Tag: chemistry

Questions Related to chemistry

Which of the following represents a physical change?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Stretched rubber band

  2. Melting of ice cream

  3. In winter, hair oil freezes.

  4. All of the above.

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Correct Option: D
Explanation:

All of the following represents a physical change.
Stretched rubber band.
Melting of ice cream.
In winter, hair oil freezes.

Which of the following is/are true?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. When a metal rod is cooled, it expands.

  2. During expansion, the length of metal rod decreases.

  3. Both of the above.

  4. None of the above.

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Correct Option: D
Explanation:

When a metal rod is heated, it expands. During expansion, the length of metal rod increases.

Which of the following represents a chemical change?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Rusting of iron.

  2. Magnesium burns in air leaving behind a powdery ash.

  3. Explosion of a firework.

  4. All of the above.

Show answer
Correct Option: D
Explanation:

All of the following represents a chemical change.

Rusting of iron.
Magnesium burns in air leaving behind a powdery ash.
Explosion of a firework.

In which type of change, alteration takes place only in specific property of matter but not composition?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Chemical change

  2. Physical change

  3. Both physical and chemical change

  4. None of the above

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Correct Option: B
When the solid A is added to water, it dissolves with the evolution of heat with the formation of two products B and C. The properties of products B and C are entirely different from those of solid A as well as water. Moreover, products B and C cannot be re-converted into solid A and water. When another solid D is added to water, it dissolves to form a product E which cools down. The product E shows the properties of both, solid D as well as water. Moreover, product E can be converted into solid D and water.
Correct statement(s) is/are:
chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. A chemical change occurs when solid A is dissolved in water

  2. A physical change occurs when solid D is dissolved in water

  3. Metal sodium could behave like solid A

  4. Metal E is a mixture

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Correct Option: A

Which of the following is not a physical change?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Tearing paper

  2. Bending an iron rod

  3. Freezing water into ice

  4. None of these

Show answer
Correct Option: D
Explanation:

No new substances are formed in all these three changes. So these are physical change. 

On heating, the colour of zinc oxide changes from white to yellow. This is a/an:

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. physical change

  2. chemical change

  3. photochemical change

  4. irreversible change

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Correct Option: B
Explanation:

Zinc oxide is a white powder, when heated strongly (above $800^0 C$) it turns yellow, but again becomes white again when cold. The hot zinc oxide absorbs some of the blue wavelengths of light making the reflected light more yellow. The loss of oxygen makes it a reversible chemical change.

In a certain change, colour and the magnetic properties of a substance changed. What reaction might this be?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Chemical combination

  2. Photochemical reaction

  3. Irreversible reaction

  4. Physical change

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Correct Option: D
Explanation:

Iron is magnetic at room temperature, but at 770 degrees Celsius iron loses its magnetism. However this change is temporary, hence it is an example of physical change.

and the change in color is a physical change because it is easily reversible without affecting the chemical nature of it.

In the_______ properties of molecules remain same even after the change.

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. physical change

  2. chemical change

  3. biochemical change

  4. photochemical change

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Correct Option: A
Explanation:

In physical change properties of molecules remain the same even after the change. Physical properties like colour, density, volume, mass, boiling point, melting point only have an effect on their physical nature, the chemical nature of the substance remains the same. Physical properties are used to observe and describe matter.

Choose the incorrect statement :

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Physical change is reversible

  2. Physical change results in the formation of new substances

  3. Chemical change is permanent

  4. Physical change is accompanied by energy change

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Correct Option: B
Explanation:

Physical change does not lead to formation of new substances but only chemical changes can produce new substances.