CBSE Class 11 Chemistry Chapter-9 Important Questions - Free PDF Download
Very Short Answer Type Questions: 1 Mark
1. Which isotope of hydrogen
(i). Does not contain neutrons?
Ans: The isotope of hydrogen that does not contain neutrons is Protium.
(ii). Is it radioactive?
Ans: The isotope of hydrogen which is radioactive in nature is Tritium.
2. Give the electronic configuration of hydrogen
Ans: The atomic number of hydrogen is one\[(1)\]. So, its electronic configuration will be: ${\text{1}}{{\text{s}}^{\text{1}}}$.
3. Name the isotopes of hydrogen.
Ans: Hydrogen has three isotopes present in the nature, namely protium ${{\text{(}}_{\text{1}}}^{\text{1}}{\text{H)}}$, deuterium ${{\text{(}}_{\text{1}}}^{\text{2}}{\text{H)}}$ and tritium ${{\text{(}}_{\text{1}}}^{\text{3}}{\text{H)}}$.
4. What is syn-gas?
Ans: Synthesis gas, often known as "syngas," is a mixture of carbon monoxide ${\text{(CO)}}$ and hydrogen ${\text{(}}{{\text{H}}_{\text{2}}}{\text{)}}$ that is used to make methanol and a variety of other hydrocarbons.
5. What is coal gasification?
Ans: Coal gasification is a process in which syn-gas is produced by heating coal at high temperature.
${\text{C (s) + }}{{\text{H}}_{\text{2}}}{\text{O (g)}}\xrightarrow{{{\text{1270 K}}}}{\text{CO (g) + }}{{\text{H}}_{\text{2}}}{\text{(g)}}$
6. Give the laboratory method of preparation of hydrogen.
Ans: The interaction of powdered zinc with dilute hydrochloric acid produces hydrogen. The reaction is as follows:
${\text{Zn + 2HCl}} \to {\text{ZnC}}{{\text{l}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}$
7. Give the commercial method of preparation of dihydrogen.
Ans: The commercial method of preparation of dihydrogen involves electrolysis of acidified water using platinum electrodes. The reaction is as follows:
${\text{2}}{{\text{H}}_{\text{2}}}{\text{O (l)}}\xrightarrow[{{\text{Traces of acid/base}}}]{{{\text{Electrolysis}}}}{\text{2}}{{\text{H}}_{\text{2}}}{\text{(g) + }}{{\text{O}}_{\text{2}}}{\text{(g)}}$
8. What is water – gas shift reaction?
Ans: By reacting carbon monoxide from syngas combinations with steam in the presence of iron chromate as a catalyst, the synthesis of dihydrogen can be enhanced. The reaction is as followed:
${\text{CO (g) + }}{{\text{H}}_{\text{2}}}{\text{O (g)}}\xrightarrow[{{\text{Catalyst}}}]{{{\text{673 K}}}}{\text{C}}{{\text{O}}_{\text{2}}}{\text{(g) + }}{{\text{H}}_{\text{2}}}{\text{(g)}}$
The above reaction is called the water gas shift reaction.
9. Why is dihydrogen gas not preferred in balloons?
Ans: Being the lightest gas dihydrogen should have been used in balloons. However, because of its high combustibility, it is not recommended.
10. What is the pH of water?
Ans: The amount of hydrogen ions ${\text{(}}{{\text{H}}^{\text{ + }}}{\text{)}}$ in a solution is measured by pH. Ions tend to form in pure water due to random processes (generating ${{\text{H}}^{\text{ + }}}$ and ${\text{O}}{{\text{H}}^ - }$ ions). In pure water, the amount of ${{\text{H}}^{\text{ + }}}$ produced is roughly equivalent to a ${\text{O}}{{\text{H}}^ - }$ . That is why the pH of $7$ is considered neutral.
11. How is methanol prepared using dihydrogen?
Ans: When carbon monoxide reacts with dihydrogen gas using cobalt as a catalyst, methanol is formed. The reaction is as followed:
${\text{CO (g) + 2}}{{\text{H}}_{\text{2}}}{\text{(g)}}\xrightarrow[{{\text{Catalyst}}}]{{{\text{Cobalt}}}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH (l)}}$
12. How is ammonia prepared using dihydrogen?
Ans: Ammonia is prepared using dihydrogen by Haber’s process. In this dihydrogen reacts with nitrogen gas under high temperature and pressure and the catalyst used is iron. The reaction of manufacturing of ammonia is as followed:
${\text{3}}{{\text{H}}_{\text{2}}}{\text{(g) + }}{{\text{N}}_{\text{2}}}{\text{(g)}}\xrightarrow[{{\text{Fe}}}]{{{\text{637 K, 200 atm}}}}{\text{2N}}{{\text{H}}_{\text{3}}}{\text{(g)}}$
13. Name the categories into which hydrides are categorized.
Ans: The categories into which hydrides are categorized are:
Ionic or saline or salt-like hydrides.
Covalent or molecular hydrides.
Metallic or non-stoichiometric hydrides.
14. What are hydrides?
Ans: Under specific reaction circumstances, dihydrogen combines with practically all elements except noble gases to create binary compounds known as hydrides.
15. Give an example of each of an ionic hydride and a covalent hydride.
Ans: The examples of ionic hydrides are: lithum hydride ${\text{(LiH)}}$ and sodium hydride ${\text{(NaH)}}$. The examples of covalent hydrides are: methane ${\text{(C}}{{\text{H}}_{\text{4}}}{\text{)}}$, ammonia ${\text{(N}}{{\text{H}}_{\text{3}}}{\text{)}}$ and water ${\text{(}}{{\text{H}}_{\text{2}}}{\text{O)}}$.
16. What happens when water is added to calcium hydride?
Ans: When water is added to calcium hydride, calcium hydroxide is formed and hydrogen gas is evolved in this process. The reaction is as followed:
${\text{Ca}}{{\text{H}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}} \to {\text{Ca(OH}}{{\text{)}}_{\text{2}}} + {{\text{H}}_{\text{2}}}$
17. Give an example of electrons – deficient hydride.
Ans: An example of electron – deficient hydride is diborane.
18. What is the behavioural similarity between ${\text{N}}{{\text{H}}_{\text{3}}}{\text{, }}{{\text{H}}_{\text{2}}}{\text{O, HF}}$ compounds?
Ans: They behave as Lewis bases i.e. electron donors. In hydrides, the existence of lone pairs on highly electronegative atoms like ${\text{N}}$ ,${\text{O}}$, and ${\text{F}}$ results in the creation of hydrogen bonds between the molecules.
19. Give a reaction in which water acts as an oxidizing agent.
Ans: The reaction in which water acts as an oxidizing agent is given as:
${\text{Na + }}{{\text{H}}_{\text{2}}}{\text{O}} \to {\text{NaOH + }}\dfrac{{\text{1}}}{{\text{2}}}{{\text{H}}_{\text{2}}}$
20. Write the name of a zeolite used in softening of hard water.
Ans: The zeolite used in softening of hard water is sodium aluminium silicate ${\text{(N}}{{\text{a}}_{\text{2}}}{\text{A}}{{\text{l}}_{\text{2}}}{\text{S}}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{8}}}{\text{.x}}{{\text{H}}_{\text{2}}}{\text{O)}}$.
21. Define hard water.
Ans: Water with a high mineral concentration is referred to as hard water. When water percolates through deposits of calcium and magnesium carbonates, bicarbonates, and sulphates, such as those found in limestone, chalk, or gypsum, hard water is created.
22. What is calgon?
Ans: Calgon consists of powdered sodium hexameta phosphate ${\text{(N}}{{\text{a}}_{\text{6}}}{{\text{P}}_{\text{6}}}{{\text{O}}_{{\text{18}}}}{\text{)}}$.
23. Why is ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ a better oxidant than water?
Ans: Hydrogen peroxide is a better oxidant than water because it gets easily reduced to water and nascent oxygen.
${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}} \to {{\text{H}}_{\text{2}}}{\text{O + [O]}}$
24. What happens when ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$reacts with ethylene?
Ans: When hydrogen peroxide reacts with ethylene, ethylene glycol is formed.
25. What do you mean by a 100volume of hydrogen peroxide?
Ans: ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ is sold as a "$100$ volume" hydrogen peroxide, which is correct because a $30$ percent solution of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ has $30$ grams of hydrogen peroxide per ${\text{100 mL}}$ of solution.
26. What happens when ${\text{Ba}}{{\text{O}}_{\text{2}}}$ is treated with phosphoric acid?
Ans: When ${\text{Ba}}{{\text{O}}_{\text{2}}}$ reacts with phosphoric acid, a white precipitate of barium phosphate and hydrogen peroxide is formed. The reaction is as followed:
${\text{3Ba}}{{\text{O}}_{\text{2}}}{\text{ + 2}}{{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}} \to {\text{B}}{{\text{a}}_{\text{3}}}{{\text{(P}}{{\text{O}}_{\text{4}}}{\text{)}}_{\text{2}}} \downarrow {\text{ + 3}}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$
Short Answer Type Questions: 2 Marks
1. Why does hydrogen occupy a unique position in the periodic table?
Ans: Despite the fact that hydrogen resembles both alkali metals ${\text{(n}}{{\text{s}}^{\text{1}}}{\text{)}}$ and halogens \[\left( {{\text{n}}{{\text{s}}^{\text{2}}}{\text{, n}}{{\text{p}}^{\text{5}}}} \right)\] to some extent, it also varies from both. Because hydrogen has such a small size, it does not exist in isolation and is always coupled with other atoms or molecules. That is why it occupies such a unique position in the periodic table.
2. Give the main characteristics of isotopes.
Ans: The main characteristics of isotopes are:
Isotopes are the atoms of the same element.
They consist of different mass numbers but the same atomic number.
They vary in the number of neutrons present.
3. How can the production of dihydrogen obtained from ‘coal gasification be increased’?
Ans: The carbon monoxide from the syngas mixture is reacted with steam in the presence of iron chromate catalyst at high temperature. This method increases the production of dihydrogen gas and this process is called coal gasification.
${\text{CO(g) + }}{{\text{H}}_{\text{2}}}{\text{O (g)}}\xrightarrow[{{\text{Catalyst}}}]{{{\text{673 K}}}}{\text{C}}{{\text{O}}_{\text{2}}}{\text{(g) + }}{{\text{H}}_{\text{2}}}{\text{(g)}}$
4. Why is dihydrogen used as fuel cells for generating electrical energy?
Ans: Dihydrogen is used as a fuel cell for generating electrical energy because it does not pollute the environment and releases more energy per unit mass of fuel than gasoline or any other fuel.
5. What is understood by hydrogenation?
Ans: The reaction between molecular hydrogen and an organic or inorganic substrate is known as hydrogenation. As a result, a hydrogenation reaction, also known as a reduction reaction, occurs when hydrogen molecules are introduced to an alkene.
6. Which fuel is used as rocket fuel?
Ans: Hydrogen is utilised as a rocket fuel because it is light and highly strong. It has the smallest molecular weight of any known chemical and burns exceedingly hot.
7. What happens when sodium hydride reacts with water?
Ans: Sodium hydride also known as saline hydride when reacts violently with water producing sodium hydroxide and hydrogen gas. The reaction of sodium hydride with water is as follows:
${\text{NaH (s) + }}{{\text{H}}_{\text{2}}}{\text{O (aq)}} \to {\text{NaOH (aq) + }}{{\text{H}}_{\text{2}}}{\text{(g)}}$
8. What is the geometry of the compound formed by group $14$ to form molecular hydride?
Ans: Electron precise hydrides are those with the correct number of electrons required to create a typical covalent bond. All of the elements in group $14$ form tetrahedral compounds (for example,${\text{C}}{{\text{H}}_{\text{4}}}$).
9. What are the characteristic features of ionic or saline hydrides?
Ans: In their solid states ionic hydrides are crystalline, non-conducting, and non-volatile. In a liquid form, however, they conduct electricity.
10. Which gas is produced on electrolysis of ionic hydride?
Ans: On electrolysis of ionic hydride, dihydrogen gas is produced at the anode.
11. How does ${{\text{H}}^{\text{ + }}}$ion forms hydronium ion ${\text{(}}{{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}{\text{)}}$ in water?
Ans: The reaction is as followed:
12. Show with reaction the amphoteric nature of water.
Ans: When reacted with ammonia, water acts as an acid and when hydrogen sulphide reacts with water it acts like a base. The reactions are given as:
${{\text{H}}_{\text{2}}}\text{O (l) }\!\!~\!\!\text{ + }\!\!~\!\!\text{ N}{{\text{H}}_{\text{3}}}\text{(aq)}\rightleftharpoons \text{O}{{\text{H}}^{-}}\text{(aq) }\!\!~\!\!\text{ + }\!\!~\!\!\text{ N}{{\text{H}}_{\text{4}}}^{\text{ + }}\text{(aq)}$
${{\text{H}}_{\text{2}}}\text{O (l) }\!\!~\!\!\text{ + }\!\!~\!\!\text{ }{{\text{H}}_{\text{2}}}\text{S (aq)}\rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}\text{(aq) + }\!\!~\!\!\text{ H}{{\text{S}}^{-}}(\text{aq)}$
13. Why is ice less dense than water and what kind of attractive forces must be overcome to melt ice?
Ans: The ice has an open structure with a number of vacant spaces. As a result, ice has a lower density than water. When ice melts, hydrogen bonds are disrupted, allowing water molecules to fill in the gaps. As a result, the structure of ice is not as open as that of liquid water.
14. Why does hard water not form lather with soap?
Ans: Because the cations (${\text{C}}{{\text{a}}^{{\text{2 + }}}}$ and ${\text{M}}{{\text{g}}^{{\text{2 + }}}}$) found in hard water react with soap to precipitate calcium and magnesium salts of fatty acids, hard water does not readily generate lather with soap.
${\text{M}}{{\text{g}}^{{\text{2 + }}}}{\text{ + 2}}{{\text{C}}_{{\text{17}}}}{{\text{H}}_{{\text{35}}}}{\text{COONa}} \to {{\text{(}}{{\text{C}}_{{\text{17}}}}{{\text{H}}_{{\text{35}}}}{\text{COO)}}_{\text{2}}}{\text{Mg + 2Na}}$
15. Why is water an excellent solvent for ionic or polar substances?
Ans: With a high dielectric constant water acts as a polar solvent. The attraction between cation and anion is reduced due to the high dielectric constant of water. As a result, water molecules may readily remove ions from the lattice site by utilising dipole forces.
16. How many hydrogen – bonded water molecule are associated in${\text{CuS}}{{\text{O}}_{\text{4}}}{\text{.5}}{{\text{H}}_{\text{2}}}{\text{O}}$?
Ans: Outside of the brackets (coordination spheres), just one water molecule is hydrogen-bonded. The remaining four water molecules are linked through coordinate bonding.
17. What happens when ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ reacts with acidified${\text{KMn}}{{\text{O}}_{\text{4}}}$?
Ans: When hydrogen peroxide reacts with acidified solution of potassium permanganate:
$\text{2Mn}{{\text{O}}_{4}}^{-}\text{ + 6}{{\text{H}}^{\text{ + }}}\text{ + 5}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}\to \text{2M}{{\text{n}}^{\text{2 + }}}\text{ + 8}{{\text{H}}_{\text{2}}}\text{O + 5}{{\text{O}}_{\text{2}}}$
$\text{2KMn}{{\text{O}}_{\text{4}}}\text{ + 3}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ + 5}{{\text{H}}_{\text{2}}}{{\text{O}}_{2}}\to {{\text{K}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ + 2MnS}{{\text{O}}_{\text{4}}}\text{ + 8}{{\text{H}}_{\text{2}}}\text{O + 5}{{\text{O}}_{\text{2}}}$
18. Hydrogen peroxide acts as an oxidizing agent as well as a reducing agent. Why?
Ans: Because hydrogen peroxide easily decomposes to produce oxygen and also absorbs oxygen from water, it can function as an oxidising agent.
19. Why is hydrogen peroxide stored in wax-lined glass or plastic vessels in dark?
Ans: The rough surfaces of glass, alkali oxides found in it, and light breakdown hydrogen peroxide. ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$is often kept in coloured paraffin wax-coated plastic or Teflon bottles to avoid decomposition.
20. What is the volume strength of ${\text{2M - }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$?
Ans: Since ${\text{1M - }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ solution contains ${\text{17g }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$
Therefore, ${\text{2M - }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$solution contains ${\text{34g }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$
But ${\text{68g}}$ of${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ contains = $\dfrac{{22400 \times 32}}{{68}}$ = ${\text{11200mL}}$ of${{\text{O}}_{\text{2}}}$ at NTP.
Thus ${\text{1000mL}}$ of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ solution gives off ${{\text{O}}_{\text{2}}}$ = ${\text{11200mL}}$ at NTP.
Hence ${\text{1mL}}$ of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ solution gives = $\dfrac{{{\text{11200}}}}{{{\text{1000}}}}{\text{ = 11}}{\text{.2mL}}$
Therefore, the volume strength of ${\text{2M - }}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$is ${\text{11}}{\text{.2mL}}$.
21. Calculate the strength in volumes of a solution containing ${\text{30}}{\text{.36 g/l}}$ of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$.
Ans: ${\text{2}}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}} \to {\text{2}}{{\text{H}}_{\text{2}}}{\text{O + }}{{\text{O}}_2}$
${\text{22}}{\text{.4 L}}$ at NTP
${\text{68g}}$ of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ produce ${\text{22}}{\text{.4 L}}$of${{\text{O}}_{\text{2}}}$ at NTP.
${\text{36}}{\text{.30 g}}$ of ${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ produce = $\dfrac{{22.4}}{{68}} \times 30.36$ = ${\text{10 L}}$ of ${{\text{O}}_{\text{2}}}$ at NTP.
Therefore, volume strength = $10$ volumes.
22. What happens when hydrogen peroxide reacts with acidified${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$?
Ans: Acidified ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ oxidises to chromium peroxide${\text{(C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{3}}}{\text{)}}$, which is unstable. However, it is soluble in ether and produces a blue coloured solution.
${{\text{K}}_{\text{2}}}\text{C}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}\text{ + 4}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\to {{\text{K}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ + C}{{\text{r}}_{\text{2}}}{{\text{(S}{{\text{O}}_{\text{4}}}\text{)}}_{\text{3}}}\text{ + 4}{{\text{H}}_{\text{2}}}\text{O+3}[\text{O}]$
$[{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}\text{ + O}\to {{\text{H}}_{\text{2}}}\text{O + }{{\text{O}}_{\text{2}}}]\times \text{3}$
${{\text{K}}_{\text{2}}}\text{C}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}\text{ + 4}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ + 3}{{\text{H}}_{\text{2}}}{{\text{O}}_{2}}\to {{\text{K}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ + C}{{\text{r}}_{\text{2}}}{{\text{(S}{{\text{O}}_{\text{4}}}\text{)}}_{\text{3}}}\text{ + 7}{{\text{H}}_{\text{2}}}\text{O + S}{{\text{O}}_{\text{2}}}$
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