Science 1 Marks Question

Rusting is aided by both moisture (water) and air (oxygen). By painting an iron gate, we prevent its contact from the air and moisture present in the atmosphere. Hence, rusting is prevented.

Photosynthesis → Chemical change

Tearing of paper is a physical change although, it cannot be reversed.

This is because magnesium reacts with oxygen in air to form white coloured magnesium oxide.

The method of coating the iron material with a more reactive metal (zinc) to prevent rusting is called galvanisation.

The ozone layer protects us from the harmful ultraviolet radiations which come from the sun. Ozone absorbs ultraviolet radiations coming from the sun and breaks down to form oxygen. In this way, ozone layer absorbs harmful ultraviolet radiations.

In a chemical reaction the old bonds of the reactants are break down and fresh bonds are formed, resulting in formation of new product with different properties of that of earlier products.

False.
Formation of manure from leaves is a physical change.

Zinc metal is used for galvanising iron.

Formation of clouds is a physical change. Clouds are formed by the condensation of water vapours present in the atmosphere. When rainwater goes back on the earth, no new product is formed. Therefore, it is a physical change.

The process of depositing a layer of zinc on iron is called galvanization.

True.
The wax meting is a physical process, while combustion of wax is chemical process.

The reddish-brown covering of flaky substance on iron objects is called rust. When an iron object is left in moist air for a considerable time, rust is formed.

Chemical change.

False.
Cutting a log of wood into pieces is a physical change.

Cooking of food and hard boiling of egg, in both the process both chemical and physical changes occur. In both cases physical appearance of the substances change and new substances are formed.

Melting of ice to form water is a physical change which occurs by the action of heat.

Explosion of a firework.

For the occurrence of any reaction, the molecules or atoms of the reactants must collide with one another, in order to break old bonds and form new bonds.

The changes are chemical in nature as new substances; iron sulphate (green) and copper (brown) are formed.

It is a chemical change because ozone gives oxygen after breaking down and oxygen is different down ozone.

For rusting the presence of both oxygen and water or water vapour is must, in coastal region the content of moisture in air is high whereas in desert region the content of moisture in air is low and thus rusting becomes faster in coastal region.

In a chemical change, the products are quite different from the reactants. Therefore, a chemical change cannot be normally reversed.

physical change.

Iron articles can be prevented from rusting by greasing, painting, galvanising electroplating, alloying, plastic coating or chromium plating.

Explosion of firework is a chemical change and produces heat, light, sound and unpleasant gases that pollute the atmosphere, so it is advised not to play with fireworks.

Dissolving sugar in water → Physical change

The common salt can be obtained by the evaporation of sea water.

Chemical change.

Formation of manure from leave is a chemical change because the manure formed has different composition from the leaves.

Changes in which only physical properties of a substance change are called physical changes.

1. Tearing of paper
2. Breaking of glass

In the process of digestion, the various food materials break down to form new substances which can be absorbed by the body. So, the process of digestion is a chemical change.

By painting or greasing and by galvanizing with chromium or zinc.

False.
Stretching of rubber band is a physical change.

1. Reaction between vinegar and baking soda
2. Burning of a matchstick

Cutting of wood is a physical change because the identity and composition of wood does not changes.

A change, in which a new substance with different properties is formed, is known as a chemical change.

True.
Salty water of sea causes faster rusting of iron.

Yes.

Explosion of a firework produces heat, light, sound and unpleasant gases. Explosion of a firework is a chemical change.

For rusting the presence of both oxygen and water or water vapour is required. The coat of the paint prevents direct contact of iron with air and oxygen and thus prevents it from rusting.

Two methods by which rusting of iron can be prevented are galvanization and painting.

1. Colour of the solution in the beaker changes from blue to green.
2. A brown coloured deposit is found on the surface of the iron nail.

True.

physical change.

Stainless steel is an alloy of iron. When iron is mixed (or alloyed) with carbon, chromium and nickel, then stainless steel is obtained. Stainless steel does not rust at all.

Chemical change.

Digestion of food → Chemical change

1. Iron + air + water → iron oxide
2. Copper sulphate + iron → iron sulphate + copper

Properties such as shape, size, colour and state of a substance are called its physical properties.

True.

When iron nails are dipped in copper sulphate solution, then the colour of the solution changes to green.

In burning always heat is produced, the old bonds of the reactants are break down and fresh bonds are formed, resulting in formation of new product with different properties of that of earlier products.

Changes in which new substances are formed are called chemical changes.

Beating aluminium to make aluminium foil → Physical change

The speed with which the chemical reaction takes place is called the rate of the chemical reaction.

Melting is the process of turning a solid to a liquid.

Metals like chromium and nickel are mixed (alloyed) with iron to make stainless steel.

The process of obtaining crystals from its hot saturated solution is called crystallisation.

Stainless steel is an alloy of Iron with carbon and other metals like chromium, nickel and manganese.

True.

Chemical process.

Magnesium oxide is basic in nature because it turns red litmus solution to blue.

Chromium, nickel and manganese.

Since Mumbai is a coastal region, the moisture content in the air is more as compared to that in Delhi. Therefore, iron articles rust faster.

For rusting the presence of both oxygen and water or water vapour is required. The coat of the paint prevents direct contact of iron with air and oxygen and thus prevents it from rusting.

Melting of ice is also a change where solid changes into liquid state.

When magnesium is burnt in air then a brilliant white flame is obtained.

Burning of coal → Chemical change

During photosynthesis, the plants intake carbon dioxide and water in the presence of chlorophyll and sunlight to form two new substances, i.e. glucose (food) and oxygen gas. So, photosynthesis is a chemical change.

Melting of wax → Physical change

We should eat freshly cut apple because if we leave the apple after cutting, it starts turn to brownish due to the oxidation of the essential nutrients present in it and its food value decreases.

Chemical change.

Ethanoic acid reacts with sodium hydrogen carbonate to evolve brisk effervescence of carbon dioxide.

When we burn a cracker, it explode Explosion produces heat, light, sound and unpleasant gases that pollute the atmosphere. Many new products are formed. So, it is a chemical change.

Ripening of a fruit is a chemical change because after ripening, a new product with different properties is formed.

Souring of milk is a chemical change because original substances present in milk lose their nature and identity and form new chemical substances.

Presence of water and presence of oxygen.

The following changes accompany the formation of new substances: change in state, colour, temperature, odour, sound may be produced or gas may evolve.

These are chemical changes.

Carbon dioxide cuts the contact of fire with oxygen which is needed for combustion and fire extinguishes from lack of oxygen.

The chemical name of baking soda is Sodium hydrogen carbonate.

Evaporation.