Tag: quantitative chemistry

Questions Related to quantitative chemistry

Statement: Equal volumes of all gases always contain equal number of moles.

State whether the given statement is true or false.
chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. True

  2. False

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Correct Option: A
Explanation:

 Avogadro law: It states that equal volumes of all gases under the same conditions of temperature and pressure contain the equal number of molecules. 

This means that as long as the temperature and pressure remain constant, the volume depends upon number of molecules of the gas.

Since volume of a gas is directly proportional to the number of moles; one mole of each gas at standard temperature and pressure (STP) will have same volume. 

Hence, the given statement is $\text{true}$

If $1$ L of $O _2$ at $15^oC$ and $750$ mm pressure contains $\text N$ molecules, the number of molecules in $2$ L of $SO _2$ under the same conditions of temperature and pressure will be :

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. $\dfrac {\text N}{2}$

  2. $\text N$

  3. $2\text N$

  4. $4\text N$

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Correct Option: C
Explanation:

Under similar conditions of temperature and pressure, equal volume of gas contains equal number of molecules.
$\therefore 1\ L=N$ molecules
$2\ L=2\ N$ molecules

Under the same conditions, two gases have the same number of molecules. They must:

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. be noble gases

  2. have equal volumes

  3. have a volume of 22.4 dm$^3$ each

  4. have an equal number of atoms

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Correct Option: B
Explanation:

Avogadro's hypothesis: Equal volume of all gases have equal number of molecules (not atoms) at same temperature and pressures conditions.

Four 1-1 litre flasks are separately filled with the gases $H _2,\, He,\, O _2$ and ozone. The ratio of total number of atoms of these gases present in different flask would be : 

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. 1 : 1 : 1 : 1

  2. 1 : 2 : 2 : 3

  3. 2 : 1 : 2 : 3

  4. 3 : 2 : 2 : 1

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Correct Option: C
Explanation:

According to Avogadro's law, all gases at same temperature and pressure will contain same number of molecules. Hence, number of molecules of all gases will be same bt ration of atoms of each gases will $2:1:2:3$.

State True or False.
Equal volumes of different gases under similar conditions of temperature and pressure contain equal number of atoms.

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. True

  2. False

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Correct Option: B
Explanation:

The statement, "Equal volumes of different gases under similar conditions of temperature and pressure contain equal number of atoms." is false. The true statement is "Equal volumes of different gases under similar conditions of temperature and pressure contain equal number of moles."  For example, at STP conditions, 22.4 L of any gas corresponds to 1 mole.

Number of water molecules in one litre of pure water is :

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. $6.023 \times 10^{23}$

  2. $3.45 \times 10^{25}$

  3. $55.4 \times 10^{23}$

  4. $18 \times 10^{23}$

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Correct Option: B
Explanation:

One mole of water has a mass of $18$ grams and a volume of $18$ mL (as the density of water is 1 g per cm$^3$).


Therefore, number of moles of water in $1$ litre $= \dfrac{1\times 1000}{18}$.

Number of molecules $= $ Number of moles $\times N _A$

                                          $= \dfrac{1\times 1000}{18} \times 6.023\times 10^{23}$

                                         $= 3.45\times 10^{25}$ molecules.

Hence, the correct answer is option $\text{B}$.

Statement 1: The number of gram molecules of oxygen in $6.02 \times 10^{24}\ CO$ molecules is 5.0.
Statement 2: The value of Avogadro number is $6.02 \times 10^{23}$

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. Statement 1 is True, statement 2 is True, Statement 2 is a correct explanation of statement 1.

  2. Statement 1 is True, statement 2 is True, Statement 2 is not a correct explanation of statement 1.

  3. Statement 1 is True, Statement 2 is False.

  4. Statement 1 is False, Statement 2 is True.

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Correct Option: B
Explanation:

$6.02\times 10^{24}$ molecules of $CO=6.02\times 10^{23}\times 10$ i.e.., 10 moles of CO.
10 moles of CO contains 10 gm atoms of oxygen i.e.  5 gm molecules of oxygen.
hence the correct answer is A the given assertion is correct and reason is the correct explanation to the assertion.

Avogadro's number is NOT equal to:

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. the number of atoms in 11.2 L of $\displaystyle { O } _{ 2 }$ at STP

  2. the number of atoms in 1 mole of $\displaystyle He$ at STP

  3. the number of electrons in 96,500 coulombs

  4. the number of $\displaystyle { SO } _{ 4 }^{ 2- }$ ions in 1 L of 0.5 M sulphuric acid

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Correct Option: D
Explanation:
$Avogadro's \ Number= N _A= 6.02 \times 10^{23}$
$1$ mole of any substance has $N _A$ number of atoms, molecules or ions etc. 
Therefore, moles of $SO _4^{2-}$ ions in $1 \ L$ of $0.5 \ M \ H _2SO _4$ will be 
$Molarity= \cfrac {Number \ of \ moles}{Volume \ of \ solution \ (in \ L)}$
$0.5 = \cfrac {moles}1$
$Number \ of \ moles = 0.5$
Hence, because $1$ mole of a substance $= N _A$
$\therefore \ 0.5$ moles of $SO _4^{2-} \neq N _A $ (Avogadro Number)

Number of molecules in one litre of water is :

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. $\displaystyle \frac {6.023}{23.4} \times 10^{23}$

  2. $18 \times 6.023 \times 10^{23}$

  3. $\displaystyle \frac {18}{22.4} \times 10^{23}$

  4. $55.5 \times 6.023 \times 10^{23}$

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Correct Option: D
Explanation:

Number of moles of water molecules in 1 litre of water = 55.5 moles

Hence, number of molecules of water = 55.5$\times$ Avogadro number
So, option D is correct.

64 g of sulphur dioxide occupies $22.4\ L$ volume at STP.

chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

  1. True

  2. False

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Correct Option: A
Explanation:

Molecular mass of $SO _2$ is 64. 

So, 1 mole (64 grams) of sulphur dioxide will occupy $22.4\ L$ at STP. ( Avogadro's law)