1 Marks Question

Question 511 Mark

What is the nature of $\mathrm{H}_2 \mathrm{O}_2$? Give chemical reaction to show its nature.

Answer

$\mathrm{H}_2 \mathrm{O}_2$ is acidic in nature.
$\text{H}_2\text{O}_2+2\text{NaOH}\xrightarrow{\ \ \ \ }\text{Na}_2\text{O}_2+2\text{H}_2\text{O}$

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Question 521 Mark

What is the hybrid orbital of oxygen atom and shape of $\mathrm{H}_3 \mathrm{O}$ ?

Answer

$\mathrm{Sp}^3$, Pyramidal shape There is coordinate bond in which lone pair of oxygen is shared by $\mathrm{H}^{+}$ion. It is denoted by $\rightarrow$.

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Question 531 Mark

In reaction of $\mathrm{F}_2$ and $\mathrm{H}_2 \mathrm{O}$, what is the role of water?

Answer

$2\text{F}_2+2\text{H}_2\text{O}\xrightarrow{\ \ \ \ }4\text{H}^++4\text{F}^-+\text{O}_2.$
Water is acting as reducing agent because $\mathrm{F}_2$ is best oxidising agent.

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Question 541 Mark

What is the molar mass of heavy water?

Answer

Molar mass of heavy water is $20\text{g}{~mol}^{-1}$,
$[\because\text{D}_2\text{O}=2\text{D}+10\\=2\times2+1\times16=4+16=20]$

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Question 551 Mark

Name the isotope of hydrogen which is commonly used as a tracer in organic reactions.

Answer

Most commonly deuterium is used as tracers in organic reactions. (Tritium can be used as tracers but it is radioactive in nature and least abundant hydrogen isotope, therefore deuterium is commonly used).

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Question 561 Mark

What do you mean by 15 volume $\mathrm{H}_2 \mathrm{O}_2$ solution?

Answer

15 volume $\mathrm{H}_2 \mathrm{O}_2$' means 1ml of a 15 volume $\mathrm{H}_2 \mathrm{O}_2$ solution gives 15ml of $\mathrm{O}_2$ at NTP.

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Question 571 Mark

Name the constituents of water gas.
Which gaseous compound on treatment with dihydrogen produces methanol?
Name one industrial method for the preparation of dihydrogen.

Answer

Carbon monoxide and hydrogen.
Carbon monoxide.
Bosch process.

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Question 581 Mark

Acetanilide prevents the decomposition of $\mathrm{H}_2 \mathrm{O}_2$. What is this compound called?

Answer

Acetanilide is a neutral compound which suppresses the decomposition of $\mathrm{H}_2 \mathrm{O}_2$ into $\mathrm{H}_2 \mathrm{O}$ and $\mathrm{O}_2$. Thus, it is called stabiliser (or negative catalyst).

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Question 591 Mark

Give reasons:
Ice floats on water.

Answer

Density of ice is less than water due to presence of empty spaces created because of H-bonding between $\text{H}_2\text{O}$ molecules. Hence, ice floats on water.

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Question 601 Mark

When sodium hydride is electrolysed, hydrogen is liberated at which electrode?

Answer

$\text{NaH}\xrightarrow{\text{electrolysis}\ \ }\text{Na}^++\text{H}^-,$
At anode: $\text{2}\text{H}^--2\text{e}^-\xrightarrow{\ \ \ \ }\text{H}_2(\text{g})$ [Loss electrons, oxidation]

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Question 611 Mark

Name the compound each in which hydrogen exists in :

negative oxidation state.
positive oxidation state.

Answer

Nah, here oxidation state of hydrogen is $- 1.$
$\text{HCI}$, here oxidation state of hydrogen is $+1.$

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Question 621 Mark

Why is water molecules polar?

Answer

It is bent molecule, has high dipole moment due to difference in electronegativity of 'H' and oxygen, it is polar molecule.

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Question 631 Mark

What happens when $\mathrm{O}_3$, is passed through $\mathrm{H}_2 \mathrm{O}_2$? $\mathrm{H}_2 \mathrm{O}_2$ is oxidising or reducing agent in the reaction.

Answer

$\mathrm{H}_2 \mathrm{O}$ and $\mathrm{O}_2$ is formed. $\mathrm{H}_2 \mathrm{O}_2$ acts as reducing agent.
$\text{H}_2\text{O}_2+\text{O}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ } \text{H}_2\text{O}+2\text{O}_2$

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Question 641 Mark

Suggest a method to show the electronegative nature of hydrogen.

Answer

When sodium hydride is electrolysed, hydrogen is evolved at anode, which shows its electronegative nature.

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Question 651 Mark

Describe the bulk preparation of hydrogen by electrolytic method. What is the role of an electrolyte in this process?

Answer

Electrolysis of acidified water using platinum electrodes gives hydrogen.
$2\text{H}_2\text{O}(\text{l})\xrightarrow[\text{Traces of acide/ base}]{\text{Electrolysis}}2\text{H}_2(\text{g})+\text{O}_2(\text{g})$
Here, the role of an electrolyte is to make water conducting.

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Question 661 Mark

Which gas is evolved when $\mathrm{Mg}_3 \mathrm{N}_2$ (magnesium nitride) is treated with $\mathrm{H}_2 \mathrm{O}$ ? Give chemical reaction.

Answer

$\text{NH}_3$ gas is evolved.
$\text{Mg}_3\text{N}_2+6\text{H}_2\text{O}\xrightarrow{\ \ \ \ }3\text{Mg}(\text{OH})_2+2\text{NH}_2$

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Question 671 Mark

Name one metal which liberates $\text{H}_2$ when treated with NaOH.

Answer

Al (Aluminium) and Be (Beryllium)
$2\text{Al}+2\text{NaOH}+2\text{H}_2\text{O}\xrightarrow{\ \ \ \ }2\text{NaAlO}_2+\text{H}_2$
$\text{Be}+\text{2NaOH}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }\text{Na}_2\text{BeO}_2+\text{H}_2$

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Question 681 Mark

What is the trade name of sodium hexa metaphosphate? Give its use.

Answer

Calgon. It is used to remove hardness of water.

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Question 691 Mark

Dihydrogen forms interstitial hydrides with which type of elements?

Answer

Transition metals form interstitial hydrides due to presence of voids in which hydrogen can fit into.

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Question 701 Mark

Why does chlorine water loses its colour if kept for long time?

Answer

$\text{Cl}_2+\text{H}_2\text{O}\xrightarrow{\ \ \ \ }\text{HCl}+\text{HOCl}$
$\text{HOCl}\xrightarrow{\ \ \ \ }\text{HCl}+[\text{O}]$
HCl is colourless, therefore, chlorine water loses its colour.

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Question 711 Mark

What type of bonds are broken when water evaporates.

Answer

Intermolecular hydrogen bonds are broken when water evaporates.

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Question 721 Mark

Explain why beryllium forms a covalent hydride while calcium forms an ionic hydride.

Answer

Because of higher electronegativity, Be (EN = 1.5) forms a covalent hydride while due to lower electronegativity Ca (EN = 1.0 ) forms an ionic hydride.

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Question 731 Mark

Write redox reaction between fluorine and water.

Answer

$2\text{F}_2(\text{g})+2\text{H}_2\text{O}\xrightarrow{\ \ \ \ }4\text{H}^+(\text{aq})+4\text{F}^-(\text{aq})+\text{O}_2(\text{g})$

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Question 741 Mark

Which out of nascent hydrogen and dihydrogen, is more reactive?

Answer

Nascent hydrogen (newly born hydrogen) [H] is more reactive
than molecular hydrogen because energy is needed to break bond in $\text{H}_2$.

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Question 751 Mark

Why does elemental hydrogen react with other substances slowly at room temperature?

Answer

It is because it has high bond dissociation energy $\left(436 \mathrm{~kJ} \mathrm{~mol}^{-1}\right)$ due to smaller bond length.

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Question 761 Mark

How does heavy water react with $\text{Al}_4\text{C}_3$?

Answer

$\text{Al}_4\text{C}_3+12\text{D}_2\text{O}\xrightarrow{\ \ \ \ }4\text{Al}(\text{OD})_3+3\text{CD}_4$

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Question 771 Mark

How does $\text{CaC}_2$ react with heavy water?

Answer

$\text{CaC}_2+2\text{D}_2\text{O}\xrightarrow{\ \ \ \ \ }\text{Ca}(\text{OD})_2+\text{C}_2\text{D}_2$

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Question 781 Mark

Complete the following reaction.
$\text{CO}(\text{g})+2\text{H}_2()\text{g}\xrightarrow[\text{CAtalyst}]{\text{Cobalt}}$

Answer

$\text{CO}(\text{g})+2\text{H}_2(\text{g})\xrightarrow[\text{Cataiyst}]{\text{Cobalt}}\text{CH}_3\text{OH}_2(\text{l})$

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Question 791 Mark

Write the name of that isotope of hydrogen which has no neutron.

Answer

Protium or ordinary hydrogen.

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Question 801 Mark

S. No.	Column I	S. No.	Column II
a.	Synthesis gas	i.	$Na_2[Na_4(PO_3)_6]$
b.	Dihydrogen	ii.	Oxidising agent
c.	Heavy water	iii.	Softening of water
d.	Calgon	iv.	Reducing agent
e.	Hydrogen peroxide	v.	Stoichiometric compounds of s-block elements
f.	Salt like hydrides	vi.	Prolonged electrolysis of water
		vii.	$Zn + NaOH$
		viii.	$Zn + dil. H_2SO_4$
		ix.	Synthesis of methanol
		x.	Mixture of CO and $H_2$

Answer

S. No.	Column I	S. No.	Column II
a.	Synthesis gas	(ix)	Synthesis of methanol
a.	Synthesis gas	(x)	Mixture of CO and $H_2$
b.	Dihydrogen	(iv)	Reducing agent
		(v)	Stoichiometric compounds of s-block elements
		(vii)	$Zn + NaOH$
		(viii)	Zn + dil. $H_2SO_4$
		(ix)	Synthesis of methanol
c.	Heavy water	(vi)	Prolonged electrolysis of water
d.	Calgon	(i)	$Na_2[Na_4(PO_3)_6]$
d.	Calgon	(iii)	Softening of water
e.	Hydrogen peroxide	(ii)	Oxidising agent
e.	Hydrogen peroxide	(iv)	Reducing agent
f.	Salt like hydrides	(v)	Stoichiometric compounds of s-block elements

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Question 811 Mark

Give an example of reaction in which $\text{H}_2$ acts as oxidising agent.

Answer

$2\text{Na}+\text{H}_2\xrightarrow{\ \ \ \ }2\text{NaH}$ (sodium hydride)
In this reaction, $\text{H}_2$ acts as oxidising agent because it can gain electron to form $\text{H}^-$ ion.

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Question 821 Mark

Classify the following as covalent, ionic or interstitial hydrides.
$\mathrm{CaH}_2, \mathrm{LaH}_2, \mathrm{RbH}, \mathrm{GeH}_2, \mathrm{TiH}_2, \mathrm{NaH}, \mathrm{NH}_3$.

Answer

Covalent hydrides $\mathrm{GeH}_2, \mathrm{NH}_3$.
Ionic hydrides $\mathrm{CaH}_2, \mathrm{RbH}, \mathrm{NaH}$.
Interstitial hydrides $\mathrm{TiH}_2, \mathrm{LaH}_2$.

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Question 831 Mark

Why is dihydrogen not preferred in balloons these days?

Answer

Dihydrogen is highly combustible and hence, is likely to catch fire in the presence of excess of air. That's why it is not preferred in balloons now a days.

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Question 841 Mark

Sodium forms a crystalline ionic solid with dihydrogen. The solid is non-volatile and non-conducting in nature. It reacts violently with water to produce dihydrogen gas. Write the formula of this compound and its reaction with water. What will happen on electrolysis of the melt of this solid?

Answer

The compound is NaH (sodium hydride)
$2\text{Na}+\text{H}_2\xrightarrow{\ \ \ \ \ \ \ \ \ }2\text{NaH} $
$\text{NaH}+\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ }\text{NaOH}+\text{H}_2\text{(g)}$
When molten sodium hydride is electrolysed, Na will be formed at cathode and dihydrogen will be liberated at anode.
$2\text{NaH}\xrightarrow{\text{electrolysis}}2\text{Na}\ \ \ +\ \ \ \ \ \text{H}_2(\text{g})\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{At cathode}\ \ \ \ \ \ \ \ \ ^\text{At anode}$

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Chemistry 1 Marks Question