Pure substance: examples and properties - class-VIII

 Description: pure substance: examples and properties Number of Questions: 26 Created by: Ankita Patil Tags: pure substances and mixtures: separation of mixtures composition of matter is matter around us pure methods of separation matter around us chemistry is matter pure element, compound and mixture structure of matter and molecule elements, compounds and mixtures the nature of matter
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The components in mixtures _______ their original properties.

1. retain

2. do not retain

3. both A and B

4. none of the above

Correct Option: A
Explanation:

The components in mixtures retain their original properties.

The components in compounds ______ their original properties.

1. retain

2. do not retain

3. both A and B

4. none of the above

Correct Option: B
Explanation:

The components in compounds do not retain their original properties.

Which of the following is not a property of compounds?

1. Components are present in a fixed proportions

2. They are always homogeneous

3. The components in compounds do not retain their original properties

4. The components in compounds can be separated by physical means

Correct Option: D
Explanation:

The components of compounds can be separated by chemical means. Rest all are properties of compounds.

Which one of the following is neither an element nor a compound?

1. Air

2. Glucose

3. Gold

4. Water

5. Carbon

Correct Option: A

The medium having same chemical properties in all directions is called :

1. Isotropic medium

2. Anisotropic medium

3. Optically denser medium

4. Light medium

Correct Option: A
Explanation:

Isotropic medium is the one in which permeability and permittivity are unifrom in all directions,

hence, it is having same chemical properties in all directions.

Which method separates a mixture of sugar and glass?

1. dissolve, filter and evaporate

2. distillation

3. fractionally distill

4. use chromatography

Correct Option: B
Explanation:

$\text{Distillation is a way of seperation substances based on the difference in their boiling points}$

In which row are the substances correctly classified?

1. element - brass; compound - sulfur; mixture - water

2. element - sulfur; compound - brass; mixture - water

3. element - sulfur; compound - water; mixture - brass

4. element - water; compound - sulfur; mixture - brass

Correct Option: C
Explanation:
$\text{1.water is a compound made by combination of hydrogen and oxygen.}$
$\text{2.sulfur is an element.}$
$\text{3.Brass is mixture of elements sulphur and zinc.}$

A commercial cake is :

1. a molecule

2. a mixture of compounds

3. an isotope

4. an isomer

5. an acid salt

Correct Option: B
Explanation:

A commercial cake is a mixture of compounds.

Cake contains various compounds such as coco, butter, milk, cream etc.

Hence the correct option is B.

Which of the following can give further simplification using ordinary means?

1. An element or a mixture

2. A mixture or a compound

3. A mixture or an atom

4. An element or a compound

Correct Option: B
Explanation:

A mixture or a compound can give further simplification using ordinary means.

A mixture can be broken into individual components.

A compound can be broken into individual elements.

A substance composed of two or more compounds, each of which retains its own properties is called a mixture.

Hence option B is correct.

Ionic compounds have ____ melting and boiling points whereas covalent compounds have _____ melting and boiling point.

1. low, high

2. moderate, low

3. high, low

4. moderate, high

Correct Option: C

Which of the following is a characteristic property of both mixtures and compounds?

1. Their properties are same as those of their components

2. Energy is released when they are formed

3. Their masses are equal to the sum of the masses of their components

4. They contain the components in fixed proportions

Correct Option: C
Explanation:

Mixture and a compound both follow the law of conservation of mass so their weight equals to the sum of mass of their components.

Which of the following statement is incorrect?

1. In compounds components are present in definite proportion whereas in mixtures components are present in varying proportion

2. Compounds are homogenous whereas mixtures are mostly heterogeneous

3. Particles in a compound are generally of same kind whereas in mixtures they are of different kind

4. None of the above

Correct Option: D
Explanation:

All the compounds are made up of different elements and have properties different from their constituent element.

Mixture composed of variant proportion of components.
Hence, all statements are correct.

Which of the following is not a property of mixture?

1. Does not have a sharp melting or boiling point

2. Heat is taken in or given out in the preparation

3. Can be separated by physical means

4. May be homogeneous or heterogeneous

Correct Option: B
Explanation:

The parts of a mixture can be separated by physical means. A mixture does not have a sharp melting or boiling point. It may be homogeneous or heterogeneous. Energy is neither given out nor absorbed in the preparation of a mixture. However, heat is taken in or given out in the preparation of a compound.

The components present in mixtures are in :

1. fixed proportion

2. variable proportion

3. Both A and B

4. None of the above

Correct Option: B
Explanation:

The components present in the mixture are in variable proportions.

Mixture is different from a compound. True or false?

1. True

2. False

Correct Option: A
Explanation:

A mixture consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined. However, a compound consists of two or more elements that are chemically combined in a fixed proportion. Hence, a compound is different from a mixture.

Which of the following is not an example of compound?

1. Brass

2. Air

3. Bitumen

4. All of the above

Correct Option: D
Explanation:

Brass, Air and Bitumen are all mixtures. None of them are compounds.

Each component of a ______ retains its individual properties.

1. Compound

2. Element

3. Mixture

4. Solute

Correct Option: C
Explanation:

Matter that consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined is called as a mixture. Each component of a mixture retains its individual properties.

For example, we could mix various proportions of hydrogen and oxygen gas, as long as you do not ignite the mixture, the combination will form a mixture that can be separated.

Which of the following methods can be used to separate hydrogen and oxygen in water?

1. Boiling

2. Electrolysis

3. Distillation

4. None of the above

Correct Option: B
Explanation:

Electrolysis decomposes the water into oxygen and hydrogen due to passage of electric current.

Which of the following is not a property of mixtures?

1. Components of mixtures are present in a varying proportions

2. They are always homogeneous

3. The components of mixtures retain their original properties

4. The components of mixtures can be separated by physical means

Correct Option: B
Explanation:

Mixtures can be homogeneous or heterogeneous. Oil and Water is a heterogeneous mixture.

_____is chemically mixed whereas____is physically combined.

1. Element, compound

2. Compound, mixture

3. Mixture, compound

4. Mixture, element

Correct Option: B
Explanation:

Compound is made up of two or more elements that are chemically combined whereas mixtures are made up of two or more pure substances that are physically combined.

Among the following, which is\are the difference between compound and mixture?

1. The constituents of a compound can be separated only by chemical methods.

The constituents of a mixture can be separated easily by physical methods.

2. Compounds are pure substances.

Mixtures are impure substances.

3. The constituents of a compound are present in a fixed ratio.

The constituents of a mixture are present in varying ratios.

4. All of above

Correct Option: D
Explanation:

Compounds are pure substances whereas mixture are impure substances. The constituents of a compound can be separated only by chemical methods and that of a mixture can be separated easily by physical methods. The constituents of a compound are present in a fixed ratio.The constituents of a mixture are present in varying ratios.

Which of the following obey the law of constant proportions in their formation?

1. Mixtures

2. Compounds

3. Elements

4. Colloids

Correct Option: B
Explanation:

A compound always follow the law of constant proportions because in a compound the elements that are present are always in the constant ratio.

Which of the following is a pure gas?

1. Ntural gas

2. Water gas

3. Laughing gas

4. Coal gas

Correct Option: C
Explanation:

Pure gas is not a mixture.

Natural gas consists of a mixture of gases like methane, higher alkanes, carbon dioxide etc. So it is not a pure gas.

Similarly, water gas is a mixture of $CO, H _2S$
Coal gas is a mixture of $H _2,CH _4,CO$
But laughing gas is only $N _2O$, So it is pure gas.

Hence, the correct option is $C$

A compound is always ______ whereas a mixture is :

1. Heterogenous, both heterogenous and homogenous

2. Homogenous, heterogenous

3. Homogenous, Both homogenous and heterogenous

4. None of above

Correct Option: C
Explanation:

Compound is made up of two or more pure substances which are always homogenous. Mixtures contains two or more pure substances physically combined which may be homogenous or heterogenous

Which of the following is/are example(s) of mixtures?

1. Air

2. $Fe + S$

3. Bronze

4. All of the above

Correct Option: D
Explanation:

Air is a mixture of gases. $Fe + S$ is also a mixture. Bronze is an alloy and all alloys are mixtures.

In which of the following compounds resonance does not occur
(i) ${H _2}O$
(ii) $Si{O _2}$
(iii) $S{O _3}$
(iv) $C{O _2}$

1. Both (i) and (iv)

2. Both (i) and (ii)

3. Both(iii) and (iv)

4. (i),(ii)and(iv)

Correct Option: D
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