Acids, Bases And Salts

A is the weakly acidic solution.

B is the strongly acidic solution.

C is strongly alkaline(basic).

D is neutral.

E is weakly alkaline.

Explanation: A scale of measuring hydrogen ion concentration in a solution is called pH scale. pH value of a solution is simply a number which indicates the acidic or basic nature of a solution.

pH of a neutral solution is 7.

Value less than 7 represent the acidic solution.

Value above than 7 represent the alkaline (basic) solution.

Neutralization reaction: The reaction of an acid with a base to give a salt and water is known as neutralization reaction.

Two examples:

HCl + NaOH → NaCl + H₂O

Acid-Base Salt Water

HBr + KOH → KBr + H₂O

Acid-Base Salt Water

When an acid or base is mixed with water, it results in the decrease of concentration of ions (H₃O⁺/OH^-) per unit volume. Such a process is called dilution and the acid or base is said to be diluted.

Tooth decay starts when the pH of mouth is lower than 5.5 because:

Tooth decays which are made of calcium phosphate are the hardest substance in the body.

It does not dissolve in water.

It gets corroded when the pH in the mouth is lower than 5.5.

Acids are produced by the bacteria present in the mouth

Distilled water does not conduct electricity because:

Distilled water is a pure form of water, is neither acidic nor basic.

It does not dissociate into ions.

As we know that, to carry out electricity, ions are needed

Due to the absence of free ions, distilled water does not conduct electricity.

An acid is a substance which has the ability to give H⁺ ion.

Dry hydrogen chloride gas is not an acid and has no ability to give hydrogen ions. Thus, it does not turn blue litmus to red.

Hydrochloric acid is an acid and has the ability to give Hydrogen ions. Thus, it turns blue litmus to red.

Pure acetic acid does not conduct electricity because pure acetic acid cannot dissociate into hydronium ion and acetate ions which are required for the conduction of electricity.

Note: On the other hand, acetic acid in water dissociates into hydronium ion and acetate ions for the conduction of electricity.

a. He shifts the pH of the fresh milk from 6 to slightly alkaline because by doing this, he can keep the milk unspoiled for little more time than usual time.

b. After adding baking soda (alkaline in nature) to the milk, it changed into a base. But curd needs an acidic environment to set. Thus, this milk takes a long time to set as curd.

Plaster of Paris should be stored in moisture-proof container because it absorbs water from moisture and it sets into hard solid mass due to the formation of gypsum.

CaSO₄. 1/2H₂O + 1 1/2H₂O → CaSO₄.2H₂O

Plaster of Paris Gypsum

When the milk is changed into curd, the pH value of milk (6) decreases due to the formation of lactic acid in the curd. Lactic acid is acidic in nature.

Thus, due to lactic acid, the pH of milk changes as it turns into curd.

Activity

Step 1: Connect two different coloured electrical wires to graphite rods separately in a 100ml beaker.

Step 2: Connect free ends of the wire to 230 volts Ac plug and complete the circuit.

Step 3: Connect a bulb to one of the wires.

Sep 4: Now pour some dilute HCl in the beaker and switch on the current.

Step 5: Repeat the same activity with glucose and alcohol solutions.

The water of crystallization: The fixed number of water molecules present in one formula unit of a salt is called water of crystallization.

In the crystals of some compounds, water molecules are included in this arrangement. That is the water of crystallization.

Activity to show water of crystallization:

Step 1: Take some crystals of copper sulfate in a test tubes

Step 2: Add some water in one test tube and shake it.

On heating, the crystalline structure of copper sulphate broke down to form a colourless powder and water came out. This water was part of the crystal structure of copper sulphate. It is called water of crystallization.

In test tube A, the fizzing will occur more vigorously.

Explanation:

HCl is a strong acid and acetic acid is a weak acid.

As HCl is a strong acid thus it releases more H⁺ ions in the solution.

Due to which, the fizzing will occur more vigorously.

This fizzling is due to the liberation of hydrogen gas which is formed by mixing HCl with magnesium ribbon.

Preparation of our own indicator using beetroot:

Step 1: Take the beetroot and peel it.

Step 2: Cut them into small pieces and make a paste by mixing them in a grinder.

Step 3: Add some water to the paste.

Step 4: Now, filter this and collect only juice from this. This filtered juice will act as indicator for acid and bases.

Step 5: Now add this juice (beetroot indicator) to orange juice.

We will see the change of colour. This shows the acidic nature of orange juice.

The flow of acid rain into a river changes the pH of the river. The pH of the water decreases due to the acid rain which is not suitable for the survival of aquatic plants and animals.

They need pH of 7 to 8 for survival. But acid rain increases the acidity of the river due to which it becomes difficult for them to survive.

Baking powder

The chemical name of the compound is sodium carbonate (NaHCO₃).

Preparation of baking powder is

NaCl + H₂O + CO₂ + NH₃→ NH₄Cl + NaHCO₃

Baking Powder

It is sometimes added for faster cooking.

It is a mild non-corrosive base.

When baking powder (a mixture of baking soda and tartaric acid) is mixed with water, the reaction takes place:

NaHCO₃ + H⁺→ CO₂ + H₂O + sodium slat of water

CO₂ which is released during the reaction makes the cake soft and spongy.

Two important uses of washing soda:

It is used as a cleaning agent for domestic purposes.

It is used in glass, soap and paper industries.

Two important uses of baking soda:

It is used as a mild antiseptic.

It is used as soda-acid in fire extinguishers.