Olympiad Test: Is Matter Around us Pure- 1 - Class 9 MCQ

Concentration of solution = (mass solute/mass of solution)*100

=(10/160)*100

=100/16

=6.25%

Milk of magnesia is a suspension. Here's why:

- Suspension: Milk of magnesia consists of undissolved particles (magnesium hydroxide) dispersed in a liquid medium (water).
- Not a Colloid or True Solution: Colloids have smaller particles that don't settle quickly, and true solutions involve completely dissolved solutes.
- Not a Homogeneous Mixture: Suspensions are heterogeneous mixtures where particles settle out over time, unlike homogeneous mixtures where components are evenly distributed.

Concentration of solution = (mass solute/mass of solution)*100

Mass of solute (salt) = 80 g

Mass of solution = 80 + 500 = 580

=(80/580)*100

=13.793 or 13.8%

When a mixture of iron and sulphur is heated strongly, they first absorb the energy to get excited. This is followed by the formation of a new compound iron sulfide (FeS)(FeS) with the release of the huge amount of energy in the form of heat and light.

A compound is an electrically neutral group of two or more atoms of different elements held together by chemical bonds.

NO and CO are compounds since they are made up of atoms of two different elements.

Whereas, Na and Co are made up of one type of atom and are elements.

Potassium is one of the major electrolytes (together with sodium, chloride and magnesium) that conducts electricity in the human body. Gallium does not conduct electricity, Chromium is a (transition) metal and conducts electricity. Germanium is a metalloid. Therefore, it is neither a good conductor of electricity nor an insulator.

Characteristics of pure substance:-

A pure substance contains only one type of particles which can either be atoms or molecules or elements or compounds.

A pure substance cannot be separated into other kinds of matter by any physical process but a mixture can as they are impure substances because they contain more than one particles. Ex: salt solutions.

A pure substance has fixed composition as well as fixed melting and boiling points. Ex: salt.

Pure substances cannot be exemplified by all elements other than nickel because pure nickel is an element containing only one kind of particle.

The boiling point of a substance is where the liquid phase changes into gas phase. The melting point of a substance is where the solid phase changes into the liquid phase. Since air is a mixture of gases, so, all the different gasses have different melting and boiling points. So, air has no boiling point and it also has no melting point. Gold is a metal, ethanol is a type of alcohol and oxygen is type of gas which have only atoms of oxygen. Hence, remaining all three have fixed substances and therefore have fixed melting/ boiling point. But air does not.

Chalk powder and water mixture form a suspension, hence, it will most likely scatter the beam of light when passed through it.

Brass is an alloy of copper and zinc. It is an example of a solution of solid in solid.