Some Basic Concepts in Chemistry MCQs for NEET — Chemistry Questions with Answers

The given problem is related to the concept of stiochiometry of chemical equations. Thus, we have to convert the given volumes into their moles and then, identify the limiting reagent [possessing minimum number of moles and gets completely used up in the reaction].

The limiting reagent gives the moles of product formed in the reaction.

              H₂(g) + Cl₂(g) $\to$2HCl (g)

Initial vol   22.4 L    11.2 L      2 mol

... 22.4 L volume at STP is occupied by,

              Cl₂ = 1 mole,

... 11.2 L volume will be occupied by,

             Cl₂ = 1x 11.2/22.4 mole = 0.5 mol

Thus, H₂(g) + Cl₂(g) $\to$2HCl (g)

(D).  22.4 litres of ${\mathrm{N}}_2$ will be present in 1 mole at 1 atmospheric pressure and 273 K or 0ºC.

$$\begin{gathered} \left(\mathrm{A}\right). 48 \mathrm{gm}. \mathrm{C} = \frac{48}{12} = 4 \mathrm{moles} \mathrm{of} \mathrm{C}. \mathrm{From} 4 \mathrm{moles} \mathrm{of} \mathrm{C}, 4 \mathrm{moles} \mathrm{of} \mathrm{CO}\left(\mathrm{g}\right) \mathrm{and} 4 \mathrm{moles} \mathrm{of} {\mathrm{H}}_2\left(\mathrm{g}\right) \mathrm{is} \mathrm{obtained}. \\ \therefore \mathrm{total} \mathrm{moles} \mathrm{of} \mathrm{gas} \mathrm{produced} = 8 \\ \therefore \mathrm{volume} \mathrm{of} \mathrm{product} \mathrm{gas} \mathrm{mixture} \mathrm{at} \mathrm{STP} = 8 \times 22.4 = 179.2 \mathrm{lit}. \end{gathered}$$

(A). Let the volume of ${\mathrm{CH}}_4$ at N.T.P. = x ml

       Let the volume of ${\mathrm{C}}_2{\mathrm{H}}_4$ at N.T.P. = y ml

       Let the volume of ${\mathrm{C}}_2{\mathrm{H}}_2$ at N.T.P. = z ml

       From question, x + y + z = 10 ............ (1)

       As we know that

       Weight of ${\mathrm{CH}}_4$ + Weight of ${\mathrm{C}}_2{\mathrm{H}}_4$ + Weight of ${\mathrm{C}}_2{\mathrm{H}}_2$ = Weight of mixture

$\frac{16\mathrm{x}}{22400}+\frac{28\mathrm{x}}{22400}+\frac{262}{22400}=\frac{11.30}{11200}\times 10$ .....................(2)

$$\begin{gathered} \mathrm{Now}, \underset{\mathrm{x} \mathrm{ml}}{{\mathrm{CH}}_4}\left(\mathrm{g}\right)+\underset{2\mathrm{x} \mathrm{ml}}{2{\mathrm{O}}_2}\left(\mathrm{g}\right) \rightleftharpoons {\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathcal{l}\right) \\ \underset{\mathrm{y} \mathrm{ml}}{{\mathrm{C}}_2{\mathrm{H}}_4}\left(\mathrm{g}\right)+\underset{3\mathrm{y} \mathrm{ml}}{3{\mathrm{O}}_2}\left(\mathrm{g}\right) \rightleftharpoons 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathcal{l}\right) \\ \underset{\mathrm{z} \mathrm{ml}}{{\mathrm{C}}_2{\mathrm{H}}_2}\left(\mathrm{g}\right)+\underset{\frac{5}{2}\mathrm{z} \mathrm{ml}}{\frac{5}{2}{\mathrm{O}}_2}\left(\mathrm{g}\right) \rightleftharpoons 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathcal{l}\right) \end{gathered}$$

        Total volume of oxygen used up in the reaction $=\left(2\mathrm{x}+3\mathrm{y}+\frac{5}{2}\mathrm{z}\right)\mathrm{ml}$

        But from question,

        Total volume of oxygen used up $=30-5.5=24.5 \mathrm{ml}$

$\therefore 2\mathrm{x}+3\mathrm{y}+\frac{5}{2}\mathrm{z}=24.5$                 ................... (3)

         Solving equations (1), (2) and (3), we get

          x=4, y=3, z=3

$\therefore {\mathrm{CH}}_4=4\mathrm{ml}, {\mathrm{C}}_2{\mathrm{H}}_4=3\mathrm{ml}, {\mathrm{C}}_2{\mathrm{H}}_2=3 \mathrm{ml}$

The reaction is

$$\begin{gathered} Na{H}_{2}P{O}_4 + 2NaOH \to N{a}_{3}P{O}_4 +2H_{2}O n \\ 120g 2\times 40=80g \\ (1 mole) (2 moles) \\ 120g Na{H}_{2}P{O}_4 requires 80g NaOH \\ 12g Na{H}_{2}P{O}_{4}requires 8 g NaOH \\ 80g NaOH is present in 1 litre i.e. 1000 ml of 2M NaOH \\ 8g NaOH is present in \frac{1000}{80}\times 8=100ml of 2M NaOH \end{gathered}$$

Dalton's theory could explain the laws of chemical combination including the Law of Conservation of Mass, Law of Constant Composition, and Law of Multiple Proportions. However, it could not explain the laws of gaseous volumes. (NCERT, Chapter: SOME_BASIC_CONCEPTS_OF_CHEMISTRY, Section 1.6)

Dalton's theory states that chemical reactions involve reorganization of atoms. These are neither created nor destroyed in a chemical reaction. (NCERT, Chapter: SOME_BASIC_CONCEPTS_OF_CHEMISTRY, Section 1.6, Point 4)

The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school teacher in 1808. (NCERT, Chapter: STRUCTURE_OF_ATOM)

Dalton's Atomic Theory regarded the atom as the ultimate indivisible particle of matter. The concept of atoms being made of sub-atomic particles like electrons, protons, and neutrons developed towards the end of the nineteenth and beginning of the twentieth century, which was a concept very different from that of Dalton. (NCERT, Chapter: STRUCTURE_OF_ATOM and SOME_BASIC_CONCEPTS_OF_CHEMISTRY, Section 1.6)