Interesting Chemistry Questions and Answers: Part 1
We find the use of chemistry in our everyday lives one way or the other. Sometimes we do have questions about how a particular thing works or what is the reason behind some chemical phenomena. Here I am presenting a simple question and answer series to answer some of the chemistry questions which might be useful in everyday life and also to chemistry learners.
Q- Why Steam causes more severe burns than boiling water?
Phenomenon- Latent Heat
Explanation- When water changes into steam, it absorbs latent heat but when steam condenses to form water, an equal amount of latent heat is given out. It has been found out that the burns caused by steam are much more severe than those caused by boiling water though both of them are at the same temperature of 100°C. This is due to the fact that steam contains more heat, in the form of latent heat, than boiling water. So, when steam falls on our skin and condenses to produce water it gives out 22.5*105 joules per kilogram more heat than boiling water at the same temperature. Since it gives out more heat, it causes more severe burns.
Q- Why Naphthalene balls disappear with time?
Explanation- In many households, small naphthalene balls are kept in stored woollen and silk clothes to protect them from the attack of the insects. It has been found that they disappear with time without leaving behind any residue. This is because they undergo sublimation. The naphthalene balls keep on forming naphthalene vapours which slowly disappear into the air.
What is Sublimation?
The changing of solid directly into vapours on heating and of vapours into solid on cooling is known as sublimation. Substances that undergo sublimation include- Iodine, Camphor, Naphthalene, Ammonium chloride, dry ice(solid carbon dioxide).
Q- Why people keep water in an earthen pot to keep it cool during hot summer days?
Phenomenon- Cooling caused by Evaporation
Explanation- The earthen pot has a large number of extremely small pores in its walls. Some of the water continuously keeps seeping through these pores to the outside of the pot. This water evaporates continuously and takes the latent heat required for vaporisation from the earthen pot and the remaining water. In this way, remaining water loses heat and gets cooled.
What is Evaporation?
The process of a liquid changing into vapour even below its boiling point is called evaporation. Other examples of cooling caused by evaporation in everyday life includes wearing cotton clothes in summer, perspiration or sweating, etc.
Q- How cream is separated from milk?
Explanation- Milk is a suspension of tiny droplets of cream in a watery liquid. The process of centrifugation is used in dairies to separate cream from milk. The milk is put in a closed container in a big centrifuge machine. When the machine is switched on, the milk is rotated at a very high speed in its container. A force acts on the heavier suspended particles in it and brings them down to the bottom. The lighter substance remains on top. Due to this, the milk separates into cream and skimmed milk. The cream, being lighter, floats over the skimmed milk. It can then be removed.
What is Centrifugation?
It is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in a centrifuge. This process is also used in washing machines to squeeze out water from wet clothes and make them dry.
Q- Why the smell of perfume or the burning of incense stick reaches us even from a considerable distance?
Explanation- When the bottle of perfume is opened then the liquid perfume quickly changes into vapour. The perfume vapours move very rapidly in all directions and hence spread with air in the whole room. Similarly the particles of gases produced by the burning of incense stick move rapidly in all directions. They collide with the particles of air present in the room, mix with air and reach every part of the room very quickly. Similarly, the smell of food being cooked in the kitchen reaches us.
What is Diffusion?
The spreading out and mixing of a substance with another substance due to the motion of its particles is called diffusion. It is fastest in gases and slowest in solids.
Q- How a mixture of water and kerosene oil is separated?
Phenomenon- Separation by a separating funnel
Explanation- Water and kerosene are two immiscible liquids. When the mixture of water and kerosene is put in a separating funnel, it forms two layers. Water, being heavier, forms the lower layer in the separating funnel whereas kerosene, being lighter, forms the upper layer. On opening the stop-cock of separating funnel, the lower layer of water comes out first and collected in a beaker. When the water layer has completely run off, then the stop cock is closed. The kerosene is left behind in the separating funnel. It can be removed in a separate beaker by opening the stopcock again.
How to separate immiscible liquids?
A mixture of two immiscible liquids can be separated by using a separating funnel. It depends on the difference of their densities. Liquids which can be separated by this method include- the mixture of petrol and water, cooking oil with water, mercury and water, chloroform and water, benzene and water, etc.
Q- Why Eno gives out bubbles when dissolved in water?
Phenomenon- Evolution of a gas during a chemical reaction.
Explanation- It is because the eno contains an organic acid and a base which is soda bicarbonate. When dry, they do not react with one another. In water, their solutions react with one another to give out a gas. This gas is carbon dioxide.
Q- Why metals corrode?
Explanation- Corrosion is a process by which metals are eaten up gradually by the action of air, water or a chemical on their surface. It is caused mainly by the oxidation of metals by the oxygen of air. Rusting of iron is the most common example of corrosion. If a metal is reactive, its surface may be attacked slowly by the air and water in the atmosphere. The metal reacts with the oxygen and water vapour forming compounds on its surface. The formation of these compounds tarnishes the metal. The compounds formed on the surface of metal are usually porous and gradually fall off from the surface of metal and then the metal underneath is attacked by air and water. This process goes on and on. In this way, the action of air and water slowly eats up the whole metal. At some places, there are some acidic gases in the air which mix with rain water to form chemicals such as acids. These acids also attack the surface of metals and eat them up slowly.
What is oxidation?
The addition of oxygen to a substance is oxidation. In other words, the addition of non-metallic element or removal of the metallic element is oxidation.
Q-Why food products containing fats and oils are packaged in nitrogen?
Phenomenon- Oxidation and Rancidity
Explanation- When the packed food is surrounded by an unreactive gas nitrogen, there is no oxygen to cause its oxidation and make it rancid. The manufacturers of potato chips and other similar products fill the plastic bags containing chips with nitrogen gas to prevent the chips from being oxidised and turn rancid.
What is rancidity?
When the food materials prepared in fats and oils are kept for a long time, they start giving unpleasant taste and smell. This condition produced by the aerial oxidation of fats and oils in foods marked by unpleasant taste and smell is called
Q- Why curd and other sour food stuffs should not be kept in metal vessels like copper or brass?
Phenomenon- Acids react with metals
Explanation- It is because curd and other sour food-stuffs contain acids which can react with the metal of the vessel to form poisonous metal compounds which can cause food poisoning and damage our health.