Tag: avogadro hypothesis

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Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Ethane burning in oxygen to give carbon dioxide and steam. The volume ratio of reactants to products is ______________.

  1. 2 : 6 : 4 : 3

  2. 2 : 7 : 2 : 5

  3. 3 : 4 : 4 : 6

  4. 2 : 7 : 4 : 6
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The equation for the combustion reaction of ethane can be written as :
$2C _{2}H _{6} + 7O _{2} \rightarrow 4CO _{2} + 6H _{2}O$
Therefore the volume ratio of reactants and products $= 2 : 7 : 4 : 6$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

The number of atoms in 67.2 L of ${ NH } _{ 3 }$(g) at STP is:

  1. 9 ${N } _{ A }$
  2. 12 ${N } _{ A }$
  3. 3 ${N } _{ A }$
  4. 4 ${N } _{ A }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
By Avogadro law,
 22.4 liter of any gas at STP$ = $1mole
                $ =6.022\times { 1 }0^{ 23 }$ molecules of gas
                $ =$NA (Avogadro number)

So, in 67.2 L of ${ NH } _{ 3 }=?$
    22.4 L of $ { NH } _{ 3 }=N _A$
     1 L of ${ NH } _{ 3 }=\cfrac { NA }{ 22.4 } $

67.2 L of $ { NH } _{ 3 }=\cfrac { 67.2 }{ 22.4 } \times NA$
                          $ =3N _A$ molecules

Now, each molecule contain 4 atoma
Number of atoms $= 4\times 3N _A = 12N _A$ atoms
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Four one litre flasks are separately filled with gases $O _2, F _2, CH _4$ and $CO _2$ under same conditions. 


The ratio of the number of molecules in these gases are:

  1. $2 : 2 : 4 : 3$
  2. $1 : 1 : 1 : 1$
  3. $1 : 2 : 3 : 4$
  4. $2 : 2 : 3 : 4$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Avogadro's law: It states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

$\\ n _{1} : n _{2} : n _{3} : n _{4} = \cfrac{PV}{RT} : \cfrac{PV}{RT} : \cfrac{PV}{RT} : \cfrac{PV}{RT} = 1 : 1 : 1 : 1 $

So, the ratio of no. of molecules $= 1: 1: 1: 1$

The correct option is $B.$
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

A sample of municipal water contains one part of urea (molecular wt $=60$) per million parts of water by weight. The number of urea molecules in a drop of water of volume $0.05\ ml$ is 

  1. $2.5\times 10^{14}$
  2. $5\times 10^{14}$
  3. $5\times 10^{13}$
  4. $5\times 10^{15}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$1 \ ppm = 1 \ mg/L = 10^{-3} g/L$

Water sample contains $1 \ ppm$ urea concentration.

$\therefore \ 10^{-3} \ g$ of urea in $ 1 \ L$

$x \ g$ urea in $0.05 \times 10^{-3} \ L$

$x= 0.05 \times 10^{-6} \ g$

$60 \ g$ urea $=6.023 \times 10^{23} \ molecules$

$0.05 \times 10^{-6} \ g = n \ molecules$

$n = \cfrac {6.023 \times 10^{23} \times 0.05 \times 10^{-6}}{60}$

$=0.005 \times 10^{17}$

$=5 \times 10^{14} \ molecules$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

According to Avogadro's law the volume of a gas will ____ as _____ if ____ are held constant.

  1. increases, number of moles; P & T

  2. decreases, number of moles; P & T

  3. increases; T & P; number of moles

  4. decreases; P & T; number of moles
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Avogadro's law: Equal volume of all gases at same temperature and pressure will have same no. of molecules.

OR
For a given mass of ideal gas,
Volume$\propto$Number of moles of the gas (if temperature and pressure are constant) 
So, volume of the gas will increase as the number of moles if pressure (P) and temperature (T) are held constant.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

What is the value of $n$ in the following equation?


$Cr\left( OH \right) _{ 4 }^{ - }+OH^{ - }\longrightarrow  Cr{ O } _{ 4 }^{ 2- }+H _{ 2 }O\ +\ ne^-$

  1. $3$
  2. $6$
  3. $5$
  4. $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the given half-reaction, chromium changes its oxidation state from +3 in Cr(OH)4(-) to +6 in CrO4(2-). This change involves the loss of 3 electrons, meaning n = 3.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

The critical density of the gas $CO _2$ is 0.44 $g\ cm^{–3}$ at a certain temperature. If $r$ is the radius of the molecule, $r^3$ in $cm^3$ is approximate: 


[N is Avogadro number]

  1. $\cfrac {25} {\pi N}$
  2. $\cfrac {100} {\pi N}$
  3. $\cfrac {6} {\pi N}$
  4. $\cfrac {25} {4N\pi}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Critical density of a gas $= 0.44 gcm^{-3}$
Molar mass of $CO _2$ = 44 g/mole

$Density = mass /volume $
Mass of N molecules = 44 g of $CO _2$    $N =6.022\times 10^{23}$

Mass of 1 molecule $= \dfrac{44}{N}$
The volume of 1 molecule $=\cfrac {4}{3}\pi r^3$
Putting the values,
$ 0.44 = \dfrac{\dfrac{44}{N}}{\cfrac {4}{3}\pi r^3}$

$ r^3 = \dfrac{100}{\pi N}$
Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Which facts are revealed from Avogadro's law for ideal gases?

  1. The distance between molecules is much large than the actual dimension of molecules.

  2. Equal number of molecules of different gases under identical conditions of temperatures and pressure occupy the same volume.

  3. Saturated vapours obey gas laws
  4. 1 mole of a gas contains $6.023\times 10^{23}$ molecules of gases.
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

Avogadro's Law :
It states "equal volumes of any two gases at the same temperature and pressure contain the same number of molecules".

$V  \propto  n$ (At constant P and T)

$\dfrac{V _1}{V _2} = \dfrac{n _1}{n _2}$

and each gas's one mole contains $6.023\times 10^{23}$ molecules.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

The law which suggests $n _1 = n _2$ for two solutions at same temperature and pressure is 

  1. van't Haff - avogadro's law

  2. van't Hoff Boyle's law

  3. van't Hoff's law

  4. Henry's law
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

van't Hoff's law for osmotic pressure states that for solutions at the same temperature and pressure, the molar concentrations (and thus the number of particles n) are equivalent.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

One gram molecule of any gas at $NTP$ occupies $22.4\ L$. This fact was derived from:

  1. Dalton's theory

  2. Avogardro's hypothesis

  3. Berzelius hypothesis

  4. Law of gaseous volume
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Avogadro's law, 1 mole of every gas occupies 22.4L at $NTP$.

From ideal gas equation,
$PV=nRT$. . . . . . .(1)
At $NTP$,
$T=273K$
$P=1atm$
$n=1$
$R=0.0821atm L/K mol$
from equation (1),
$V=\dfrac{nRT}{P}$
$V=\dfrac{1\times 0.0821\times 273}{1}=22.4L$
The correct option is B.