Acids, Bases And Salts

Differences between acids and bases are as follows:

The substances that turn red litmus* to blue are basic in nature. Ammonia also turns red litmus to blue. Thus, it is basic in nature.

litmus* : Litmus is a dye that becomes red in acidic conditions and blue under alkaline conditions as shown in the pic below:

Litmus is most commonly used natural indicator which is extracted from lichens*. Litmus solution has mauve (purple) colour in distilled water. It is used as an indicator to distinguish between acids and bases. When acidic solution is added in it, it turns red and when basic solution is added, it turns blue.

Lichen* is a symbiotic relationship between algae and fungi.

The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. When the nature of distilled water is tested with litmus paper, we have found neither red nor blue changes in the colour which verify its neutral nature.

The reaction between an acid and a base is known as neutralization. Neutralization reaction result in the formation of salt and water. During this reaction, energy in the form of heat is evolved.

Acid + Base Salt + Water + Heat

Example: When sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water are obtained.

i. False.

Nitric acid is acidic in nature. Thus, it turns blue litmus to red.

ii. False.

The substances that turn red litmus to blue are basic in nature. Sodium hydroxide also turns red litmus to blue. Thus, it is basic in nature.

iii. True.

When sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water are obtained. It is an example of neutralization reaction.

iv. True.

Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators.

v. False.

Tooth decay is caused by the presence of a acid.

Since the drinks are edible, Dorji can take decision by testing the drinks. Acidic drinks will be sour in taste whereas basic drinks will be bitter in taste and neutral drinks will have no taste.

Dorji can decide which drink is acidic by taking the litmus test:

(i) If drink turns blue litmus paper to red, then it is acidic in nature and hence it will be served to first customer who wants acidic drink.

(ii) If drink turns red litmus paper to blue, then the drink is basic and hence it will be served to another customer who wants basic drink.

(iii) If drink does not show change in colour, then it will be neutral drink and hence it will be served to third customer who wants neutral drink.

a. Antacid is a substance that neutralizes the acidity in the stomach because it contains bases. We take antacid such as milk of magnesia, which contains magnesium hydroxide. These bases react with excess of acids released in stomach and neutralize their effects, thus giving us relief.

b. The sting of an ant contains formic acid. When an ant bites, it injects the formic acid into the skin which causes the burning sensation. The effect of acid can be neutralized by applying a base to it. Thus, by applying calamine solution which contain a base called zinc carbonate will neutralize the formic acid and relives us from the pain.

c. The wastes of many factories contain acids. If they are directly disposed into waters then, the water will become acidic and it will harm the aquatic life i.e. plants and animals inside the water. The acid can even kill the fish and the organism under water. Hence, these factory wastes are neutralized with basic substances before disposing to water bodies.

Turmeric is a natural indicator. Turmeric solution turns red, when it comes in contact with bases. It is not affected by acids and neutral substances.

Applying turmeric solution to the test tube, the results are:-

(1) test tube A (Hydrochloric acid): No , change will happen since turmeric is not affected by acids and HCL is a acid
(2) test tube B (sodium hydroxide): Yes , turmeric will change its color to red since sodium hydroxide is basic nature.
(3) test tube c (sugar solution) : NO, change will happen as sugar solution is neither basic nor acidic in nature

Hence, we can only identify basic solution using turmeric as an indicator

The blue litmus paper is an indicator which turn red when come in contact with acidic solution with pH<4.5 since, blue litmus paper does not change its color when placed in contact with solution this means that solution is either basic or neutral in nature.

All indicators do not change colour with acids as well as bases, e.g. turmeric changes its colour to pink with base but it remains yellow with acid. Litmus paper, methyl orange are some indicators which changes colour with both acids and bases.