Topic 4b - Group 7 Flashcards Preview

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Flashcards in Topic 4b - Group 7 Deck (18):
1

What is the trend in melting/ boiling points as you go down group 7

They increase because the number of electrons in the molecule and the surface area of contact between molecules increases therefore the intermolecular forces (London forces) increase

2

What is the trend in X-X bond strength going down group 7

It decreases as the size of X increases and the bond length increases therefore the orbital overlap is less effective (EXCEPTION F-F BOND IS WEAK AS IT IS SHORT)

3

What is the trend in the H-X and C-X bonds going down group 7

It decreases as the size of X increases and bond length increases less effective orbital overlap

4

Equation and conditions of reaction of chlorine and hydrogen

Cl2 + H2 -> 2HCl
In sunlight

5

Equation and conditions of reaction of bromine and hydrogen

Br2 + H2 -> 2HBr
300C & Pt catalyst

6

Equation and conditions of reaction of iodine and hydrogen

I2 + H2 -> 2HI
300 C & Pt catalyst
(Slow and reversible)

7

How do distinguish between I2 and Br2

Add chlorine water to a solution of X- ions
- if Br- is present solution goes orange
- if I- is present solution goes brown & black precipitate may form

8

Test for halide ions

CHLORINE turns damp red litmus paper white and blue litmus paper red then white
BROMINE turns damp red litmus paper white slowly and will turn starch-iodide paper blue-black
IODINE turns blue-black with starch

9

Equation for reaction of chlorine and water

Cl2 + H2O -> HCl + HOCl


HOCl + H2O -> H3O + OCl-

Has to be stored in brown bottle away from sunlight or else:
2HOCl -> 2HCl + O2

10

Equation of reaction of chlorine and cold alkali (15c)




Cl2 + 2OH- -> Cl- + ClO- + H2O

11

Equation for reaction of chlorine with cold alkali heated

3ClO- -> ClO3- + 2Cl-

12

Equation for reaction of chlorine with hot alkali (60 degrees)

3Cl2 + 6OH- -> 5Cl- + ClO3- + 3H2O

13

How do you test for halide ions with aqueous silver nitrate

Add dilute aqueous nitric acid (HNO3) to destroy any OH- (brown ppt) or CO3-- (cream ppt) ions which may interfere. Then add AgNO3

14

What are the result when you test a halide ion with aqueous silver nitrate AgNO3

- AgF no ppt (soluble in dilute & conc ammonia)
- AgCl white ppt (soluble in conc ammonia not dilute)
- AgBr cream ppt (not soluble in ammonia)
- AgI primrose yellow ppt (not soluble in ammonia)
- AgAs dark yellow ppt (not soluble in ammonia)

15

Reaction of chlorine with concentrated sulfuric acid

KCl + H2SO4 -> KHSO4 + HCl(g)

Stops at first step
Steamy fumes of HCl test with stopper from bottle of ammonia solution gives white smoke

16

Reaction of bromine with concentrated sulfuric acid

KBr + H2SO4 -> KHSO4 + HBr

2HBr + H2SO4 -> Br2 + SO2 + 2H2O

Steamy fumes of HBr & orange liquid Br2

17

Reaction of iodine with concentrated sulfuric acid

KI + H2SO4 -> KHSO4 + HI

6HI + H2SO4 -> 3I2 + S + 4H2O

8HI + H2SO4 -> 4I2 + H2S + 4H2O

Yellow solid - S
Rotten egg smell - H2S
Steamy fumes - HI
Black solid - I2

18

Reaction of hydrogen halide with water

HX + H2O -> H3O + X-

All HX form strong acids in water except for HF as the H-F bond is small and strong

2HF + H2O -> H3O+ + HF-