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Acid Base and Salt Question and Answers
We have learnt that an acid is any compound which yields hydrogen ions (H+) in its aqueous solution. In place of hydrogen ion, it’s batter to write hydronium ions which form due to reaction of H+ with water. For example the reaction of hydrochloric acid (HCl) in water can be written as given below;
HCl + H2O → H3O+ + Cl-
At the same time bases are the substance which produces hydroxide ion (OH-) in water. This concept is given by Arrhenius and known as Arrhenius theory. Both of these compounds; acids and bases react with one another to yield two products. One is water, and another is an ionic compound which is known as salt. Such reactions are called as called a neutralization reaction. For example the reaction of sodium hydroxide with hydrochloric acid can be written as given below;
Na+ OH- + H+Cl- → H2O + Na+Cl –
Neutralization reactions are always exothermic in nature means they liberate heat which is called as heat of neutralisation. The amount of it is fixed for any acid and base that is 57.7 kJ per mole of H+. For any acid and base combination the net reaction is
H+ (aq) + OH- (aq) → H2O
Since the salts are ionic in nature therefore can exist in the form of ions just as before the reaction. One of the most common salt, NaCl or basically the table salt which is formed when sodium hydroxide (base) combines with hydrochloric acid. Other examples include epsom salts (MgSO4) used in bath salts, ammonium nitrate (NH4NO3) used as fertiliser, and baking soda (NaHCO3) used in cooking. We can observe many neutralization reactions in our daily lives. Remember when you have stomach burns that are because of hydrochloric acid. When the hydrochloric acid touches the inner layers of our stomach, we get a burning sensation. We can take a medicine called antacid which is a chemical that has aluminium hydroxide or magnesium hydroxide. These alkalis can easily neutralize the excess acid in our stomach. Similarly acidic bee stings can be neutralized by calamine lotion, which is a mild base based of zinc oxide. Sulphate and nitrate salts of ammonium are considered to be important agro-chemical fertilisers used for good yield in cultivation. They are formed due to neutralization reaction of ammonia gas and sulphuric acid or nitric acid. The harmful acidic sulphur dioxide gas evolved as this gaseous product from the power generating units could be absorbed by basic calcium hydroxide solution to form harmless calcium sulphate. Let’s do some questions o acid, base and salts. The chemical formula of salts provides the idea about the constituent acids and bases. The cationic part of salt comes from base with the anionic part comes from acid. For example; NaCl is composed of Na+ and Cl- ion. Therefore Na+ must come from base that can be NaOH and Cl- from acid so it can be HCl. So now can you predict the acid and base which forms ammonium nitrate (NH4NO3). It must be NH4OH (base) and HNO3 (acid).