Acids, Bases And Salts Online Test 9th Science Lesson 14 Questions in English

Soil, air, water, all the life forms and the materials that they use are all consist of chemicals. Out of such chemicals, acids, bases and salts are mostly used in everyday life.

Our body metabolism is carried out by means of hydrochloric acid secreted in our stomach.

An acid is a the compound which is capable of forming hydrogen ions (H+) in aqueous solution whereas a base is a compound that forms hydroxyl ions (OH–) in solution.

When an acid and a base react with each other a neutral product is formed which is called salt.

A certain type of chemical compounds present in them gives sour taste. These are called acids. Substances with sour taste are called acids.

The word ‘acid’ is derived from the Latin name “acidus”.

In 1884 a Swedish chemist Svante Arrhenius proposed a theory on acids and bases.

According to Arrhenius theory an acid is a substance which furnishes H+ ions or H3O+ ions in aqueous solution.

Hydrogen ions in HCl are produced in the presence of water. The separation of H+ ion from HCl molecules cannot occur in the absence of water.

Hydrogen ions cannot exist alone but they exist in combined state with water molecules. Thus hydrogen ions must always be H+ (or) Hydronium (H3O+).

All acids essentially contain one or more hydrogen. But all the hydrogen containing substances are not acids. For example, methane (CH4) and ammonia (NH3) also contain hydrogen. But they do not produce H+ ions in aqueous solution.

Based on their sources: Organic Acids: Acids present in plants and animals (living things) are organic acids. Example: HCOOH, CH3COOH

Inorganic Acids: Acids prepared from rocks and minerals are inorganic acids or mineral acids. Example: HCl, HNO3, H2SO4

Monobasic Acid: Acid that contains only one replaceable hydrogen atom per molecule is called monobasic acid. It gives one hydrogen ion per molecule of the acid in solution. Example: HCl, HNO3

For acids, we use the term basicity that refers to the number of replaceable hydrogen atoms present in one molecule of an acid. For example, acetic acid (CH3COOH) has four hydrogen atoms but only one can be replaced. Hence it is monobasic.

Dibasic Acid: An acid which gives two hydrogen ions per molecule of the acid in solution. Example: H2SO4, H2CO3
Tribasic Acid: An acid which gives three hydrogen ions per molecule of the acid in solution. Example: H3PO4

Acids get ionized in water (produce H+ ions) completely or partially. Based on the extent of ionization acids are classified as below.
Strong Acids: These are acids that ionize completely in water. Example: HCl
Weak Acids: These are acids that ionize partially in water. Example: CH3COOH.

Ionization is the condition of being dissociated into ions by heat or radiation or chemical reactions or electrical discharge.

Concentrated Acid: It has relatively large amount of acid dissolved in a solvent. Dilute Acid: It has relatively smaller amount of acid dissolved in solvent.

Properties of Acids: They have sour taste. Their aqueous solutions conduct electricity since they contain ions. Acids turn blue litmus red.

Acids react with active metals to give hydrogen gas.
Mg + H2SO4 → MgSO4 + H2
Zn + 2HCl → ZnCl2 + H2

Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2 ↑
NaHCO3 + HCl → NaCl + H2O + CO2 ↑

Acids react with metallic oxides to give salt and water. CaO + H2SO4 → CaSO4 + H2O
Acids react with bases to give salt and water. HCl + NaOH → NaCl + H2O
The reaction is known as neutralization reaction.

Acids react with bases to give salt and water. The reaction is known as neutralization reaction

Sulphuric acid is called King of Chemicals because it is used in the preparation of many other compounds. It is used in car batteries also.

Hydrochloric acid is used as a cleansing agent in toilets. Citric acid is used in the preparation of effervescent salts and as a food preservative.

Nitric acid is used in the manufacture of fertilizers, dyes, paints and drugs.

Oxalic acid is used to clean iron and manganese deposits from quartz crystals. It is also used as bleach for wood and removing black stains.

Carbonic acid is used in aerated drinks. Tartaric acid is a constituent of baking powder.

Acids show their properties only when dissolved in water. In water, they ionize to form H+ ions which determine the properties of acids. They do not ionize in organic solvents. For example when HCl is dissolved in water it produces H+ ions and Cl- ions whereas in organic solvents like ethanol they do not ionize and remain as molecule.

Metals like gold and silver are not reactive with either HCl or HNO3. But the mixture of these two acids can dissolve gold. This mixture is called Aquaregia.

Aquaregia is a mixture of hydrochloric acid and nitric acid prepared optimally in a molar ratio of 3:1. It is a yellow-orange fuming liquid. It is a highly corrosive liquid, able to attack gold and other substances.

Aquaregia
Chemical formula: 3 HCl + HNO3
Solubility in Water: Miscible in water
Melting point: – 42°C (- 44°F, 231K)
Boiling point: 108°C (226°F, 381K)

The term Aquaregia is a Latin phrase meaning ‘King’s Water’. The name reflects the ability of aquaregia to dissolve the noble metals such as gold, platinum and palladium.

Uses of Aquaregia
1. It is used chiefly to dissolve metals such as gold and platinum.
2. It is used for cleaning and refining gold.

According to Arrhenius theory bases are substances that ionize in water to form hydroxyl ions (OH–). There are some metal oxides which give salt and water on reaction with acids. These are also called bases.

Bases that are soluble in water are called alkalis. A base reacts with an acid to give salt and water only. Base + Acid → Salt + Water

Sodium hydroxide ionizes in water to give hydroxyl ions and thus get dissolved in water. So it is an alkali. NaOH (aq) → Na+ (aq) + OH- (aq)

All alkalis are bases but not all bases are alkalis. For example: NaOH and KOH are alkalis whereas Al (OH)3 and Zn(OH)2 are bases.

Explanation
Classification of Bases: Based on their Acidity
Monoacidic Base: It is a base that ionizes in water to give one hydroxide ion per molecule. Example: NaOH, KOH
Diacidic Base: It is a base that ionizes in water to give two hydroxide ions per molecule. Example: Ca(OH)2. Mg(OH)2
Triacidic Base: It is a base that ionizes in water to give three hydroxide ions per molecule. Example: Al(OH)3, Fe(OH)3

Based on concentration
Concentrated Alkali: It is an alkali having a relatively high percentage of alkali in its aqueous solution. Dilute Alkali: It is an alkali having a relatively low percentage of alkali in its aqueous solution.

Weak Bases: These are bases that ionize partially in aqueous solution. Example: NH4OH, Ca(OH)2

The term acidity is used for base which means the number of replaceable hydroxyl groups present in one molecule of a base.

Properties of Bases
a) They have bitter taste.
b) Their aqueous solutions have soapy touch.
c) They turn red litmus blue.
d) Their aqueous solutions conduct electricity.

Bases react with metals to form salt with the liberation of hydrogen gas.
Zn + 2 NaOH → Na2ZnO2 + H2↑

Bases react with non-metallic oxides to produce salt and water. Since this is similar to the reaction between a base and an acid we can conclude that nonmetallic oxides are acidic in nature. Ca(OH)2 + CO2 → CaCO3+ H2O

Explanation
Bases react with acids to form salt and water. KOH + HCl → KCl + H2O
The above reaction between a base and an acid is known as Neutralization reaction.

On heating with ammonium salts, bases give ammonia gas. NaOH + NH4Cl → NaCl + H2O + NH3↑

Few metals do not react with sodium hydroxide. Example: Cu, Ag, Cr

Uses of Bases
(i) Sodium hydroxide is used in the manufacture of soap.
(ii) Calcium hydroxide is used in white washing of building.
(iii) Magnesium hydroxide is used as a medicine for stomach disorder.
(iv) Ammonium hydroxide is used to remove grease stains from cloths.

Test with a litmus paper: An acid turns blue litmus paper into red. A base turns red litmus paper into blue. Test with an indicator Phenolphthalein: In acid medium, phenolphthalein is colorless. In basic medium, phenolphthalein is pink in color.

Test with an indicator Methyl orange: In acid medium, methyl orange is pink in color. In basic medium, methyl orange is yellow in color.

A scale for measuring hydrogen ion concentration in a solution is called pH scale.

The ‘p’ in pH stands for ‘potenz’ in German meaning power.

The pH scale is a set of numbers from 0 to 14 which is used to indicate whether a solution is acidic, basic or neutral.

Acids have pH less than 7, Bases have pH greater than 7 and a neutral solution has pH equal to 7.

When you say salt you may think of the common salt. Sea water contains many salts dissolved in it. Sodium chloride is separated from these salts.

Salts are the products of the reaction between acids and bases. Salts produce positive ions and negative ions when dissolved in water.

Explanation
Normal Salts: A normal salt is obtained by complete neutralization of an acid by a base.
NaOH + HCl → NaCl + H2O

Acid Salts: It is derived from the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained.
NaOH + H2SO4 → NaHSO4 + H2O

Basic Salts: Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base with an acid radical. Pb(OH)2 + HCl → Pb(OH)Cl + H2O

Double Salts: Double salts are formed by the combination of the saturated solution of two simple salts in equimolar ratio followed by crystallization. For example, potash alum is a mixture of potassium sulphate and aluminum sulphate. KAl(SO4)2·12H2O

Properties of Salts: Salts are mostly solids which melt as well as boil at high temperature. Most of the salts are soluble in water. For example, chloride salts of potassium and sodium are soluble in water. But silver chloride is insoluble in water. They are odorless, mostly white, cubic crystals or crystalline powder with salty taste. Salt is hygroscopic in nature.

Many salts are found as crystals with water molecules. These water molecules are known as water of crystallization. Salts that contain water of crystallization are called hydrated salts.

The number of molecules of water hydrated to a salt is indicated after a dot in its chemical formula. For example, copper sulphate crystal has five molecules of water for each molecule of copper sulphate. It is written as CuSO4.5H2O and named as copper sulphate pentahydrate. This water of crystallization makes the copper sulphate blue. When it is heated, it loses its water molecules and becomes white.

Salts that do not contain water of crystallization are called anhydrous salt. They are generally found as powders.

The physical examination of the unknown salt involves the study of color, smell and density. This test is not much reliable.

Flame Test: Certain salts on reacting with concentrated hydrochloric acid (HCl) form their chlorides. The paste of the mixture with con. HCl is introduced into the flame with the help of platinum wire.

When HCl is added with a carbonate salt it gives off CO2 gas with brisk effervescence.

Common Salt (Sodium Chloride – NaCl) It is used in our daily food and used as a preservative.

Washing Soda (Sodium Carbonate-Na2CO3) is used in softening hard water. It is used in glass, soap and paper industries.

Baking Soda (Sodium bicarbonate -NaHCO3): It is used in making of baking powder which is a mixture of baking soda and tartaric acid. It is used in soda-acid fire extinguishers. Baking powder is used to make cakes and bread, soft and spongy. It neutralizes excess acid in the stomach and provides relief.

Bleaching powder (Calcium Oxychloride – CaOCl2): It is used as disinfectant. It is used in textile industry for bleaching cotton and linen.

Plaster of Paris (Calcium Sulphate Hemihydrate – CaSO4 .½ H2O)
i. It is used for plastering bones.
ii. It is used for making casts for statues.

Potash alum is a chemical compound widely used as the potassium sulfate dodecahydrate. It is double salt that is used commonly in medicine and the water treatment process.