8 Reactivity Trends

Question 1

What is the trend in reactivity down group 2?

Answer 1

More reactive down group

Question 2

Why does reactivity change down group 2?

Answer 2

More shells, bigger atomic radius
More shielding, weaker nuclear attraction all outweighs greater nuclear charge
So first and second ionisation energy decrease down group so less energy to form 2+ ion down group there fore more reactive

Question 3

What is the trend in solubility down group 2 hydroxides?

Answer 3

More soluble down group 2

Question 4

What does magnesium hydroxide look like in aqueous soloution and why?

Answer 4

Slight white precipitate as only slightly soluble in water

Question 5

What does Barium hydroxide look like In aqueous soloution and why?

Answer 5

Colourless, soluble In water

Question 6

What is the trend in alkalinity in group 2 hydroxides and why?

Answer 6

More soluble down group so greater OH- concs so more alkaline down group

Question 7

What is calcium hydroxide used for?

Answer 7

Neutralises acidic soil

Question 8

What group 2 compounds can be used to treat indigestion? And why?

Answer 8

Mg(OH)2 (milk of magnesia), CaCO3

Used as bases to neutralise HCL in stomach

Question 9

Method for experiment to show trend in solubility and alkalinity of hydroxide?

Answer 9

Add spatula or metal oxides In water test tube and shake
Not much water so saturated solution therefore precipitate of hydroxides in tube
Measure PH of soloution w litmus paper
Alkalinity (and solubility) increases down group

Question 10

Explain the trend in BP of halogens?

Answer 10

More electrons down group
Greater London forces
More energy to overcome forces
Increased BP down group

Question 11

Appearance of F2 at RTP

Answer 11

Pale yellow gas

Question 12

Appearance of Cl2 at RTP

Answer 12

Pale green gas

Question 13

Appearance of Br2 at RTP

Answer 13

Brown liquid

Question 14

Appearance of I2 at RTP

Answer 14

Grey black solid

Question 15

Appearance of At2 at RTP?

Answer 15

Not seen

Question 16

Appearance of Cl2 in H20?

Answer 16

Pale green liquid

Question 17

Appearance of Br2 in H20?

Answer 17

Orange liquid

Question 18

Appearance of I2 in H20?

Answer 18

Brown liquid

Question 19

Appearance of Br2 in Cyclo hexane?

Answer 19

Orange liquid

Question 20

Appearance of Cl2 in Cyclohexane?

Answer 20

Pale green liquid

Question 21

Appearance of I2 in cyclohexane?

Answer 21

Violet liquid

Question 22

Why do we add cyclohexane to halogens?

Answer 22

To distinguish between Br2 and I2 as they look similar in water, I2 is violet in cyclo hexane

Question 23

Explain the trend in reactivity in halogens?

Answer 23

Down group there is
Bigger atomic radius,more shells,more shield
Ing ( this outweighs increase nuclear charge)
So nuclear attraction decreases down group
Therefore harder to gain an electron to become an X- ion down group
So less reactive down group

Question 24

What is a disproportionate on reaction

Answer 24

Same element is simultaneously oxidised and reduced

Question 25

What is the reaction between Cl2 and H20? W names of products ?

Answer 25

Cl2 + H20 makes HCl + HClO Hydrochloric acid Chloric(I) acid

Question 26

What does chloric acid do?

Answer 26

Kill a bacteria | Acts as a weak bleach

Question 27

How do we demonstrate chloric acids bleaching ability?

Answer 27

Add indicator to chlorine in water | Turns red bc acidic and then goes colourless as is bleached

Question 28

What do we react Cl2 with to get concentrated bleach?

Answer 28

Cold dilute aqueous NaOH

Question 29

Why do we get concentrated bleach from Cl2 in NaOH and not water ?

Answer 29

Cl2 not very soluble in water so low conc of Chlorate(I) ions formed

Question 30

Write equation for Cl2 in cold dilute aqueous NaOH

Answer 30

Cl2 + 2NaOH makes Nacl + NaClO +H20

Question 31

Why is chlorine dangerous ?

Answer 31

Chlorine gas is very toxic

Question 32

How do u test for carbonate? Reagent,equation,positive result

Answer 32

Dilute nitric acid CO3^2- (aq) + 2HNO3 (aq) -> H20(l) + CO2 (g) + NO3^- Positive test: effervescence

Question 33

How do u prove the gas from carbonate test is CO2? (W equation)

Answer 33

Bubble through like water (Ca(OH)2) will turn cloudy | Ca(OH)2 + CO2 -> CaCO3 (s) + H20

Question 34

How do u test for sulfates? Reagent,equation,positive result

Answer 34

Ba(NO3)2 Ba (aq) + SO4^2- -> BaSO4 (s) Positive : white ppt

Question 35

How do u test for a halide ? Reagent,equation,positive result

Answer 35

``` AgNO3 Ag^+1(aq) + X^-1 (aq) -> AgX (s) Positive: AgCl white ppt AgBr cream ppt AgI yellow ```

Question 36

Further test to distinguish Silver halides?

Answer 36

AgCl dissolves in dilute NH3 AgBr dissolves in conc NH3 AgI insoluble in NH3

Question 37

What sequence do we do tests in and why?

Answer 37

Carbonate then sulphate then halide -first use up all carbonate ions if present so no BaCo3 white precipitate -then use all sulfate ions present so no Ag2SO4 or Ag2CO3 as both are white precipitates Eliminates false positives

Question 38

Test for ammonium ion

Answer 38

Warm NaOH NH4^+1 (aq) + OH^-1 (aq) -> NH3 (g) + H20 (l) Will smell, test w indicator paper will go blue bc alkaline gas