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Chemistry > Chapter 8 > Flashcards

Chapter 8 Flashcards

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1
Q

What is the outer shell electron configuration of group 2 atoms and ions?

A
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2
Q

What is the reactivity series for group 2 elements?

A
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3
Q

What is the most common type of reaction of group 2 elements?

A

Redox reactions

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4
Q

What happens in a redox reaction involving metals?

A

Each metal atom is oxidised, losing two electrons to form a 2+ ion with the electron configuration of a noble gas

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5
Q

How do group 2 elements react with oxygen?

A

The group 2 elements react in a redox reaction with oxygen to form a metal oxide with general formula MO. The metal oxidises whilst the oxygen reduces.

2Mg(s) + O2(g) –> 2MgO(s)

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6
Q

How do group 2 elements react with water?

A

They react in a redox reaction with water to form an alkaline hydroxide, with the general formula M(OH)2, and hydrogen gas.

Sr(s) + 2H2O(l) –> Sr(OH)2(aq) + H2(g)

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7
Q

How does the reactivity of group 2 metals with water vary?

A

Reactivity increases down the group as the reaction with water becomes more vigorous

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8
Q

How do group 2 elements react with dilute acids?

A

Many metals take part in redox reactions with dilute acids to form a salt and hydrogen gas.
Metal + acid –> salt + hydrogen

Mg(s) + 2HCl(aq) –> MgCl2(aq) + H2(g)

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9
Q

How does the reactivity of group 2 metals with acid vary?

A

Similar to water, reactivity increases down the group

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10
Q

What is the trend in reactivity for group 2 elements in terms of the first and second ionisation energies?

A

Reactivity increases down group 2 as a result of the ionisation energies decreasing down the group. They decrease because the attraction between the nucleus and the outer electrons decreases as a result of increasing atomic radius and increased shielding.
As they become more reactive, they also become stronger reducing agents.

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11
Q

Give a general equation for the second ionisation energy of a group 2 element:

A

M+(g) –> M2+(g) + e-

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12
Q

How do group 2 compounds react with water?

A

The oxides of group 2 elements react with water, releasing hydroxide ions and forming alkaline solutions of the metal hydroxide.
The hydroxides are only slightly soluble in water, so once the solution becomes saturated, any further metal and hydroxide ions will form a solid precipitate.

CaO(s) + H2O(l) –> Ca2+ (aq) + 2OH- (aq)

Ca2+ (aq) + 2OH- (aq) –> Ca(OH)2(s)

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13
Q

What is the trend in solubility of the group 2 hydroxides in water?

A

The solubility of the hydroxides in water increases down the group

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14
Q

What is the trend in alkalinity of the group 2 hydroxides?

A
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15
Q

Describe the solubility and alkalinity of magnesium hydroxide

A

Magnesium hydroxide is only slightly soluble in water and is the least soluble out of the group 2 compounds. The solution has a low hydroxide concentration and a pH of 10

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16
Q

Describe the solubility and alkalinity of barium hydroxide

A

Barium hydroxide is very soluble in water and the most soluble out of the group 2 compounds. The solution has a greater hydroxide concentration and a pH of 13

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17
Q

What method is used to show the trend in alkalinity of the group 2 compounds?

A
  1. Add a spatula of each group 2 oxide to water in a test tube
  2. Shake the mixture. A white precipitate should have formed and settled at the bottom of the test tube
  3. Measure the pH of each solution, and the alkalinity will be seen to increase down the group
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18
Q

How are group 2 compounds used in agriculture?

A

They are added to fields by farmers to increase the pH of acidic soils. They neutralise the acid to form neutral water.

Ca(OH)2(s) + 2H+(aq) –> Ca2+(aq) + 2H2O(l)

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19
Q

How are group 2 compounds used in medicine?

A

They are often used as antacids for treating acid indigestion. They neutralise the acid in your stomach to reduce pain. Common examples include, magnesium and calcium carbonates as well as milk of magnesia, a suspension of magnesium hydroxide

Mg(OH)2(s) + 2HCl(aq) –> MgCl2(aq) + 2H2O(l)

20
Q

What is the trend in boiling point for the halogens?

A

As you go down the group, there are more electrons, thus there are stronger London forces which require more energy to overcome. As a result boiling point increases.

21
Q

What happens in a redox reaction involving halogens?

A

Each halogen atom is reduced, gaining one electron to form a 1- halide ion, with the electron configuration of the nearest noble gas

Cl2 + 2e- –> 2Cl-

22
Q

How can we test for the reactivity of the halogens?

A

By carrying out displacement reactions.

23
Q

What is the trend in reactivity of the halogens?

A

Reactivity decreases down the group

24
Q

Explain the trend in reactivity of the halogens

A

As you go down the group, the reactivity decreases. This is because the atomic radius increases down the group, there are more inner shells so shielding increases, and there is less nuclear attraction to capture an electron.

25
Q

What is disproportionation?

A

A redox reaction in which the same element is both oxidised and reduced

26
Q

What are some examples of disproportionation reactions?

A

Chlorine with water
Chlorine with cold, dilute sodium hydroxide

27
Q

Describe the reaction of chlorine with water as used in water treatment

A

Small amounts of chlorine are added to water in order to disinfect it. When this happens, a disproportionation reaction takes place. For each chlorine molecule, one chlorine atom is oxidised and the other chlorine atom is reduced

Cl2(aq) + H2O(l) –> HClO(aq) + HCl(aq)

28
Q

Describe the reaction of chlorine with cold, dilute sodium hydroxide as used to form bleach

A

The reaction of chlorine with water is limited by the low solubility of chlorine in water, however if the water contains dissolved sodium hydroxide, much more chlorine dissolves and another disproportionation reaction takes place

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

29
Q

What are the benefits of chlorine use?

A

It ensures our water is fit to drink
Ensures bacteria is killed
Quality of drinking water is made better by reducing water-borne diseases such as cholera and typhoid

30
Q

What are the risks of chlorine use?

A

It is an extremely toxic gas
A respiratory irritant in small concentrations and fatal in large concentrations
Chlorinated hydrocarbons can also be formed which are suspected to cause cancer

31
Q

Describe the precipitation reactions of the halides with aqueous silver ions

A

Aqueous halide ions react with aqueous silver ions to form precipitates of silver halides.

32
Q

Ionic equation for the reaction between chlorine and silver:

A

Ag+(aq) + Cl-(aq) –> AgCl(s)

33
Q

Ionic equation for the reaction between bromine and silver:

A

Ag+(aq) + Br-(aq) –> AgBr(s)

34
Q

Ionic equation for the reaction between iodine and silver:

A

Ag+(aq) + I-(aq) –> AgI(s)

35
Q

How to test for carbonates?

A

Add dilute nitric acid to the unknown solid/solution
If bubbles are observed, then it is likely that the compound is a carbonate
To ensure it is a carbonate, bubble the gas produced through limewater, and the limewater should turn cloudy - this proves that CO2 has been produced

36
Q

How to test for sulfates?

A

The test involves adding aqueous barium ions (as aqueous barium chloride or barium nitrate) to a solution of an unknown compound
A dense white precipitate forms when Ba2+ ions are added to a solution containing sulfate ions SO4-

37
Q

How to test for halides?

A

Add aqueous silver nitrate to an aqueous solution of a halide
A coloured precipitate should form depending on the halide present - silver chloride is white, silver bromide is cream coloured and silver iodide is yellow
Add aqueous ammonia to test the solubility of the precipitate.

38
Q

What is the solubility of chloride ions in NH3?

A

They are soluble in dilute ammonia

39
Q

What is the solubility of bromide ions in NH3?

A

They are soluble in concentrated ammonia

40
Q

What is the solubility of iodide ions in NH3?

A

They are insoluble in concentrated ammonia

41
Q

How to test for ammonium ions?

A

Aqueous sodium hydroxide is added to a solution of an ammonium ion
Ammonia gas is produced.
The mixture is warmed and the gas is released
Test the gas present with moist pH indicator paper.
Since ammonia is alkaline, its presence will turn the paper blue

42
Q

What is the correct order of tests for anions?

A

Carbonate
Sulfate
Halides

43
Q

Why is the carbonate test done first?

A

The carbonate test involves looking for effervescence. Neither sulfate nor halide ions produce effervescence thus the test can be carried out without the possibility of an incorrect conclusion.

44
Q

Why is the sulfate test done after the carbonate test but not after the halide test?

A

In the sulfate test, you are looking for a white precipitate.
Barium carbonate form a white precipitate when reacted with water too, so it is important to carry out the carbonate test first to eliminate the possibility of any carbonate ions present

45
Q

Why is the halide test done last?

A

Silver carbonate and silver sulfate are both insoluble in water and will form a precipitate in the test.
Thus it is important to carry out the halide test last to rule out the possibility of any carbonate or sulfate ions present

Chemistry (20 decks)

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