Tag: law of constant proportion

Questions Related to law of constant proportion

Potassium combines with two isotopes of chlorine $(^{35} Cl\,\, and\,\, ^{37}Cl)$ respectively to form two samples of $KCl$ Their formation follows the law of:

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  1. constant proportions

  2. multiple proportions

  3. reciprocal proportions

  4. none of these

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Correct Option: A
Explanation:
According to the Law of Definite Proportions, a chemical compound will always have exactly the same proportion of elements by mass.
This means that the elements that make up a compound will always have the same per cent composition by mass, regardless of the actual mass of the sample.
In this case, potassium chloride has a molar mass of 74.551 g/mol. The two elements that form potassium chloride are potassium, which has a molar mass of 39.0983 g/mol, and chlorine, which has a molar mass of 35.4527 g/mol.
This tells you that every mole of potassium chloride weighs 74.551 g, out of which 39.0983 g is potassium and 35.4527 g is chlorine.

Therefore, chlorine and potassium will always be in a ratio by mass of
$\dfrac{35.4527g}{39.0983g}$=0.90681
so the constant proportion is the right answer 

In the reaction, $N _2 + 3H _2 \rightarrow 2NH _3$, the ratio of volumes of nitrogen, hydrogen and ammonia is 1 : 3: 2. These figures illustrate the law of: 

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  1. constant proportions

  2. Gay-Lussac

  3. multiple proportions

  4. reciprocal proportions

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Correct Option: B
Explanation:

ANS; B
Gay Lussac’s Law of Combining Volumes states that when gases react, they do so in volumes which bear a simple ratio to one another, and to the volume of the product(s) formed if gaseous, provided the temperature and pressure remain constant.

The law of constant proportions was enunciated by: 

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  1. Dalton

  2. Berthelot

  3. Avogadro

  4. Proust

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Correct Option: D
Explanation:

Proust defined law of constant proportions. It is also called as $\text{Proust's law}$. it states that a given chemical compound always contains its component elements in fixed ratio by mass and does not depend on the method of preparation of the compound. 
Hence, answer is option D.

Zinc sulphate contains 22.65% Zn and 43.9% $H _2O$. If the law of constant proportions is true, then the mass of zinc required to give 40 g crystals will be:

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  1. 90.6 g

  2. 9.06 g

  3. 0.906 g

  4. 906 g

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Correct Option: B
Explanation:

$ZnSO _4-22.65\% Zn $ $43.9\% H _2O$


$100g$ crystal has $22.65$ $Zn$


$40g$ crystal has $x$ $Zn$

$x=\cfrac{40\times 22.65}{100}=\cfrac{906}{100}=9.06g$
Hence, mass of $Zinc$ required is $9.06g$.

3 volumes of hydrogen are required to combine with one volume of nitrogen to form 2 volumes of ammonia. When 1 mole of hydrogen is allowed to react with the mole of nitrogen, the two gases?

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  1. Do not combine

  2. Combine and both the gases are used up completely

  3. 2/3 mole of nitrogen remains unreacted

  4. Some hydrogen remains uncombined

Show answer
Correct Option: C
Explanation:

$3H _2+N _2\rightarrow 3NH _3$
So 3 moles of hydrogen produced 1 mole of ammonia
1 mole hydrogen produces $X$ moles of ammonia
$X=\dfrac{1\times 1}{3}=\dfrac{1}{3}$ moles
Hence option $C$ is correct.

If a mixture containing 3 moles of hydrogen and 1 mole of nitrogen is converted completely into ammonia, the ratio of initial and final volumes under the same temperature and pressure would be:

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  1. 3 : 1

  2. 1 : 3

  3. 2 : 1

  4. 1 : 2

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Correct Option: C
Explanation:

3 moles of hydrogen and 1 mole of nitrogen is convened completely into ammonia.

$3H _2+N _2\rightarrow 2NH _3$

Hence option C is correct.

So 4 volumes of reactants (3+1) and 2 volumes of products that is the ratio of initial and final is 2:1

If water samples are taken from the sea, rivers, clouds, lakes or snow, they will be found to contain hydrogen and oxygen in the ration of $1 : 8$. This clearly demonstrates the law of ?

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  1. Chemical equilibrium

  2. Definite proportions

  3. Combining volumes

  4. The relation of elements in the periodic tables

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Correct Option: B
Explanation:
In chemistry, the law of definite proportion states that a given chemical compound always contains its component elements in a fixed ratio (by mass) and does not depend on its source and method of preparation. Since in all the water samples given, taken from the sea, rivers, clouds, lakes or snow, the hydrogen and oxygen ratio is constant, hence it clearly demonstrates the law of definite proportions.

If you put a waterproof, nine-volt battery in a mug of water containing two teaspoonfuls of salt, the water will be broken into gases and bubbles will start forming. What are these gases?

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  1. Carbon dioxide and nitrogen

  2. Hydrogen and oxygen

  3. Fluorine and chlorine

  4. Sulphur dioxide and 'laughing gas'

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Correct Option: B
Explanation:

Water will start comparing electrostatically,


$2H _2O \underset{electroysis}{\rightarrow} 2H _2+O _2$


These gases are hydrogen and oxygen.

A sample of pure water, irrespective of source, contains 88.89% oxygen and 11.11% hydrogen
by mass. The data supports the:

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  1. law of conservation of mass

  2. law of constant composition

  3. law of multiple proportion

  4. law of reciprocal proportion

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Correct Option: B
Explanation:

According to the law of constant composition in a given compound, the elements always combine in the same proportion as each other.

Water($H _{2}O$) molecule consists of two hydrogen atoms of relative mass 1 and one oxygen atom of relative mass 16. 

Therefore, the ratio in which 2 atoms of hydrogen and one atom of oxygen are combined is $1:8$ and will always be the same irrespective of the source of water.

Therefore, the correct option is $B$

When one mole each of CO and $O _2$ are made to react at STP, the total number of moles at an end of the reaction is:

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  1. 1.5 moles

  2. 1 mole

  3. 4 moles

  4. 2 moles

Show answer
Correct Option: A
Explanation:

$2CO + O _2 \rightarrow 2CO _2$


Initially, we have one mole of each CO and $O _2$.

1 mole of CO will react with 0.5 mole of $O _2$ to form 1 mole of $CO _2$.

the total no. of moles at the end of the reaction is 0.5 mole $O _2$ + 1 mole of CO$ _2$= 1.5 moles