Tag: law of constant proportion

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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

Zinc sulphate contains $22.65$% $Zn$ and $43.9$% ${H} _{2}O$. If the law of constant proportions is true, then the mass of zinc required to give $40g$ crystal will be:

  1. $9.06g$
  2. $90.6g$
  3. $0.906g$
  4. $906g$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
100g of crystals are obtained from = 22.65g of $Zn$

$\therefore $ 40 g of crystals are obtained from =$\frac { 22.65 }{ 100 } \times40$

= 9.06g 
Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

Which of the following statements is/are correct?

  1. A sample of $CaCO _3$ contains $Ca = 40\%,\ C = 12\%$ and $O= 48\%$. If the law of constant composition is true, then the mass of $Ca$ in $10$ g of $CaCO _3$ from another source is $4.0$ g.
  2. $12$ g of carbon is heated in vacuum and there is no change in the mass. This is the best example of the law of conservation of mass.

  3. Air is heated at constant pressure and there is no change in mass but the volume increases. This is the best example of the law of conservation of mass.
  4. $SO _2$ gas was prepared by (i) heating $Cu $ with conc. $H _2SO _4$ (ii) burning sulphur in oxygen (iii) reacting sodium sulphite $(Na _2SO _3)$ with dilute $H _2SO _4$. It was observed that is each case, $S$ and $O$ combine in the ratio of $1:1$. This data illustrates the law of constant composition.
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

(A) A sample of $CaCO _3$ contains $Ca = 40\%$, $C = 12\%$ and $O= 48\%$. If the law of constant composition is true, then the mass of $Ca$ in $10$ g of $CaCO _3$ from another source is $\dfrac {40 \times 10 }{100}= 4.0 $ g


According to the law of constant composition, all samples of a given chemical compound have the same elemental composition by mass.
Hence, the statement A is true.

(B) $12$ g of carbon is heated in vacuum and there is no change in the mass. This is not the best example of the law of conservation of mass as there is no chemical transformation involved since there is a vacuum.
The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made and pure substances can be decomposed but the total amount of mass remains constant.
Hence, the statement B is false.

(C) Air is heated at constant pressure and there is no change in mass but the volume increases. This is not the best example of the law of conservation of mass as there is no chemical transformation involved since there is a vacuum.

The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made and pure substances can be decomposed but the total amount of mass remains constant.
Hence, the statement C is false.

(D) $SO _2$ gas was prepared by (i) heating $Cu$ with conc. $H _2SO _4$ (ii) burning sulphur in oxygen (iii) reacting sodium sulphite $(Na _2SO _3)$ with dilute $H _2SO _4$. It was observed that is each case, S and O combine in the ratio of $1:1$. This data illustrates the law of constant composition.

According to the law of constant composition, all samples of a given chemical compound have the same elemental composition by mass.

Hence, the statement D is true.

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

$14$ g of element X combines with $16$ g of oxygen. On the basis of this information, which of the following is a correct statement?

  1. The element X could have an atomic weight of $7$ amu and its oxide is $XO$
  2. The element X could have an atomic weight of $14$ amu and its oxide is $\displaystyle X _{2}O$
  3. The element X could have an atomic weight of $7$ amu and its oxide is $\displaystyle X _{2}O$
  4. The element X could have an atomic weight of $14$ amu and its oxide is $\displaystyle XO _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$14$ g of an element X combines with $16$ g of oxygen, then the element X could have an atomic weight of $7$ amu and its oxide is $X _2O $.
When the atomic weight is $7$, $14$ g will corresponds to $2$ moles.
$16$ g of oxygen corresponds to $1$ mole. 

The formula $X _2O $ suggests the valency of $1$ for X.

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

The % loss in mass after heating a pure sample of potassium chlorate (Mol. mass = 122.5) will be:

  1. 12.25

  2. 24.50

  3. 39.17

  4. 49.0
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$2KClO _3\rightarrow 2KCl+3O _2$
$2\times 122.5$ grams shows a wieght loss of  $3\times32 grams$
So 245 grams of $KClO _3$ is 100%
96 grams of $O _2$ is X%
$x=\frac{100\times 96}{245}=39.17$.
Hence option C is correct.

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

The volume of oxygen at NTP evolved when 1.70 g of sodium nitrate is heated to a constant mass is: 

  1. 0.112 litre

  2. 0224 litre

  3. 22.4 litre

  4. 11.2 litre
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The chemical equation is:

$2NaNO _3(s)→  2NaNO _2 (s)+ O _2(g)$

2 moles of NaNO$ _3$ give one mole of Oxygen/22.4 L oxygen at STP

weight of NaNO$ _3$ = 85g

2 moles of NaNO$ _3$ weigh = 2(23+14+48) = 170g

170 g of NaNO$ _3$ will produce 22.4 L Oxygen at STP

​1.70 g will produce $= \cfrac{1.70}{170}×22.4 =0.224$ litres

Hence, the correct option is $\text{B}$
Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

The mass of residue left after strongly heating 1.38 g of silver carbonate will be: 

  1. 1.16 g

  2. 1.33 g

  3. 2.66 g

  4. 1.08 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$Ag _2CO _3\rightarrow Ag _2O+CO _2(g)$
I mole of $Ag _2CO _3$ (275.74) grams  on decomposition gives a mass residue of 231.73 grams of $Ag _2O$ remaning mass is liberated as $CO _2$ gas.
If 1.38 grams $Ag _2CO _3$ is hetaed it produces X grams of mass residue of  $Ag _2O$
$X=\frac{1.38\times 231.739}{275.745}=1.16$ grams
Hence 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

At NTP, 10 litre of hydrogen sulphide gas reacted with 10 litre of sulphur dioxide gas. The volume of gas, after the reaction is complete, would be:

  1. 5 litre

  2. 10 litre

  3. 15 litre

  4. 20 litre
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$2H _2S+SO2\rightarrow 2H _2O+3S$

According to the equation $2\times 22.4 $ litre of  $H _2S$ gas reacts with $22.4$ litre of $SO _2$
So $5$ litre of $H _2S$ reacts with $10$ litre of $SO _2$
Hence option $A$ is correct.

Multiple choice chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions

Which of the following is a limitation of the law of constant composition is not applicable?

  1. When same isotopes of an element take part in the formation of a particular compounds.

  2. When different isotopes of different elements take part in the formation of a particular compound.

  3. When different isotopes of an element take part in the formation of a particular compound.

  4. None of the above.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Law of constant composition is not applicable if an element exists in different isotopes which may be involved in the formation of the compound. The elements may combine in the same ratio but the compounds formed may be different.

Hence, the correct option is $(C)$
Multiple choice chemistry atoms, molecules and chemical reactions law of constant proportion - i law of constant proportion law of definite proportions
Assertion (A): Pure water obtained from different sources such as a river, well, spring, the sea always contains hydrogen and oxygen in the ratio of 1:8 by mass.

Reason (R): The total mass of reactants and products during chemical or physical change is always the same.

  1. Both A and R are true and R is the correct explanation of A

  2. Both A and R are true and R is not correct explanation of A

  3. A is correct and R is incorrect

  4. A is incorrect and R is correct
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Assertion states the law of definite proportions, which is true for pure water regardless of source. Reason states the law of conservation of mass, which is also a true chemical principle. However, the constant composition by mass is not explained by the conservation of mass during reactions.