NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL
EDUCATION DEPARTMENT
JAMMU AND KASHMIR
Lesson 5
ACIDS, BASES AND SALTS
Points to Remember
- In our daily life, we consume number of substances having different tastes.
- Substances are sour, bitter, sweet and salty to taste
- Sour taste of substances is due to presence of acids in them,
- Acid is derived from Latin word 'acere' which means Sour,
- Substances with bitter taste and soapy touch feeling have bases in them.
- Indicators are substances which are used to test acidic or basic nature of substances,
- Indicators give different colours in different solutions.
- Turmeric, litmus, china rose petals are naturally occurring indicators.
- Neutral solutions do not change the colour of either red litmus or blue litmus because they are neither acidic nor basic.
- . Phenolphthalein is a type of indicator
- Some acids are strong while some others are weak.
- The reaction between an acid and a base is known as neutralization.
- Salt and water are products of neutralization reaction.
- Indigestion is relieved by taking antacids.
- Ant and Bee sting pain is relieved by rubbing sodium bicarbonate or calamine solution.
- When soil becomes acidic, it is treated with quick lime.
- If the soil is basic, organic matter is added to it.
- The factory wastes are neutralized by adding basic substances,
SOME IMPORTANT DEFINITIONS
Neutralization reaction. The reaction of an acid and a base is called neutralization reaction.
Neutral solution. A solution which is neither acidic nor basic in nature or a solution which does not change the colour of indicator is called neutral solution.
TEXT BOOK EXERCISES
(1) Fill in the blanks by choosing correct words from the list given below :
List : bitter, ants, corrosive, citric, soapy, slaked lime.
1. The acid found in lemons is .......... acid.
2. The bases have a........... taste and touch.
3. The sting of the...........contains formic acid.
4. Sulphuric acid is highly ..... acid.
5. Acidic soils are neutralized with............
Ans. 1. citric 2. bitter, soapy 3. ant 4.
4 .corrosive 5. quick lime, /slaked lime,
(II) Statements given below are incorrect. Write correct Statementsents.
1 .Sulphuric acid is an example of organic acid .
2. Blue litmus paper turns red in a basic solution.
3. China rose solution turns green in citric acid solution.
4. Formic acid is found in the sting of a grasshopper.
5. During neutralization, an acid reacts with a salt to form water and base, as products.
Ans. Correct statements :
1. Sulphuric acid is an example of mineral acid
2. Blue litmus paper turns red in an acidic solution.
3. China rose solution turns green in sodium hydroxide solution.
4. Formic acid is found in the sting of an ant.
5. During neutralization, an acid reacts with a base to form water and salt, as products.
Statement True/False
Ans. 1. False 2. True 3. False 4. True 5. False 6. True.
Organic Acids Inorganic Acids
Examples of Indicators colour change in
Q. 3. What are neutral substances ? Give examples of two neutral substances.
Ans Neutral substances. By neutral substances we mean such substances which are neither acidic nor basic and do not affect indicators
Examples : (1) Distilled water (2) Alcohol (3) Common salt solution.
Q. 4. You are given three unlabelled bottles A, B and C. containing colourless solutions, such that one of them is acid, the other being basic and neutral. How will you distinguish between them by using china rose as an indicator
Ans. (i) Soak china rose petals in boiling water contained in a bowl for half an hour. On cooling crush the petals with hand and then filter the mixture. You will get pink coloured clear solution to be used as an indicator).
(ii) Add 1 ml of the china rose indicator solution in each of the tubes A, B and C. The tube in which its colour changes to green colour contains base while the other tube in which its colour changes to deep pink contains acidic solution and the other tube in which its colour does not change contains neutral solution. So, in this way we can identify as to which tube contains which solution.
Q. 5. What do you understand by the term neutralisation ? Describe an activity in which neutralisation of hydrochloric acid takes place with indicator. sodium hydroxide, using phenolphthalein as an indicator
Ans. Neutralisation. The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the only products, is called neutralisation
Activity. (i) Pour 20 ml of sodium hydroxide solution in a glass beaker.
ii) Add a few drops of phenolphthalein solution into the glass beaker when you will see that the solution turns pink.
(iii) Fill the dropper with dil. hydrochloric acid. Allow the
acid to fall drop by drop into the beaker. Go on stirring the beaker contents gently. You will notice that at some stage with the addition of one drop of acid the solution becomes colourless. At this stage hydrochloric acid has become neutralised on reaction with sodium hydroxide producing salt and water. Addition of the last drop of hydrochloric acid makes changes from pink to colourless. the acid in excess, and hence the colour of phenolphthalein changes from pink to colourless
Hydrochloric acid + Sodium hydroxide ⟶ Sodium chloride
HCI + NaOH ⟶ NaCl + H2O + ∆
(Acid) + (Base) Salt + Water
(iv) Touch the glass beaker from outside. You will notice that it has become warm confirming the evolution of heat during this process of neutralisation.
Q. 6. Explain why :(a) Farmers add slaked lime to acidic soils.(b) Soap solution or baking soda paste is applied on the part of body stung by a bee.(c) Factory wastes and city sewerage is neutralised before discharging in rivers.(d) Antacids are used for relieving stomach activity (acidity).
Ans. (a) Plants grow well only in neutral soil. Acidic soil reduces the fertility of the soil. In order to convert acidic soils into neutral soils, the farmers add/spray slaked lime (calcium hydroxide) which being basic in nature neutralise the excess acid present in the soil.
(6) The sting of bee contains formic acid. When bee stings our body part, it injects formic acid causing painful irritation. To reduce the effect of formic acid, the effected part of the body is scrubbed with soap solution or baking soda paste which neutralises the effect of formic acid and hence help in relieving pain.
(c) Factory wastes and city sewerage contains acids. If these wastes are directly discharged in rivers, they kill fish and other aquatic organisms. To prevent them from being killed by the presence of acid, the wastes are treated with lime before discharging into rivers. This neutralises the effect of acids.
(d) To relieve activity of stomach such as indigestion, ant- acids are used. It contains milk of magnesia (magnesium hydroxide and aluminium hydroxide). These hydroxides neutralise the effect of excess hydrochloric acid and thus help in controlling the damage to the walls of stomach which may otherwise cause stomach ulcers.
Q. 7. Give four differences between the acids and the alkalies.
Acids Alkali (Bases)
Q. 8. Write an equation when hydrochloric acid neutralises sodium hydroxide.
ADDITIONAL LONG ANSWER QUESTIONS
Q. 1. What is indigestion ? How can it be cured?
Ans. Our stomach contains hydrochloric acid (HCI) for digestion of food. Due to spicy and hot food, there is an excess secretion of HCl which results in indigestion (commonly known as acidity). Acidity is also caused by emotional disturbance in a person. This can be cured by taking some alkaline preparation for neutralizing the effect of acidity in stomach. These preparations are known as antacids. e.g. Milk of magnesia (Mg (OH)2). Aluminium hydroxide (Al(OH)2) etc.
0 Comments