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chemistry > P block - 17 and 18 > Flashcards

P block - 17 and 18 Flashcards

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1
Q

which is the major noble gas in the atmosphere

A

argon

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2
Q

which is the main commercial source of helium

A

natural gas

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3
Q

how was oganesson synthetically produced

A

collision of Cf atoms and Ca ions

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4
Q

What is the trend of ionisation enthalpy

A

generally decreases down the group

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5
Q

Which element in group 18 has largest ionisation enthalpy

A

Neon

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6
Q

Why do noble gases have low bp and mp

A

the only interaction in these elements is weak dispersion force

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7
Q

What is the colour of O2(+)PtF6(-)

A

Red

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8
Q

Why was Xe(+)PtF6(-) made

A

same first ionisation enthalpy as oxygen

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9
Q

What are the three fluorides xenon forms

A

XeF2, XeF4, XeF6

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10
Q

What are the conditions required to form xenon fluorides

A

for XeF2 - 673K, 1 Bar
XeF4 - 873k, 7Bar
XeF6 - 573K, 60-70 Bar

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11
Q

What happens when XeF4 and O2F2 interact at 142 K

A

XeF6 is formed

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12
Q

What are the structures of xenon fluorides

A

XeF2 - linear
XeF4 - square planar
XeF6 - distorted octahedral structure

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13
Q

How to prep XeO3 and what are its properties

A

Hydrolysis of XeF4 and XeF6 gives XeO3. It is a colourless explosive solid with a pyramidal molecular structure

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14
Q

How to prep XeOF4 and what are its properties

A

partial hydrolysis of XeF6 . Colourless volatile liquid with a square pyramidal structure

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15
Q

Does the hydrolysis of XeF6 lead to a redox reaction

A

No, the products are XeOF4 and XeO2F2 where the oxidation states of all elements remain the same

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16
Q

What is the trend of electron gain enthalpy in group 17

A

FBr>I . F is small - interelectronic repulsion

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17
Q

What are the trend of melting and boiling points

A

increase down the group

18
Q

What are the colours of different halogens

A

F2- yellow, Cl2- greenish-yellow, Br2 - red, I2- violet

19
Q

Comment on the solubility of group 17

A

F and Cl react with water. Br and I are sparingly soluble in water. They react with organic solvents like chloroform, CCl4, carbon disulphide and hydrocarbons to give coloured solutions

20
Q

What is the trend for oxidising ability in group 17

A

they are oxidising agents because of their tendency to accept electrons. F2 is the strongest oxidising halogen. It decreases down the group.

21
Q

What happens when halogens react with water

A

Fluorine oxidises it to Oxygen. cl and br react to form corresponding hydrohalic and hypohalic acids. I + H2O is non-spontaneous. I can be oxidised by O in acidic medium.

22
Q

What does the oxidising ability of group 17 depend on

A

Enthalpy of dissociation, electron gain enthalpy, enthalpy of hydration

23
Q

What are anomalies in F

A
  • only one oxoacid
    HF is a liquid ( due to H-bonding) - others are gases
  • higher ionisation enthalpy, EN, electrode potential
  • lower radii, mp, bp, egh, enthalpy of bond dissociation
24
Q

What is the acidic strength of hydrohalic acids

A

HF

25
Q

What is the stability of hydrohalic acids

A

HF>HCl>HBr>HI due to decrease in bond dissociation enthalpy

26
Q

What are the oxides of fluorine

A

OF2 (stable), O2F2

27
Q

What is the order of stability of oxides of group 17

A

I>Cl>Br. I has greater polarisability. Cl has multiple bond formation between cl and O due to d orbital. Br lacks both. Higher oxides have more stability than lower ones.

28
Q

Are oxides of halogens good oxidising agents

A

Yes, they are very powerful

29
Q

What is the trend of ionic character of metal halides

A

MF>MCl>MBr>MI. Higher oxidation state is more covalent than the lower one.

30
Q

How can Cl2 be prepared

A

By heating MnO2 with conc HCl ( mixture of NaCl and H2SO4 can be used in place of HCl)
By the action of HCl on KMnO4

31
Q

How is Cl2 manufactured

A

Deacons process: oxidation of HCl gas by atmospheric O2 in presence of CuCl2 at 723 K
Electrolytic process: electrolysis of brine. Cl is liberated at anode

32
Q

What is the reaction of Cl2 with alkalies

A

cold and dil alkalis - mixture of chloride and hypochlorite

hot and conc alkalies - chloride and chlorate

33
Q

What is the reaction of Cl2 with hydrocarbons

A

saturated - substitution products

unsaturated - addition products

34
Q

What is responsible for bleaching properties of chlorine

A

Hypochlorous acid - HOCl - gives nascent oxygen

35
Q

How to prep HCl

A

NaCl+ H2SO4 at 420K gives NaHSO4 and HCl

NaHSO4 + NaCl at 823K gives Na2SO4 + HCl

36
Q

What is aqua regia

A

3 parts HCl and 1 part HNO3

37
Q

What is the oxoacid formed by fluorine

A

HOF - fluoric (I) acid or hypofluorous acid

38
Q

How are interhalogen compounds prepared

A

Direct combination with specefic conditions

39
Q

What are properties of interhalogen compounds

A
  • diamagnetic
    -volatile solids of liquids (except ClF)
  • mp and bp are higher than expected
    more reactive than halogens (except f)
40
Q

What are the molecular structures of interhalogen compounds

A

XX3 has bent T shape
XX5 has square pyramidal
IF7 has pentagonal bipyramidal

chemistry (3 decks)

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