AP State Board new syllabus 8th Class Physics Guide 6th Lesson Synthetic Fibres and Plastics Textbook Exercise Questions and Answers.
AP 8th Class Physical Science 6th Lesson Questions and Answers Synthetic Fibres and Plastics
8th Class Physics 6th Lesson Synthetic Fibres and Plastics Questions and Answers (Exercise)
Question 1.
Which of the following can be beaten into thin sheets?
a) Zinc
b) Phosphorus
c) Sulphur
d) Oxygen
Answer:
(a) Zinc
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.
e) Some non-metals are ductile
Answer:
(c) Generally, metals are ductile
Question 3.
Fill in the blanks.
a) Phosphorus in 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) reactive
b) good, electricity
c) more
d) hydrogen
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:
a) False
b) True
c) False
d) False
Question 5.
Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.
Answer:
| Properties | Metals | Non-metals |
| 1. Appearance 2. Hardness 3. Malleability 4. Ductility 5. Heat conduction 6. Conduction of Electricity |
have metallic lustre hard malleable ductile good conductors good conductors |
dull soft non – malleable non ductile bad conductors bad conductors/insulators |
Question 6.
Give reason for the following.
a) Aluminium foils are used to wrap food items.
b) Immersion rods for beating liquids are made of metallic substances.
c) Copper cannot displace zinc from its salt solution.
d) Sodium and potassium are stored in kerosene.
Answer:
(a) Aluminium is highly malleable metal and it is very easy to make aluminium foil in comparison to other metals.
(b) Immersion rods are made up of metallic substances because metals are good conductors of heat and electricity.
(c) Copper cannot displace Zinc fron its salt shem because Zinc is more reactive than copper (i.e. Copper is less reactive than Zinc).
(d) Sodium and potassium metals are very reactive because they react with oxygen and water easily, so sodium and potassium are always stored in kerosene.
Question 7.
Can you store lemon pickle in an aluminium utensil? Explain
Answer:
No. This is because acids react with aluminium.
Question 8.
Match the substances given in Column A with their uses given in Column B.
| A | B |
| (i) Gold | (a) Thermometers |
| (ii) Iron | (b) Electric wire |
| (iii) Aluminium | (c) Wrapping food |
| (iv) Carbon | (d) Jewellery |
| (v) Copper | (e) Machinery |
| (vi) Mercury | (f) Fuel |
Answer:
| Column A | Column B |
| (i) Gold | (d) Jewellery |
| (ii) Iron | (e) Machinery |
| (iii) Aluminium | (c) Wrapping food |
| (iv) Carbon | (f) Fuel |
| (v) Copper | (b) Electric wire |
| (vi) Mercury | (e) Thermometers |
Question 9.
What happens when
a) Dilute sulphric acid is poured on a copper plate?
b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.
Answer:
a) Copper sulphate is formed and hydrogen gas is released.
Copper + dil. Sulphuric acid → Copper sulphate + Hydrogen (gas)
b) Brown coating is deposited on the iron nails. This is because of the displacement of copper from copper sulphate solution by iron.
Iron + Copper sulphate (solution) → Iron sulphate (solution) + Copper.
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 the process.
Answer:
a) She will bring a wet litmus paper in contact with the gas. If the gas turns wet blue litmus paper into red, the gas will be acidic.
b)
- carbon + oxygen → carbon dioxide
- carbondioxide + water → carbonic acid
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:
The jeweller dipped the Jewellery in the solution of acid, which reacts with the outer covering of metals. In the process gold shines but dissolves in acid. Thus, there is net loss of weight in the metal of the ornament.
Extended Learning – Activities and Projects
Question 1.
Prepare Index Cards for any four metals and four non-metals. The card should have information like name of metal/non-metal; its physical properties, chemical properties and its uses.
Answer:
An index card consists of heavy paper cup to standard size, used for recording and storing small amounts of discrete data. Here one is done for you.
Question 2.
Visit a blacksmith and observe how metals are moulded.
Answer:
Activity for home.
Question 3.
Suggest an experiment to compare the conductivity of electricity by iron, copper, aluminium and zinc. Perform the experiment and prepare a short report on the results.
Answer:
Make four electric testers with similar kind of material. Test the conductivity of four metals with the wires of similar length and thickness. Observe the brightness of the glowing bulb. Compare the conductivity of metal according to brightness.
Question 4.
Find out the locations of the deposits of iron, aluminium and zinc in India. Mark these in an outline map of India. In which form are the deposits found? Discuss in the class.
Answer:
Activity for home. Discussion may be carried out in the school.
Question 5.
Discuss with your parents/neighbours/goldsmiths why gold is preferred for making jewellery.
Answer:
Gold is an outstanding metal in terms of ductility and malleability. It is possible to draw wires of gold thinner than hair or beaten into thin sheets. This makes it useful for making jewellery.
8th Class PS 6th Lesson Questions and Answers (Lab Activities)
Activity – 1
Take a small iron nail, a coal piece, a piece of thick aluminium wire and a pencil lead. Beat the iron nail by a hammer. Beat the aluminium wire also. Repeat the same kind of treatment on coal piece and pencil lead. Record you observations in table
| Object/Material | Change in shape (Flattens/Breaks into pieces) |
| Iron nail | Flattens |
| Coal piece | Breaks into pieces |
| Aluminium ware | Flattens |
| Pencil lead | Breaks into pieces |
Observation : We observed that the shape of the iron nail and aluminium wire changed on beating. If they were beaten harder, these could be changed into sheets. But coal piece and pencil lead did not show this property. They broke down on beating.
Conclusion : This shows that iron and aluminium wire being metals show malleability, whereas coal piece and pencil lead being non-metals do not show malleability.
Activity – 2
Take a cell, a bulb, some coal wires on iron rod/nail. Connect them to make an electric circuit with the help of copper wires. Insert a rod/nail of iron between the ends of copper wire as shown in figure.
Observation : The bulb will glow in iron nail and copper iron case, but it will not glow in sulphur and coal piece case.
Conclusion : This shows that iron/nail and copper wire are good conductors while rolled sulphur piece and coal piece are poor conductors of electricity.
Activity – 3
To check the nature of rust formed as a result of the reaction between iron, oxygen and water.
Take a spoonful of rust (from any rusted iron piece) in a test tube and dissolve it in a very little amount of water. We will get a suspension of iron oxide (rust) in water. Test the solution with red and blue litmus papers one by one.
Observation : We will find that red litmus paper turns blue.
Conclusion : This shows that iron oxide suspension is basic in nature.
Activity – 4.
Take a small amount of sulphur powder (non-metal) in a deflagrating spoon and heat it. As soon as sulphur starts burning with a blue flame, introduce the spoon into a gas jar.
Cover the jar with a lid to ensure that the gas produced does not escape. Sulphur burns in the air of gas jar to form a gas, sulphur dioxide having pungent smell. Remove the deflagrating spoon from gas jar. Now, put some water in the gas jar and cover it and shake to dissolve the sulphur dioxide gas. Test the solution with red and blue litmus papers one by one.
Observation : We will see that the blue litmus paper turns red.
Conclusion : This shows that sulphur dioxide gas is acidic in nature.
Activity – 5.
Take a 250 ml beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in a small piece of cotton. Put the sodium piece wrapped in cotton into the beaker.
We will find that sodium piece starts moving in water making a hissing sound which is due to the formation of bubbles of hydrogen gas. Sodium reacts
with water causing little explosions soon it catches fire. When the reaction stops touch the breaker. We will feel the beaker to be hot. It is because heat is produced in this reaction. Then, test the solution with red and blue litmus papers one by one.
Observation : We will find that this solution turns red litmus paper blue. It indicates the basic nature of the solution.
Conclusion : Sodium + water → Sodium hydroxide + Hydrogen gas + Heat
2 Na+2 H2O → 2 NaOH+H2+ Heat
This activity shows that sodium hydroxide is basic in nature.
Activity – 6
Take samples of metals and non-metals listed in table below in separate test tubes and label them as A, B, C, D, E and F. With the help of dropper add 5 ml of dilute hydrochloric acid to each test tube one by one. Observe the reactions carefully. If no reaction occurs in the cold solution, warm the test tube gently.
Bring a burning matchstick near the mouth of each test tube.
Repeat the same activity using dilute sulphuric acid instead of the dilute hydrochloric acid. Record your observations in Table.
Answer:
Observation: The gas produced from test tubes A, B and C burns with a ‘pop’ sound showing that it is hydrogen gas. But no H2 gas is produced from test tubes D, E and F in which copper, charcoal and sulphur are placed.
Repeat the same activity with dilute sulphuric acid. But the results are same. Copper does not react with dilute sulphuric acid to produce hydrogen gas. It however reacts with hot and concentrated sulphuric acid but no hydrogen gas is produced.
Conclusion : This activity shows that most of the metals-react with dilute acids to produce salt and hydrogen gas but non-metals do not react with dilute acids.
Activity – 7
Prepare a fresh solution of sodium hydroxide (base) in a test tube by dissolving 3-4 pellets of it in 5 ml of water. Drop a piece of aluminium foil into it. Bring a lighted match stick near mouth of the test tube.
Observation : We will find that the gas produced burns with a ‘pop’ sound showing that it is hydrogen gas.
Conclusion : This activity shows that metals react with base to produce salt and hydrogen gas.
Metal + Base → Salt + Hydrogen gas.
Activity – 8
Take 50 ml of water in each of the five beakers and label them as A, B, C, D and E. Dissolve 5 g of each substance in each beaker as indicated below in the figure.
Observation : In beaker A, blue colour of copper sulphate solution gradually disappears due to the formation of colourless. Zinc Sulphate solution and copper metal deposite as a powdery red mass at the bottom of the beaker. It means that zinc (more reactive) displaces copper (less reactive) from its copper sulphate solution. The reaction can be represented as follows.
Similarly, in beaker B, blue colour of copper sulphate changes to greenish due to the formation of iron sulphate and copper metal produced forms a led-brown coating over the iron nail. It means that iron displaces copper from its copper sulphate solution.
The reaction can be represented as follows.
In beakers C, D and E, no change or displacement reaction takes place as copper is less reactive than zinc and iron. Also iron is less reactive than zinc.
