Tag: chemistry

Questions Related to chemistry

Dalton based his relative atomic weight scale on :

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. hydrogen

  2. oxygen

  3. helium

  4. lithium

  5. carbon

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Correct Option: A
Explanation:

Dalton published his table of relative atomic weights and six elements appeared in table which are hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus with atom of hydrogen which assumed to weigh 1.

The existence of isotopes violated which one of the postulates of Dalton's atomic theory?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. All matter is made of very tiny particles called atoms

  2. Atoms of a given element are identical in mass and chemical properties

  3. Atoms are indivisible particles and cannot be created nor destroyed

  4. Atoms of same elements are alike in all respects

Show answer
Correct Option: D
Explanation:

Isotopes are atoms of same elements having same atomic number but different atomic masses.

Which postulates of Dalton's atomic theory can explain the Law of definite proportion?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. All matter is made of very tiny particles called atoms.

  2. Atoms of a given element are identical in mass and chemical properties.

  3. Atoms are indivisible particles and cannot be created nor destroyed.

  4. The relative number and kind of atoms in a given compound remain constant.

Show answer
Correct Option: D
Explanation:

The law of definite proportion states that in compounds , the elements are always present in definite proportions by mass.

According to Dalton's atomic theory, atoms of a given element are identical in: 

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. chemical properties and size

  2. weight and colour

  3. properties and colour

  4. colour and size

Show answer
Correct Option: A
Explanation:

According to atomic theory, atoms of a given element are identical in size and chemical properties.

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. All matter is made of very tiny particles called atoms

  2. Atoms of a given element are identical in mass and chemical properties

  3. Atoms of different elements have different masses and chemical properties

  4. Atoms are indivisible particles and cannot be created nor destroyed

Show answer
Correct Option: D
Explanation:

According to Dalton's  theory atoms are indivisible particles and cannot be created nor destroyed.

Which of the following correctly represents symbol for chlorine in Berzelius system?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. M

  2. Cl

  3. Mn

  4. C

Show answer
Correct Option: A
Explanation:

M correctly represents a symbol for chlorine in Berzelius system. The symbol M was derived from the word Muriatic Radicle which signifies element chlorine. At present, the symbol M is replaced with symbol Cl.

The water of crystallisation is the fixed number of _________ molecules in one formula unit of salt.

chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

  1. hydrogen

  2. water

  3. oxygen

  4. hydroxide

Show answer
Correct Option: B
Explanation:

Water of crystallisation are water molecules that form an essential part of the crystal structure of some compounds.

It is the fixed number of water molecules in one formula unit of salt.
For example Glauber's salt has 10 water of crystallisation and it's formula is $Na _2SO _4.10H _2O$.
Hence, the correct answer is option (B).

Water of crystallisation is responsible for ......... of the crystals.

chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

  1. geometric shape and colour

  2. colour

  3. geometric shape

  4. number of crystal

Show answer
Correct Option: A
Explanation:

Water of crystallisation are water molecules that form an essential part of the crystal structure of some compounds.

Thus, the water of crystallisation is responsible for the geometric shape and colour of the crystals.
For example, Glauber's salt (Sodium sulphate decahydrate) $Na _2SO _4.10H _2O$ has ten water of crystallisation and it is responsible for the colourless monoclinic geometry of the crystals.
Hence, the correct answer option is (A).

Water of crystallization is the fixed number of water molecules chemically attached to a unit of a salt in its crystalline form.

chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

  1. True

  2. False

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Correct Option: A
Explanation:

Water of crystallization means the number of water molecules present in one formula unit of a salt.
For example: $CaSO _4.2H _2O$ is called calcium sulphate dihydrate with and it has $2$ molecules of water of crystallization.

The crystalline salt, $Na _{2}SO _{4}xH _{2}O$ on heating losses $55.9\%$ of its weight. The formula of the crystalline salt is :

chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

  1. $Na _{2}SO _{4}.5H _{2}O$

  2. $Na _{2}SO _{4}.7H _{2}O$

  3. $Na _{2}SO _{4}.10H _{2}O$

  4. $Na _{2}SO _{4}.2H _{2}O$

Show answer
Correct Option: C
Explanation:

$Na _2SO _4.xH _2O$


Mass of hydrate $=23\times 2+32+64+18x$
$=46+96+18x$
$=142+18x$
Mass of water of hydration=$18x$
% of water in hydrate=$55.9$%

$\cfrac {18x}{142+18x}\times 100=55.9$

$1800x=7937.8+1006.2x$

$793.8x=7937.8$

$x=9.99\sim 10$

Answer= $Na _2SO _4.10H _2O$