Question 1

Q1: Consider the following reaction where two substances, A and B , combine to form a product C : $$A+B \rightarrow C$$ Assume that A and B cannot be brok...

Accepted Answer

The correct statement is (iv): A and B are elements, C is a compound, and has a fixed composition. Elements are substances that cannot be broken down into simpler substances by chemical reactions. Compounds are formed when different elements combine in fixed ratios.

Question 2

Q10: Analyse Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Accepted Answer

Based on the context of the chapter (Activity 8.3), Fig 8.24 likely depicts the electrolysis of water. In this process, Gas A, which occupies twice the volume of the other gas, is Hydrogen. The word equation for the chemical reaction is: Water → Hydrogen + Oxygen

Question 3

Q11: Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.

Accepted Answer

1.  Carbon dioxide (CO2):        Uses: Used in fire extinguishers to put out fires. Used by plants for photosynthesis. 2.  Water (H2O):        Uses: Essential for life and used for drinking, cleaning, and agriculture. Used as a solvent in many chemical reactions.

Question 4

Q12: How can gold be classified as both a mineral and a metal?

Accepted Answer

Gold can be classified as both a mineral and a metal because:    Mineral: Gold occurs naturally in the Earth's crust as a solid substance with a definite chemical composition. Some of the minerals are called native minerals, which are pure elements and not compounds. These can be metals, such as gol...

Question 5

Q2: Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change. (i) Both Asser...

Accepted Answer

The correct answer is (i): Both Assertion and Reason are true and Reason is the correct explanation for Assertion. Air is a mixture of gases like nitrogen, oxygen, argon, and carbon dioxide. A mixture is formed when two or more substances are mixed together, where each substance retains its properti...

Question 6

Q3: Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Accepted Answer

Water is a compound formed from the elements hydrogen and oxygen. Hydrogen is a flammable gas, and oxygen supports combustion. However, water extinguishes fire. Therefore, the properties of water are different from the properties of the elements that form it. Compounds are formed when different elem...

Question 7

Q4: In which of the following cases are all the examples correctly matched? Give reasons in support of your answers. (i) Elements - water, nitrogen, iron,...

Accepted Answer

The examples are correctly matched in case (iii): Pure substances - carbon dioxide, iron, oxygen, sugar.    Elements are the simplest substances that cannot be broken down further. Nitrogen and iron are elements, but water and air are not.    Uniform mixtures have components that are evenly distribu...

Question 8

Q5: Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved in the abov...

Accepted Answer

Iron: Element, as it cannot be broken down into simpler substances.    Moist air: Mixture, as it is a combination of gases and water vapor.    Iron oxide (rust): Compound, as it is formed by the chemical combination of iron and oxygen.    Magnesium: Element, as it cannot be broken down into simpler...

Question 9

Q6: Classify the following as elements, compounds, or mixtures in Table 8.3. Carbon dioxide, sand, seawater, magnesium oxide, muddy water, aluminium, gold...

Accepted Answer

Table 8.3 | Elements | Compounds | Mixtures | |---|---|---| | Aluminium | Carbon dioxide | Sand | | Gold | Magnesium oxide | Seawater | | Oxygen | Rust | Muddy water | | Nitrogen | Iron sulfide | Air | | Sulfur | Glucose | Fruit juice | | Hydrogen | Water | Baking soda | |  | Sodium chloride |  | Pu...

Question 10

Q7: What new substance is formed when a mixture of iron filings and sulfur powder is heated, and how is it different from the original mixture? Also, writ...

Accepted Answer

When a mixture of iron filings and sulfur powder is heated, a new substance called iron sulfide is formed. Iron sulfide is different from the original mixture because iron and sulfur are chemically combined, and the properties of the compound are different from those of the elements. In the original...

Question 11

Q8: Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.

Accepted Answer

It is not possible for a substance to be classified as both an element and a compound. Elements are the simplest substances that cannot be broken down into simpler substances by chemical means. Compounds are formed when two or more elements are chemically combined in a fixed ratio. Therefore, a subs...

Question 12

Q9: How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Accepted Answer

If water were a mixture of hydrogen and oxygen instead of a compound, our daily lives would be significantly different. Since mixtures retain the properties of their constituents, water would exhibit the properties of both hydrogen and oxygen. This would mean:    Water would be flammable due to the...

NCERT Solutions