Group 2 And Group 7

Question 1

Describe the solubility trend of hydroxides as you go down the group and list their solubility

Answer 1

Increases going down group two.
Mg(OH)2– sparingly soluble
Ca(OH)2– sparingly soluble
Sr(OH)2– more soluble
Ba(OH)2– completely dissolves

Question 2

Describe the solubility of sulphates going down the group and list their solubility

Answer 2

Solubility decreases down the group
MgSO4– completely dissolved
CaSO4– fairly soluble
SrSO4– sparingly soluble
BaSO4– insoluble

Question 3

Describe the test for sulfate ions- SO4

Answer 3

Add BaCl2, forms white precipitate. Sulfate ions present as barium sulfate has been produced

Question 4

Flourine electronegativity and observation

Answer 4

F-F covalent bond is weak. Atom is very small meaning that the non- bonding pairs of electrons are held so close that they start to repel. 4.0- pale yellow gas

Question 5

Appearance and electronegativity of Cl

Answer 5

Pale green, 3.0

Question 6

Appearance and electronegativity of Br

Answer 6

Yellow brown or if non polar- orange/ brown. 2.8

Question 7

Iodine

Answer 7

Brown, non polar- purple, solid- black. 2.5

Question 8

Test Halide ions

Answer 8

To unknown sample add nitric acid, needed to remove any carbonate ions. Add silver nitrate. Once a precipitate has formed ammonia can be added.

Question 9

Observations after the addition of nitric acid and silver nitrate

Answer 9

Flouride: No visible change, no precipitate
Chloride: White precipitate
Bromide: Cream precipitate
Iodide: Yellow precipitate

Question 10

Observations after adding dilute ammonia

Answer 10

Fluoride: N/A
Chloride: White precipitate dissolves
Bromide: Cream precipitate remains
Iodide: Yellow precipitate remains

Question 11

Observations after concentrated ammonia is added

Answer 11

F- N/A
Cl- White precipitate dissolves
Br- cream precipitate dissolves
I- yellow precipitate remains

Question 12

Describe the trend in atomic radius as you go down the group- provide reason

Answer 12

Atomic radius increases due to more shielding, further from the nucleus meaning a weaker nuclear attraction on outer electrons

Question 13

Describe the trend in ionisation energies as you go down group 2

Answer 13

Decreases: Atomic radius gets bigger, further from the nucleus, weaker nucleus attraction on outer electrons

Question 14

Describe the trend in melting point as you go down group 2

Answer 14

Decreases: Ionic size increases, lower charge density so weaker attraction on delocalised electrons

Question 15

Which substances form white precipitate

Answer 15

Mg(OH)2 and BaSO4

Question 16

Test for sulfate:

Answer 16

BaCl2 + sample. A positive result shows a white precipitate

Question 17

Test for hydroxides:

Answer 17

NaOH and metal ion. Positive test= white precipitate

Question 18

What is Mg(OH)2 used for

Answer 18

Treating indigestion (milk of magnesia)

Question 19

What is barium sulfate used for

Answer 19

Taking x -ray images of the stomach. Insoluble so doesn’t dissolve

Question 20

Describe the change in state down group 7

Answer 20

Melting point and boiling point increases, van der waals get stronger between molecules. All simple molecules require more energy to break

Question 21

Describe the electronegativity down group 7

Answer 21

Decreases, atom radius increases, shielding increases, nuclear attraction on pair of electrons gets weaker

Question 22

State and explain the trend in atomic radius from Mg-Ba.

Answer 22

Atomic radius increases going down the group. Every element has an extra electron shell that is an increased distance from the nucleus.

Question 23

State and explain the trend in first ionisation energy from Mg-Ba.

Answer 23

First ionisation energy decreases going down the group. There is an increased atomic radius and more shielding; therefore, it requires less energy to remove an electron from group two elements that are lower in the periodic table.

Question 24

State and explain the trend in melting point from Mg-Ba.

Answer 24

From calcium to barium the trend is a decrease in melting point. This is because the ionic radius increases while the charge remains constant, thus lowering charge density. Therefore, the delocalised electrons are less strongly attracted to the metallic cations, causing a reduction in melting point. Magnesium is an exception to the trend (its melting point is lower than calcium’s) as it forms a different crystal structure to the other elements.

Question 25

State and explain the general trend in reactivity of the elements in group two with water.

Answer 25

The elements become more reactive as you go down the group. This is because it becomes increasingly easier to lose the two outer electrons for a reaction to happen.

Question 26

Write equations for the following reactions:
* Mg with water
* Mg with steam

Answer 26

• Mg (s) + 2H2O (l)  Mg(OH)2 (s) + H2 (g)
• Mg (s) + H2O (g)  MgO (s) + H2 (g)
• Ba (s) + 2H2O (l)  Ba(OH)2 (s) + H2 (g

Question 27

Explain why it is dangerous to put out a magnesium fire using water.

Answer 27

The magnesium reacts with water at high temperatures to produce hydrogen gas, which is explosive.

Question 28

Write an equation for the reaction to extract titanium from titanium (IV) chloride using magnesium.

Answer 28

TiCl4 (g) + 2Mg (l)  Ti (s) + 2MgCl2 (l)

Question 29

TiCl4 is produced from TiO2. Why isn’t Ti extracted from this using reduction with carbon?

Answer 29

Although carbon is more reactive than titanium, reacting the two substances together produces brittle titanium carbide (TiC).

Question 30

State the trend in solubility of group two hydroxides.

Answer 30

Going down the group, the group two hydroxides become more soluble.

Question 31

Comment on the solubility of magnesium hydroxide in water.

Answer 31

Magnesium hydroxide is sparingly soluble in water.

Question 32

State a medical use of magnesium hydroxide, Mg(OH)2.

Answer 32

Commonly referred to as milk of magnesia, it used as an indigestion remedy

Question 33

State a use for calcium hydroxide, Ca(OH)2, in agriculture.

Answer 33

Calcium hydroxide, also known as slaked lime, is used to neutralise acidic soil.

Question 34

Sulfur dioxide (SO2) is a common pollutant produced when fossil fuels are burnt. Give a substance that can be used to remove it from flue gases and name the type of reaction this represents.

Answer 34

Calcium oxide or calcium carbonate can be used because they are basic substances and sulfur dioxide is acidic. The reaction is a neutralisation, or acid-base, reaction.

Question 35

State the trend in solubility of group two sulfates.

Answer 35

Going down the group, the group two sulfates become less soluble.

Question 36

State a medical use of barium sulfate and explain why it can be used in this way even though barium is highly toxic.

Answer 36

Barium sulfate is used as the barium meal. It is safe to use because barium sulfate is completely insoluble, which means it cannot be absorbed by the human body, so highly toxic Ba2+ ions would not be able to pass into the bloodstream.

Question 37

Barium chloride is used to test for the presence of which ions? What would the result of a positive test be?

Answer 37

Sulfate ions would produce a white precipitate in the presence of barium chloride due to the formation of barium sulfate.

Question 38

Why must the solution be acidified with hydrochloric acid before this test is carried out?

Answer 38

To remove ions such as carbonate ions that would give a false positive result of a white precipitate.

Question 39

Outline a method to identify and distinguish between samples of calcium, strontium and barium ions.

Answer 39

This test relies on the differing solubilities of the hydroxides and sulfates of each metal ion.
Take a sample of each metal ion and add sodium hydroxide to it. The resulting solutions can be distinguished based on which forms precipitates – calcium hydroxide is sparingly soluble, strontium hydroxide more soluble and barium hydroxide more soluble. By comparing the amounts of sodium hydroxide that each will react with until a precipitate forms one can identify them accordingly. The same method can be used by adding sulfuric acid although this time the trend is opposite – barium sulfate is completely insoluble, calcium sulfate will dissolve in water.