Tag: let's play with water

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

Law of constant proportion states that :

  1. a chemical compound always contains exactly the same proportion of elements by mass.

  2. mass can neither be created nor destroyed in a chemical reaction.

  3. when two elements combine with each other to form two or more than two compounds, the masses of one the element which combines with the fixed mass of the other, bears a simple whole number ratio.

  4. total mass of products is always equal to the total mass of reactants.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Law of Constant Proportion states that a chemical compound always contains exactly the same proportion of elements by mass. This law is also known as Law of definite proportions. Joseph Louis Proust gave this law hence, this law is also known as Prousts Law.

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions
Four different experiments were conducted in the following ways-

I) $3g$ of carbon was burnt in $8g$ of oxygen to give $11g$ of $CO _2$

II) $1.2g$ of carbon was burnt in air to give $4.2g$ of $CO _2$,

III) $4.5g$ of carbon was burnt in enough air to give $11g$ of $CO _2$

IV) $4g$ of carbon was burnt in oxygen to form $30.3g$ of $CO _2$


Law of constant proportions is illustrated in which of the following experiment(s)?

  1. I and III only

  2. II and III only

  3. IV only

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

The law of constant proportions states that a chemical compound always contains its component elements in a fixed ratio by mass. Experiment I shows 3g C + 8g O2 = 11g CO2, a ratio of 3:8. Experiment III also shows 4.5g C + 6.5g O2 = 11g CO2, which is not 3:8, but the question asks for the experiment illustrating the law. Experiment I is the standard demonstration.

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.

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

Two gases found dissolved in natural water are 

  1. oxygen and carbon dioxide

  2. hydrogen and oxygen

  3. sulphur dioxide and hydrogen

  4. chlorine and ammonia
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Natural water, such as that found in rivers and lakes, contains dissolved gases like oxygen (essential for aquatic life) and carbon dioxide (from the atmosphere and respiration).

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

A sample of pure carbon dioxide, irrespective of its source contains 27.27 % carbon and 72.73% oxygen. The given data supports: 

  1. Law of constant composition

  2. Law of conservation of mass

  3. Law of reciprocal proporties

  4. Law of multiple proportions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The law of constant composition (or definite proportions) states that a chemical compound always contains the same elements in the same proportions by mass, regardless of the source.

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

In Haber's process, the volume of ammonia relative to the total volume of reactants at STP is:

  1. one fourth

  2. one half

  3. same

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

This reaction occurs in Haber's process-


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

The total volume of reactants at STP is 4x

The volume of ammonia is 2x.

Hence, Volume of ammonia = $\dfrac{1}{2}$(Volume of reactant)

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

$2.16$ grams of Cu, on reaction with $HNO _{3}$, followed by ignition of the nitrate, gave $2.7$ g of copper oxide. In another experiment $1.15$ g of copper oxide, upon reaction with hydrogen, gave $0.92$ g of copper. This data illustrate the law of:

  1. multiple proportions

  2. definite proportions

  3. reciprocal proportions

  4. conservation of mass
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the first sample of copper oxide (obtained by the action of nitric acid on Cu), the mass of Cu is 2.16 g and the mass of oxygen is $\displaystyle 2.7 - 2.16  =  0.54$ g. 

The ratio of the mass of Cu to the mass of oxygen is $\displaystyle \dfrac {2.16}{0.54} = 4 :1$

In the second sample of copper oxide (which reacts with hydrogen) , the mass of Cu is 0.92 g and the mass of oxygen is $\displaystyle 1.15 - 0.92  =  0.23$ g. 
The ratio of the mass of Cu to the mass of oxygen is $\displaystyle \dfrac {0.92}{0.23} = 4 :1$
Hence, this illustrates the law of definite Proportions.

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

An experiment showed that a lead chloride solution is formed when 6.21 g of lead combines with 4.26 g of chlorine. What is the empirical formula of this chloride? 

[Pb = 207; Cl = 35.5]

  1. $PbCl _3$
  2. $PbCl _2$
  3. $PbCl _4$
  4. $PbCl$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  Mass        Atomic weight    Relative no. of moles    Simplest ratio
Lead           6.21 g        207     6.21/207 = 0.03    0.03/0.03 = 1
Chlorine 4.26 g        35.5     4.26/35.5 = 0.12    0.12/0.03 = 4


Hence, empirical formula is $PbCl _4$. 

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

Common salt obtained from Clifton beach contained $60.75\%$ chlorine while $6.40$ g of a sample of common salt from Khewra mine contained $3.888$ g of chlorine. State the law illustrated by these chemical combinations.

  1. Law of reciprocal proportion

  2. Law of multiple proportion

  3. Law of constant composition

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

First case :


Common salt from Clifton beach contains $=$ $60.75\%$ $Cl _2$

$100$ g of salt $=60.75$ g of $Cl _2$

$1$ g of salt $=\dfrac {60.75}{100}=0.6075$ g of $Cl _2$

Second case :


$6.40$ g of $NaCl$ from Khewra mine $=3.888$ g of $Cl _2$

$1$ g of $NaCl$ from Khewra mine $=\dfrac {3.888}{6.40}=0.6075$ g of $Cl _2$

Thus, the weight of $Cl _2$ in $1$ g of salt in both the cases is same. Hence, the law of constant composition is verified.


Hence the correct option is C.