Acid and Base-few points to remember
1- An acid, when dissolved in water, furnishes H3O+ ions as the only positively charged ions. A mineral acid does not contain H3O+ ions as such.
It furnishes H ions in the solution which combine with water molecules to form H3O+ ions.
2– The basicity of an acid is the number of H3O+ or (H+) ion furnished by one molecule of the acid in aqueous solution. On the basis of basicity, acids are classified as monobasic, dibasic, and tribasic.
3– Acid can be prepared from non-metals by direct combination and by oxidation, from non-metallic oxides by dissolving them in water and by the displacement of more volatile acids from their salts by less volatile acids.
4– Acids taste sour, conduct electricity in solution and turn blue litmus red.
5– Acids react with active metals to liberate hydrogen gas, neutralize bases to form salts, decompose carbonate, bicarbonate, sulphides, sulphites, bisulphites, nitrates, etc., to form corresponding compound.
6– A base reacts with hydronium ions given by an acid to form a salt and water only.
Alkalies are those bases which are soluble in water and furnish hydroxide ion (OH–) as the only negative ions in the solution.
7– The acidity of a base is the number of hydroxide ion furnished by one molecule of the base in aqueous solution. On the basis of acidity, bases are classified as monoacidic base (e.g., NaOH, KOH, etc.), diacidic base (e.g., Ca(OH)2, .Ba(OH)2, etc.), and triacidic base (e.g., Fe(OH)3, Al(OH)₃, etc.)
8– Bases can be prepared by oxidation of metals, by the action of water on very active metals, by dissolving metallic oxide in water, by thermal decomposition of carbonates and nitrates and by double decomposition. NH4OH can be obtained by dissolving ammonia (NH3) in water.
9– Bases taste bitter and soapy to touch. Alkalis are soluble in water, give a pink colour with phenolphthalein and turn red litmus blue.
10– Bases neutralise acids to form salts. Alkalis react with carbon dioxide (CO2) to form carbonates, react with certain metallic salts to precipitate insoluble hydroxides and react with ammonium salts to liberate ammonia (NH3).
11– An alkali is a water-soluble base.
12– Alkalis provides hydroxide ion on dissolution in water.
13– All alkalis are base but all bases are not alkalis.
14– Fe(OH)3, Cu(OH)3 are bases and not alkalis as they are insoluble in water.
15– A salt is an electrovalent compound formed by the partial or complete replacement of the replaceable hydrogen atoms of an acid by a metallic ion or ammonium ion.
16– Salts are classified as normal salts, acid salts, basic salts, double salts, mixed salts, and complex salts.
17– Normal salts (e.g., NaCl, K2SO4, etc.) are formed by the complete replacement of the replaceable hydrogen ion of an acid. They contain a positive ion other than hydrogen ion and a negative ion other than the hydroxide ion.
18– Acid salts (e.g., NaHSO4, KHCO3, etc.) are formed by the partial replacement of the replaceable hydrogen atom(H) of an acid molecule. They contain a metallic cation of the base and one or more hydrogen atoms of the acid attached to the anion of the acid.
19– Basic salts (e.g., Mg(OH)Cl, Cu(OH)NO3, etc.) are formed by the partial replacement of hydroxide ion of a diacidic or triacidic base. They contain a metallic cation, a hydroxyl ion of the base, and an anion of the acid.
20– Double salts are formed by the combination of two simple salts in the simple molecular ratio. They contain all the ions of their constituent simple salts.
21– Mixed salts are obtained by the neutralization of a dibasic or tribasic acid with different monoacid bases or by the neutralization of a diacidic or triacid base with different monobasic acid. They contain two or more acidic or basic radicals.
22– Complex salts furnish a simple ion and a complex ion in the solution. A complex ion consists of a central metal atom or ion attached to the several unionisable atoms or groups of atoms.
They contain one or more simple ions and a complex ion. (Acid and Base-few points to remember)
23– All the salts are strong electrolytes.
24– Salt can be prepared by direct combination of elements, by decomposition of carbonates, bicarbonates, chlorides, nitrates, etc., by acid, by double decomposition, by displacement and by neutralization reaction.
25– Salts made up of strong acid + strong base do not hydrolyse in
water and their solution has pH = 7.
26– Salts made up of weak acid + weak base provide its almost
neutral solution pH greater or less than 7.
27– Salts made up of weak acid + strong base give their aqua
solution having a pH greater than 7.
28– Salts made up of strong acid +weak base give their aqua solution having pH less than 7.
29– Water molecules associated in loose chemical combination with a molecule of a salt are called the water of crystallisation and such a salt is called hydrated salt.
30– When a crystalline hydrated salt on exposure to the atmosphere loses partly or wholly its water of crystallisation, the phenomenon is called efflorescence, and such a salt is called an efflorescent salt.
The crystalline salt crumbles to an amorphous powder due to efflorescence.
31– When a water-soluble substance on exposure to atmosphere absorbs moisture, becomes moist and finally dissolves to form a saturated solution, the phenomena is called deliquescence and such a substance is called a deliquescent substance.
When the substance absorbs moisture but does not dissolve to form a solution, it is called a hygroscopic substance.
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