Acids, Bases And Salts

Indicators are those artificial or natural substances which changes its colour according to the acidic or basic medium. Indicator as the name suggests whether the medium is acidic or basic depending upon the specific colour change.

Indicator show one colour in acidic medium and a different colour in basic medium.

Artificial indicator is prepared from artificial chemicals or synthetically prepared from laboratory chemicals.

Example: Phenolphthalein, Methyl Orange etc.

Natural Indicators are the indicator derived from naturally occurring materials.

Examples: Litmus, China Rose Petal, Red Cabbage, Turmeric etc.

CaOCl₂ chemically known as Calcium Oxychloride. The common name or local name was given to this compound is bleaching powder. It is prepared by passing the chlorine gas through dry slaked lime. The reaction is given as follows:

Bleaching Powder is used as a disinfectant in water treatment. Bleaching powder is also widely used in the textile industry like cotton textile industry etc.

Zinc is a transition element and it shows amphoteric nature which means that zinc can react as an acid as well as a base to form corresponding amphoteric oxides or hydroxides.

So when zinc reacts with sodium hydroxide, it forms sodium zincate and hydrogen gas is evolved. The reaction is as follows:

Zn + 2NaOH → Na₂ZnO₂ + H₂

The bacteria present in our mouth is not washed away by the saliva. It reacts with the sugar present in the food material to form acid which remains adhered to the teeth. Therefore, to remove the acidic film on the teeth, most of the toothpastes are basic in nature. These basic ingredients like sodium fluoride or sodium bicarbonate present in the toothpaste react with acidic films and hence helps to clean the mouth effectively.

The acid present in the ant sting is called as methanoic acid or commonly called formic acid. The chemical structure of Formic acid is HCOOH. Whenever a person is suffering from the sting of an ant, then baking soda [NaHCO₃] is applied to neutralize the acidic nature.

Any solution will conduct electricity only when it has free mobile ions in it. So in the case of the aqueous solution of acids, free ions of hydrogen are present in the solution which makes the solution to behave like an electrolyte and hence conducts electricity. Depending upon the number of free hydrogen ions, acidic electrolytes can be further classified as a strong and weak electrolyte.

Cake and other bakery products like bread etc are expected to become fluffy and soft. So during the preparation of such food items, baking powder is one of the most important ingredient added to the item.

So when the batter of the cake is heated, the baking powder present in the batter of the cake gets decomposed to form sodium carbonate, water, and carbon dioxide gas are given off. The pore present in the cake represents the location from the gas is liberated. So the main substance which causes effervescence is baking soda.

The reaction is given as:

2NaHCO₃→ Na₂CO₃ + H₂O + CO₂

the Universal indicator is a solution or a pH paper which is made of several compounds which change its colour according to the given solution to denote the nature of the solution and also the strength of the solution.

Diluting an acid is an exothermic reaction. So when water is added to the acid, a lot of heat is released and this heat is strong enough to convert the water into steam and cause the acid to spurt out and can harm anyone.

On the other hand when acid is added to water, water has the ability to absorb the heat generated during the dilution and thus avoids any undesirable consequences.

(a) Whenever a strong acid reacts with a weak base, the salt formed is termed as an acidic salt. The examples of acidic salts include Ammonium Chloride- NH₄Cl [Salt formed when HCl reacts with NH₄OH], Aluminium Sulphate -Al ₂(SO₄)₃ [Salt formed when H₂SO₄ reacts with Al (OH) ₃].

(b) Whenever a strong base reacts with a weak acid, the salt formed is termed as a basic salt. The examples of basic salt is as follows: Sodium Carbonate- Na₂CO₃ [salt formed when NaOH reacts with H₂CO₃] etc

Plants grown in soil depend a lot on the nature of the soil. Plants cannot grow in the soil which is more alkaline and having a pH greater than 7.

On the other hand, animals require to maintain the pH level in their stomach for the digestion process to get completed smoothly as digestion occurs at a particular pH only. If the level is disturbed then problems like acidity etc can be faced.

Hence even a small change in the pH level can affect the metabolic functioning of the animals as well as plants. In the following figure, it is visible how the pH affects the growth of the plant in soil.

The reaction of an acid with a base is a common reaction. It is a double decomposition type of reaction in which exchange of cations and anions takes place. The acid reacts with the base to form salt and water and the reaction is termed as neutralization reaction.

Let us take the example of sodium hydroxide reacting with hydrogen chloride. The reaction is as follows:

NaOH + HCl → NaCl + H₂O

So the salt obtained is called as sodium chloride.

The compound X has to be Sodium hydroxide as when zinc reacts with sodium hydroxide, then only hydrogen gas is liberated. Also, sodium hydroxide reacts with hydrochloric acid to give water. Also, sodium hydroxide reacts with acetic acid to form sodium acetate and water. The reactions are as follows:

The most commonly used bleaching agent in the industry is bleaching powder or calcium oxychloride.

It is prepared by passing the chlorine gas through dry slaked lime. The reaction is given as follows:

So X is chlorine and Y is calcium oxychloride.

(a) The pH of seven indicates that the given solution is neutral in nature.

(i) In order to increase the pH of the solution that is to make the solution more alkaline, one needs to add base to the solution.

(ii) In the similar manner to decrease the pH which means the solution should become more acidic, one needs to add an acid to the given

(b) The pH of the solution which can liberate CO₂ from sodium carbonate has to be less than seven because sodium carbonate is a basic salt and an acidic solution can only liberate the CO₂ from it. The reaction is as follows:

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Let us write the chemical reactions of each set so as to get the answer for the spaces. These reactions are all neutralization reactions.

(i)

(ii)

(iii)

(iv)

(v)

(vi)

After referring to the above six reactions, the blank spaces in the table can be easily filled.

Put the blue litmus paper in each of the three test tubes. The test tube which changes the blue litmus to red is an acidic solution.

No the litmus which turned red by acidic solution can be used to test for basic solution.

Dip the red litmus in the two test tubes. The test tube which change the red litmus back to blue colour is basic solution and the solution which shows no change to litmus colour is distilled water.

To prove that the given salt is a carbonate of a metal, add a few drops of Hydrochloric or Sulphuric acid to the salt and when the reaction is completed brisk effervescence is observed and pass the escaping gas through lime water. Lime water will turn milky in appearance which proves that the liberated gas is carbon dioxide and the salt was a carbonate of a metal.

The above explanation can be described by following reactions:

MCO₃ + HCl → MCl + H₂O + CO₂

Where M is any metal

(a) (i) The most commonly used bleaching agent in the industry is bleaching powder or calcium oxychloride.

It is prepared by passing the chlorine gas through dry slaked lime. The reaction is given as follows:

(ii) Gypsum is a naturally occurring mineral form of hydrated calcium sulphate. It can be obtained from Plaster of Paris by adding water to it. The reaction is as follows:

CaSO₄.1/2H₂O + 3/2 H₂O → CaSO₄.2H₂O

Bleaching Powder is used as a disinfectant in water treatment. Bleaching powder is also widely used in the textile industry like cotton textile industry etc. The main purpose of using bleaching powder in the textile industry is to remove stains from the clothes or fabric as it is a decolorizing agent.

Since the compound X is a washing powder then it has to be sodium carbonate whose common name is washing powder. When sodium carbonate reacts with dilute HCl, carbon dioxide gas is liberated.

This gas reacts with lime water to form calcium carbonate which gives the temporary milky appearance.

On further passing the gas, the calcium carbonate reacts to calcium bicarbonate and the milky appearance disappears.

X is Sodium Carbonate [Na₂CO₃]

Y is Carbon Dioxide [CO₂]

Z is Calcium Carbonate [CaCO₃]

P is Calcium Bicarbonate [Ca (HCO₃)₂]

The reactions is as follows:

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Ca (OH) ₂ + CO₂→ CaCO₃ + H₂O

CaCO₃ + CO₂ + H₂O → Ca (HCO₃)₂

(a) On adding baking soda to the cake instead of baking powder, the cake would taste bitter because sodium bicarbonate is a mild base and on being heated gets decomposed giving a bitter taste to the cake.

(b) Baking soda can be converted to baking powder by adding tartaric acid and starch to it.

(c) Tartaric acid plays a major role in maintaining the taste of the cake as it reacts with the decomposed sodium bicarbonate during heating thereby nullifying the effect of bitter taste on the overall taste of the cake.