The Magic of Chemical Reactions – Maharashtra Board Class 10 Solutions for Science and Technology (English Medium)
- The chemical formula of POP is 2CaSO4.H2O
- The chemical reaction during which H2(g) is lost is termed as oxidation.
- Corrosion can be prevented by using Anti-rust solution.
- When acids and alkalis react together, salt and water are formed.
- The chemical reactions in which heat is liberated are called exothermic reactions.
- Reactants are converted into products.
- Mass is conserved.
- Atoms are conserved.
- The properties and compositions of the products are different from those of its reactants.
- Energy is either absorbed or evolved.
When hydrogen sulphide H2S gas is passed through cadmium chloride solution, a yellow precipitate of cadmium sulphide and hydrochloric acid is obtained. The reaction is a double displacement reaction.
CdCl2(aq) + H2S(g) → CdS(s)↓ + 2HCl(aq)
When oxidation and reduction take place simultaneously in a given chemical reaction, it is known as a redox reaction.
When hydrogen sulphide reacts with sulphur dioxide, H2S is oxidised and SO2 is reduced.
2H2S + SO2 → 3S + 2H2O
- The slow process of decay or destruction of metal due to the effect of air, moisture and acids on it is known as corrosion.
- Gold is a noble metal. There is no effect of air, moisture and acid. Pure gold is a very soft metal. To make it hard and resistant to corrosion, metals such as copper and silver are alloyed with it.
Grills of doors and windows are made of iron. Iron has a tendency to undergo corrosion.
Paint does not allow air or moisture to come in contact with the iron surface. Thus, to prevent the rusting of iron, grills of doors and windows are always painted before they are used.
Physical states of the reactants and products are mentioned in a chemical equation to make it more informative. The gaseous, liquid, solid and aqueous states are symbolised as (g), (l), (s) and (aq), respectively. The symbols (g), (l), (s) and (aq) are written in brackets as a subscript along with the formulae of the reactants and products.
Potassium ferrocyanide undergoes a chemical change in the presence of sunlight. It oxidises to form potassium ferricyanide. Hence, it is stored in a dark-coloured bottle and kept away from sunlight.
Iron has a tendency to corrode. It reacts with oxygen and the moisture of air to form its hydroxide and oxide.
Steel is an alloy of iron, carbon and chromium. The properties of an alloy are different from the properties of its constituents. The added metals make it durable, clean and more resistant to corrosion. Hence, iron articles rust readily, whereas steel, which is also mainly made of iron, will not undergo corrosion.
Edible oil stored in an iron or tin container gets oxidised, becomes rancid and its smell and taste change. Hence, edible oil is not allowed to stand for a long time in an iron or tin container.
In the morning, more oxygen is present in the air. Oxygen enters the lungs while inhaling, so we feel fresh.
As time passes, and after 10 a.m., the morning air gets polluted by industrial gases (e.g. CO2 and SO2) and exhaust gases from vehicles (e.g. CO) during rush hours. As a result, enough oxygen is not available for respiration. Hence, we don’t feel fresh after 10 a.m.
Fats and oils in food, if kept for a long time, get oxidised and become rancid, and their smell and taste change. This process is known as rancidity.
The reaction in which heat is absorbed is called an endothermic reaction. In such reactions, the reactants require heat to form products.
When KNO3(s) dissolves in water, heat is absorbed and the temperature of the solution falls.
KNO3(s) + H2O(l) + Heat→ KNO3(aq)
The reaction in which oxidation and reduction take place at the same time is known as a redox reaction.
In a redox reaction, one reactant gets oxidised while the other gets reduced during the reaction.
Example: CuO + H2 → Cu + H2O
CuO is reduced and H2 is oxidised.
The reaction between an acid and a base to form salt and water is termed neutralisation.
Example: HCl + NaOH → NaCl + H2O
Acid Base Salt Water
The speed or the rate of reaction depends on the particle size of the reactant.
Smaller the size of the particles of the reactants, the faster is the reaction.
Hence, the reaction in which zinc powder is used will react faster with copper sulphate solution as compared to zinc granules.