Acids is defined as the one which produces hydrogen ions in water. For Example, Sulphuric Acid, Hydrochloric Acid etc.
They give sour taste.
Acids turn blue litmus to red. This is used as confirmation test for the presence of acid.
When acids react with metals, gases are evolved.
Reactions with Acids-
1. Reaction of Acid with MetalAcid + Metal → Salt + Hydrogen gas Mg + H2 SO4 → H2 + Mg SO4
2. Reaction of Acid with Carbonates Na2 CO3 (s) + 2 HCl (aq) → 2NaCl (aq) +H2O(l) + CO2(g)
3. Reaction of Acid with Bicarbonates NaHCO3(s) + HCl (aq) → NaCl(aq) + H2O(l) + CO2(g)
Acid + metal carbonate or bicarbonate → salt + water + carbon dioxide
Similarity between Acids and Bases
1. Both acids and base react with water. They produce ions in water 2. Both acids and bases acts as electrolytes, so are good conductors of electricity
Classification of Acids
1. Acids are classified as Organic Acids and Mineral Acids. Acids which are derived from plants and animals, they are known as Organic Acids. For Example, Citric Acid from fruit. Mineral acids are inorganic acids such as Sulphuric Acid. They are dangerous to be used, so need more precautions.
2. Acids are also classified as Strong Acids or Weak Acids. Strong acid is an acid, that completely dissociates into ions in aqueous solutions. For Example, Sulphuric Acid, Hydrochloric Acid.
HCI acid + H2O = H3O+ + CI–
Weak acid is the one which does not dissociate completely into ions in aqueous solutions. For Example, Acetic Acid.
CH3COOH + H2O ⇌ CH3CHOO– + H+
1. Acids can also be as Dilute Acid and Concentrated Acids. The one which has low concentration of acids in aqueous solution, they are known as Dilute Acids whereas the one which has high concentration of acids in aqueous solution, are known as Concentrated Acids.
2. It is advisable to add acid to water and not vice versa because large amount of heat is released if water is added to acid. This released heat is large enough to cause harm.
3. Acids can also be classified based on number of hydrogen ions. Monoprotic acid is the one which gives one mole of hydrogen ions per mole of acid, such as HCl. Diprotic Acid is the one which produces two mole of hydrogen ions per mole of acid. For Example, H2SO4.
Bases
Bases are the one which produces hydroxide ions in aqueous solutions. Bases which are water soluble they are known as Alkalis.
They turn red litmus to blue.
They have a bitter taste.
They also produced carbon-dioxide when reacted with carbonates.
They also evolved hydrogen gas when bases react with metals.
Reactions of Bases
Reaction with Metals-Base reacts with metals and produce hydrogen gas. 2NaOH + Zn → Na2 → Na2ZnO2 +H2
Reaction with Acids-Base reacts with acids to form salts. For Example, KOH + HCl → KCl + H2O
Classification of Bases
Bases are classified as Strong Base and Weak Base. Strong base is the one which dissociates completely into its ions in aqueous solution. For Example, NaOH.
Weak base is the one which does not dissociate completely into its ions in aqueous solutions. For Example, Ammonium Hydroxide, NH4OH
Bases are also classified as Dilute Base and Concentrated Base. The solution which has low concentration of base in aqueous solution is defined as Dilute Base whereas the one which has high concentration of base in aqueous solution is known as Concentrated Base
Effect on indicators by acids and bases-
An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base. Below mentioned are commonly used indicators and the different colours they exhibit:
a) Litmus
In a neutral solution – purple In acidic solution – red In basic solution – blue Litmus is also available as strips of paper in two variants – red litmus and blue litmus. An acid turns a moist blue litmus paper to red. A base turns a moist red litmus paper to blue.
b) Methyl orange
In a neutral solution – orange In acidic solution – red In basic solution – yellow
c) Phenolphthalein
In a neutral solution – colourless In acidic solution – remains colourless In basic solution – pink Litmus is also available as strips of paper in two variants – red litmus and blue litmus. An acid turns a moist blue litmus paper to red. A base turns a moist red litmus paper to blue.
Importance of pH in everyday life
1.pH sensitivity of plants and animals-Plants and animals are sensitive to pH. Crucial life processes such as digestion of food, functions of enzymes and hormones happen at a certain pH value.
2. pH of a soil-The pH of a soil optimal for the growth of plants or crops is 6.5 to 7.0.
3. pH in the digestive system-The process of digestion happens at a specific pH in our stomach which is 1.5 to 4.The pH of the interaction of enzymes, while food is being digested, is influenced by HCl in our stomach.
4. pH in tooth decay-Tooth decay happens when the teeth are exposed to an acidic environment of pH 5.5 and below.
5. pH of self-defence by animals and plants-Acidic substances are used by animals and plants as a self-defenses mechanism. For example, bee and plants like nettle secrete a highly acidic substance for self-defenses. These secreted acidic substances have a specific ph.
Salts
When acid and base neutralize, salts are formed. Strong acid and strong base combines to form neutral salt.
NaOH + HCl → NaCl + H2O Strong acid and weak base combine to form acidic salt. For Example, Hydrochloric Acid and ammonium hydroxide combine to form ammonium chloride. Other examples, sodium hydrogen carbonate, sodium hydrogen sulphate etc.
HCl + NH4OH → NH4Cl + H2O Similarly, weak acid and strong base combine to form basic salt. For Example, Acetic Acid and sodium hydroxide combine to form sodium acetate. Other examples are calcium carbonate, potassium cyanide etc.
CH3COOH + NaOH → CH3COONa + H2O The most common salt is table salt or sodium chloride (NaCl).
Preparation of Sodium hydroxide
Chemical formula – NaOH Also known as – caustic soda
Preparation (Chlor-alkali process)
Electrolysis of brine (solution of common salt, NaCl) is carried out. At anode: Cl2 is released At cathode: H2 is released Sodium hydroxide remains in the solution.
Bleaching powder
Chemical formula – Ca(OCl)Cl or CaOCl2
Preparation – Ca(OH)2(aq)+Cl2(g)→CaOCl2(aq)+H2O(l) On interaction with water – bleaching powder releases chlorine which is responsible for bleaching action.
Baking soda
Chemical name – Sodium hydrogen carbonate Chemical formula – NaHCO3
Preparation (Solvay process):
a. Limestone is heated: CaCO3→CaO+CO2 b. CO2 is passed through a concentrated solution of sodium chloride and ammonia: NaCl(aq)+NH3(g)+CO2(g)+H2O(l)→NaHCO3(aq)+NH4Cl(aq)
Uses: 1. Textile industry 2. Paper industry 3. Disinfectant
Washing soda
Chemical name – Sodium hydrogen carbonate Chemical formula – NaHCO3
Preparation (Solvay process)
a. Limestone is heated: CaCO3 → CaO + CO2 b. CO2 is passed through a concentrated solution of sodium chloride and ammonia: NaCl(aq) + NH3(g) + CO2(g) + H2O(l) → NaHCO3(aq) + NH4Cl(aq)
Uses 1. In glass, soap and paper industries 2. Softening of water 3. Domestic cleaner
Crystals of salts-
Certain salts form crystals by combining with a definite proportion of water. The water that combines with the salt is called water of crystallisation.
Plaster of Paris
Gypsum, CaSO4.2H2O (s) on heating at 100°C (373K) gives CaSO4. ½ H2O and 3/2 H2O CaSO4. ½ H2O is plaster of paris. CaSO4. ½ H2O means two formula units of CaSO4 share one molecule of water.
Uses cast for healing fractures.
Write the answer of the following questions.
What happens when a solution of an acid is mixed with a solution of a base in a test tube? (i) Temperature of the solution decreases (ii) Temperature of the solution increases (in) Temperature of the solution remains the same (iv) Salt formation takes place
(a) (i) and (iv) (b) (i) and (iii) (c) (ii) only (d) (ii) and (iv)
When hydrogen chloride gas is prepared on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to (a) absorb the evolved gas (b) moisten the gas (c) absorb moisture from the gas (d) absorb Cl– ions from the evolved gas
Which one of the following salts does not con-tain water of crystallisation? (a) Blue vitriol (b) Baking soda (c) Washing soda (d) Gypsum
In terms of acidic strength, which one of the following is in the correct increasing order? (a) Water < Acetic acid < Hydrochloric acid (b) Water < Hydrochloric acid < Acetic acid (c) Acetic acid < Water < Hydrochloric acid (d) Hydrochloric acid < Water < Acetic acid
What is formed when zinc reacts with sodium hydroxide? (a) Zinc hydroxide and sodium (b) Sodium zincate and hydrogen gas (c) Sodium zinc-oxide and hydrogen gas (d) Sodium zincate and water
Tomato is a natural source of which acid? (a) Acetic acid (b) Citric acid (c) Tartaric acid (d) Oxalic acid
Brine is an (a) aqueous solution of sodium hydroxide (b) aqueous solution of sodium carbonate (c) aqueous solution of sodium chloride (d) aqueous solution of sodium bicarbonate
Na2CO3 . 10H2O is (a) washing soda (b) baking soda (c) bleaching powder (d) tartaric acid
At what temperature is gypsum heated to form Plaster of Paris? (a) 90°C (b) 100°C (c) 110°C (d) 120°C
How many water molecules does hydrated cal-cium sulphate contain? (a) 5 (b) 10 (c) 7 (d) 2
Sodium carbonate is a basic salt because it is a salt of a (a) strong acid and strong base (b) weak acid and weak base (c) strong acid and weak base (d) weak acid and strong base
Alkalis are (a) acids, which are soluble in water (b) acids, which are insoluble in water (c) bases, which are insoluble in water (d) bases, which are soluble in water
Which of the following statements is correct about an aqueous solution of an acid and of a base? (i) Higher the pH, stronger the acid (ii) Higher the pH, weaker the acid (in) Lower the pH, stronger the base (iv) Lower the pH, weaker the base
(a) (i) and (iii) (b) (ii) and (iii) (c) (i) and (iv) (d) (ii) and (iv)
The apparatus given in the adjoining figure was set up to demonstrate electrical conductivity. Which of the following statement(s) is (are) correct? (i) Bulb will not glow because electrolyte is not acidic. (ii) Bulb will glow because HCl is a strong acid and furnishes ions for conduction. (iii) Bulb will not glow because circuit is incomplete. (iv) Bulb will not glow because it depends upon the type of electrolytic solution.
(a) (i) and (iii) (b) (ii) and (iv) (c) (ii) only (d) (iv) only
Lime water reacts with chlorine to give (a) bleaching powder (b) baking powder (c) baking soda (d) washing soda
Nettle sting is a natural source of which acid? (a) MetiWanoic acid (b) Lactic acid (c) Citric acid (d) Tartaric acid
Tooth enamel is made up of (a) calcium phosphate (b) calcium carbonate (c) calcium oxide (d) potassium
What is the pH range of our body? (a) 7.0 – 7.8 (b) 7.2 – 8.0 (c) 7.0 – 8.4 (d) 7.2 – 8.4
Rain is called acid rain when its: (a) pH falls below 7 (b) pH falls below 6 (c) pH falls below 5.6 (d) pH is above 7
Sodium hydroxide is a (a) weak base (b) weak acid (c) strong base (d) strong acid
An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change? (a) Baking powder (b) Lime (c) Ammonium hydroxide solution (d) Hydrochloric acid
When copper oxide and dilute hydrochloric acid react, colour changes to (a) white (b) bluish-green (c) blue-black (d) black
Sodium hydroxide is used (a) as an antacid (b) in manufacture of soap (c) as a cleansing agent (d) in alkaline batteries
