Acids, Base And Salts

1M HCl has a higher concentration of H⁺ ions because it is a comparatively strong acid whereas CH₃COOH is a weak acid and contains lesser concentration of H⁺ ions.

CH₃COOH is considered a weak acid because when diluted it does not get completely dissociated to liberate the H⁺ ions i.e. CH₃COOH upon dilution liberates a very small amount of H⁺ ions and considered a weak acid. HCl on the other hand upon dilution dissociates completely to generate the H⁺ ions and liberates a huge amount of H⁺ ions per unit volume and hence, considered a strong acid.

Carbon dioxide gas is evolved when dil. HCl reacts with metal bicarbonate.

It could be recognized by bringing a burning matchstick to the area where the gas is evolved. It would be observed the matchstick will stop burning.

The value of pH is inversely related with the concentration of hydrogen ions. Hence, when we increase the concentration of H⁺ (aq) ions in a solution the pH of the solution decreases.

When dil. HCl reacts with an active metal hydrogen gas is evolved.

It could be recognized by bringing a burning matchstick or candle towards the place from which the gas is being evolved, it would be observed that the matchstick would burn with a pop sound.

When the pH of the mouth falls below 5.5 then our enamel which is composed of calcium phosphate gets corroded leading to tooth decay.

When a solution of an acid is diluted then, the concentration of H⁺ ions per unit volume in the solution reduces. Hence, any given sample of the solution now contains a lesser amount of H⁺ ions as it was present before dilution. Therefore, the pH of a solution of an acid upon dilution increases.

Fresh milk has a pH of 6. When it changes into curd its pH will decrease as curd contains lactic acid making the curd comparatively more acidic in nature than the fresh milk.

The smaller the pH the more the H⁺ (aq) ions concentration would be.

Hence, the pH values of 0, 2, 4 and 6 in the increasing value of H⁺ (aq) ions concentration is: -

6 < 4 < 2 < 0

The aquatic life survives in an optimum pH value. It is difficult for the aquatic life to maintain their metabolism in a pH value greater or less than the optimum pH value. When acid rainwater flows into a river it makes the river water acidic and disturbs the pH from its optimum value due to which the survival of aquatic life in the river becomes difficult.

a.

i. The colour of CuSO₄ crystals before heating is blue.

ii. after heating the colour of CuSO₄ crystals changes to white.

b. The source of liquid droplets seen on the inner upper side of the test tube during the heating process is the water of crystallization present in the formula unit of copper sulphate. These water of crystallization upon heating is removed from the formula unit and gets condensed on the inner upper side of the test tube during the heating process as liquid droplets.

i. The products formed when NaHCO₃ is heated are sodium carbonate water and carbon dioxide.

ii. The chemical equation for the reaction involved above is:-

2NaHCO₃ 2Na₂CO₃ + H₂O + CO₂

i. The name and chemical formula of the calcium compound used for disinfecting drinking water is:-

Chemical name - Calcium oxychloride

Formula - CaOCl₂

ii. This compound is manufactured by the action of chlorine on dry slaked lime as per the following reaction:

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

The decomposition of gypsum to Plaster Of Paris is as follows:-

CaSO₄.2H₂O CaSO₄.1/2H₂O

Plaster of Paris is prepared by decomposing gypsum at 373K.

Interconversion of Plaster Of Paris into gypsum is as follows:-

CaSO₄.1/2H₂O + 1H₂O CaSO₄.2H₂O

a. When CO₂ is passed through lime water in a limited quantity than calcium carbonate gets precipitated as a white colour mass at the bottom of the test tube according to the following reaction: -

Ca(OH)₂ + CO₂→ CaCO₃ + H₂O

b. When CO₂ is passed through lime water in excess then the white precipitate initially formed gets dissolved forming Ca(HCO₃)₂ which is soluble in water as per the following reaction: -

CaCO₃ + H₂O + CO₂→ Ca(HCO₃)₂

a. Bleaching powder is produced by the action of chlorine on dry slaked lime according to the following reaction:-

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

Hence, bleaching powder smell strongly of chlorine.

b. Bleaching powder does not dissolve completely in water because bleaching powder is actually a quite complex molecule. It contains various other heavy calcium salts in it like calcium chloride, calcium hydroxide and calcium hypochlorite. These salts are insoluble in water. Hence, bleaching powder does not dissolve completely in water.

the chemical formula for washing soda is - Na₂CO₃.10H₂O

It is prepared by heating baking soda and then recrystallizing the product so obtained.

The equations related to the above reaction are:-

2NaHCO₃ Na₂CO₃ + H₂O + CO₂

Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O

Two applications of washing soda are:-

1. It is used in glass, soap and paper industries

2. It is used for removing permanent hardness of water.

Litmus solution indicator just shows us whether the given sample is acidic or basic and tells us nothing about the strength of the acid or the base. Blue litmus solution turns red under acidic conditions; red litmus solution turns blue under basic /alkaline conditions.

On the other hand, universal indicator solution tells us or depicts through its colour exactly how much strong an acid or a base is. It has different colours as reference for different pH values from 0 to 14 indicating the strength of the acid or the base.

Natural indicators- The indicators which are prepared from natural substances are known as natural indicator.

Example – litmus, turmeric indicator.

Synthetic indicators – The artificial indicators which are prepared in the lab are known as synthetic indicators.

Example – Phenolphthalein, methyl orange etc.

a. When zinc reacts with NaOH the following reaction takes place: -

2NaOH + Zn Na₂ZnO₂ + H₂

Hydrogen gas is evolved with the formation of the corresponding salt.

b. When zinc reacts with HCl the following reaction takes place: -

2HCl + Zn → ZnCl₂ + H₂

Hydrogen gas is evolved with the formation of the corresponding salt.

Two characteristics of acids:-

i. Acids are sour in taste.

ii. They produce H⁺ ions upon dilution.

Two characteristics of bases:-

i. Bases are bitter in taste.

ii. They produce OH^- ions upon dilution.

When electricity is passed through an aqueous solution of sodium chloride, it decomposes to form sodium hydroxide. This process is called chlor-alkali process.

It is called so because the products formed in the reaction are chlorine and sodium hydroxide. Here chlor stands for chlorine and alkali is for sodium hydroxide.

a. Water should not be added to concentrated acid because the process of dissolving an acid or a base in water is a highly exothermic one. If water is added to an acid then the heat generated may cause the acid to splash out and cause burns.

b. Pain or irritation is caused in our stomach when there is production of an excess amount of acid in our body. Antacids are basic in nature. Hence antacids are required when there is pain or irritation in the stomach to neutralize the effect of the excess acid.

c. Bee-stung injects acid in our body. Baking soda is a base. Hence, baking soda should be rubbed on bee-stung area to neutralize the effect of the acid.

Water of crystallization is the fixed number of water molecules present in one formula unit of a substance

Four salts which contain water of crystallization are – copper sulphate, gypsum, Plaster of Paris, washing soda.

P.O.P. is written as CaSO₄.1/2H₂O because two formula unit of CaSO₄ shares one molecule of water.

When NaHCO₃ is heated or mixed with water a reaction takes place which leads to the evolution of carbon dioxide gas. Now carbon dioxide extinguishes fire very well hence, it is used in soda-acid fire extinguisher and also the carbon dioxide produced during the reaction causes the bread or cake to rise making them soft and spongy. Hence, NaHCO₃ is used for making baking powder.

a. While making baking powder tartaric acid id being added to it because when this mixture is heated or mixed with water carbon dioxide gas is evolved which causes the bread or cake to rise making them spongy and soft.

b. Bleaching powder is used for disinfecting drinking water because bleaching powder is an oxidizing agent and helps in removing or killing the germs.

c. Strong acid means those acids which gives a very high H⁺ ion concentration upon dilution or those which are able to generate a greater volume of H⁺ ions per unit quantity whereas concentrated acid means how many moles of the acid is present in a given quantity of a solvent. Higher concentration means greater amount of the acid per unit of the solvent.

The value of pH is inversely related with the concentration of hydrogen ions. Hence, if the concentration of hydrogen ions then pH decreases.

At the pH value of 1 the pH paper strip is Red, at the pH value of 7 the pH paper strip is green and at the pH value of 14 the pH paper strip is blue in colour.

Sulphuric acid is a strong acid amongst all of the above.

Except ethanoic acid all are strong acids.

Except nitric acid, all the others could be obtained from edible substances.

Tomato contains oxalic acid.

Washing powder has extensive uses and is used in glass, soap and paper industries.

The formula of Gypsum is: CaSO₄.2H₂O and plaster of Paris having formula CaSO₄.H₂O is obtained upon heating gypsum.

Bleaching powder which is used as an oxidizing agent in many chemical industries.

Na₂CO₃.10H₂O commonly known as washing soda is used for removing permanent hardness of water.

Common salt or Sodium Chloride is used in the manufacturing process of a variety of other salts like washing soda, bleaching powder, slaked lime etc.

When HCl is added to water it is dissociated to give H⁺ ions which combines with water molecules to give H₃O⁺ and Cl^– remains after the dissociation in the solution.

The value of pH is inversely related with the concentration of hydrogen ions. Hence, Higher the pH, weaker the acid and Lower the pH, weaker the base.

A basic salt is formed when a strong base combines with a weak acid.

Calcium phosphate which is present in tooth enamel is basic in nature because the acid produced by the bacteria in our mouth easily corrodes it.

Antacids are basic in nature. Hence, if an antacid is added it would change the colour of this pH paper to greenish-blue.

Water is normally neutral, acetic acid is a weak acid and Hydrochloric acid is a strong acid. Hence, the above order.

When a solution of an acid is mixed with a solution of a base then the temperature of the solution increases as it is an exothermic reaction and the corresponding salt formation takes place.

False

The separation of H⁺ ion from HCl molecules cannot occur in the absence of water. As in the absence of any solvent, the H⁺ would not be able to dissociate from its formula mass.

True

A substance is called an acid if it has the ability to produce H⁺ ions in the solution. These H⁺ ions combine with water molecules to give H₃O⁺. Hence, acids give H₃O⁺ or H⁺(aq) ion in water is correct.

True

The process of dissolving an acid or a base in water is highly exothermic one as a huge amount of heat is evolved during the process owing to the production of H⁺ or OH^- ions.

False

The process should be that acid must be added slowly to water with constant stirring. If water is added slowly to the acid with constant stirring then due to the exothermic reaction going on the acid might splash away from the beaker causing burns.

True

If water is added slowly to the acid with constant stirring then the heat generated may cause the mixture to splash out and cause burns. Hence, care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to the water with constant stirring.

False

The universal indicator shows different colours at different concentrations of hydrogen ions in a solution.

True

pH scale is being made to act as a reference to check the acidity or basicity of a substance and it shows or measures the pH from 0 (very acidic) to 14 (very alkaline).

False

The value of pH is inversely related with the concentration of hydrogen ions. Hence, higher is the hydronium ion concentration, lower will be the pH value.

True

Acidity of a substance is measured with respect to the number of H⁺ ions it can generate. Acids that give rise to more H⁺ ions are said to be strong acids, and acids that give less H⁺ ions are said to be weak acids.

False

_{When the pH of rainwater is less than 5.6, it is called acid rain.}