Acids, Bases and Salts
The chapter is an introduction to the Chemistry section of your Science. The Acids , Bases and Salts that we are referring to in this chapter are the basics of Chemistry. The detail of which we will be studying in our future classes. Acids and Bases are two very different substances by means of its chemical properties.
Acidic
All those substances which contain acids in them are called to have acidic nature. Acidic substances that we come across in our daily life are generally sour in taste. Vinegar, Curd, Lemon juice, all fruits of Lemon species are acidic in nature. The word acid itself comes from a Latin word acere which means sour. The acids in the above-mentioned substances are natural acids.
Basic
All those substances which contain bases in them are said to have basic nature. In general substances like baking soda, soap solution, etc. are basic in nature. They are generally bitter in taste and are soapy when we touch them.
Indicators
We can never assure the substances to have either acidic or basic nature by only tasting or touching them. Moreover, some of the substances may be very dangerous to touch or taste. Hence, we need some other things which could help us to indicate whether the substances are acidic or basic in nature. The substances which help us to identify the nature of the substances are called indicators. The indicators tend to change their colour according to the kind of substance put into them or added to them. There are many natural indicators which help us to determine the nature of substances eg: Turmeric, China Rose(Gudhal) etc.
Litmus
It is the most common indicator used for determining the nature of substances. It is generally present in blue and red paper forms. Acid turns blue litmus red , while bases turn red litmus blue. It is a natural dye and is extracted from litchens. Its solution has purple color. This solution if added to acidic solution turns red while added to basic solution it turns blue. The paper strip of Litmus is used in labs.
Turmeric
Turmeric is also a natural indicator. It gets converted into reddish colour if added to a basic solution and turns whitish if acidic solution is added to it.
China Rose Petals
The China Rose petals are also good indicators. Solution of these petals in water can be used as indicators. The solution gets converted into reddish bright color if acidic substances are added and it gets converted into greenish color if basic substances are added.
What if the indicator doesn’t change colour?
If the indicator doesn’t indicate any change, it means that the substance being observed is neither acidic nor basic, but is neutral. The distilled water is one example of such neutral substances. These are neither acidic nor basic.
Neutralization
The process of mixing of acid with base so that the acidic nature and basic nature of both substances gets destroyed and we get a neutral product, is called Neutralisation. In neutralisation reaction a new substance is formed which is called as salt. Salt may be acidic, basic or neutral in nature.
Acid + Base ——à Salt + Water (Heat is evolved)
Hydrochloric Acid (HCl) + Sodium Hydroxide (NaOH)———àSodium Chloride (NaCl) + Water (H2O)
Importance of Neutralization in daily life
- To maintain the fertility of soil the fertilizers or manure are added as per requirement. If the soil is basic in nature acidic fertilizers and manures made from organic wases are added as they are acidic in nature. Basically, Neutralisation of soil is done for increasing its fertilization.
- When an ant bites, our skin gets rashes and reddened. It is because of formic acid injected by it. Calamine solution if applied over it relieves us from pain and discomfort. Calamine solution is nothing but a basic solution which neutralises the formic acid.
3. Acidity is caused in our stomach for many reasons. It is the increase of acidic juices in our stomach. This acidity is relieved by eating or drinking some antacid or milk of magnesia. These medicines are basic in nature and they neutralize the acidic juices of stomach.
4. Factory wastes thrown in rivers or other water sources make them acidic and can harm the life in those sources. For neutralizing their effect of acids, basic solutions are added to those water sources.
KEY WORDS
Acids: Acids are those substances which are acidic in nature. The natural acids are generally sour in taste.
Acidic : The acids are acidic in Nature.
Base: Bases are those substances which are basic in nature. The natural bases are generally bitter in taste and are soapy to touch.
Basic: The Bases are basic in nature.
Indicator: Those substances that react differently with acids and bases and hence indicate the nature of substance are called indicators. Eg: Turmeric Powder, Litmus etc.
Neutral: All those substances which are neither acidic, nor basic are called Neutral substances. Distilled water is neutral in nature.
Neutralization: The reaction between an acid and base is known as neutralization. Salt and water are produced in this process with the evolution of heat.
Acid + Base ——à Salt + Water (Heat is evolved)
Salt: The product that we get in neutralization reaction is salt. It may be acidic, basic or neutral in nature.
NCERT Exercise Questions, Answers
1. State differences between acids and bases.
Acids | Bases |
1. Sour in taste | 1. Bitter in taste |
2.Turn blue litmus red | 2. Turn red litmus blue. |
3.Contains hydrogen ion H+ ion | 3. Contains hydroxyl ion OH– ion |
2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer- Ammonia has basic nature.
3. Name the source from which litmus solution is obtained. What is the use of this solution?
Answer- Litmus solution is extracted from lichens. It is used to determine whether the given solution is acidic or basic.
4. Is the distilled water acidic/basic/neutral? How would you verify it?
Answer- Distilled water will be neutral. We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in it.
5. Describe the process of neutralisation with the help of an example.
Answer- The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Antacids like milk of magnesia (magnesium hydroxide), baking soda, etc. which contain a base are used for reducing acidity in stomach when excessive acid released by glands.
6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i)Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. (F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T)
(v) Tooth decay is caused by the presence of a base. (F)
7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Answer- Dorji can decide with the help of litmus paper:
(i) The drink which would turn a red litmus blue would be basic.
(ii) If the drink turns a blue litmus to red would be acidic.
(iii) The drink which would not affect both red and blue litmus would be neutral.
8. Explain Why?
- An antacid tablet is taken when you suffer from acidity.
Answer- We take an antacid such as milk of magnesia to neutralises the excessive acid released in stomach.
- Calamine solution is applied on the skin when an ant bites.
Answer- Ant injects an acidic liquid (Formic acid) into the skin on biting which causes inflammation, to the skin. The effect of the acid can be neutralised by rubbing. Calamine solution which contains zinc carbonate which is very weak base and causes no harm to the skin.
(c ) Factory wastes is neutralised before disposing it into the water bodies.
Answer- The wastes of factories contain acids. If acids are disposed of in the water body, the acids will harm the organisms. So, factory wastes are neutralised by adding basic substances.
Q.9. Three liquids are given to you. One is hydrochloric acid; another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric
Answer:- Name of the substances Effect on turmeric indicator
1. Hydrochloric acid: Yellow to blue
2. Sodium hydroxide: Yellow to red
3. Sugar solution: No change
Q.10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:- (i) It can be identified on the basis of the following observations: Bases change the colour of litmus paper to blue. As the colour of blue litmus paper is not affected, the solution must be basic.
(ii) If the solution is neutral, even then colour of litmus will not change.
Q. 11. Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?
Answer:- (ii) (a) and (d)