chlorine, Sulphur, Oxygen Fatty acids Fats, and Oil Trioxonitrate
(v) acid Hydrogen, Nitrogen, Oxygen
STRENGTH OF AN ACID
3 The strength of an acid is defined as the degree or the extent to which an acid ionizes in water.
Based on this fact, acids can be weak or strong. Strong acids are those that ionize completely in water. Examples of strong acids are H2SO4, HCl, HNO3, HBr, HI, etc. For example, HCl ionizes completely according to the equation below: HCl→H+ + Cl- (100% ionization) Strong acids are also strong electrolytes i.e. they have high electrical conductivity. Weak acids are those that ionize partially in the water.
Examples are organic acids, such as (Ethanoic acids, Citric acids, and amino acids) and some inorganic acids such as HNO2, H2CO3, H3PO4, HF, etc.
For example ethanoic acid, CH3COOH, ionizes partially in water according to the equation below: CH3COOH⇋CH3COO- + H+ Weak acids are also weak electrolytes because they are poor conductors of electricity.
BASICITY OF AN ACID
All acids in an aqueous solution yield hydrogen ions which can be replaced by metallic ions. The basicity of an acid is the number of replaceable hydrogen ions, H+, in one molecule of the acid. ACIDS BASICITY HCl 1 H2SO4 2 H3PO4 3 H2CO3 2 CH3COOH
CHARACTERISTICS OF ACIDS (PHYSICAL PROPERTIES)
1. Acids turn blue litmus paper red.
2. They have a sour taste; e.g. sour taste of unripe fruits.
3. Strong acids are corrosive in concentrated form; e.g.HCl, H2SO4
EVALUATION
1. Define acid and give two examples each of organic acid and inorganic acid
2. Differentiate between a strong acid and a weak acid. Give two examples of each.
3. (a) What is the basicity of an acid? (b). Mention four physical properties of an acid.
4. Compare and contrast the electrical conductivity of HCl and CH3COOH PERIOD
2: PREPARATION OF ACIDS
1. Dissolving non-metallic oxide (acid anhydride) in water. Carbon (iv) oxide dissolves in water to form a weak acid, trioxocarbonate (iv) acid. CO2(g)+ H2O(l) H2CO3(aq)
2. Direct combination of constituent elements. Hydrogen reacts directly with Halogens in the presence of a catalyst to form halogen acid gas which dissolves readily in water to form acid. H2(g)+ Cl2(g) 2HCl(g) 𝐴𝑐𝑡𝑖𝑣𝑎𝑡𝑒𝑑 𝑐ℎ𝑎𝑟𝑐𝑜𝑎𝑙 → ℎ𝑒𝑎𝑡
3. Heating Hydrogen gas and bromine vapor, in the presence of platinum as the catalyst, produces hydrogen bromide gas, which dissolves readily in water to form hydrobromic acid.
4. Displacement of weak or volatile acid from its salt by a strong acid. Concentrated H2SO4 is stronger but less volatile than HCl and, H2SO4 can therefore be used to displace the weaker HCl acid from its salt (NaCl). NaCl(s)+ H2SO4(aq) NaHSO4(aq) + HCl(g) The hydrogen chloride gas dissolved in water readily to produce hydrogen chloride acid.
EVALUATION
Mention the methods of preparing acids PERIOD
3: REACTION OF ACIDS (CHEMICAL PROPERTIES)
1. The reaction of an acid with metals Acids react with some metals to liberate hydrogen gas. Zn(s)+ 2HCl (aq) ZnCl2(aq) + H2(g) Mg(s)+ H2SO4 (aq) MgSO4+ H2(g) NOTE:Dilute HNO3does not react with metals to produce hydrogen gas.
2. Reaction of acids with Base and Alkalis Dilute acids react with bases and alkalis to form salts and water (known as neutralization reaction) HCl(aq) + NaOH(aq) NaCl(aq)+ H2O(l) H2SO4(aq) + CaO(aq) CaSO4(aq) + H2O(l)
3. Reaction of acids with Trioxocarbonate (iv) and hydrogen trioxocarbonate (iv). An acid reacts with CO32-or HCO3- to liberate carbon (iv) oxide (CO2). NaCO3(s)+ 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g) NaHCO3 + HCl(aq) NaHCll(aq) + H2O(l) + CO2(g) EVALUATION 1.What is neutralization? 2. State three chemical properties of acids
USES OF ACIDS
Name Uses Hydrochloric acid in industries to make chemicals to remove rust Tetraoxosulphate (vi) acid to make chemicals as drying and dehydrating agent as an electrolyte in lead-acid accumulators
trrioxonitrate (v) acid for making fertilizers, explosives, etc. Acetic acid (ethanoic) In preserving food In dyeing silk and other textiles. Tartaric In making baking soda, soft drinks, and health salt Citric acid In making fruit juice Fatty acids (e.g. palmitic and stearic acids) In manufacturing soap. ( A process known as Saponification)
EVALUATION
Give three (3) uses of each of the following acids: HCl, H2SO4, HNO3, Citric acid
GENERAL EVALUATION OBJECTIVE TEST:
A weak acid is one which A. is not corrosive B. is slightly ionized in water. C. does not produce salts with alkalis. D. form acid salt with water
The number of replaceable hydrogen ions in one molecule of an acid indicates its A. basicity B. acidity C. alkalinity D. reactivity Which gas is liberated when an acid reacts with metals? A.O2 B. H2 C. CO2 D.NO2
The reaction of acid and base to produce salt and water is A. precipitation B. neutralization C. evaporation D. decantation H2(g) + Cl2(g) 2HCl(g). The catalyst in this reaction is ℎ𝑒𝑎𝑡 → A. activated charcoal B. platinum C. yeast D. heat
ESSAY QUESTIONS:
1. Give three physical properties of an acid.
2. Write an equation for the reaction between iron fillings and tetraoxosulphate(vi) acid.
3. State how hydrogen chloride gas can be obtained from tetraoxosulphate (vi) acid
4. (a) What is basicity? (b). State the basicity of the following acids: i. HNO3 ii. H2SO4 iii. CH3COOH.
5. State the natural source of i. ethanoic acid ii. Citric acid iii. Amino acid
6. (a) Why is ethanoic acid regarded as weak acid?
6(b). Hydrochloric acid is regarded as a strong acid. Why?
WEEKEND ASSIGNMENT:
New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio; pages 97 – 100 PRE–READING
ASSIGNMENT: Read about Bases and Alkalis
WEEKEND ACTIVITY: How are bases prepared and, what are their characteristics?
