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Chemistry A-level > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

What is the trend in electronegativity in the halogens? Why?

A

Decreases down the group. Larger atoms attract electrons less than smaller ones, electrons further from nucleus and shielded by more electrons.

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2
Q

What is the trend in boiling point down group 7? Why?

A

Increases down the group. Due to increasing strength of Van der Waals forces as size and relative mass of molecules increases.

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3
Q

Trend in oxidising ability in the halogens?

A

Halogens become less oxidising down the group. A halogen will displace a halide from the solution it the halide is below it in the periodic table.

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4
Q

Trend in reducing ability in the halogens?

A

Increases as you go down the group

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5
Q

Reaction of sodium fluoride with sulphuric acid

A

NaF + H2SO4 → NaHSO4 + HF

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6
Q

Reaction of sodium chloride with sulphuric acid

A

NaCl + H2SO4 → NaHSO4 + HCl

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7
Q

Reaction of sodium bromide with sulphuric acid (2)

A

NaBr + H2SO4 → NaHSO4 + HBr
2HBr + H2SO4 → Br2 + 2H2O

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8
Q

Reaction of sodium iodide with sulphuric acid (3)

A

NaI + H2SO4 → NaHSO4 + HI
2HI + H2SO4 → l2 + SO2 + 2H2O
6HI + SO2 → H2S + 3I2 + 2H2O

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9
Q

Silver nitrate used to test for what ions and how?

A

Test for halides
1) add dilute nitric acid to remove ions which may interfere
2) add silver nitrate solution
Precipitate forms
F- none Cl- white Br- cream I- yellow

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10
Q

Why is silver nitrate used?

A

Silver ions combine with halide ions to produce silver halide precipitates

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11
Q

Why is silver nitrate acidified for testing for ions?

A

Prevents unreacted OH- ions from reacting with silver ions to give an unrecognisable precipitate.

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12
Q

Why is ammonia solution added to precipitates of silver halides

A

To confirm, by checking the solubilities of the halides

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13
Q

What happens when you add NH3 to CI - precipitate

A

Dissolves white precipitate

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14
Q

What happens when you add concentrated NH3 to br- precipitate

A

Cream precipitate dissolves

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15
Q

What happens when you add concentrated NH3 to I- precipitate

A

Yellow precipitate remains as it’s insoluble

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16
Q

Reaction of chlorine with water

A

Chlorine undergoes disproportionation resulting in a mixture of chlorine and chlorate ions
Cl2 + H2O ⇌ 2H⁺ + Cl⁻ + ClO⁻

17
Q

Decomposition reaction of chlorine in sunlight in water

A

Produces chloride ions and oxygen
2Cl2 + H2O ⇌ 4H⁺ + 4Cl⁻ + O2

18
Q

What do chlorate ions do?

A

Kill bacteria

19
Q

Advantages of using chlorine in water treatment (3)

A

Kills disease-causing microorganisms
Some persists in water and prevents infection further down supply
Prevents growth of algae, removing bad tastes and smells as well as colour due to organic compound

20
Q

Disadvantages of using chlorine in water treatment.(2)

A

Chlorine gas is harmful when breathed in. Liquid chlorine on skin or eyes can cause severe chemical burns
Water contains organic compounds which could chlorinated hydrocarbons which can be carcinogenic
Benefits of water treatment outweigh toxic effects.

21
Q

Reaction of chlorine gas with cold, dilute, aqueous NaOH

A

Product is sodium chlorate(I) solution NaClO - bleach
2NaOH + Cl2 → NaClO + NaCl + H2O
Chlorine is oxidised and reduced - disproportionation

22
Q

Uses of NaClO - bleach

A

Water treatment, bleaching paper and textiles and cleaning

23
Q

What is the test for ammonium ions?

A
  • Add NaOH to produce ammonia gas
  • Red litmus paper turns blue
    NH4⁺ + OH⁻ → NH3 + H2O
24
Q

OH⁻ test

A

Dip a piece of litmus paper, in presence of hydroxide ions, red litmus paper turns blue

25
Q

Carbonate ion test

A

Add HCI which produces CO2 - bubble gas through limewater - turns milky/cloudy
CO3²⁻ + 2H⁺ → CO2 + H2O

26
Q

Test for sulfate ions

A

Add dilute hydrochloric acid and barium chloride solution
Produces white precipitate of barium Sulfide
Ba²⁺ + SO4²⁻ → BaSO4

27
Q

Why is HCI added when testing for sulfate ions?

A

Removes any traces of carbonate ions which would produce a precipitate.

28
Q

What would you use to test group 2 ions?

A

Dilute sodium hydroxide solution
Add NaOH dropwise to test tube

29
Q

Magnesium ion in NaOH and in excess

A

With OH- slight white precipitate
In excess - white precipitate

30
Q

Calcium ion in NaOH and in excess

A

In OH- slight white precipitate
In excess - slight white precipitate

31
Q

Strontium ion in NaOH and in excess

A

With OH- slight white precipitate
With excess- slight white precipitate

32
Q

Barium ion in NaOH and in excess

A

No changes

33
Q

Flame tests for calcium, strontium and barium ions.

A

Calcium - brick red
Strontium- red
Barium - pale green

Chemistry A-level (14 decks)

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