Ch. No. 3. THE ACID BASE CHEMISTRY
Q1. Fill in the blanks:
1. Most of the acidic substances are sour in taste.
2. Phenolphthalein is synthetic type of indicator.
3. The strength of basic substance is represented by pOH.
4. pH scale ranges from zero to fourteen.
5. Acids and bases neutralize each other to form salt and water.
6. Sodium or potassium salts of higher fatty acids are termed as soap.
7. In FeSO4. 7H2O.H2O represents water of crystallization.
8. 10% NaCl is known as brine.
9. Litmus paper or solution is obtained from a plant named lichen.
Q2. Name the carboxylic acids present in
Acid | Acid | ||
Tamarind Butter Roots of plant valerum Lemon | Tartaric acid Butyric acid Valine Citric acid | Milk Orange Red ants Honey bee sting | Lactic acid Citric acid Formic acid Melittin |
Q3. Write short notes on
1. Indicators (with proper example).
Ans. The acidic and basic nature of the compounds can also be indicated by some natural as well as chemical substances. They are known as indicators.
i. There are many natural substances such as rose petals, turmeric, beet root, etc that can be used as indicators. They are called natural indicators.
ii. Some chemical substances such as phenolphthalein, methyl orange, eosin are synthetic indicators.
iii. Olfactory indicators: Substances whose odour changes in acidic or basic solution are called olfactory indicator. An olfactory indicator works on the principle that when an acid or base is added to it, then its odour cannot be detected. Examples: onion and clove extract.
iv. Universal indicators: Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.
v. Uses of indicators: The acidic or basic nature of a compound can be judged. It is used in agriculture to determine the pH of the soil.
2. pH scale (with proper diagram).
Ans.
i. pH helps in measuring hydrogen ion concentration in solutions. In pH, p stands for “potenz” means “strength” in German.
ii. The scale reads from O (zero) (most acidic) to 14 (most basic).
iii. The value of pH indicates acidic or basic nature of a solution. The strength of base is represented by pOH.
iv. When the pH value is in between 0 to 7, the solution is acidic in nature. At value 7, the solution is neutral and between 7 to 14 the nature of the solution becomes alkaline/ basic.
v. Lower the pH of an acid, greater is the concentration of H+ ions, greater the pH of a base, greater is the concentration of OH ions.
3. Water of crystallization (with proper example)
Ans.
i. Water of crystallization is the fixed number of water molecules present in the crystal structure.
ii. For example, chemical formula of hydrated copper sulphate is CuSO4.5H2O. Copper sulphate has 5 molecules of water of crystallization.
iii. Sodium carbonate is Na2CO3.10H2O. Sodium carbonate has 10 molecules of water of crystallization.
iv. On heating or on exposure to air, the above salts lose water of crystallization and form anhydrous substances.
Q4. Answer the following:
1. How do metal carbonates react with acids?
Ans. When a metal carbonate or metal hydrogen carbonate reacts with an acid, it forms corresponding salt and carbon dioxide gas.
2. Explain in detail about hydronium ion.
Ans.
i. The strength of an acid is measured in terms of the extent of ionization of the acid in aqueous solution.
ii. Higher the H+ ions concentration stronger is the acid.
iii. Hydrogen ion (H+) does not exist alone. H+ ion being unstable, it combines with H2O to form hydronium ion (H3O+).
3. What is universal indicator? Does Mg(OH)2 react with sodium hydroxide? If not, why?
Ans.
i. Universal indicator is an indicator which is a mixture of several indicators.
ii. It has a very wide range and can indicate pH value almost from 0 to 14.
iii. When one or two drops of universal indicator is added to a solution, it changes its colour. This colour is matched against the colour on a standard colour chart (usually given on its bottle) to find the pH, and the pH value can be read. This indicates the strength of the solution too.
iv. Universal indicator is available as a solution or in the form of paper strips.
v. Mg(OH)2 does not react with sodium hydroxide as both are bases.
4. State application (uses) of baking soda.
Ans. The white amorphous powdered soda is termed as baking soda. Its chemical name is Sodium Hydrogen Carbonate or Sodium bicarbonate and its formula is NaHCO3. When tested with litmus, NaHCO3 turns red litmus blue, which indicates that it is alkaline in nature.
Sodium bicarbonate is extensively used in day – to – day life.
i. It is used to prepare light spongy bread, cakes and dhokala.
ii. It also helps to reduce acidity in stomach being alkaline.
iii. It is very useful in preparing CO2gas and is one of the content of fire extinguishers.
Q5. How do acids and bases react with each other? What is the name of the process? What product is obtained out of these reaction?
Ans.
i. Acid reacts with base to form salt and water.
ii. It is known that, acid generates H+and base generates OH- ions.
iii. The H+ ions of an acid and OH-ions of a base react with each other to form unionized water. The process is termed as neutralization.
iv. The product obtained out of this reaction is salt and water.