Tag: let's play with water

Questions Related to let's play with water

When $1.375\ g$ of cupric oxide is reduced on heating in a current of hydrogen, the weight of copper remaining $1.098\ g$. In another experiment, $1.179\ g$ of copper is dissolved in nitric acid and resulting copper nitrate converted into cupric oxide by ignition. The weight of cupric oxide formed is $1.476 \ g$. This is in agreement with :

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

  1. Law of definite proportion

  2. Law of mass conservation

  3. Law of momentum conservation

  4. None of the above

Show answer
Correct Option: A
Explanation:

First experiment
$\bullet$ Copper oxide $=1.375 g$
$\bullet$ Copper left $= 1.098 g$
$\bullet$ Oxygen present $= 1.375 - 1.098 = 0.277 g$
Percentage of oxygen in $CuO = (0.277) (100$ %) $1.375 = 20.15$ %

Second Experiment
$\bullet$ Copper taken $= 1.179 g$
$\bullet$ Copper oxide formed $= 1.476 g$
$\bullet$ Oxygen present $= 1.476 - 1.179 = 0.297 g$
Percentage of oxygen in $CuO = (0.297) (100$ %) $1.476 = 20.12$ %
Percentage of oxygen is approximately (within significant figures limit) the same in both the above cases. So the law of constant composition is illustrated.

In chemistry, the law of definite proportion, sometimes called Proust's law or the law of definite composition, or law of constant composition states that a given chemical compound always contains its component elements in fixed ratio and does not depend on its source and method of preparation.

Who stated the law of constant proportion?

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

  1. Archimedes

  2. Dalton

  3. Proust

  4. Antony Lavoisier

Show answer
Correct Option: C
Explanation:

The law ofconstant proportion is given by Proust.

A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen.  What is the percent by mass of hydrogen in the compound?

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

  1. 25%

  2. 35%

  3. 16%

  4. 50%

Show answer
Correct Option: C
Explanation:

% of $H$$=$$\dfrac{12.4}{78}\times100$$=16$%

The percentage of copper and oxygen in samples of CuO obtained by different methods were found to be the same. This illustrates the law of:

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

  1. Constant proportion

  2. Conservation of mass

  3. Multiple proportion

  4. Reciprocal proportion

Show answer
Correct Option: A
Explanation:

In chemistry, the law of definite proportions, sometimes called Proust's law or the law of definite composition, states that a chemical compound always contains exactly the same proportion of elements by mass and this law further says that, in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio. For example, any water molecule is always made up of two hydrogen atoms and one oxygen atom in a ratio.

Which of the following statement is incorrect for the composition of water?

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

  1. For water, the gravimetric or mass ratio of hydrogen to oxygen is $1:8$

  2. In water, the ratio of hydrogen and oxygen is $2:1$ by volume

  3. The ratio in which hydrogen and oxygen combine gives the composition of water.

  4. None of the above

Show answer
Correct Option: D
Explanation:

All of the following statements are correct for the composition of water.
A
For water, the gravimetric or mass ratio of hydrogen to oxygen is 1:8.
B
In water, the ratio of hydrogen and oxygen is 2:1 by volume.
C
The ratio in which hydrogen and oxygen combine gives the composition of water.
Note:
$2H _2 + O _2 \rightarrow 2H _2O$
Thus, the composition of water is $H : O = 2: 1 $
It is the ratio in which hydrogen and oxygen combine. The atomic masses of H and O are 1 and 16 respectively. Hence, for water, the gravimetric or mass ratio of hydrogen to oxygen is 2:16 or 1:8.
In water, the ratio of hydrogen and oxygen is 2:1
by volume. It is equal to the ratio in which hydrogen and oxygen combine.

Nitrogen reaction with oxygen to form nitrogen (III) oxide.


What will be the volume ratio of the reactants and products of the given reaction?

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

  1. 2 : 3 : 2

  2. 2 : 3 : 4

  3. 1 : 3 : 2

  4. 2 : 1 : 2

Show answer
Correct Option: A
Explanation:

$2 N _2 + 3 O _2 \rightarrow 2N _2 O _3$

reactants = $N _2 \, \& \, O _2$
Product = $N _2O _3$
Ratio are $2 : 3 : 2$ by law of constant proportions 
{stionchiometry coefficient) 


A sample of $CaCO _3$ has Ca - 40%, C = 12% and 0 = 48%. If the law of constant proportions is true, then the mass of Ca in 5 g of $CaCO _3$ from another source will be:

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

  1. 2.0 g

  2. 0.2 g

  3. 0.02 g

  4. 20.0 g

Show answer
Correct Option: A
Explanation:

Since, mass percentage of Ca in $CaCO _3 = 40 \text{%} $ and law of constant proportion is true.
So, the mass percentage of $Ca $ in $ 5gm$ $CaCO _3$ will also be $40\text%.$
Hence,$ 40\text{% of 5gm =}$$ 5\times $$\dfrac{40}{100}$ $= 2gm $
Hence, answer is option A.

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:

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

  1. constant proportions

  2. multiple proportions

  3. reciprocal proportions

  4. none of these

Show answer
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: 

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

  1. constant proportions

  2. Gay-Lussac

  3. multiple proportions

  4. reciprocal proportions

Show answer
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: 

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

  1. Dalton

  2. Berthelot

  3. Avogadro

  4. Proust

Show answer
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.