Tag: changes around us

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Questions Related to changes around us

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Which of the following represents correct statement(s)?

  1. Salt can be obtained by the evaporation of sea water.

  2. The salt obtained during crystallisation is pure and its crystals are large.

  3. After crystallisation, the shape of the crystals can be seen clearly.

  4. Large crystals of pure substances cannot be formed from their solutions.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The option (A) represents correct statements.
Salt can be obtained by the evaporation of sea water.
The salt obtained during crystallisation is not pure and its crystals are small.
After crystallisation, the shape of the crystals cannot be seen clearly.
Large crystals of pure substances can be formed from their solutions.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Salt can be obtained by ___________ of sea water.

  1. sublimation

  2. cooling

  3. evaporation

  4. heating
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

On evaporation of seawater in shallow pools, salt along with impurities remain behind. Impured salt is taken in a tank and its saturated solution is prepared. In a saturated solution of salt, HCl vapours are passed. Chloride ions being common to both, it's concentration increases, and NaCl gets precipitated which is free from impurities.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

The process of forming large crystals of pure substances from their solutions is known as __________.

  1. evaporation

  2. purification

  3. condensation

  4. crystallisation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The process of forming large crystals of pure substances from their solutions is known as Crystallization. The principle of crystallization is concerned with the thermodynamic conditions of crystallization and the kinetics of crystal nucleation and growth.
Crystallization is the physical transformation of a liquid solution or gas to a crystal which is a solid with an ordered internal arrangement of molecules, ions or atoms.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Crystallisation is an example of ____________.

  1. physical change

  2. biological change

  3. chemical change

  4. fundamental change
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The process of formation of solid crystals from a homogeneous solution is called crystallization. It is a physical change. Crystallization is the solidification of atoms or molecules into a highly structured form called a crystal. It can also refer to the solid-liquid separation and purification technique in which mass transfer occurs from a liquid solution to a pure solid crystalline phase.

For example Salt we get from seawater can have many impurities in it. To remove these impurities, the process of crystallization is used.

Hence, the correct option is $A$

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

A synthetic indicator phenolphthalein gives _____ colour in acidic solution.

  1. red

  2. blue

  3. pink

  4. colourless
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Phenolphthalein [3,3-Bis (4- hydroxyphenyl)- 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and usually dissolved in alcohols for use in experiments. It is a weak acid which can loose $H^{+}$ ions in solution.

Multiple choice chemistry changes around us effects of oxidation reactions in daily life corrosion of metals electroplating and its application

Any article of iron if left in open for some time, acquires a film of brownish substance (rust) having chemical formula:

  1. $Fe _3O _4$
  2. $Fe _2O _3$

  3. FeO
  4. $Fe(OH) _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Iron reacts with air to form iron oxide(III) which is known by the name rust or rusting of iron. Rust is an iron oxide or red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Rust consist of hydrated iron oxide.

Multiple choice chemistry changes around us effects of oxidation reactions in daily life corrosion of metals electroplating and its application

Corrosion occurs due to:
a) action of water on the metal.
b) action of air on the metal.
c) action of temperature on the metal.

  1. a, b

  2. b, c

  3. a, c

  4. all of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An action of air and water gradually eats up the metal. This eating up of metals by the action of air and moisture on their surface is called corrosion.

Multiple choice chemistry changes around us effects of oxidation reactions in daily life corrosion of metals electroplating and its application

Which of the following methods is suitable for preventing an iron frying pan from rusting?

  1. Applying grease

  2. Applying paint

  3. Applying a coating of zinc

  4. All of the above.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We can prevent iron getting rusted by applying a coat of zinc or a thin coat of plastic helps to prevent rust. The process for coating metal like iron or steel with a thin zinc layer is known as galvanization.