Tag: chemistry

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Questions Related to chemistry

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

The existence of isotopes violated which one of the postulates of Dalton's 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
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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

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

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

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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

  1. M

  2. Cl

  3. Mn

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

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

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

  1. hydrogen

  2. water

  3. oxygen

  4. hydroxide
Reveal answer Fill a bubble to check yourself
B Correct answer
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).

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

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

  1. geometric shape and colour

  2. colour

  3. geometric shape

  4. number of crystal
Reveal answer Fill a bubble to check yourself
A Correct answer
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).

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

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 :

  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. $Na _{2}SO _{4}.2H _{2}O$
Reveal answer Fill a bubble to check yourself
C Correct answer
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= $Na _2SO _4.10H _2O$