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Physical Chemistry > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

What is the reactivity down group 2? How does it compare to the reactivity of group 1?

A

Reactivity increases:
- easier to lose 2 outer electrons due to increasing atomic radius and more electron shielding = decreasing ionisation energy
Same as group 1

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2
Q

What is an oxidising agent?

A

Causes another species to be oxidised (it itself gets reduced)

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3
Q

What is a reducing agent?

A

Causes another species to be reduced (it itself gets oxidised)

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4
Q

Are group 2 elements reducing agent or oxidising agent?

A

They lose 2 electrons so are oxidised = reducing agents

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5
Q

Why do melting points decrease down group 2?

A
  • atomic radius increases down the group = weaker forces of attraction between the positive ions and delocalised electrons
  • requires less energy to break = decreasing melting points
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6
Q

Which element’s melting point is an exception?

A

Magnesium as it’s lower than expected

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7
Q

Which redox reactions do group 2 elements occur in?

A

Metal + oxygen -> metal oxide
Metal + water -> metal hydroxide + hydrogen
Metal + acid -> salt + hydrogen

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8
Q

How can you check if something is a redox reaction?

A

Check the ionisation energies
See if one element is oxidised and one is reduced

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9
Q

What happens when oxides of group 2 elements react with water?

A

Hydroxide ions are released and form alkaline solutions of the metal hydroxides
Group 2 hydroxides are only slightly soluble in water

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10
Q

What is the trend in solubility down group 2?

A

Increases down the group as more hydroxide ions are released which makes the solution more alkaline

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11
Q

What group are the halogens?

A

Group 17

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12
Q

What is the trend in reactivity down group 17?

A

Decreases down the group:
- group it react by gaining an electron
- as atomic radius & electron shielding increase down the group, nuclear attraction to outer electrons decreases which makes it less easy to gain/pull electrons

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13
Q

What intermolecular forces do halogen molecules ( F2, H2, CI2) have?

A

Only London forces (electro-negativities cancel so cannot have permanent dipole- dipole interactions)

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14
Q

What is the trend in mp/bp for halogens down the group? Why this trend?

A

MP/ BP increases down the group:
- more electrons down the group so stronger London forces
- require more energy to overcome the stronger forces = higher mp/bp

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15
Q

What are the physical appearances and states of the halogens?

A

Fluorine: pale yellow gas
Chlorine: pale green gas
Bromine: red-brown liquid
Iodine: shiny grey-black solid
Astatine: never been seen

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16
Q

What are the 2 uses of group 2 compounds?

A
  1. In agriculture - lime water (calcium hydroxide) added to fields to neutralise the acid in the soil/increase the pH of acidic soils
  2. In medicine - magnesium hydroxide or calcium carbonate used in antiacid medication to neutralise excess stomach acid / treating acid indigestion
17
Q

What is the acid + base reaction?

A

ACID + BASE -> SALT + WATER

18
Q

What happens when universal indicator is added to HClO (hypochlorous acid)?

A

First turns red as it’s an acid then the colour disappears as bleaching action takes action

19
Q

Why is chlorine added to water?

A

Used as a disinfectant for drinking water
Hypochlorous acid (HClO) produced kills bacteria and acts as a weak bleach

20
Q

What happens if chlorine reacts with NaOH?

A

Much more chlorine dissolved than when in water as it is less soluble in water

21
Q

What are chlorine reacting with water & chlorine reacting in with cold, dilute aqueous sodium hydroxide examples of?

A

Disproportionation reactions (chlorine)

22
Q

What are the risks of chlorine use?

A
  • toxic gas
  • respiratory irritant in small concentrations
  • fatal in large concentrations
  • if it reacts with hydrocarbons, chlorinated hydrocarbons form which are suspected carcinogens
23
Q

What colours do Cl2, Br2, I2 form in water and cyclohexane?

A

Cl2 - pale green in both
Br2 - orange in both
I2 - brown in water, violet in cyclohexane

24
Q

What is the test for carbonate ions?

A
  • add nitric acid
  • effervescence will be observed as gas is produced
  • to prove it is CO2 (from the carbonate ions) bubble it through limewater (Ca(OH)2) which will turn cloudy
25
Q

What is the equation of CO2 with limewater (Ca(OH)2)?

A

CO2 + Ca(OH)2) -> CO3 + H2O

26
Q

What is the test for sulfate ions?

A
  • add a solution that contains aqueous barium ions (e.g. barium nitrate)
  • if sulfate ions present, insoluble barium sulfate forms as a white precipitate
27
Q

What is the ionic equation for the sulfate ion test?

A

Ba^2+ (aq) + SO4^2- (aq) -> BaSO4 (s)

28
Q

What is the test for halide ions?

A
  • add a solution that contains aqueous silver ions (e.g. silver nitrate solution)
  • if halide ions are present an insoluble silver halide precipitate forms
  • silver halide precipitates have different colours
29
Q

What is the ionic equation for the halide ion test?

A

Ag^+ (aq) + X^- (aq) -> AgX (s)

30
Q

What are the colours of the precipitates formed in the halide test?

A

Chlorine = white precipitate
Bromine = cream precipitate
Iodine = yellow precipitate

31
Q

What sequence should the tests be done? Why?

A

1) carbonate - can result in false positives (white precipitate) forming in both the sulfates and halide tests
2) sulfate - can result in false positives (white precipitate) in halide tests
3) halide

32
Q

What is the ammonium ion test?

A

1) Add an aqueous hydroxide
2) Warm gently -> if ammonium ions present, ammonia gas will be released (an alkali)
3) Damp red litmus paper will turn blue in the presence of ammonia gas

33
Q

What is the equation for the ammonium ion test?

A

NH4^+ (aq) + OH- (aq) -> NH3 (g) + H2O (l)

Physical Chemistry (7 decks)

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