An indicator
ACIDS, BASES AND SALTS
An acid is a substance which produces hydrogen ions (H+ ) when dissolved in water. Acid are also called
proton donors. Acids form hydronium ions when dissolved in water
HCl(g)
H+ + Cl-
H3O+ + Cl
HCl + H2O
PROPERTIES OF ACIDS
1. They are clear colorless liquids
2. They have sour taste
3. They are corrosive
4 They are electrolytes- conduct electricity
5 Change blue litmus paper to red.
6. They have pH less than 7
COMMON ACIDS IN THE LAB
NAME
Hydrochloric acid
Sulphuric acid
Nitric acid
Ethanoic acid
FORMULA
HCl
H2SO4
HNO3
CH3COOH
COMMON ACIDS IN NATURE
NAME
SOURCE
Hydrochloric acid
Citric acid
Lactic acid
Stomach
Citrus fruits
Sour milk/in the muscles
during exercise
Grapes
vinegar
Tartaric acid
Ethanoic acid
Acids can be classified in different ways
1.
Strength of acids
Strong acids are fully/totally ionized when dissolved in water. Eg HCl, H2SO4, HNO3. They have a low pH
value (1-4). They have a high conductivity. All he hydrogen ions are available for reaction
Weak acids are partially ionized when dissolved in water. CH3COOH. . They are only partially ionized
when dissolved in water. Not all the hydrogen ions are available for reaction—only a few. They have a
pH value between 4 & 7. CH3COOH
CH3 COO- + H+. They have low conductivity.
There are two types of acids: mineral acids (inorganic acid) and organic acids.
2.
ORGANIC AND INORGANIC
Inorganic or mineral acids are made from the nonmetallic elements or polyatomic ions with hydrogen.
They are strong acids. These acids are totally ionized when dissolved in water.
Organic acids are from plants and animals and are weak acids. They all have the carboxyl group COOH.
3.
BASICITY
Basicity is the number of moles of hydrogen ions liberated from one mole of acid when dissolved in
water. It is also called its Protocity. Acids can either be:
 Monobasic HCl
H+ + Cl-. Monobasic acids produce one mole of H+ ions
 Dibasic H2SO4
2H+ +SO42-. Dibasic acids produce two moles of H+ ions
 Tribasic H3PO4
3H+ + PO43-. Tribasic acids produce three moles of H+ ions
Dibasic Tribasic acids can form normal or acid salts. Monobasic acids can only form normal salts.
4.
DILUTE AND CONCENTRATED ACIDS
A dilute acid contains a lot of water. A concentrated acid is one that contains very little water
Reactions of acids:
 Acid + Base
 Acid + Metal
Salt + Water
Salt + Hydrogen
 Acid + Carbonate/Hydrogen carbonate
Salt + water + Carbon dioxide
Acids in living systems: Vitamin C, methanoic acid, lactic acid, Ethanoic acid, citric acid
BASES
PROPERTIES OF BASES
1. They have taste bitter
2. They feel soapy/Slippery
3. They are corrosive
4. Have pH above 7
5. They are electrolytes
A base is a substance that will react with an acid to produce a salt and water as the only products. They
are also the oxides and hydroxides of metals and are described as proton acceptors. Bases include
ammonia, metal oxides and hydroxides. A soluble base is called an alkali.
A strong base ionized fully when dissolved in water to form hydroxide ions. They have a pH between 11
and 14. All hydroxide ions are available for reaction
NaOH(aq) + H2O(l)
NH4(aq) + OH-(aq)
Weak bases are partially ionized when dissolved in water forming low concentration of hydroxyl ions.
They have pH between 7 and 11. Only a few hydroxide ions are available for reactions.
Reaction of bases:
 Base + acid
salt + water
 Base (alkali) + ammonium compound
salt + water + ammonia
Oxides: An oxide is a compound containing oxygen and one other element.
Acidic oxides: the oxide of a non-metal which will form an acid when dissolved in water eg. SO2, SO3,
CO2.
Basic oxides/hydroxides: metallic oxide/hydroxide which contains oxide ions/hydroxide ions and will
react with an acid to form a salt and water only.
Neutral oxides: oxides of some non-metals that is neither acidic nor basic eg. NO, CO, N2O.
Amphoteric oxides/hydroxides: oxides/hydroxides that will react with both acids bases to form salt and
water. Eg. PbO, Al(OH)3, Al2O3, ZnO, Zn(OH)2, Pb(OH)2.
INDICATORS
An indicator is a substance that shows the presence of an acid or an alkali. The give one colour in an acid
and another in an alkali
INDICATOR
LITMUS
PHENOLPHTHALEIN
METHYL ORANGE
SCREENED METHYL ORANGE
COLOUR IN ACID
RED
COLOURLESS
RED
RED
COLOUR IN ALKALI
BLUE
PINK
YELLOW
GREEN
The strength of an solution can be measured by its pH. The pH scale is a number line from 0 to 14, It
indicates whether a solution is acidic, alkaline or neutral. Each number is accompanied by a different
colour. A pH of 7 means that the solution is neutral, pH below 7 means that its acidic and over 7 means
that it alkaline.
SALTS
Substance formed by replacing some or all of the hydrogen ions in an acid by a metal. It is an ionic
compound formed by the metallic ion and the anion from the acid. There are two types of salts: normal
and acid.
Normal salts are formed when all the hydrogen ions are replaced. They are neutral with a pH of 7.
Acid salts are formed when some of the hydrogen ions are replaced. They still have some hydrogen ions
from the acid. They have a pH below 7.
The first part of the name of a salt comes from the metal and the second part from the acid
NAME OF ACID
Hydrochloric acid
Sulphuric acid
Nitric acid
Ethanoic acid
NAME IN SALT
Chloride
Sulphate
Nitrate
Ethanoate
Water of crystallization: This is a fixed amount of water that is locked in the crystal lattice structure of
some salts. It is responsible for the shape and sometimes the colour of salt crystals. These salts are
called hydrated salts. This water can be removed by heating. Salts without water are called anhydrous
salts. When heated the shape and colour may change.
Salt Preparation
Salts can be prepared based on the following: ion solubility of salt, solubility so starting materials,
hydration of salt.
Solubility of substances
Bases/salts
Solubility in water
Chlorides
All are soluble except Ag & Pb salts. PbCl2 soluble in hot
water
Nitrates
All are soluble
Carbonates
All are insoluble except K, Na, NH4 salts
Sulphates
All soluble except Pb & Ba salts. CaSO4 slightly soluble
Oxides
Insoluble except K, Na, Ca
Hydroxides
All insoluble except Na, K, NH4. Ba & Ca are slightly soluble
Nb: All Na, K, and NH4 salts are soluble.
METHODS OF PREPARATION
1. Precipitation method: This method is used to prepare insoluble salts. The starting materials are two
soluble solutions. One provides the cation and the other provides the anion of the salt.
Procedure: The two solutions are mixed. A precipitate (solid substance), which is the insoluble salt, is
formed. This is then filtered, washed with distilled water, and dried.
2. Direct Combination method: This method is used to prepare binary anhydrous soluble salts. The two
elements that make up the salt are heated together. A metal provides the cation and a non-metal
provides the anion.
Iron + Chlorine
2Fe + 3Cl2
Iron Chloride
2 FeCl3
3. Neutralisation Method: This method is used to prepare soluble salts. An acid is neutralized using a
solid metal, solid base, solid carbonate or an alkali solution.
Procedure: The solid metal, base or carbonate is added in excess to the acid. This is to ensure that all the
acid is used up. The mixture is then filtered to remove the excess solid (metal, oxide or carbonate). The
solution is then gently heated until crystallization begins. The solution is then allowed to cool and
crystallize. The crystals are then washed in a small quantity of distilled water and dried
Titration is used to obtain the salt from an acid and an alkali solution. The acid and alkali are titrated
with an indicator to obtain exact volumes of both solutions. The exact solutions are then combined
without the indicator. The solution is then evaporated until crystallization begins. The solution is then
cooled until it crystallized. The crystals are then washed and dried.
USES AND OF SALTS IN EVERYDAY LIFE: sodium hydrogen carbonate as an ingredient in baking powder
Sodium carbonate (washing soda) used to soften water
Calcium carbonate (limestone) use to make cement
Magnesium sulphate (Epsom salt) many medicinal uses. Also taken as a laxative
Sodium chloride, sodium nitrate and sodium nitrite, sodium benzoate used as a food preservative
Calcium sulphate (gypsum) used to make plaster of Paris and building materials
DANGERS OF SALTS IN EVERYDAY LIFE: Sodium chloride can lead to hypertension
Sodium benzoate, sodium nitrate and sodium nitrite are carcinogenetic.
VOLUMETRIC ANALYSIS involves performing titration to determine the exact volume of one solution,
usually an acid, required to neutralize a fixed volume of another solution, usually an alkali or carbonate.
The results can be used quantitatively to determine:

Mole ratio of the reactants

Molar and mass concentration of one of the reactants.