Tag: atoms and molecules

Quizzes (16) Questions (33)

Questions Related to atoms and molecules

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A definite mass of $ H _{2}O _{2} $ is oxidized by excess of acidified $ KMnO _{4} $ and acidified $ K _{2}Cr _{2}O _{7} $, in separate experiments. Which of the following is/are correct statements? 
(K = 39, Cr = 52, Mn = 55 )

  1. Mass of $ K _{2}Cr _{2}O _{7} $ used up will be greater than that of $ KMnO _{4} $
  2. Moles of $ KMnO _{4} $ used up will be greater than that of $ K _{2}Cr _{2}O _{7} $

  3. Equal mass of oxygen gas is evolved in both the experiments.
  4. If equal volumes of both the solutions are used for complete reaction, then the molarities of $ KMnO _{4} $ and $ K _{2}Cr _{2}O _{7} $ solutions are in $6:5$ ratio.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

According to question, reaction of experiment (1) and (2)
(1)$ 5H _{2}O _2+2KMnO _{4}+3H _{2}SO _{4}\rightarrow 5O _{2}+2MnSO _{4}+K _{2}SO _{4}+8H _{2}O $


(2)$ 3H _{2}O _{2}+K _{2}Cr _{2}O _{7}+4H _2SO _{4}\rightarrow Cr _{2}(SO _{4}) _{3}+3O _{2}+K _{2}SO _{4}+7H _{2}O $

(a) According to reaction (1)
5 mole $ H _{2}O _{2} = 2\,mole KMnO _{4} $

1 mole $ H _{2}O _{2} = \dfrac{2}{5} = 0.4\,mole\,KMnO _{4} = 63.2\,g\,KMnO _{4} $

According to reaction (2)
3 mole $ H _{2}O _{2} = 1\,mole\,K _{2}Cr _{2}O _{7} $

1 mole $ H _{2}O _{2} = \dfrac{1}{3} mole\,K _{2}Cr _{2}O _{7} = 98.1 g \, K _{2}Cr _{2}O _{7} $

Mass of $ K _{2}Cr _{2}O _{7}> KMnO _{4} $

(b) Moles of $ KMnO _{4}> $ moles of $ K _{2}Cr _{2}O _{7} (0.333) $

(c)In reaction 1, 5 Mole $ H _{2}O _{2} $ released = 5 mole $ O _{2}\Rightarrow 32\times 5=160g $
In reaction 2, 3 mole $ H _{2}O _{2} $ released = 3 mole $ O _{2}=3\times 32= 96 g$ 

(d) 1 mole of $ H _{2}O _{2} = \dfrac{2}{5} $ moles $ KMnO _{4} $ exp...(1)
1 mole of $ H _{2}O _{2} = \dfrac{1}{3}$ mole $ K _{2}Cr _{2}O _{7} $ exp...(2)
$ \dfrac{KMnO _{4}}{K _{2}Cr _{2}O _{7}} = \dfrac{\dfrac{2}{5}}{\dfrac{1}{3}} = \dfrac{2}{5}\times \dfrac{3}{1} = \dfrac{6}{5}\Rightarrow 6:5 $

Options A, B and D are correct.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

Two acids $ H _{2}SO _{4} $ and $ H _{3}PO _{4} $ are neutralized separately by the same amount of an alkali when sulphate and dihydrogen orthophosphate are formed, respectively. Find the ratio of the masses of $ H _{2}SO _{4} $ and $ H _{3}PO _{4} $ 

  1. $ 1:1 $
  2. $ 1:2 $
  3. $ 2:1 $
  4. $ 2:3 $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$H _{2}SO _{4}+2NaOH\rightarrow Na _{2}SO _{4}+2H _{2}O$

$H _{3}PO _{4}+NaOH\rightarrow NaH _{2}PO _{4}+H _{2}O$

Equivalent of alkali $= 19$ eq of $H _{2}SO _{4}= 1g$ eq of $H _{3}PO _{4}$

Two acids must be reacting in the ratio of their equivalent masses

Eq. wt. of $H _{2}SO _{4}=\dfrac{98}{2}=49$

Eq. wt. of $H _{3}PO _{4}= \dfrac{98}{1}=98$

$\therefore $ ratio of masses of $H _{2}SO _{4}$ & $H _{3}PO _{4}$
$49:98=1:2$

$\Rightarrow 1:2$

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A gaseous alkane is exploded with oxygen. The volume of ${O} _{2}$ for complete combustion of alkane to $C{O} _{2}$ formed is in the ratio $7:4$. The molecular formula of alkane is:

  1. ${C} _{2}{H} _{6}$
  2. ${C} _{3}{H} _{8}$
  3. ${C} _{4}{H} _{10}$
  4. $C{H} _{4}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The balanced reaction is given below:


${C} _{n}{H} _{2n+2} +[n+\displaystyle\frac{n+1}{2}]{O} _{2}\rightarrow nC{O} _{2} +(n+1){H} _{2}O$

Given, 

$\displaystyle\dfrac{n+\dfrac{n+1}{2}}{n}=\dfrac{7}{4}\implies n=2$

Hence, the alkane is ${C} _{2}{H} _{6}$.

Hence, the correct option is $A$

Multiple choice chemistry atoms and molecules avogadro hypothesis avogadro's law avogadro law

At constant temperature, in a given mass of an ideal gas:

  1. the ratio of pressure and volume always remains constant

  2. volume always remains constant

  3. pressure always remains constant

  4. the product of pressure and volume always remains constant
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Boyle's Law states that, at constant temperature, the product of the pressure and volume of a given mass of an ideal gas in a closed system, is always constant.

Multiple choice chemistry atoms and molecules avogadro hypothesis avogadro's law avogadro law

A mixture of helium and argon contains 3 moles of $He$ for every 2 moles of $Ar$. The partial pressure of argon in the mixture is

  1. two thirds the total pressure

  2. one third the total pressure

  3. three fifths the total pressure

  4. two fifths the total pressure
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The partial pressure of any gas is the product of mole fraction and total pressure


$P _{Ar}=\dfrac{2}{2+3}.P _{total}$

Multiple choice chemistry atoms and molecules avogadro hypothesis avogadro's law avogadro law

In the ideal gas equation, the unit of universal gas constant R is?

  1. Mole-atm/K

  2. Litre/mole

  3. Litre-atm/mole.K

  4. erg/K
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In ideal gas equation,


$R=\dfrac{PV}{nT}$ where, 
$P$ is the pressure in 'Atmosphere (atm)'
$V$ is the volume in Litre
$n$ is the number of moles
$T$ is the Temperature in Kelvin (K) 

$ \therefore $Units of $R$= litre.atm/mol.K