Inorganic chemistry

What is the physical state of the 4 first halogens?

What is the physical state of the 4 first halogens?

1. Fluorine - gas

2. Chlorine - gas

3. Bromine - liquid

4. Iodine - solid

What is the color of the first 4 halogens?

1. Fluorine - Pale yellow

2. Chlorine - green

3. Bromine - red-brown

4. Iodine - grey

Describe and explain the trend in the boiling points of the halogens (3 marks)

• Boiling points increase down the group

• Increasing strength of VDWs forces.

• As the size and relative mass of molecules increases..

Describe and explain the trend in the electronegativity of the halogens (3 marks)

• Electronegativity decreases down the group

• The larger the atoms attract electrons less than smaller ones.

• As the electrons are further away from the nucleus and are shielded by more electrons.

Describe and explain the trend in the oxidizing ability of the halogens (3 marks)

• Decreases down the group

• Atoms are larger, meaning the outer shell is further from the nucleus.

• Electrons are less strongly attracted to the nucleus so more easily lost

What is the color of the 3 halogens in aqueous solutions?

1. Chlorine - pale yellow

2. Bromine - orange

3. Iodine - brown

What is the color of the 3 halogens in cyclohexane?

Chlorine - pale yellow

Bromine - orange

Iodine - purple

Write overall equation for chlorine gas with cold, dilute, aqueous sodium hydroxide.

Image →

What is special about what happens to chlorine in the reaction to form bleach, and what is this called?

The oxidation state of chlorine goes up and down, which is called disproportionation.

What is the sodium chlorate solution called and what are some uses?

Bleach and its used in:

• Water treatment

• Bleach paper

• Textiles

• Bathroom cleaner

Give equation for when chlorine is mixed with water and state what happens to chlorine.

Image → (chlorine undergoes disproportionation)

Give equation for when chlorine is mixed with water in presence of sunlight .

2Cl₂ + 2H₂O → 4H⁺ + 4Cl^- + O₂

What is special about chlorate ions in terms of water?

Chlorate ions kills bacteria, so adding it to water makes it safe to swim in or drink.

Give 3 ways chlorine is an important part of water treatment

1. It kills pathogens

2. Some chlorine persists in water and prevents re-infection further down supply

3. Prevents growth of algae, eliminating bad tastes and smells. Removes discoloration caused by organic compounds.

What are two risks of using chlorine to treat water?

1. Chlorine gas is very harmful if breathed in. Liquid chlorine can causes chemical burns. Accidents involving chlorine can be fatal.

2. Water contains organic compounds and when chlorine reacts with these compounds chlorinated hydrocarbons are formed. They are carcinogenic.

Describe and explain how the reducing power of the halides changes down the group? (4 marks)

• Reducing power increases down the group

• This is because the attraction between the nucleus and the outer electrons decreases.

• As the ions get bigger, so the electrons are further away from the positive nucleus.

• There are also extra electron shells, so there is a greater shielding effect.

What do all the halides react with concentrated sulfuric acid to give?

A hydrogen halide.

Describe and explain the reactions of NaF and NaCl with sulfuric acid? (3 marks)

• Forms Hf and HCl (misty fumes as gas comes into contact with moisture in air may appear).

• HF and HCl aren’t strong enough reducing agents to reduce sulfuric acid, so reaction stops.

• Not a redox reaction as the oxidation states of the halide and sulfur stay the same.

Describe and explain the reactions of NaBr with sulfuric acid? (3marks)

• First reaction gives misty flames of hydrogen bromide gas.

• HBr stronger reducing agent than HCl so reacts with sulfuric acid in a redox reaction.

• Reaction produces choking fumes of sulfur dioxide and orange fumes of bromine gas.

Describe and explain the reactions of NaI with sulfuric acid? (4marks)

• Same initial reaction giving HI gas.

• HI reduces sulfuric acid like in NaBr

• HI is a very strong reducing agent so reduces SO2 to H2S

• Solid iodine also formed

What is the test for halide ions? (3 points)

1. Add dilute nitric acid

2. Add a few drops of silver nitrate

3. Add ammonia solution

Why is dilute nitric acid added for the test of halides?

To remove ions like hydroxide and carbonate which may produce unwanted precipitates.

Why is silver nitrate solution added for the test for halides?

To react with with halide ions to produce silver halide precipitates.

Why is ammonia solution added for the test for halides?

To distinguish between closely colored precipitates which form

What is the trend in speed of silver halide precipitate formed in the test for halides?

Increases down group

What is the trend in solubility in ammonia solution of silver halide precipitates?

Decreases down group

Describe and explain the trend in atomic radius across a period (4 marks)

• Decreases across a period

• This is because the number of protons increases so the positive charge of the nucleus increases.

• This means electrons are pulled closer into the nucleus.

• The electrons gained by elements across the period are added to the outer energy level so they don’t provide any extra shielding effects.

Describe and explain the trend in melting points across period 3 (6 marker)

Going left to right (see graph):

1. Sodium, magnesium, and aluminum are metals and their melting points increase across the group because the metal-metal bonds get stronger. This is because the metal ions have increasing positive charge, an increasing number of delocalized electrons, and a decreasing atomic radius.

2. Silicon is macromolecular with a regular tetrahedral structure. Strong covalent bonds link all the atoms together and a lot of energy is needed to break all of these bonds to break silicon.

3. Phosphorus (P4), sulfur (S8), and chlorine (Cl2) are all molecular substances. The VdW’s forces between molecules here are weak and easily overcome so these elements have low melting points.

4. More atoms in a molecule mean stronger VdW’s forces, so S8 has the highest.

5. Argon has a very low melting point because it exists as individual atoms, meaning very weak VdW’s forces.

Describe the trend in the first ionization energy across group 3 (2 marks).

It generally increases, however there is a decrease between Mg and Al and between P and S.

Describe and explain how the first ionization energy of the group 2 metals decreases down the group.

1. Each element down group 2 has an extra electron shell compared to the one above. The extra inner shells shields the outer electrons from the attraction of the nucleus.

2. The extra shell means the outer electrons are also further away from the nucleus, which greatly reduces the nucleus’ attraction.

3. Both of these factors make it easier for the electron to get lost, lowering the first ionization energy.

Describe and explain the trend in reactivity down group 2

• As the first ionization energy decreases as you go down the group, it is easier for the group 2 elements to lose electrons to form positive 2+ ions down the group.

• This means the reactivity increases down the group

Describe and explain the trend in melting points down group 2

1. The group 2 metals have typical metallic structures, with positive ions in a crystal structure surrounded by delocalized electrons.

2. Going down the group the metal ions get bigger, but the number of delocalized electrons per atom doesn’t change.

3. The larger the atomic radius, the further away the delocalized electrons are from the positive nuclei and the less attraction they feel. This means it takes less energy to break bonds, which means the melting points generally decrease down the group.

4. However, Mg is lower than Ca because the crystal structure changes.

What do group 2 metals react with water to give?

A metal hydroxide and hydrogen

Describe the trend in solubility of group 2 hydroxides

Increases down the group

Describe the trend in solubility of group 2 sulfates

Decreases down the group

What is the term given to compounds like magnesium hydroxide which have very low solubilities?

Sparingly soluble

Which sulfate is insoluble in water, and for what test does it make it especially useful for?

Barium sulfate, the test for sulfate ions.

Give 2 ways in which group 2 compounds are used to neutralize acidity

1. Calcium hydroxide is used in agriculture to neutralize acid soils

2. Magnesium hydroxide is used in indigestion tablets as an antacid to neutralize excess stomach acid.

Describe and explain how barium sulfate is used in medicine (3 marks)

1. X-rays usually pass straight through soft tissues in the body

2. Barium sulfate is opaque to x-rays, they won’t pass through it. It is used in ‘barium meals’ to help diagnose problems with the oesophagus, stomach, or intestines.

3. A patient swallows this barium meal, which is a suspension of barium sulfate. The barium sulfate coats the tissues, making them show up on x-rays.

Why is BaCl2 used to test for sulfate ions and why is it acidified? (2 marks)

1. If it is added to a solution containing sulfate ions a white precipitate of barium sulfate will form.

2. The solution is acidified with HCl to get rid of any sulfate or carbonate ions, which will also produce white precipitates.

Describe and explain how magnesium is used in the extraction of titanium (3 marks)

1. Used to extract titanium from its ore.

2. The main titanium ore, titanium(IV) oxide, is first converted to titanium(IV) chloride by heating it with carbon in a stream of chlorine gas.

3. The titanium chloride is then purified by fractional distillation before being reduced by magnesium in a furnace at around 1000 degrees C.

How is calcium oxide and calcium carbonate used to remove sulfur dioxide? (5 marks)

• Burning fossil fuels also produces sulfur dioxide.

• The acidic sulfur dioxide can be removed from flue gases by reacting with an alkali - which is called wet scrubbing

• Calcium oxide and calcium carbonate are usually used for this.

• A slurry is made by mixing the calcium oxide or calcium carbonate with water.

• It’s then sprayed onto the flue gases. This reaction causes a solid waste product, calcium sulfite, to be produced.

How would you carry out a flame test to test for group 2 ions, and what are the results for Ca, Sr, and Ba.

1. Dip a nichrome wire loop in concentrated HCl.

2. Dip the wire in unknown substance

3. Hold it over a Bunsen burner.

4. Ca - brick red, Sr - red, Ba - pale green

Give the results for the NaOH test for ions of Mg, Ca, Sr, and Ba. (excess and not excess). (8 marks)

For not in excess:

• Mg - slight white precipitate

• Ca - slight white precipitate

• Sr - slight white precipitate

• Ba - no change

For in excess:

• Mg - white precipitate

• Ca - slight white precipitate

• Sr - slight white precipitate

• Ba - no change

Describe how to test for ammonium ions with NaOH

1. Add some dilute sodium hydroxide solution to a substance in a test tube and heat gently in a water bath.

2. If ammonium ions are present, ammonia gas will be given off.

3. Ammonia gas is alkaline, so a piece of damp red litmus paper can be used to test if ammonia is present - it will turn it blue

How would test for hydroxides?

Hydroxide ions turns solutions alkaline. This means any pH indicator can be used to test if a solution contains hydroxide ions.

How can carbonates be detected?

1. When you add HCl to a solution containing carbonate ions, it will fizz.

2. This is because carbonate ions react with hydrogen ions to give CO2.

3. You can then test for CO2 by bubbling it through limewater, if it goes cloudy the solution contains carbonate ions.