Tag: let's play with water

Questions Related to let's play with water

For $\displaystyle 4{ NH } _{ 3 }\left( g \right) +5{ O } _{ 2 }\left( g \right) \rightarrow 4NO\left( g \right) +6{ H } _{ 2 }O\left( g \right) $, if you begin with 66.00 g ammonia and 54.00 g oxygen, how many grams of water will be obtained?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. 2.294

  2. 36.51

  3. 1.409

  4. 25.3

  5. 2.513

Show answer
Correct Option: B
Explanation:

The molecular weights of ammonia, oxygen and water are 17 g/mole, 32 g/mole and 18 g/mole respectively.

66.00 g ammonia $= \dfrac {66.00}{17} = 3.88$ moles ammonia.
54.00 g oxygen $=\dfrac {54.00}{32.0}=1.6875$ moles oxygen.
4 moles ammonia reacts with 5 moles oxygen.
Hence, 3.88 moles ammonia will react with $3.88 \times \dfrac {5}{4} = 4.85$ moles oxygen but only 1.6875 moles oxygen are present. Hence oxygen is the limiting reagent.

5 moles of oxygen gives 6 moles of water.
1.728 moles of oxygen will give $1.6875 \times \dfrac {6}{5} = 2.025$ moles of water.
The mass of water obtained is $18 \times 2.025 = 36.51$ g of water.

Dissolved salts in water are important because :

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. they provide taste

  2. growth of plants

  3. minerals essential for body

  4. all of the above

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Correct Option: D
Explanation:

Dissolved salts in water are important because
(A) They provide taste
(B) Growth of plants
(C) Minerals essential for body
Water contains dissolved salts which provide taste to water for drinking purposes. Also these salts are essential for growth and development of plants. These dissolved salts provide the essential minerals which are required for growth of body.

Dissolved gases can be removed from water by:

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. chlorination

  2. boiling

  3. filtration

  4. both A and C

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Correct Option: B
Explanation:

Dissolved gases can be removed from water by boiling.
Water contains certain gases in dissolved state. The higher the temperature of a solution becomes, the less a gas dissolves provided it doesn't react with the solvent. Consequently, heating/boiling a solution can expel the remaining gas.

How many grams of water can be produced when 8 g of hydrogen react with 8 g oxygen?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. 8 g

  2. 9 g

  3. 18 g

  4. 27 g

  5. 30 g

Show answer
Correct Option: B
Explanation:
The molecular masses of hydrogen, oxygen and water are 2 g/mole, 32 g/mole and 18 g/mole respectively.
$2H _2 + O _2 \rightarrow 2H _2O$
 $2 \times 2 = 4$ g of hydrogen reacts with  $1 \times 32 = 32$ g of oxygen to form  $2 \times 18 = 36$ g of water.
Hence, $\dfrac {4}{4} = 1$ g of hydrogen reacts with  $\dfrac {32}{4}  = 8$ g of oxygen to form  $\dfrac {36}{4}= 9$ g of water.

9 grams of water can be produced when 8 g of hydrogen reacts with 8 g oxygen.

The colour of anhydrous $CoCl _2$ is:

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. pink

  2. blue

  3. red

  4. white

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Correct Option: B
Explanation:

Anhydrous $CoCl _2$ is blue in colour.


As it absorbs water, it turns pink.

Hence,option B is correct.

The discovery of the fact that oxygen and hydrogen combine to form water, was a major step in the development of science. Who made this discovery?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. Carl Wilhelm Scheele

  2. Isaac Newton

  3. Joseph Priestley

  4. Henry Cavendish

Show answer
Correct Option: D
Explanation:
It was the chemist Henry Cavendish (1731 – 1810), who discovered the composition of water when he experimented with hydrogen and oxygen and mixed these elements together to create an explosion (oxyhydrogen effect). In 1811, the Italian physician Amadeo Avogadro finally found the ${H} _{2}O$ formula for water.

What is the final product when oxygen and hydrogen are mixed in a test tube at room temperature?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. Hydrogen peroxide

  2. Water

  3. A base

  4. A zwitterion

  5. No reaction takes place

Show answer
Correct Option: E
Explanation:

The gas-phase oxidation of hydrogen has been extensively studied over a wide range of temperatures and pressures.


$H _2 + \dfrac {1}{2} O _2 \rightarrow H _2O$ ,$ \Delta H^o= -242 kj/mol$
$H _2(g) + \dfrac {1}{2}O _2(g) \rightarrow H _2O(g) $        $\Delta H^o = –242 kJ/mol$

This reaction does not take place at all when the two gases are simply mixed at room temperature. 

At temperatures around 500-600°C it proceeds quite smoothly, but when heated above 700° or ignited with a spark, the mixture explodes.

Hence the correct option is E.


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?

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

  1. Law of constant proportions

  2. Law of multiple proportions

  3. Law of reciprocal proportions

  4. Law of conservation of mass

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Correct Option: A
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

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:

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

  1. 0.016 g

  2. 0.16 g

  3. 1.6 g

  4. 16 g

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Correct Option: C
Explanation:

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

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

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 ?

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

  1. 0.016 g

  2. 0.16 g

  3. 1.6 g

  4. 16 g

Show answer
Correct Option: C
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 $=4\times 0.4=1.6g$