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Class 8 Science Chapter 8 Nature of Matter Elements Compounds and Mixtures Extra Questions
Class 8 Science Chapter 8 Extra Questions on Nature of Matter Elements Compounds and Mixtures
Nature of Matter Elements Compounds and Mixtures Class 8 Very Short Question Answer
Question 1.
Rahul was experimenting at home and poured some cooking oil into a glass of water. After stirring the mixture for a while, he observed the formation of two separate layers. Identify the type of mixture Rahul prepared.
Answer:
Rahul has formed a non-uniform mixture. Oil and water do not mix uniformly and form two distinct layers.
Question 2.
Reena took a glass of water and added some table salt to it. She stirred it until all the salt disappeared and the solution looked clear. What kind of mixture did Reena create? (Competency Based Que.)
Answer:
A salt solution is formed, which is a uniform mixture as the composition is uniform throughout.
Question 3.
Identify whether sugar solution is a pure substance or mixture.
Answer:
No, it is a mixture. Sugar and water are only physically combined and can be separated by physical methods.
Question 4.
Brass and bronze are two commonly used alloys in tools and art. Name the metal that is common in both brass and bronze.
Answer:
Copper is common in both alloys. It is mixed with zinc in brass and with tin in bronze.
Question 5.
Kavya reads about ‘Dhokra art’ in her textbook. Name the alloy commonly used in making such artifacts.
Answer:
The alloy is bronze, made of copper and tin, traditionally used in tribal metal art like Dhokra.
Question 6.
A chemical reaction takes place when carbon dioxide is passed through lime water. Complete the word equation:
Calcium hydroxide + Carbon dioxide → _____________ + _____________ (Competency Based Que.)
Answer:
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water.
Question 7.
During a lab demonstration, a teacher blew into limewater using a straw, and the solution turned milky. What is the name of the gas responsible for this change?
Answer:
The gas is carbon dioxide. It reacts with calcium hydroxide to form calcium carbonate.
Question 8.
Water is a well-known compound found abundantly in nature. How many elements are there in water?
Answer:
Water is made of two elements – hydrogen and oxygen, combined in a fixed ratio of 2 : 1.
Question 9.
Brinda saw a brown-red substance in a bottle, in her chemistry lab. It was labelled bromine. What is its physical state at room temperature?
Answer:
Bromine is a liquid at room temperature.
Question 10.
Samar performed an activity by mixing sand with iron filings and wanted to separate them. Which physical property will help Samar separate iron from the mixture? (Competency Based Que.)
Answer:
Magnetic property. Iron filings can be easily separated using a magnet.
Nature of Matter Elements Compounds and Mixtures Class 8 Short Question Answer
Question 1.
Rahul adds sand to water and stirs it. He notices the sand settles down after some time. What type of mixture is this? Justify. (Competency Based Que.)
Answer:
This is a non-uniform mixture because sand does not dissolve and settles at the bottom, making the composition non-uniform throughout.
Question 2.
Define “alloy” and give one reason why alloys are preferred in making tools.
Answer:
An alloy is a uniform mixture of two or more metals or metals and non-metals. Alloys are preferred in making tools because they are more durable, strong and resistant to corrosion.
Question 3.
What is observed when carbon dioxide is passed into lime water?
Answer:
Lime water turns milky due to the formation of calcium carbonate, showing a chemical reaction between carbon dioxide and calcium hydroxide.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Question 4.
Complete the reaction:
Sugar (on heating) → _____________ + _____________ .
Water (Electrolvsis) → _____________ gas + _____________ gas (Competency Based) Que.
Answer:
Sugar (on heating) → Carbon (black residue) + Water vapour
Water (Electrolysis) → Hydrogen gas + Oxygen gas
Question 5.
Fill the table given below
| Substance | Element/Compound/Mixture |
| Mercury | |
| Steel | |
| Water |
Answer:
Mercury – Element
Steel – Mixture (alloy)
Water – Compound
Question 6.
Study the table and answer the questions. (Competency Based Que.)
| Material | Type | Properties |
| Water | Compound | Fixed composition, no layers |
| Copper | Element | Excellent conductor |
| Soil | Mixture | Varies from sample to sample |
(i) Which is chemically combined?
(ii) Which is the best conductor of electricity?
(iii) Which retains individual properties of its constituents?
Answer:
(i) Water
(ii) Copper
(iii) Soil
Question 7.
A tanker with oil spilled near a water body. Suggest a material to clean the spill. Justify your answer based on the special property of this material discussed in the chapter.
Answer:
Graphene aerogel is ideal for cleanup as it is super lightweight and has high oil-absorption capacity, making it suitable for absorbing oil without soaking water.
Question 8.
Rakhi was performing the activity of heating of sugar. What two observations indicate that sugar is a compound of carbon, hydrogen and oxygen? (Competency Based Que.)
Answer:
(i) On heating, sugar changes into a black residue (carbon), and water vapour is released – this shows the presence of carbon, hydrogen and oxygen.
(ii) The chemical change breaks down sugar into new substances, indicating it is a compound made of multiple elements chemically combined.
Question 9.
A student adds iron filings and sulphur powder in a petri dish. Later, she heats the mixture and finds the new substance does not respond to a magnet. What does this indicate?
Answer:
This shows a chemical change occurred, forming iron sulphide, a compound where iron loses its magnetic property, unlike in the original mixture.
Question 10.
Riya’s teacher gave her samples of gold and quartz. She was asked to identify which one is a native mineral and which is a compound. How should Riya answer? (Competency Based Que.)
Answer:
Gold is a native mineral because it is found in pure elemental form, whereas quartz is a compound mineral made of silicon and oxygen.
Nature of Matter Elements Compounds and Mixtures Class 8 Long Question Answer
Question 1.
Radhika was performing the electrolysis of water in her school lab. She noticed that one gas collected relit a glowing splinter and the other popped when tested with a flame. (Competency Based Que.)
(i) Identify the two gases.
(ii) Explain the principle of electrolysis in simple terms.
(iii) Why are the volumes of the gases collected in a 2:1 ratio?
(iv) How does this activity prove water is a compound?
Answer:
(i) The gas that relit a glowing splinter is oxygen, and the one that made a popping sound with a burning splinter is hydrogen.
(ii) Electrolysis is the process of using an electric current to break down a compound. In this case, electricity is used to split water (H2O) into hydrogen and oxygen gases.
(iii) Water contains two atoms of hydrogen and one atom of oxygen. So, during electrolysis, hydrogen gas is produced in double the volume of oxygen gas, giving a 2:1 ratio.
(iv) Water breaks down into two entirely different gases-hydrogen (flammable) and oxygen (supports burning). This shows water is a compound of hydrogen and oxygen, not a mixture, because its components are chemically combined and not just physically mixed.
Question 2.
Aarav accidentally mixed iron nails with powdered sulphur. Describe a step-by-step method he should follow to separate the components and prove that it’s a mixture.
Answer:
Use a magnet : Move a magnet over the mixture. The iron nails will be attracted and can be separated easily.
Observe physical properties : Both iron and sulphur retain their original properties-iron is magnetic and sulphur is a yellow powder.
No new substance formed : If not heated, there is no chemical reaction. This confirms it is a physical mixture.
Conclusion : Since the components can be separated by physical means and do not form a new substance, the mixture is not a compound.
Question 3.
Why does heating iron and sulphur lead to formation of a new substance? What gas is released on adding dilute HCI to the compound? Explain how this proves it’s a chemical change. (Competency Based Que.)
Answer:
When iron and sulphur are heated strongly, they chemically react to form iron sulphide (FeS), which is a new substance with entirely different properties.
When dilute hydrochloric acid (HCl) is added to iron sulphide, hydrogen sulphide (H2S) gas is released, which smells like rotten eggs.
This reaction is irreversible and produces a new substance with new properties, showing that a chemical change has occurred. Unlike in a mixture, the original properties of iron and sulphur are lost in the compound.
Nature of Matter Elements Compounds and Mixtures Class 8 Case Based Questions
Question 1.
Anaya visited a local handicraft fair with her classmates. At one stall, an artisan was showcasing Dhokra art, a traditional craft using a metal alloy to make tribal figurines. The artisan explained that the alloy gives strength and durability to the art pieces.
In another stall, Anaya noticed beautiful quartz crystals used in watches and glass decorations.
(Competency Based Que.)
(i) What kind of substance is the alloy used in Dhokra art-element, compound, or mixture? Justify your answer.
(ii) What is the nature of quartz: element or compound? Name the elements it is made of.
(iii) How are minerals different from native elements like gold?
Answers:
(i) The alloy used in Dhokra art is a mixture, specifically a uniform mixture of metals. Alloys are mixtures because their components (like copper and tin) are not chemically combined but uniformly blended.
(ii) Quartz is a compound mineral made of silicon and oxygen. It has a fixed chemical composition (Si02), meaning its elements are chemically combined in a definite ratio.
(iii) Minerals are mostly compounds formed from multiple elements, whereas native elements like gold exist in pure elemental form in nature.
Question 2.
A tanker transporting crude oil accidentally tipped over near a riverbank, leading to a major oil spill in the water. The local science team was called to control the damage. They used a lightweight, sponge-like material that could soak up the oil without mixing with the water. The team demonstrated how this method saved aquatic life by preventing oil from spreading further. (Competency Based Que.)
Answer the following
(i) What type of mixture is formed when oil spills into water? Give one reason.
(ii) Which material, mentioned in the case, can be used to clean the oil spill? State one special property that makes it suitable for this job.
(iii) Why is it possible to separate oil from water by physical means in this case? Explain in terms of the nature of the substances involved.
Answers:
(i) It forms a non-uniform mixture because oil and water do not mix uniformly. The oil floats on the surface due to differences in density and immiscibility.
(ii) Graphene aerogel can be used for cleaning oil spills,.It is extremely light and highly absorbent, which allows it to soak up oil without absorbing water.
(iii) Oil and water form a mixture, not a compound, so they can be separated physically.
Skill Based Questions
Question 1.
Use the given hints and solve the word puzzle. (Thinking Skill)
(i) A substance formed when two or more elements chemically combine.
(ii) This gas supports burning.
(iii) The simplest form of matter, made of only one kind of atom.
(iv) An example of a uniform mixture of gases we breathe.
(v) A non-uniform mixture of salt and water.
Question 2.
Read the following case and answer the given questions. (Analytical Skill)
A science teacher took a small quantity of iron filings and sulphur powder and mixed them. The students could still see both substances. When the mixture was heated, a new black-coloured substance was formed that did not show magnetic properties and released a foul-smelling gas when reacted with dilute hydrochloric acid. The students concluded that a new compound was formed.
(i) What type of substance was formed after heating iron and sulphur — a mixture or a compound?
(ii) Name the gas formecFwhen the black substance reacted with dilute hydrochloric acid.
(iii) Why does the black substance not get attracted to a magnet?
Question 3.
Study the table given below and answer the questions that follow. (Analytical Skill)
| Property | Element | Compound | Mixture |
| Number of substances | One | Two or more | Two or more |
| Can be separted | No | Only by chemical means | By physical means |
| Properties | Same throughout | Different from elements | Properties retained |
| Example | Oxygen (O2) | Water (H2)O | Air |
(i) Which type of matter can be separated by physical methods?
(ii) Which type of matter has properties different from the substances that form it?
(iii) In which type is only one kind of atom present?
(iv) Give one example of a compound given in the table.
(v) Why is air considered a mixture?
Nature of Matter Elements Compounds and Mixtures Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
State one key difference between a uniform mixture and a non-uniform mixture.
Question 2.
When iron sulphide reacts with dilute hydrochloric acid, a gas with a foul smell is released. Name this gas.
Question 3.
Minerals contain both elements and compounds. Name one mineral that is an element and one that is a compound.
Short Answer Type Questions
Question 1.
What are alloys? Give two examples and state how they are different from compounds.
Question 2.
Why is water considered a compound, not a mixture?
Question 3.
When sugar is heated, it decomposes and leaves a black residue. Why does this happen? Write the word equation for the change.
Long Answer Type Questions
Question 1.
Explain how passing electricity through water proves that it is a compound. Include a labelled diagram in your answer?
Question 2.
What are minerals? What are native minerals? Give examples of minerals.