12th Class Chemistry Chapter 5 Halogens and Noble Gases Short Question Answers

Chemistry short QA

12th Class Chemistry Chapter 5 Halogens and Noble Gases Short Question Answers Below

1.Why the elements of group VII-A are called halogens?
The term halogen is derived from the Greek halos which means salts and genes mean born.The most of the salts are the derivatives of halogens.
2.How does astatine differ its own family members?
Astatine was discovered in 1940 much after other halogens.It is an unstable element and it is radioactive in nature.Its half life period is 8.3 hours.
3.What are the important ores and minerals of fluorine and iodine?
The important minerals of fluorine and iodine are as follows.
Fluorine:      Fluorsper      CaF2
Cryolite         Na3AIF6
Apatite          [CaF2.3Ca3(PO4)2]
Iodine           NaIO3 and NalO4 are the deposits in Chile brine wells.
4.What is iodized salt?
When sodium iodide is added in a definite ratio with NaCI then it is called iodized salt.Iodine is good for health and this iodized salt is suitable in those areas where there is a deficiency of iodine in water.
5.Compare the physical states and colors of halogens at room temperature?
F2 and CI2 arre gases Br2 is a liquid while I2 is a solid.Fluorine is the yellow gas chlorine is greenish yellow gas bromine is a reddish brown liquid while iodine is a deep violet solid.
6.Why the dissociation energies of halogens go on decreasing down the group?
The size of the halogen atoms go on increasing down the group.Their bond lengths go on increasing.Longer bonds are weaker so their dissociation energies go on decreasing down the group.
7.Halogens are strong oxidizing agents.justify it?
Halognes have tendencies to accept one electron and so they oxidize other species.Anyhow their oxidizing capabilities decrease down the group.Fluorine is the strongest oxidizing agent while iodine is the weakest.
8.Due to which reasons fluorine shows peculiar behavior from other family member?
There are many aspects the size of F and Fᵒ are very small.Fluorine has high intonation potential and electronegativity as compared to other halogens.Moreover its bond dissociation energy is very small as compared to CI2.It has no available d.orbital to expand its oxidation state.
9.How does the hydrogen boding in HF change the properties of this compound from other halogen acids?
HF undergoes extensive hydrogen bonding and forms the zigzag structure.Due to this reason it is the weakest acid among the halogen acids.
10.Arrange the following ions in the order of increasing sizes?
The size of the halogens atoms and halogen ions increase down the group from F-1 to I-1.The reason is the increasing number of shells and increasing shielding effect.
11.What are those factors which affect the oxidizing power of halogens?
These are the electrons affinity values which affect the oxidizing power halogens.The electrons affinities decrease down the group so their oxidizing powers decrease.But fluorine show an exceptional behavior.
12.Why iodine has metallic Iustre?
The melting and boiling points of halogens increase down the group.Iodine is solid at room temperature.This is due to the presence of dispersion forces among the molecules of I2.
13.Why fluorine and chlorine act as decolourizing agents?
They can oxidize dyes to colorless substances.Litmus and universal indicators can be decolorized.Chlorine is used in the bleaching powder which bleaches the substances due to oxidizing capabilities of chlorine.
14.Which halogen is used as an antiseptic?
Iodine is used in the form of tincture of iodine.This medicine is prepared by dissolving iodine in ethyl alcohol.It is antiseptic and kills the germs.
15.Which halogen is used in water treatment to kill bacteria?
Chlorine is used in water treatment.Chlorine is an oxidizing agent and releases atomic oxygen by reacting with water.That atomic oxygen is very reactive and kills the bacteria present in water.
16.How do you compare preparations of halogen acids?
The reaction of H2 and F2 is very fast.HCI and HBr can be prepared form H2 and halogens at high temperature.The reaction of H2 and I2 is very slow and is reversible.
17.How are halogen acids in water?

Halogen acids break the H-X bonds in water.All the HX molecules are polar.Water is also polar.H+ ions after dissociation are converted into hydronium ions.X ions are solvated by water  molecules.In this way the products are stabilized as compared to the reactants.

Anyhow the tendency to be ionized increases from upper to the downward direction.

18.How do you justify the decreasing bond dissociation energy of halogen acids?
Bond dissociation energy of halogen acids go on decreasing from upper to the downward direction.This is due to increasing bond lengths and decreasing differences of electronegativities between hydrogen and halogen.
19.How the thermodynamic properties of halogen acids change in a group from upper to the downward direction?
The heat of fusion and heat of vaporization do not show the regular trend from HF to HI but the gear of formation and bond dissociation energy change in a systematic way.
20.Compare the halogen acids in their reducing properties?
The reducing properties of halogen acids increase from HF to HI.HI is the best reducing agent.It can reduce S to H2S.
21.Why HF is a weaker acid than HCI and HI is strongest in the series?
HF has sufficient hydrogen bonding.H+ ions are entrapped between two strongly electrcnegative atoms of fluorine.So it is difficult for H+ ions to be dispersed in water and to make HF to act as a good acid.The acid strength goes on increasing from HF to HI.HI has least bond dissociation energy.
22.Give the formulas and names of important oxides of chlorine and bromine?
Important oxides of chlorine and bromine are as follows:
Chlorine:     Dichlorine monoxide CI2O
Chlorine dioxide CIO2
Chlorine hexaoxide CI2O6
Chlorine heptaoxide CI2O7
Bromine:         Bromine monoxide Br2O
Bromine dioxide BrO2
Bromine  trioxide Br2O3
23.How do you justify that CI2O7 is the anhydride of perchloric acid?
When  CI2O7  is reacted with water.It gives HCIO4 which shows that CI2O7  is the anhydride of HCIC4.
24.Justify that reaction of chlorine with NaOH in the cold state is disproprotiontion reaction?
CI2 reacts with NaOH is cold state to give NaCI and NaCIO.The oxidation number of chlorine changes from zero to -1 and zero to +1.This is self oxidation-reduction reaction.
2NaOH + CIᵒ2………………. NaCI-1+ NaCIO++H2O
25.Justify that the reaction of chlorine with NaOH in the hot state is disproprotionation reaction?
When chlorine reacts with NaOH in the hot state.NaCI and NaCIO3 are produced.It shows that chlorine atoms change their oxidation number from zero to -1 and +5.This is a self oxidation reduction reaction.
26.Give the names and formulas of oxyacids of chlorine and iodine?
The general formulas for oxyacids of halogens are:
Fluorine does not have such compounds.Moreover bromine  and iodine also do not give HbrO2 and HIO2.
27.How do you compare the stabilities of oxyacids of halogens?
Oxyacids of fluorine do not exist.The oxyacids of other halogens are mostly unstable compounds and can not be isolated in pure form.They are stable in aqueous solution or in the form of their salts.
28.How do you justify the increasing acid strengths of oxyacids of chlorine with increasing no.of O-atoms?
Greater the number of oxygen atoms in the oxyacids greater the polarity of the OH bonds and greater the dissociating powers in the solution of that acid.
29.Why HCIO4 is a stronger acid than HBrO4 than HIO4?
Since the electronegativity of chlorine is greater than bromine which is greater than iodine so acid strengths decrease from HCIO4 to HIO4.
30.HCIO4 may cause explosion.Give reason.Give its preparation?
HCIO4 is a powerful oxidizing agent when it is hot.When it is heated it decomposes with explosion.Pure anhydrous HCIO4 can be prepared by distilling the mixture of KCIO4 and concentrated H2SO4 under reduced pressure.
KCIO4 + H2SO4……………………. KHSO4+HCIO4
conc.                                             Perchloric acid.
It is prepared at a pressure of 10-20 torr.But it is distilled at 40-60ᵒC under a pressure of 60 torr.
31.How bleaching powder can act as an oxidizing agent?
It is due to the presence  of OCI ion.This ion is generated when bleaching powder  is dissolved in water.OCI gives oxygen which oxidizes which oxidizes and bleaches the other substances.
CaCI(OCI)……..H2O………Ca+2 +CI+OCI
32.What do you mean by available chlorine and how is it calculated?
Amount of chlorine which is set free during the reaction of bleaching  powder with acid is called available chlorine.It is calculated  by reacting bleaching powder with H2SO4.The theoretical percentage of available chlorine is 49 but mostly its varies from 35 to 40%.
33.How does bleaching powder act as an oxidizing agent towards halogen acids?
When bleaching powder is reacted with HCI HBr,and HI then CI2 Br2 and I2 are produced.In other words halogen acids are oxidized.The oxidation number of halogens increase from-1to zero.
34.How does bleaching powder act as a bleaching agent for fabrics?
Bleaching powder can bleach cotton linen pulp and wood pulp.The colored matter is oxidized and becomes colorless.
35.What are freons.Give there uses?
Chlorofluorocarbons obtained from CCI4 are called freons.It is a mixture of CCI2F2 and CCIF3.They are used as solvents lubricants insulators and in refrigeration.
36.What is teflon.Give its uses?
When C2F4 is polymerized.It give called telfon.It is used in the construction of chemical planets.It is used as insulating in cables.
37.Give important uses of chlorine?
Chlorine acts as a bleaching agent in the manufacture of antiseptics insecticides weed killers and herbicides.It is also used for the preparation of HCI,PVC.CHCI3and CCI4.
38.Give the important uses of bromine and iodine?
Bromine is used for the preparation of C2H4Br2 which acts as germicide fungicide and as an oxidizing agent.AgBr is used in photography.Iodine is used in pharmaceutical industries and in the prepatation of tincher of iodine and as an analgesic.I2 is used in the preparation of iodoform and dyes.
39.Why the elements of group VIII-A are called noble gases?
The elements of group VIII-A have complete outermost orbitals.So they do not show tendency to react with others.That is why they are chemically inert and are though to be noble in reactivity.
40.What are noble gases.Why are they inert?
Elements of group VIII i.e.He Ne,Ar,Kr,Xe, and Rn are noble gases.They have fulfilled outer shell and are least reactive.Their least reactivity makes then inert.
41.Why the oxidation states of noble gases are usually zero?
The oxidation states of element develop due to incomplete shell.Noble gases have complete shells,so have zero oxidation states.
42.How does radon differ from its own family members?
Radon is present is very small amounts in air.It is radioactive and it is the decay product of Ra226.
43.How the solubilities of noble gases are affected in water?
They are least soluble in water.Xe is slightly soluble in water that is 110 cm3 in 1 dm3 at 20ᵒC.Anyhow solubility increases down the group.
44.Give the important applications of helium and argon?
Helium is used in the treatment of asthama filling of weather balloons producing low temperature preservation of food creating inert atmosphere and in welding.It is used in signal lights and atomic reactors.Argon is used in filling electrical bulbs in Geiger counter producing inert atmosphere filling fluorscent tubes and mixing with neon in neon signs.
45.Give the important uses of radon?
Radon is used in the radiotherapy of cancer earthquake predictions preparation of ointments for the treatment of cancer and photographing the interior of opaque materials.
46.What is the effect of high voltage on noble gases?
When noble gases are maintained at low pressure in the discharge tube and electric current is passed through them spectra of different colors are produced.These spectra are utilized in advertising lamps.

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