With a soapy touch and bitter taste, bases are another important component of chemistry that, when dissolved in an aqueous solution, releases OH- ions.

Tests for Base

Test	Before	After
Red cabbage juice	Purple	Greenish yellow
Methyl orange	Orange	Yellow
Blue litmus	Blue	No change
Phenolphthalein	Colourless	Pink
Red litmus paper	Red	Blue

Types of Bases

The different types of bases are as follows:

• Strong Base

The base that completely dissolves or dissociates in water is considered to be a strong base.

A few of the strong bases are as follows:

• • Potassium Hydroxide (KOH)
  • Sodium Hydroxide (NaOH)
• Weak Base

The base that does not completely dissolve or dissociate in water is considered to be a weak base.

A few of the weak bases are as follows:

• • Ammonia (NH₃)
  • Water (H₂O)

The ionic compounds produced after the neutralisation reaction between acid and bases are called salts. They are generally crystalline solid in texture.

Types for Salts

Depending upon the formation, salts are divided into three major types.

Neutral Salts

The salts formed by the reaction between strong acid as well as strong base are called neutral salts. Examples of neutral salts are:

• NaCl
• KCl

Acidic Salts
 
The salts formed by the reaction between a strong acid and weak base are called acidic salts. Examples of acidic salts are:

• Ammonium Chloride (NH₄Cl)
• Ammonium Sulphate [(NH₄)₂SO₄]

Basic Salts

The salts formed by the reaction between weak acid and strong base are called basic salts.
Examples of basic salts are:

• Sodium Carbonate (Na₂CO₃)
• Sodium Acetate (CH₃COONa)

Question- 1

In an experiment, you are provided with three chemical test tubes; among them, one has distilled water, the other contains an acidic solution, and the last one has a basic solution. You are provided with just one red litmus paper in order to identify or find out what is present in each respective test tube. What will you do in order to find out the content present in each of the given test tubes?

Solution-1

• It is easy to identify the content present in each of the test tubes using the test of red litmus paper. This test can be applied by noticing the change in colour of the red litmus paper for each of the cases.
• Make sure that on the litmus paper, the three solutions of the test tube are properly poured separately on the paper.
• The solution of the test tube that happens to turn the red litmus to blue is known to contain a basic solution.
• Now, divide the changed blue litmus paper into two parts.
• Hence the solution of the chemical test tube that changes blue litmus paper into red will, therefore, be an acidic solution.
• And the solution of the chemical test tube, which does not change the solution either into red or into blue litmus paper, thus has water.

Question- 2

Why do acids such as HCl, HNO₃, and others showcase acidic characters in the aqueous solutions, while on the other hand, the solutions of compounds like alcohol or glucose do not show any acidic character?

Solution-2

It is the release of H+ ions in the water that makes any particular compound acidic or non-acidic in nature.

Acids are thus the substances that upon dissociating or dissolving in the water produce Hydrogen or H+ ions. Some of the compounds showcase an acidic character as they readily get dissociated or dissolved in the aqueous solution, which subsequently results in the production of hydrogen ions (in acids like HCl, HNO₃).

Compounds similar to glucose or alcohol, majorly basic compounds, do contain hydrogen elements or H+ ions in them. Hence they do not show any signs of acidic nature or properties. Therefore, it is a fact that the hydrogen in them will not get separated like the hydrogen in the acids. Hence, they will not separate to become hydrogen ions on dissolving in the water or an aqueous solution in general.

Question- 3

Dry ammonia is known to have no action on the litmus paper, but on the other hand, it is seen that the solution of ammonia in water turns red litmus paper blue in colour. What is the reason behind the occurrence of this change? Give reasons.

Solution- 3

Dry ammonia happens to have no action or reaction on the litmus paper because it contains zero hydroxyl ions when in the absence of water or H₂O. On being dissolved in water, it leads to the formation of ammonium hydroxide or NH₄OH, which has a basic nature because it dissociates in order to give NH⁴ ions as well as OH- ions. Thus, this is the reason why the red litmus paper turns into blue colour.

This is the reaction for the above-mentioned phenomena

NH₃(g) + H₂O → NH₄OH (aq)

NH₄OH (aq) → NH₄+ (aq) + OH- (aq)

Question- 4

Give the answer to the following questions:

1. A metal compound 'p' reacts with dilute H2SO4 in order to produce effervescence. The gas so evolved can extinguish a burning candle. If one of such compounds is calcium sulphate, then what is 'p' and the gas which evolved?
2. Name anyone antacid, and how does it happen to help in relieving indigestion caused in the stomach?
   
   
3. A farmer treats the soil present in his farm with quicklime or calcium carbonate. After treatment, what will be the nature of the soil, and what is the reason that the farmer treats the soil of his farm with quick lime?

Solution- 4

1. P mentioned in the question is actually calcium carbonate, and the gas so evolved is CO₂ or carbon dioxide.

2. NaHCO₃ is an antacid. It is known to neutralise the excess of acid formed in the stomach, thereby aiding indigestion and acidity.

3. The soil is now acidic in its nature. The farmer aims at making it neutral in nature by the addition of quicklime which is considered to be good for the crops.

Question- 5

A metal carbonate termed as 'q,' when it reacts with an acid, happens to produce a gas which, when passed through a solution termed as 'r', gives back the carbonate. Whereas, on the other hand, a gas 'x' which is obtained or collected as an anode during the process of electrolysis of brine, is then passed on dry 'r' and gives a compound called 's,' which is also used for disinfecting drinking water. Therefore, identify q, r, x, and s.

Solution- 5

q here is Calcium carbonate or CaCO₃

Reaction-

CaCO₃ + Acid = Metal Salt + Water + CO₂

If we take the acid to be HCl, then the reaction would have been:

CaCO₃ + 2HCl -------> CaCl2 + CO₂ + H₂O

R is the Lime water Ca(OH)² or slaked lime. When this CO² gas is passed through the Lime water, then the lime water turns its watery texture into milky due to the formation of Calcium Carbonate or CaCO³, which is thus formed again.

Reaction-

Ca(OH)₂ + CO₂ ---------> CaCO₃ + H₂O

The gas so evolved at the anode during the process of electrolysis of brine is chlorine (x). When chlorine gas is made to pass through dry Ca(OH)² (r), then it produces bleaching powder (s) which is used for the purpose of disinfecting drinking water.

Reaction-

2Ca(OH)₂ + 2Cl₂ ------> Ca(OCl)₂ + CaCl₂+ 2H₂O

Acids, Bases and Salts is the building block of chemistry. In this chapter, we have focused on the theoretical aspects along with equations and Acid Bases And Salts Class 10 Solutions for a better understanding.

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