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My AS Level Chemistry - OCR A > 8.1(3.1.2) - Reactivity Trends > Flashcards

8.1(3.1.2) - Reactivity Trends Flashcards

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1
Q

Name of Group 2 elements

A

Alkaline earth metals

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2
Q

What form are group 2 elements usually found in?

A

Oxides, as are very reactive

E.g. CaCO3

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3
Q

Most common type of reaction in Group 2 metals

A

Redox reactions
They are seen as reducing agents
They reduce another species in the reaction

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4
Q

Redox reaction of group 2 with oxygen

A

All react with oxygen to form a metal oxide
E.g. Magnesium reacts with oxygen in the air
Burns with a very bright white light
Forms magnesium oxide

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5
Q

Oxidation number changes in redox of magnesium with oxygen

A

Each Mg increases by +2 - (2Mg so +4)

Each O decreases by -2 - (O2 so -4)

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6
Q

Redox reactions of group 2 with water

A

React with water to form an alkaline hydroxide and hydrogen gas.
Water and Mg reacts slowly
Reaction becomes more vigorous with metals further down the group
Therefore reactivity increases down the group

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7
Q

Oxidation no.s in redox with water(group 2)

A

E.g Sr + 2H2O —> Sr(OH)2 + H2
Sr increases by 2(+2)
Two H decrease by 1 forming H2
Two H don’t change - forming Sr(OH)2

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8
Q

Group 2 redox reaction with dilute acids

A

Metal + acid —> salt + hydrogen
Mg - +2 so is oxidised
2H in HCl - each H decreases by 1 (-2 in total)

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9
Q

Group 2 trend in reactivity and ionisation energy

A

Reactivity increases down the group

Ionisation energy decreases down the group

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10
Q

Explanation for Group 2 trends in reactivity and ionisation energy

A

Ionisation energies decrease because:
Atomic radius and shielding increases
So attraction to nucleus decreases
Reactivity increases because ionisation energy decreases when forming 2+ ions/losing electrons more readily to react.

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11
Q

Reaction and equation for formation of bleach

What are the conditions needed?

A

Cl2(aq) + 2NaOH(aq) —> NaClO(aq) +NaCl(aq) + H2O(l)

Conditions required:

  • Dilute aqueous sodium hydroxide
  • cold conditions
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12
Q

What is a disproportionation reaction?

A

Where an element in a reaction is both oxidised and reduced

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13
Q

Trend in reactivity of the halogens and explanation

A

-Reactivity decreases down the group
Explanation:
-Atomic radius increases
-More inner shells so shielding increases
-Less nuclear attraction to capture an electron
-Reactivity decreases

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14
Q

What colour are some of the halogens?

A

Bromine - Orange/Yellow
Chlorine - pale yellow
Iodine - Brown in solution and purple when a gas

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15
Q

Which halogens displace others and why?

A

H

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16
Q

Trend in melting point of the halogens

A

-Boiling and melting point increase down the group

Explanation:

  • Elements have more electrons down the group
  • So they have more/stronger London Forces
  • More energy is required to break more/stronger intermolecular forces
  • So boiling point increases
17
Q

What is a redox reaction?

A

A redox reaction is a reaction in which one element is reduced and another element is oxidised

18
Q

What is oxidation?

A

Loss of electrons

19
Q

What is reduction?

A

Gain of electrons

20
Q

How to test for displacement reactions in halogens - full mechanism

A

-Add solution of each halogen to aqueous solutions of the other halides
-e.g. add Cl2 to solutions of NaI and NaBr
-If the halogen added is more reactive than the halide present then:
-A reaction takes place, the halogens displaces the glide from solution
-The solution changes colour
-Colours in solutions for halogens are as follows:
-Iodine is brown
-Bromine is orange
-Chlorine is pale green
-Add a solution of cyclohexane to each test tube and shake the mixture fully tell them apart
The colours of the halogens in solution of cyclohexane are as follows:
-Chlorine - pale green
-Bromine - orange
-Iodine - violet
-Then displacements can be shown by presenting reactions as ionic equations - more reactive halogen displaces present halide ion

21
Q

Benefits and risks of chlorine use

A

Pros:

  • Used in water treatment
  • Helps kill bacteria in drinking water(makes it drinkable and safe) and in swimming pools

Cons:
-Chlorine is toxic to humans(in larger quantities) - is an irritant

22
Q

What are the four quantitative tests?

A
  • Test for carbonates
  • Test for sulfates
  • test for halides
  • Test for ammonium ions
23
Q

Describe the carbonate test

Outline the equation for the reaction that occurs during testing for CO2

A
  • Add dilute nitric acid to the solid or solution to be tested in the test tube
  • If bubbles are produced, the unknown compound could be a carbonate
  • To prove the gas is CO2:
  • Bubble the gas through lime waterCa(OH)2
  • CO2 reacts to form a fine white precipitate of calcium carbonate
  • This turns the lime water milky

-CO2(g) + Ca(OH)2(aq) —> CaCO3(s) + H20(l)

24
Q

Describe the sulfate test

A
  • Add barium chloride
  • A white precipitate of barium sulfate forms(BaSO4 is insoluble)
  • Ionic equation shown:
  • Ba2+(aq) + SO4^2-(aq) —BaSO4
25
Q

Describe the halide ion test

What are the ionic equations that occur?

A
  • Add aqueous silver nitrate to an aqueous solution of a halide
  • The silver halide precipitates are different colours:
  • Silver chloride - white
  • Silver Bromide - Cream-coloured
  • Silver Iodide - yellow
  • Add aqueous ammonia to test the solubility of the precipitate
  • This stage helps tell the different colours, and so halides, apart clearer
  • Chlorine —> Ag+(aq) + Cl-(aq) —> AgCl
  • Bromine—> Ag+(aq) + Br-(aq) —> AgBr
  • Iodine —> Ag+(aq) + I-(aq) —> AgI
26
Q

Describe the test for ammonium ions

A
  • Add aqueous sodium hydroxide to solution of an ammonium ion
  • Ammonia gas is produced, gas bubbles are unlikely to form, as ammonia is soluble in water
  • The mixture is warmed and ammonia gas is released
  • Test the gas with MOIST pH indicator paper
  • Ammonia is alkaline and will turn the paper blue.

Equation:

NH4+ + OH- —> NH3 + H2O

27
Q

What is an oxidising agent?

A

A species in a reaction that oxidises another species, but is reduced in the reaction itself.

28
Q

What is a reducing agent?

A

Species that reduces another species in a reaction, becomes oxidised itself

29
Q

What is the order for doing consecutive ion tests on a substance or solution in a test tube without contaminating, etc.

A

Find on textbook.

Need to know.

My AS Level Chemistry - OCR A (14 decks)

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