NCERT Solutions Class 8 Science Chapter 4 Materials Metals and Non Metals

NCERT Solutions for Class 8 Science fopr chapter 4 Materials Metals and Non-Metals

Question. Which of these molecules is composed of EXACTLY 5 atoms?
(a) NaHCO₃
(b) Ba(OH)₂
(c) K₂SO₄
(d) N₂O₅

Answer : B

Question. Hydrated copper sulphate is a blue crystalline solid. When heated, it changes to anhydrous copper sulphate, a white powder. Which of these occurs in that process?
(a) Loss of water
(b) Absorption of water
(c) Loss of oxygen
(d) Oxidation

Answer : A

Question. If you took all of the atoms out of a chair, what would be left?
(a) The chair would still be there, but it would weigh less.
(b) The chair would be exactly the same as before.
(c) There would be nothing left of the chair.
(d) A pool of liquid would be left in place of the chair.

Answer : C

Question. The percentages given in the chart represent the number of atoms of each element in a compound. The chart correctly represents the atoms in which of these compounds? 

(a) C₂H₅OH
(b) CH₃COOH
(c) C₂H₅COOH
(d) C₃H₆

Answer : B

Question. The 'Flame Test' is used in the identification of certain metals. It is based on the observation that light emitted by any element gives a unique spectrum when passed through a spectroscope. When a salt of the metal is introduced into a Bunsen burner flame, the metallic ion produces characteristic colour in the flame. Some metals and the colours they produce are: In a flame test, if a distinct blue green colour is observed which of the following chemicals could it be?

(a) Barium sulphate
(b) Copper chloride
(c) Strontium nitrate
(d) Calcium carbonate 

Answer : B

Question. The 'Flame Test' is used in the identification of certain metals. It is based on the observation that light emitted by any element gives a unique spectrum when passed through a spectroscope. When a salt of the metal is introduced into a Bunsen burner flame, the metallic ion produces characteristic colour in the flame. Some metals and the colours they produce are:
White light can be considered the sum of RED, BLUE and GREEN coloured light. In other words, if all RED was absorbed from WHITE light, it would appear to be CYAN. That is:
CYAN = GREEN + BLUE
MAGENTA = RED + BLUE
YELLOW = RED + GREEN 
The colour of the flame produced by sodium ion masks many other coloured flames. What would be the best filter to use in order to block the colour of sodium flame?

(a) Red
(b) Yellow
(c) Blue
(d) Plane glass

Answer : C

Question. Which of the following would be a chemical change?
(a) A metal on heating to a high temperature turns into liquid form.
(b) A metal gets a greenish coating on exposure to air.
(c) A metal is drawn into wires.
(d) A metal is beaten into thin sheets.

Answer : B

Question. Which of the following represents a correct chemical reaction?
(a) Sodium + Hydrogen  ------> Sodium hydroxide
(b) Sulphur trioxide + Water  ---->  Sulphuric acid
(c) Carbon + Chlorine   ----->  Potassium chloride
(d) Nitrogen + Oxygen  ----->  Hydrogen peroxide

Answer : B

Question. Which of the following minerals would give a fizz with dilute hydrochloric acid?
Use the information given in the table belowand answer the question.

(a) Apatite
(b) Galena
(c) Stibnite
(d) Calcite

Answer : D

Question. Which letter - A, B, C or D, represents the mineral chalcopyrite?

(a) A
(b) B
(c) C
(d) D

Answer : C

Question. Which of these can be decomposed by a chemical change?
(a) Co
(b) CO
(c) Cr
(d) Cu

Answer : B

Question. The graph below represents the uniform cooling of a substance, starting with the substance as a gas above its boiling point. During which interval is the substance completely in the liquid phase?

(a) PQ
(b) QR
(c) RS
(d) ST

Answer : C

Question. Inside an atom, which of these occupies the MAXIMUM VOLUME?
(a) The electrons
(b) The protons
(c) The neutrons
(d) Empty space (vacuum)

Answer : D

Question. Anand took four colourless solutions P, Q, R and S, and performed the following tests. What is the definite conclusion that Anand can reach

(a) Both P and S are salt solutions.
(b) Both Q and S are basic solutions.
(c) Both Q and R are salt solutions.
(d) Both P and R are neutral solutions.

Answer : D

Question. Water can be made to boil above its normal boiling point of 100° Celsius by_______________.
(a) increasing the quantity of water being boiled
(b) boiling the water in a tightly closed container
(c) heating the water on low flame in a wide vessel
(d) boiling the water at a high altitude, like in the hills

Answer : B

Question.1 - Which of the following can be beaten into sheets? 
(a) Zinc
(b) Phosphorous
(c) Sulphur
(d) Oxygen

Answer : Correct option is (a) Zinc.

Explanation: Generally metals can be beaten into sheets. Zinc is metal while phosphorus, sulphur and oxygen are non-metals.

Question.2 Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.

Answer : Correct statement is option (c), Generally, metals are ductile.

Explanation: Mercury is a metal but it cannot be drawn into wires because it is liquid at room temperature. Therefore, it is non-ductile.

Question.3 Fill in the blanks.

(a) Phosphorous is a very_____ non-metal.

(b) Metals are______ conductors of heat and ______

(c) Iron is reactive than copper.

(d) Metals react with acids to produce_____ gas.

Answer : 

(a) Phosphorous is a very reactive non-metal.

(b) Metals are good conductors of heat and electricity.

(c) Iron is more reactive than copper.

(d) Metals react with acids to produce hydrogen gas.

Question.4 Mark ‘T’ if the statement is true and ‘F’ if it is false.

(a) Generally, non-metals react with acids. ( )

(b) Sodium is a very reactive metal. ( )

(c) Copper displaces zinc from zinc sulphate solution. ( )

(d) Coal can be drawn into wires. ( )

Answer : 

Question.5 Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties.

Answer : 

Question.6 - Give reasons for the following.

(a) Aluminium foils are used to wrap food items.

(b) Immersion rods for heating liquids are made up of metallic substances.

(c) Copper cannot displace zinc from its salt solution.

(d) Sodium and potassium are stored in kerosene.

Answer : 

(a) Aluminium is a highly malleable cheap metal which does not react with food items. Therefore, aluminium foils are used to wrap food items.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made up of metallic substances.

(c) A less reactive metal cannot replace more reactive metal from its salt solution. Since, copper is less reactive than zinc, therefore, it cannot replace zinc from its salt solution.

(d) Sodium and potassium are very reactive metals. They react vigorously with oxygen and water. A lot of heat is generated in the reaction. If kept in open, they react with oxygen and moisture present in air and catch fire immediately. Therefore, sodium and potassium are stored in kerosene.

Question.7 - Can you store lemon pickle in an aluminium utensil? Explain.

Answer : 

No, lemon pickle cannot be stored in an aluminium utensil. This is because lemon pickle contains acid which reacts with aluminium (metal) to liberate hydrogen gas. The liberated hydrogen gas can spoil lemon pickle.

Question.8

Match the substances given in column A with their uses given in column B.

Answer : 

Question.9 What happens when

(a) Dilute sulphuric acid is poured on a copper plate?

(b) Iron nails are placed in copper sulphate solution?

Answer : 

(a) When sulphuric acid is poured on a copper plate, the copper metal reacts with sulphuric acid to form copper sulphate and hydrogen gas.

Question.10 - Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

(a) How will she find the nature of the gas?

(b) Write down word equations of all the reactions taking place in this process.

Answer : 

(a) To find the nature of the gas, add a small amount of water into the test tube in which gas is collected. Quickly cover the test tube and shake it well. Now test the solution with red and blue litmus paper one by one. You will observe that solution turns blue litmus red while red litmus remains unaffected. This confirms that gas evolved during burning of charcoal is acidic in nature.

(b) Name of the product formed in the reaction of charcoal with oxygen is carbon dioxide. When carbon dioxide is dissolved in water, carbonic acid is formed. The carbonic acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature.

Question.11 - One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day, when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Answer : 

To polish gold jewellery, it is dipped in a mixture of acids called aqua regia (a mixture of hydrochloric acid and nitric acid). The outer layer of gold jewellery dissolves in the acid mixture and the inner shiny layer appears. Due to dissolution of upper layer of gold, its weight gets reduced.