2 Marks Questions

Question 12 Marks

What kind of information about an electron in an atom is obtained from its wave function?

Answer

The square of the amplitude of the electron wave, i.e, $\Psi^2$ at any point gives the probability of finding an electron at that point. since the region around the nucleus which represents the electron density at different points is called an orbital, hence the wave function for an electron in an atom is called orbital wave function.

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Question 22 Marks

Write a short note on hydrogenation of unsaturated aliphatic hydrocarbons.

Answer

When unsaturated compounds, i.e. alkenes or alkynes, are treated with dihydrogen in the presence of finely divided catalysts (i.e. Pt , Pd or Ni ), alkanes are obtained and the reaction is called hydrogenation reaction. As represented in the following reaction where ethene is converted into ethane.
$
\underset{\text { Ethene }}{eg CH_2}=CH_2+H_2 \xrightarrow{Pt \backslash Pd \backslash Ni} \underset{\text { Ethane }}{CH_3-} CH_3
$

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Question 32 Marks

Hydrocarbon A (molecular formula is $C _5 H _8$ ) gave a white precipitate with ammoniacal silver nitrate. Oxidation of A with hot alkaline $KMnO _4$ gave 2-methyl propanoic acid. What is the structural formula of A?

Answer

White precipitate indicates that the triple bond is present at terminal position. The compound (A) is 3-methyl-1-butyne. It will oxidised in the presence of hot alkaline $KMnO _4$ to give 2-Methylpropanoic acid.

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Question 42 Marks

What will be the mass of one ${ }^{12} C$ atom in g ?

Answer

Since,
the number of atoms in 1 mol of ${ }^{12} C$ atoms $=6.022 \times 10^{23}$ atoms $=$ Atomic mass of carbon -12 in gms. $=12 g$ Thus, $6.0022 \times 10^{23}$ atoms of ${ }^{12} C$ have mass $=12 g$ $\therefore 1$ atom of ${ }^{12} C$ will have mass $=\frac{12}{6.022 \times 10^{23}} g$ $=1.9927 \times 10^{-23} g$

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Question 52 Marks

1. How do the electronic configurations of the elements with $Z =107-109$ differ from one another?
2. $Rn ( Z =86)$ is the last noble gas discovered. Predict what will be the atomic number of the next noble gas to be discovered. Write its symbol.

Answer

Atomic Number of element (Z)	Electronic configuration	Number of electrons in 6d orbital	Group Number
107	$\begin{gathered}{[R n] 5 s^{14} 6 d^5} 7 s^2\end{gathered}$	5	7
108	$\begin{gathered}{[ Rn ] 5 s^{14} 6 d^6} 7 s^2\end{gathered}$	6	8
109	$\begin{gathered}{[R n] 5 s^{14} 6 d^7} 7 s^2\end{gathered}$	7	9

It is clear that these elements differ in the number of electrons in the 6d-subshell and group number in periodic table.
2. 118, Uuo

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Question 62 Marks

The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen ion in it.

Answer

We know that, $pH =-\log \left[ H ^{+}\right]$or $\log \left[ H ^{+}\right]=- pH =-3.76=\overline{4} .24$ Before taking antilog, add -1 in the characteristic $(-3)$ and +1 in mantissa (0.76), i.e. $(-3.76-1+1=\overline{4} .24)]$
$
\therefore\left[H^{+}\right]=\text {Anti } \log \overline{4} .24=1.738 \times 10^{-4} M=1.74 \times 10^{-4} M
$

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