Question

IV. Short answer questions (Any 5) :3×5=15

1.What are cathode rays? Give two feature of it. (1+2)

2.What do you understand by the term chemically stable or inert?(3)

3.What is a pure substance? Give two of its characteristics. (1+2)

4.(a)What is the principle of froth floatation?(1)

(b)Give two applications of chromatography. (2)

5.A distillation flask is used for the process of distillation. Why?(3)

6.What does a downward arrow represent in a chemical equation? Give an example. (2+1)

7.How are valency of elements and the number of valence electrons related?(3​

Answer 1

Answer:

1. They are produced by the negative electrode, or cathode, in an evacuated tube, and travel towards the anode. They travel in straight lines and cast sharp shadows. They are deflected by electric and magnetic fields and have a negative charge. They are beams of tiny, negatively charged particles called electrons.
2. In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. These elements are stable in their naturally occurring form (gaseous form) and they are called inert gases.
3. The characteristics of a pure substance is that it only contains atoms of only one kind. It has fixed chemical and physical properties , for example, melting point, boiling point, density, solubility, etc.
4. Froth floatation process is based on the principle that the metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water. Collectors attach themselves by polar groups to grains of minerals which then become water repellent and thus, pass on into the froth. Examples are ethyl xanthate and potassium ethyl xanthate.
5. Distilling flasks are used to separate mixtures of two liquids with different boiling points.
6. An arrow pointing down (as in PbI2↓) indicates that the product will spontaneously precipitate from the solution. ("Precipitate," in this sense, means the formation of a solid from the combination of two aqueous solutions.)
7. An element's valency is determined by the number of electrons in its outer shell. Hence, the number of valence electrons obtained from the electronic configuration of the element gives the valency i.e. the number of electrons lost, gained or shared by the element to attain the noble gas configuration.

Answer 2

Answer:

1. They are produced by the negative electrode, or cathode, in an evacuated tube, and travel towards the anode. They travel in straight lines and cast sharp shadows. They are deflected by electric and magnetic fields and have a negative charge. They are beams of tiny, negatively charged particles called electrons.

2. In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. ... These elements are stable in their naturally occurring form (gaseous form) and they are called inert gases.

3. The characteristics of a pure substance is that it only contains atoms of only one kind.It has fixed chemical and physical properties , for example, melting point, boiling point, density, solubility,etc.

4. (a) Froth flotation is a technique commonly used in the mining industry. In this technique, particles of interest are physically separated from a liquid phase as a result of differences in the ability of air bubbles to selectively adhere to the surface of the particles, based upon their hydrophobicity.

(b) Chromatography is used for quality analyses and checker in the food industry, by identifying and separating, analyzing additives, vitamins, preservatives, proteins, and amino acids. Chromatography like HPLC is used in DNA fingerprinting and bioinformatics.

5. It is primarily used for distillation, the process of separating a mixture of liquids with different boiling points through evaporation and condensation. ... In this way, the distillation flask serves a similar purpose to the retort.

6. An arrow pointing down (as in PbI2↓) indicates that the product will spontaneously precipitate from the solution. ("Precipitate," in this sense, means the formation of a solid from the combination of two aqueous solutions.)

7. The valency of an atom is determined by the number of valence electrons present in the outermost shell of its atom. The number of electrons lost or gained or shared by an atom of element to achieve the nearest inert gas electron configuration, gives us the valency of an element.