Group II and Group VII

Question 1

What is the trend of atomic radius down group 2?

Answer 1

There is an increase in atomic radius due to the fact there are more electrons and therefore more electron shells.

Question 2

What is the trend in first ionization energy down group 2?

Answer 2

(Decreases) Each element has an extra electron shell compared to the one above- this links to increasing atomic radius. This means there is more shielding of the outer electrons from the nucleus. The distance from the nucleus also increases. All these factors make it easier to remove outer electrons, resulting in a lower first ionization energy.

Question 3

What is the trend in reactivity down group 2?

Answer 3

As you go down the group, the first ionization energy decreases. When group 2 elements react they lose electrons, forming positive ions. The easier it is to lose electrons, the more reactive the element. Therefore reactivity increases down the group.

Question 4

What is the trend of melting points down group 2?

Answer 4

• The group 2 elements have typical metallic structures, with positive ions in a crystal structure surrounded by delocalized electrons from the outer electron shells.
• Going down the group the metal ions get bigger. But the number of delocalized electrons doesn’t change.
• The larger the ionic radius, the further away the delocalized electrons are from the positive nuclei and the less attraction they feel. So it takes less energy to break the bonds, which means the melting points generally decrease down the group

Question 5

What is the exception to melting points down group 2?

Answer 5

Magnesium is the exception because the crystal structure changes.

Question 6

What do group 2 metals form when reacted with water and what is the trend?

Answer 6

They all, except Mg, form metal hydroxides and hydrogen. Mg forms MgO. It is an oxidation reaction. Group 2 metals react more readily down the group because the ionization energies decrease.

Question 7

What is the trend of group 2 metal hydroxide solubility?

Answer 7

It increases down the group

Question 8

What is the trend of group 2 metal sulfate solubility?

Answer 8

It decreases down the group

Question 9

What group 2 metal sulfate is insoluble?

Answer 9

Barium sulfate is insoluble- most of the others are soluble

Question 10

How do you test for sulfate ions?

Answer 10

Adding HCl and barium chloride/acidified barium chloride. If a white precipitate is formed then sulfate ions are present.
It is important to acidify the solution with hydrochloric acid to get rid of any lurking sulfites or carbonates, which will also produce a white precipitate.

Question 11

Why are group 2 metals also called alkaline earth metals?

Answer 11

Many of their common compounds are used for neutralizing acids.

Question 12

What are the uses of Calcium hydroxide?

Answer 12

Also known as slaked lime, it is used in agriculture to neutralize acid soils.

Question 13

What are the uses of Magnesium hydroxide?

Answer 13

It is used in some indigestion tablets as an antacid- this is a substance that neutralizes excess stomach acid.

Question 14

What is the problem with using X-ray imaging?

Answer 14

X-rays are great for finding broken bones, but they pass straight through soft tissue- so soft tissues, like the digestive system, don’t show up on conventional X-ray pictures.

Question 15

Why is Barium sulfate useful in medical X-ray imaging?

Answer 15

Barium Sulfate is opaque to X-rays- they won’t pass through it. It’s used in ‘barium meals’ to help diagnose problems with the oesophagus, stomach, or intestines.
A patient swallows the barium meal, which is a suspension of barium sulfate. The barium sulfate coats the tissues, making them show up on the X-rays, showing the structure of the organs.

Question 16

What is an example of a practical use of magnesium?

Answer 16

Magnesium is used to extract Titanium from its ore. TiO2 is first converted to TiCl4 by heating it with carbon in a stream of chlorine gas. The Titanium chloride is then purified by fractional distillation before being reduced by magnesium in a furnace at almost 1000 degrees.

Question 17

What are the uses of calcium oxide and calcium carbonate?

Answer 17

Burning fossil fuels with sulfur impurities also produces sulfur dioxide, which pollutes the atmosphere. The acidic sulfur dioxide can be removed from flue gases by reacting with an alkali- this is a process called wet scrubbing.
A slurry is made by mixing the calcium oxide or calcium carbonate with water. It is then sprayed onto the flue gases. The sulfur dioxide reacts with the alkaline slurry and produces a solid waste product, calcium sulfate.

Question 18

What is the trend for boiling points down group 7?

Answer 18

It increases due to the increasing strength of van der Waals forces as the size and relative mass of the molecules increase. This trend is shown in the changes in physical state from fluorine to iodine.

Question 19

What is the trend for electronegativity down group 7?

Answer 19

Electronegativity decreases down the group. The halogens are all highly electronegative elements. But larger atoms attract less than the smaller ones. This is because electrons are further from the nucleus and are shielded by more electrons.

Question 20

What is the trend for reactivity down group 7?

Answer 20

Reactivity decreases down the group because the atoms become larger. The outer shell is further from the nucleus, so electrons are less strongly attracted to it. So you can also say that the halogens become less oxidizing down the group.

Question 21

How do you make bleach?

Answer 21

If you mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate solution, NaClO which just happens to be common household bleach. It can be used in water treatment, bleaching paper, and textiles, cleaning toilets, etc.

Question 22

What happens when you mix chlorine and water?

Answer 22

When you mix chlorine with water, it undergoes disproportionation. You end up with a mixture of chloride and chlorate ions.
In sunlight, chlorine can also decompose water to form chloride ions and oxygen

Question 23

How is chlorine used in water treatment?

Answer 23

• it kills disease-causing microorganisms
• some chlorine persists in the water and prevents reinfection further down the supply
• It prevents the growth of algae, eliminating bad tastes and smells, and removes discoloration caused by organic compounds.

Question 24

What are the risks in using chlorine to treat water?

Answer 24

• Chlorine gas is very harmful if it is breathed in it irritates the respiratory system. Liquid chlorine on the skin or eyes causes severe chemical burns. Accidents involving chlorine could be really serious, or fatal.
• Water contains a variety of organic compounds, e.g. from the decomposition of plants. Chlorine reacts with these compounds to form chlorinated hydrocarbons. And many of these are carcinogenic. However, this increased cancer risk is small compared to the risks from untreated water- a cholera epidemic, say, could kill thousands of people.

Question 25

What is the trend of reducing power down group 7?

Answer 25

To reduce something, the halide ion needs to lose an electron from its outer shell and as you go down group 7 the attraction between the electron and the nucleus decreases.
- the ions get bigger, so the electrons are further away from the positive nucleus.
- there are extra inner electron shells, so there’s a greater shielding effect

Question 26

What happens when NaF or ClF reacts with sulphuric acid?

Answer 26

Either HF or HCl gas is formed, but they aren’t strong enough reducing agents to reduce the sulphuric acid so the reaction stops there. It is not a redox reaction.

Question 27

What happens when NaBr reacts with sulphuric acid?

Answer 27

The first reaction produces HBr gas, but as it is a stronger reducing agent it reacts with the sulphuric acid in a redox reaction to produce sulfur dioxide and bromine gas.

Question 28

What happens when NaI reacts with sulphuric acid?

Answer 28

The first reaction produces HI gas and the HI then reduces the sulphuric acid, but as it is a very strong reducing agent it keeps going and reduces the SO2 to H2S. Solid iodine is also formed during this reaction.

Question 29

How do you test for halide ions?

Answer 29

First, add dilute nitric acid to remove ions that may interfere with the test. Then you just add a few drops of silver nitrate solution. A precipitate is formed.
Fluoride: no precipitate as it is soluble
Chloride: white precipitate
Bromide: cream precipitate
Iodide: yellow precipitate
Iodide forms the quickest and chloride is the slowest

Question 30

How can you check your test for halide ions using ammonia solution?

Answer 30

Each silver halide has a different solubility in ammonia
Chloride, a white precipitate that dissolves in dilute ammonia solution
Bromide, a cream precipitate that dissolves in conc ammonia solution
Iodide, a yellow precipitate that is insoluble in conc ammonia solution

Question 31

How do you carry out a flame test?

Answer 31

1. Dip a nichrome wire loop in concentrated hydrochloric acid
2. Then dip the wire loop into the unknown compound
3. Hold the loop in the clear blue part of a bunsen flame
4. Observe the color change in the flame

Question 32

What colors do the group 2 metals go in a flame test?

Answer 32

Calcium: brick red
Strontium: red
Barium: pale green

Question 33

How can you use sodium hydroxide solution to test for group 2 ions?

Answer 33

Add the dilute sodium hydroxide dropwise to a test tube containing the metal ion solution and observe the precipitate that forms if there is one. Keep adding the sodium hydroxide until it is in excess. Record any changes that you see.

Question 34

What precipitates are formed when group 2 metals react with dilute sodium hydroxide?

Answer 34

Mg: slight white with NaOH, white with excess
Ca: slight white with NaOH, slight white with excess
Sr: slight white with NaOH, slight white with excess
Ba: no change with NaOH, no change with excess

Question 35

How can you test for ammonia gas?

Answer 35

Ammonia gas is alkaline so you can test for it using a piece of damp red litmus paper. (needs to be damp so the gas can dissolve). If there is ammonia present the litmus paper will turn blue.

Question 36

How do you test a solution for ammonium ions?

Answer 36

If you add hydroxide ions to a solution containing ammonium ions they will react to produce ammonia gas and water. So you can test by adding dilute sodium hydroxide and heating. If ammonia gas is given off, then ammonium ions must be present.

Question 37

How do you test for hydroxide ions?

Answer 37

Use a pH indicator as OH- ions make a solution alkaline.
- Dip a piece of red litmus paper into the solution
- If hydroxide ions are present, the paper will turn blue.

Question 38

How do you test for sulfates?

Answer 38

To identify a sulfate ion you add a little dilute hydrochloric acid, followed by barium chloride solution. If a white precipitate is formed then it means the original compound contained a sulfate.

Question 39

How do you test for carbonates?

Answer 39

When you add dilute hydrochloric acid, a solution containing carbonate ions will fizz. This is because the carbonate ions react with the hydrogen ions in the acid to give carbon dioxide.
You can test for carbon dioxide using limewater. Carbon dioxide gas, when bubbled through limewater, turns it cloudy.