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12th Class
12th Class Punjab
Chemistry
Chemistry Short Question
The Halogens And The Noble Gases Short Questions Preparation

Chapter 5 The Halogens And The Noble Gases Chemistry 12th Class Punjab Short Questions

Question No. 1 - What is Halothane? Write its formula.

Answer No. 1 - Definition: Chemical compounds of halogens with ethylene is called halothane.
Formula: Fluorine is used to firm Teflon-CF2-CF2-n.

Question No. 2 - Why the lattice energy of Fluorides is greater than Chlorides?

Answer No. 2 - Due to small size of fluoride ionsf, there will be a better overlap of orbitals and consequently leads to shorter and stronger bonds with other elements. Ionic fluorides have higher lattice energies than the chlorides and the value is responsible for the insolubility of the fluorides in water. Due to low dissociation energy of fluorine molecule, it is highly reactive. The other halogens react slowly under similar conditions. The fluorides are, however more stable with respect to dissociation into elements.

Question No. 3 - Give reason that fluorine is gas, iodine is solid?

Answer No. 3 - Iodine molecule has larger size than fluorine. The intermolecular attraction is greater in the larger molecule having greater masses. Due to the larger size of iodine molecule the van der Wall forces are stronger than smaller size molecule of fluorine.

Question No. 4 - The elements of group VIII-A are called noble gases. Comment?

Answer No. 4 - Elements of group VIII-A are called noble gases because, these elements are colourless, odourless monoatomic gases which are chemically un-reactive.

Question No. 5 - Compare halogen acids in their reducing properties?

Answer No. 5 - HF, HCI, HBr and HI acts as reducing agents in the following order:
HF

Question No. 6 - Why oxidizing power of halogens decreases down the group?

Answer No. 6 - Oxidizing power of halogens depends upon the following factors:
1. Energy of dissociation
2. Electron affinity of atoms
3. Hydration energy if ions
4. Heat of Vaporization
While going down the group all above mentioned factors decreases. All the free halogens acts as oxidizing agents when they reacts with metals or non metals. On forming ionic compound with metals, the hydrogens as gain of electrons and are converted to negative halide ions.

Question No. 7 - What is meant by available chlorine?

Answer No. 7 - If excess of an acid is added to bleaching powder, chlorine is given out. The amount of chlorine thus set free is called available chlorine. The activity of bleaching powder is measured in terms of available chlorine. The average percentage of available chlorine in bleaching powder is 35-40%.

Question No. 8 - Why iodine has metallic luster?

Answer No. 8 - Due to big size of lodine outer electrons are excited by taking light and due to excitation and de-excitation gives metallic luster.

Question No. 9 - Write two uses of halogen?

Answer No. 9 - 1. Fluorine is used for the preparation of freons, which is
being used in refrigerator and aerosol propellants.
2. Chlorine is used in the manufacturing of bleaching
powder.

Question No. 10 - HXO4 is strongest oxyacid. Explain.

Answer No. 10 - The acidic strength increase with the increase in the number of oxygen atoms. As the oxidation state of the halogen increase the bonding electrons are shifted away from the H-atom and the tendency of the molecule to loss a proton increase. This accounts for the change of strength of oxyacids, HXO4 has four oxygen atom, so it is strongest oxyacid.

Question No. 11 - Why Fluorine acts as a strong oxidation agent?

Answer No. 11 - Oxidizing power of fluorine is higher, because it has low energy of dissociation and higher hydration energy of its ions. Due to the relative strength as oxidizing agents, it is possible for each free halogen to oxidize the ions of other halogens next to it in the family. Fluorine can oxidize all the halide ions molecule halogens.

Question No. 12 - How bleaching powder is prepared by Hasenclever method?

Answer No. 12 - The apparatus used in this method consists of 4 to 8 iron cylinders placed one above the other horizontal. They are interconnected and provided with stirrers. The slaked lime is added in through a hopper in the upper cylinder and transported from one cylinder rises p and reacts with slacked lime form bleaching powder, which is collected through the outlet in the lower cylinder.

Question No. 13 - Describe factor of acidic strength of oxyacids of halogens?

Answer No. 13 - 1. Number of oxygen atoms attached to the oxyacid halogens.
2. Oxidation state of hydrogen in oxyacid of halogens.
3. Tendency to lose proton from oxyacid of halogens.

Question No. 14 - Arrange the following oxyacids in increasing order of acid strength and oxidizing power; HCIO4>HCIO2>HCIO

Answer No. 14 - HCIO4>HCIO2>HCIO

Question No. 15 - What are the commercial use of halogens and their compounds?

Answer No. 15 - 1. Fluorine is used for the preparation of ferons. Which is
being used in refrigerants and aerosol propellants.
2. Fluorine is used to prepare Teflon.
3. Iodine is used in pharmaceutical industries as
disinfectants and germicides.

Question No. 16 - Write two use of bleaching powder?

Answer No. 16 - Bleaching powder is used :
1. For the laboratory preparation of chlorine and oxygen.
2. For making unshrinkable wool.

Question No. 17 - Halogens are strong oxidizing agents. Justify.

Answer No. 17 - All the free halogens acts as oxidizing agents when they reacts with metals or nonmetals. On forming ionic compounds with metals, the halogen s gain electron and are converted to negative halide ions.

Question No. 18 - Why HF is weaker acid that other halogen acid?

Answer No. 18 - In water hydrogen halides give hydrofluoric, hydrochloric, hydrobromic and hydroiodic acid. The strength hydrogen halogen bond is very high in HF.The bond strength is reflected in the case of dissociation of hydrogen and halides. Hydrofluoric acid is week acid due to limited ionization. The other three acid are very strong acids. The acidic strength increase in order.

Question No. 19 - Give two used of bromine?

Answer No. 19 - Ethylene dibromide added to gasoline to save the engine from lead oxide and leaf sulphate deposits. Bromide is also used as fungicide. Silver bromide is used in photography.

Question No. 20 - What are the major application of Neon?

Answer No. 20 - Neon is largely is used in making neon advertising signs in high voltage indicators and TV tubes. Neon and helium arc is used in making glass laser.

Question No. 21 - Define "disproportion reaction".

Answer No. 21 - A reaction in which a species molecule atom or ion is simultaneously oxidized and reduced is called disproportion reaction.

Question No. 22 - What is iodize salt?

Answer No. 22 - When sodium or potassium iodine is added to the common salt, then the common salt is called iodized salt.

Question No. 23 - Write four properties of hydrogen fluorides?

Answer No. 23 - 1. HF is a colourless volatile liquid.
2. HF attacks glass and has found application as non
aqueous solvent.
3. HF has meeting point as -83.8 degree,
4. HF has boiling point as 19.5 degree.

Question No. 24 - Write two application of noble gases?

Answer No. 24 - 1. Helium is used in weather balloons, in welding and in
traffic signal light.
2. Helium is used as a cooling medium for nuclear laser.
3. Argon is used for arc welding and cutting.

Question No. 25 - Give uses of iodine.

Answer No. 25 - The major application of iodine are in pharmaceutical industry. It is used as disinfectants and germicides. Tincture of iodine and iodex are popular preparation of iodine. Diet with insufficient iodine ions leads to an enlargement of the thyroid. To ensure the present of iodine ion in the diet, sodium or potassium iodine is added to the common salt which is known as iodized salt.

Question No. 26 - What is peculiar behaviour of Fluorine?

Answer No. 26 - The halogen form a homologous series but fluorine differ from the other halogens in many respects which is due to :
1. Small in size of D atom and F ion.
2. High first ionization energy and electronegativity.
3. Low dissociation energy of F2 molecule as compared to
CI2and Br2.
4. Restriction of the valence shell to an octet.
5. Direst combination with inert gasses.

Question No. 27 - Arrange the following ions in order of increasing size F, CI, Br, I.

Answer No. 27 - F

Question No. 28 - How halogen acids are ionized in water?

Answer No. 28 - In water hydrogen halides give hydroflorine, hydrochloric, hydrobromic and hydrochloric acids. Hydrofluoric acid is week acid due to limited ionization. The other three acids are vert strong acid. The acidic strength increases in the order.

Question No. 29 - Give two application of Radon gas.

Answer No. 29 - 1. Radon is being radioactive is used in earthquake
prediction.
2. Radon being radioactive is used in radiotherapy for
cancer.

Question No. 30 - What are noble gasses? Why are they inert?

Answer No. 30 - Elements of group VIII-A are called noble gases because these elements are colourless odourless monatomic gases which are chemically unreactive.
Noble gases are inert due to the completion of their outermost shell. These gases have complete electronic configuration and have filled duplet and octet.

Question No. 31 - On what factor oxidizing power of halogens depends upon?

Answer No. 31 - 1. Energy of dissociation
2. Electrons affinity of atoms
3. Heat of vapourization

Question No. 32 - What are ferons and Teflons?

Answer No. 32 - Ferons: Fluorine is used for the preparation of freons. Freons is the commercial name of low molecular mass fluoro chloro carbons. These are being used as the refrigerants and aerosol propellants.
Teflons: Fluorine is used for the preparation of Teflon,It is polymerized tetrafluoroethylene compound. It is valuable plastic which resists the action of oxidants, acid and alkalies.

Question No. 33 - Why oxidizing power of F2 is higher than other halogens?

Answer No. 33 - Oxidizing power of F2 is higher ,because it has low energy of dissociation and higher hydration energy of its ions. Due to the relative strength as oxidizing agents it is possible for each free halogens to oxidize the ions of other halogens next to it in the family.

Question No. 34 - Perchloric acid is considered as valuable analytical reagent. Why?

Answer No. 34 - Due to oxidizing effect of perchloric acid it is considered as valuable analytical reagent.

Question No. 35 - HF is a weak acid while HCI is strong acid. Give reason.

Answer No. 35 - The strength hydrogen halogen bond is very high in HF. The bond strength is reflected in the case of dissociation of hydrogen and halides. Hydrofluoric acid is a week acid due to limited ionization than hydrochloric acid.

Question No. 36 - Write any two use of Krypton?

Answer No. 36 - Krypton is used to fill fluorescent tubes and in flash lamps for high speed photography.

Question No. 37 - What is bleaching powder?

Answer No. 37 - Bleaching powder is yellowish white powder with strong smell of chlorine and is used to bleach different things. It has chlorine known as "available chlorine".

Question No. 38 - Give one method of preparation and one use of I2O5?

Answer No. 38 - Preparation: It can be prepared by heating iodic acid at 240° Degree, it is used for the quantitative analysis of CO.

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