Here are the answers to the questions as per the numbering in the image:
Q.4 What is bleaching powder? How is it prepared commercially? Give its uses.
Answer:
- Bleaching powder (chemical name: calcium hypochlorite, Ca(OCl)₂) is an inorganic compound used as a disinfectant and bleaching agent.
- Preparation: Bleaching powder is commercially prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]:
Ca(OH)2 + Cl2 → Ca(OCl)2 + H2O - Uses:
- It is used for bleaching cotton and linen in the textile industry.
- It is used as a disinfectant for drinking water and swimming pools.
- It is used in the paper industry for bleaching wood pulp.
- It is used as an oxidizing agent in many chemical industries.
Q.5 (a) Discuss the oxides of chlorine.
Answer:
Chlorine forms several oxides, including:
- Dichlorine monoxide (Cl₂O): A pale yellow gas, used in water treatment.
- Dichlorine dioxide (ClO₂): A yellow-green gas, widely used for bleaching wood pulp and disinfecting water.
- Chlorine dioxide (ClO₂): A powerful bleaching agent, it is used in bleaching paper and textiles.
- Dichlorine heptoxide (Cl₂O₇): An unstable and highly reactive liquid, it is the anhydride of perchloric acid.
(b) What are disproportionation reactions? Explain your answer with an example.
Answer:
- Disproportionation reaction: A type of redox reaction where a single substance is simultaneously oxidized and reduced, forming two different products.
- Example: The decomposition of hydrogen peroxide:
2H2O2 → 2H2O + O2
In this reaction, oxygen is both reduced (to water) and oxidized (to oxygen gas).
Q.6 Discuss the system of nomenclature used for oxyacid of halogens. Support your answer with examples.
Answer:
- The oxyacids of halogens are named based on the oxidation state of the halogen. The system of naming involves prefixes and suffixes.
- Hypo- is used when the halogen is in its lowest oxidation state.
- Per- is used when the halogen is in its highest oxidation state.
- -ous is used when the halogen is in a lower oxidation state.
- -ic is used when the halogen is in a higher oxidation state. Examples:
- Hypochlorous acid (HClO): Chlorine is in the +1 oxidation state.
- Chlorous acid (HClO₂): Chlorine is in the +3 oxidation state.
- Chloric acid (HClO₃): Chlorine is in the +5 oxidation state.
- Perchloric acid (HClO₄): Chlorine is in the +7 oxidation state.
Q.7 (a) How are the halogen acids ionized in water?
Answer:
- Halogen acids (HX, where X is a halogen) ionize in water by dissociating into hydrogen ions (H⁺) and halide ions (X⁻). The degree of ionization depends on the strength of the acid, which is influenced by the bond strength between hydrogen and the halogen.
(b) Why is HF a weaker acid than HCl?
Answer:
- HF is a weaker acid than HCl because the bond between hydrogen and fluorine is much stronger than the bond between hydrogen and chlorine. The strong H-F bond makes it difficult for HF to dissociate completely in water, resulting in fewer hydrogen ions (H⁺) and, therefore, a weaker acid. In contrast, HCl dissociates more easily in water.
Here are the answers to the questions as per the numbering in the image:
Q.8 In the following sets, arrange the substances in order of the property indicated. Give reasons.
(a) Increasing acidic character
Order: HClO < HClO₂ < HClO₃ < HClO₄
Reason: The acidic strength increases with the increase in the oxidation state of chlorine. HClO₄ (perchloric acid) is the strongest acid as chlorine is in the +7 oxidation state, while HClO (hypochlorous acid) is the weakest with chlorine in the +1 oxidation state.
(b) Increasing oxidizing power
Order: F₂ > Cl₂ > Br₂ > I₂
Reason: The oxidizing power decreases down the group in halogens because the ability to gain electrons (electron affinity) decreases as the size of the atom increases.
Q.9 What happens when bleaching powder reacts with the following reagents:
(a) Dil. H₂SO₄:
When bleaching powder reacts with dilute sulfuric acid, chlorine gas is liberated:
Ca(OCl)2 + H2SO4 → CaSO4 + H2O + Cl2
(b) Excess of Conc. H₂SO₄:
With excess concentrated sulfuric acid, more chlorine is liberated along with the formation of calcium sulfate and water.
(c) NH₃:
Bleaching powder reacts with ammonia to form nitrogen trichloride and calcium hydroxide:
3Ca(OCl)2 + 2NH3 → 3Ca(OH)2 + NCl3
(d) HI:
When bleaching powder reacts with hydrogen iodide, iodine is liberated:
Ca(OCl)2 + 4HI → CaI2 + 2H2O + I2
(e) CO₂:
When bleaching powder reacts with carbon dioxide, calcium carbonate is formed:
Ca(OCl)2 + CO2 → CaCO3 + Cl2
Q.10 Discuss the various commercial uses of halogens and their compounds.
Answer:
- Fluorine: Used in the production of fluorocarbons (refrigerants), Teflon coatings, and in toothpaste as fluoride.
- Chlorine: Used as a disinfectant in water treatment, in the production of PVC (polyvinyl chloride), and as a bleaching agent in the paper and textile industries.
- Bromine: Used in fire retardants, certain dyes, and pharmaceuticals.
- Iodine: Used as an antiseptic (e.g., iodine tincture) and in iodized salt to prevent iodine deficiency.
Q.11 What are noble gases? Explain their inertness on the basis of their electronic configuration.
Answer:
- Noble gases are elements of Group 18 in the periodic table, which include helium, neon, argon, krypton, xenon, and radon.
- Inertness: Noble gases are inert because they have completely filled outer electron shells (octet configuration), which makes them highly stable and unreactive under normal conditions.
Q.12 Write notes on the followings:
(i) Oxyfluorides of xenon:
- Xenon oxyfluorides (XeOF₂, XeOF₄) are compounds of xenon, oxygen, and fluorine. These compounds are examples of noble gases forming stable compounds under specific conditions. They exhibit interesting bonding due to xenon’s ability to expand its octet.
(ii) Applications of noble gases:
- Helium: Used in balloons, as a coolant in nuclear reactors, and in MRI machines.
- Neon: Used in neon signs for advertising.
- Argon: Used in light bulbs and as an inert shielding gas in welding.
- Krypton: Used in high-performance lighting products.
- Xenon: Used in xenon flash lamps and as an anesthetic.
- Radon: Used in some cancer treatments.
Q.13 Short questions:
(i) What is “Iodized Salt”?
Answer: Iodized salt is table salt that has been fortified with iodine, which is essential to prevent iodine deficiency, which can lead to thyroid problems such as goiter.
(ii) What are Freons and Teflon?
Answer:
- Freons: A group of halogenated hydrocarbons used as refrigerants in air conditioners and refrigerators.
- Teflon: A brand name for polytetrafluoroethylene (PTFE), a fluoropolymer known for its non-stick properties and used in cookware.
(iii) Arrange the following ions in order of increasing size: F⁻, Cl⁻, I⁻, Br⁻
Answer: F⁻ < Cl⁻ < Br⁻ < I⁻
Reason: The size of halide ions increases down the group due to the addition of electron shells.
(iv) Why does iodine have metallic luster?
Answer: Iodine exhibits metallic luster because it has a crystalline structure where delocalized electrons can reflect light, giving it a shiny appearance.
(v) Which halogen sublimes to violet vapors?
Answer: Iodine sublimes to violet vapors when heated.
(vi) Which halogen is used as an antiseptic?
Answer: Iodine is used as an antiseptic, commonly in the form of tincture of iodine.
(vii) Which halogen is used in water treatment to kill bacteria?
Answer: Chlorine is used in water treatment to disinfect and kill bacteria.
(viii) Name the gas used in earthquake prediction.
Answer: Radon gas is sometimes monitored for earthquake prediction as its levels can rise before seismic activity.
(ix) Name the gas used in bactericidal lamps.
Answer: Mercury vapor is used in bactericidal lamps, which emit ultraviolet light to kill bacteria.
