Is Matter Around Us Pure? — Science STD 9 — Question

Explain the terms 'compression' and 'rarefactions' of a wave. What type of waves consist of compressions and rarefactions?

There are three substances X, Y and Z. The substance X does not have a fixed melting point or boiling point and it still shows the individual properties of its constituents. The substance Y is a pure substance which occurs in nature as such. The substance Y has a fixed melting point and boiling point but it cannot be broken down into simpler substances by any chemical means. The substance Z is also a pure substance whose properties are entirely different from those of its constituents. The substance Z can, however, be divided by electrolysis into two substances which belong to the same class of substances as Y.

1. What type of substance could X be? Name one substance like X.
2. What type of substance could Y be? Name one substance like Y.
3. What type of substance could Z be? Name one substance like Z.
4. Whish process involves absorption or release of an appreciable amount of energy: formation of substance X or formation of substance Z?
5. Name the three groups into which all the substances like Y are divided on the basis of their properties.

A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20m in 25 seconds to reach the bookshop. After buying a book, he travels the same distance in the same time to reach back in the classroom. Find (a) average speed, and (b) average velocity, of the boy.

Write the differences between mass and weight of an object.

A mixture contains water, kerosene and sand. How will you separate this mixture?

How can you obtain pure water from a salt-water mixture (or salt-solution)? Draw a meat and labelled diagram of the apparatus you would use to obtain pure water from a salt-water mixture (or salt-solution).

A liquid compound X of molecular mass 18u can be obtained from a number of natural sources. All the animals and plants need liquid X for their survival. When an electric current is passed through 200 grams of pure liquid X under suitable conditions, then 178 grams of gas Y and 22 grams of gas Z are produced. Gas Y is produced at the positive electrode whereas gas Z is obtained at the negative electrode. Moreover, gas Y supports combustion whereas gas Z burns itself causing explosions.

1. Name (i) liquid X (ii) gas Y, and (iii) gas Z
2. What is the ratio to the mass of element Z to the mass of element Y in the liquid X?
3. Which law of chemical combination is illustrated by this example?
4. Name two sources of liquid X.
5. Gate an important use of Y in our life.