NCERT Solutions for Class 5 EVS Chapter 7

Ayesha watched as her mother rolled out the puri and put it in the hot oil. She saw that at first the puri sank to the bottom of the pan. As it puffed up, the puri came up and started floating on the oil.

A puffed puri floats in oil whereas a flat puri sinks because puris float on oil as the hot oil makes the puri to rise up and get filled up with air. The air which is lighter than the oil makes the puris to float on oil. So,it is the hot oil that makes the puris float.

A heavy ship floats in water because the weight of water that is displaced by the flooded or submerged part of the ship is more than that of the ship whereas the weight of water that is displaced by the needle is more than the actual weight of the needle.

When we add salt to the water the density of the solution increases as salt helps in increasing the mass
without changing the volume very much. When enough salt is added to the water, the saltwater solution’s density becomes higher than the egg’s, so the egg starts floating.

Oil does not get dissolved in water because the molecules of oil and water do not get attracted to each other.

Water is called a ‘Universal Solvent’ as it can dissolve many substances in it. The water molecule gets attracted to many other different types of molecules.

When we mix sugar in water it gets dissolved in it and we can no longer see the sugar although it is still in the water because the sugar molecules get scattered and disconnected from one another.

a. That can float: Wood, pencil, cork, plastic bottle (closed cap), bowl etc.
b. That can sink: needle, stone, marble, eraser etc.

A steel plate would start floating on water as it is lighter than water. The size of a body does not decide whether a thing floats or sinks. It is the mass and volume of the body that collectively decide whether it will float or sink.

Puffed puri if put in a bowl of water would float as it is lighter than water. But after sometime it would start sinking due to absorption of water by the dough of puri.

The ball of dough weighs more than the same amount, or volume, of water, and is denser than water, it sinks in water, no matter how big or small it is.

The soap cake sinks in water and the soap case floats because the soap cake is solid and doesn’t have any empty spaces to be able to float in water whereas soap case has empty space in which soap settles. The empty space of the soap case gets filled with air which is less dense than water and helps the case to float.

Evaporation is a process in which the liquid turns into a gas. When water gets heat energy it changes to a gas. An increase in temperature speeds up the rate of evaporation. Water evaporates when it is boiled.

An iron nail sinks in water but a ship made of iron floats because of the density of the iron nail and the ship. The iron ship has larger surface than an iron nail and has spaces that get filled with air. Because of this the density of the ship is less as compared to water.
The ship is hollow from inside and this space is filled with air which reduces the average density of the ship lower than that of water. Thus, even with a small portion of the ship submerged under water, the weight of the water displaced by it becomes equal to the weight of the entire ship.

The handkerchief that is kept in the sun will dry at a faster rate than the one kept in shade as the heat from the sun evaporates the water molecules from the handkerchief leaving it dry. Warm water evaporates much faster than cool water. So, the heat from the sun dries the handkerchief quickly.

The Dead Sea is almost nine times as salty as the ocean. That makes it impossible for most life to exist in it. This is the reason it is called dead sea.

When we dissolve chalk powder in water it does not mix in it rather it settles down at the bottom of water and some particles spread throughout the water.

Since water is denser than oil it has a lesser volume than oil. Water therefore has a higher amount of inter molecular force of attraction.
But as oil is stickier than water and has a higher amount of inter molecular force of attraction than water. That is why water slides faster than oil.

Aluminium foil when spread it is spread out floats in water because the weight of aluminium foil is less than that of water displaced by it.

When aluminium foil is pressed tightly into a ball it sinks because of the weight of aluminium ball is more than that of the water displaced by it.

The oil is less dense than the water. This is because the molecules of oil are larger than the molecules of water, so oil particles take up more space. As a result, the oil will rise to the top of the water. The water molecules attract each other, and the oil molecules stick together so it causes oil and water to form two separate layers. Thus, leaving oil sitting on top of the water when mixed in it.

Water can be separated from salt by a process called distillation. In this method water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into another container. Thus, it is separated from water.

Chalk is insoluble in water and forms a heterogeneous mixture when mixed with water. As chalk is heavier, therefore it will settle at the bottom of the mixture when it is left undisturbed for some time. Thus, water can be separated from chalk powder by sedimentation, decantation and filtration

Mahatma Gandhi and his followers left from the Sabarmati Ashram on March 12, 1930, to protest against the British salt law as per which the Indians were not allowed to make salt. This is called the Dandi March. The British had a control over the production of salt and collected a heavy salt tax.

Salt production is done by capturing the salt water in shallow ponds where the sun evaporates most of the water. The method of making salt from sea water includes the process evaporation is used on a large scale to obtain common salt from sea water. Sea water is then trapped in shallow lakes and allowed to stand there. The heat of sun evaporates water in the shallow lakes and common salt is left behind.

Displacement means that an object has been moved, or has been displaced. Displacement is defined to be the change in position of an object.

On a cloudy day, the air is full of water vapour. As the air gets warmer, its capacity to hold water vapour increases. And the condition becomes more and more humid. So, wet clothes take more time to dry on a cloudy day. Atmosphere has moisture in it so the clothes need high temperature so the water in the clothes can evaporate and on a rainy day the temperature is low. Wet clothes take longer time to dry on a rainy day because evaporation of water does not take place in clothes.

Many substances do not dissolve in water example- oil, paraffin wax and sand, chalk powder, ghee, oil, stone, wood.

Things like salt, sugar and coffee, milk, mud, lemon juice dissolve in water. They are soluble and dissolve faster in warm or hot water.

To dissolve the mishri in water. We need to crush it to make powder of it. Then we have to add it into water and stir it thoroughly. It can also be heated over the flame to dissolve the mishri quickly.