Chemistry

Mole Concept and Stoichiometry

354 Questions

The mole concept is a core area of chemistry focusing on the quantitative relationships between reactants and products in chemical reactions. Questions cover molecular mass calculations, stoichiometric conversions, and determining the number of molecules. This topic is essential for most science entrance and competitive examinations.

molecular mass calculationsstoichiometric conversionsmole fraction problemsheavy water reactionsoxidation calculations

Mole Concept and Stoichiometry Questions

Multiple choice chemistry basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

Carbon and oxygen from two compounds. Carbon content in one of them is 42.9% and in the other is 27.3%. The given data is in agreement with :

  1. law of conservation of mass

  2. law of multiple proportions

  3. law of reciprocal proportions

  4. law of definite proportions.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Since the two compounds are composed of the same two elements (carbon and oxygen) with different mass percentages, they illustrate the law of multiple proportions.

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

The weight of one mole of heavy water is:

  1. $18$ gm
  2. $20$ gm
  3. $19$ gm
  4. $21$ gm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
 Deuterium is called as heavy water,

As atomic mass of Deuterium is 2 and atomic mass of oxygen is 16

So Molar mass of $D _2O$ is = $2\times2 +1\times 16= 20$

Weight of $1$ mole of ${ D } _{ 2 }O =$ Molecular mass of ${ D } _{ 2 }O = 20$ gm

Option B is correct.
Multiple choice chemistry water drying and dehydrating agents hydrolysis of salts and the ph of their solutions chemical equilibrium and acids-bases

If there are three moles of $H _2O$ for every one mole of $LiClO _4$, what is the hydrate formula?

  1. $\displaystyle LiClO _4 \cdot 3H _2O $
  2. $\displaystyle 3LiClO _4 \cdot 3H _2O $
  3. $\displaystyle 3LiClO _4 \cdot H _2O $
  4. $\displaystyle LiClO _4 \cdot (H _2O) _3 $
  5. $\displaystyle 3(LiClO _4) \cdot 3(H _2O) _3 $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If there are three moles of $H _2O$ for every one mole of $\displaystyle LiClO _4$. The hydrate formula would be $\displaystyle LiClO _4 \cdot 3H _2O $

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

How many water molecule splite during light reaction for evolution of $4$ oxygen molecule?

  1. $2$
  2. $4$
  3. $6$
  4. $8$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In order to split water, four photochemical reactions are needed to take out four electrons and four protons from two water molecules. This leads to the formation of one oxygen molecule. Protons form water are released into the lumen (donor side of PSII) and electrons are moved to the plastoquinone (QB) binding site. So, the correct option is "A" (2).

Multiple choice chemistry properties of natural resources conservation of water and recycling properties of water structure and properties of water

What is the molecular weight of water?

  1. 21

  2. 18

  3. 20

  4. 16
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The atomic masses of O and H are 16 g/mol and 1 g/mol respectively.
The molecular formula of water is $H _2O$ and its molecular weight $2(1) + 16=18$ g/mol.
Note:
Water is one of the most precious resources on earth and is necessary for all living beings. We use water for different purposes like drinking, cooking, bathing, washing and many more activities. Pure water is colorless, odorless and tasteless.

Multiple choice chemistry properties of natural resources conservation of water and recycling properties of water structure and properties of water

Ratio of hydrogen to oxygen in water is:

  1. $2:1$
  2. $1:2$
  3. $7:1$
  4. $8:1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The ratio of hydrogen to oxygen in water is 2:1.
Two molecules of the diatomic hydrogen gas, combine with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2.
$2H _2 + O _2 \rightarrow 2H _2O$

Multiple choice chemistry properties of natural resources conservation of water and recycling properties of water structure and properties of water

Molecular mass of water ______.

  1. $18 u$
  2. $16 u$
  3. $15 u$
  4. $10 u$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As we know the molecular formula of water is H2O which means that one molecule of water contain 2 atoms of hydrogen and 1 atom of oxygen.

Then weight of 1 atom of hydrogen= 1 u

so weight of 2 atom= 2 u

Weight of 1 atom of oxygen= 16 u

Then molecular weight of water= 2* weight of 1 atom of hydrogen+ weight of 1 atom of oxygen

Thus molecular weight of water is approximately 2+16 u = 18 u

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

In an experiment, 2.4 g of iron oxide on reduction with hydrogen gave 1.68 g of iron. In another experiment, 2.9 g of iron oxide gave 2.09 g of iron on reduction. Which law is illustrated from the above data?

  1. Law of constant proportions

  2. Law of multiple proportions

  3. Law of reciprocal proportions

  4. Law of conservation of mass
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
In experiment 1,
$2.4\ g$ of iron oxide gives $1.68\ g$ iron on reduction with hydrogen.
$FeO \rightarrow Fe+O _2$
Percent of $Fe$ in $FeO$ is = $\frac{1.68}{2.4} \times 100=70$
Therefore ratio of $m _{Fe}:m _{O}::7:3$
In experiment 2:
$2.9\ g$ of iron oxide gives $2.09\ g$ iron on reduction.
Percent of $Fe$ in $FeO$ is = $\frac{2.09}{2.9} \times 100=72$

Therefore ratio of $m _{Fe}:m _{O} \approx 7:3$
When a given chemical compound contains its component elements in fixed ratio (by mass) and does not depend on its source and method of preparation, it follows law of constant proportion.
option A is correct

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

A sample of calcium carbonate $(CaCO _{3})$ has the following percentage composition:
Ca = 40%; C = 12%; O = 48%.
If the law of constant proportions is true, then the weight of calcium in 4 g of a sample of calcium carbonate from another source will be:

  1. 0.016 g

  2. 0.16 g

  3. 1.6 g

  4. 16 g
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In $100$ $g$ $CaCO _3$, $40$ $g$ $Ca$ is present.

In $4$ $g$ $CaCO _3$, Let $x$ $g$ $Ca$ be present
$\cfrac{x}{4}=\cfrac{40}{100}$
$\implies x=1.6$ $g$

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

A sample of calcium carbonate $\left( CaC{O} _3 \right)$ has the following percentage composition:
Ca = 40%; C = 12%; O = 48%.
If the law of constant proportions is true, then the weight of calcium in 4 g of a sample of calcium carbonate from another source will be ?

  1. 0.016 g

  2. 0.16 g

  3. 1.6 g

  4. 16 g
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Calcium carbonate from any source contains 40% calcium. 

So each 1 g of calcium carbonate contains 0.4g of calcium.
Thus, for 4 g of calcium carbonate, the amount of calcium $=4\times 0.4=1.6g$

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

Hydrogen combines with oxygen to form $H _2O$ in which 16 g of oxygen combine with 2 g of hydrogen. Hydrogen also combines with carbon to form $CH _4$ in which 2 g of hydrogen combine with 6 g of carbon.If carbon and oxygen combine together then they will do show in the ratio of 

  1. 13 : 32

  2. 6 : 16

  3. 1 : 2

  4. 12 : 24
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

From H2O: 2g H reacts with 16g O. From CH4: 2g H reacts with 6g C. Therefore, 6g C reacts with 16g O. The ratio of C:O is 6:16.