Chapter 2: Is Matter around us Pure?

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Is Matter around us pure?

Question:

Q.7: Which of the following materials fall in the category of a “pure substance”?

(a)     Ice

(b)     Milk

(c)     Iron

(d)     Hydrochloric acid

(e)     Calcium oxide

(f)     Mercury

(g)     Brick

(h)     Wood

(i)      Air

Answer:

(a) Ice is the solid form of water that contains a compound of hydrogen and oxygen. In water, hydrogen and oxygen are combined in a fixed ratio and have properties different from hydrogen and oxygen. So, water is a pure substance that is formed by the combination of two elements. Thus, ice is a pure substance

(b) Milk is an emulsion that is formed when the fat particles are dispersed in water. So, it is a heterogeneous mixture. Thus, milk is not a pure substance.

(c) Iron is an element that contains one type of atom and cannot be broken down into simpler substances. Thus, iron is a pure substance.

(d) Hydrochloric acid is a compound that is formed by the combination of hydrogen and chlorine atoms. Thus, hydrochloric acid is a pure substance.

(e) Calcium oxide is a compound that is formed by combining oxygen and calcium atoms. Thus, it is a pure substance.

(f) Mercury is an element that contains one type of atom and cannot be broken down into simpler substances. Thus, mercury is a pure substance.

(g) Brick is made from clay, sand, concrete lime, etc, that are mixed to form a mixture that does not has a uniform composition. So, it forms a heterogeneous mixture. Thus, brick is not a pure substance.

(h) The wood consists of cell and cell wall which is made up of cellulose and hemicellulose that mixed to form a heterogeneous mixture Thus, wood is not a pure substance.

(i) The air is a homogeneous mixture because it contains mixtures of different gases like nitrogen gas, oxygen gas, and so on. Thus, the air is not a pure substance.


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