5.3.2: Transition metal compounds

Question 1

What are the physical properties of transition elements?

Answer 1

• They are all metals.
• Lustrous in appearance.
• High densities.
• High melting and boiling points
• Able to conduct electricity.

Question 2

Why are transition metals able to conduct electricity?

Answer 2

-When solid, transition metals exist as giant metallic lattices containing delocalised electrons, which move freely to conduct electricity.

Question 3

What are the chemical properties of transition elements?

Answer 3

• Can have different oxidation states.
• The compounds of transition metals form colourless solutions when dissolved in water.
• Transition metals often catalyse chemical reactions.

Question 4

What are the chemical properties of transition elements a result of?

Answer 4

-These properties are a result of the electron configurations of the transition elements. In particular, the partially filled d-orbitals.

Question 5

Describe the variable oxidation states of transition elements.

Answer 5

• The transition elements, from titanium to copper, all form ions with more than one oxidation state.
• These metals also all form compounds with metal ions in the 2+ oxidation state.
• Often, this results in from losing the two electrons in the 4s-orbital.

Question 6

Which electrons are usually lost first in transition elements?

Answer 6

• The 4s electrons are lost first because they are in the highest occupied energy level.
• However, because the 3d and 4s energy levels are so close in energy, the 3d electrons can also be lost when an atom forms a stable ion.

Question 7

Where are the highest oxidation states of a transition element often found?

Answer 7

• In a strong oxidising agent.
• Manganese forms a compound called potassium manganate (KMnO4), a purple solid used as an oxidising agent in redox titrations.
• Chromium is found in potassium dichromate, K2Cr2O7, an orange crystalline solid that acts as an oxidising agent in the preparation of aldehydes and ketones from alcohols.
• In these compounds, manganate and chromium have their maximum oxidation states of +7 and +6, respectively.

Question 8

What is the oxidation number of potassium manganate (VII), KMnO4?

Answer 8

Mn= +7

Question 9

What is the oxidation state of potassium dichromate (VI), K2Cr2O7?

Answer 9

Cr= +6

Question 10

What is disproportionation?

Answer 10

Where one species is both oxidised and reduced in the same chemical reaction.

Question 11

When copper(I) oxide is reacted with dilute H2SO4, a brown precipitate of copper and a blue solution of copper (II) sulfate are formed. Write the symbol equation and describe how this is an example of disproportionation.

Answer 11

Cu2O + H2SO4 → Cu + CuSO4 + H2O
-In this reaction, the Cu+ is both oxidised to Cu2+ and reduced to Cu.
see figure 6.

Question 12

What happens when white light passes through a solution containing transition metal ions?

Answer 12

• Some of the wavelengths of visible light are absorbed.

- The colour that we observe is a mixture of the wavelengths of light that have not been absorbed.

Question 13

Why is a solution of copper (II) sulfate pale blue?

Answer 13

-Because the solution absorbs the red/orange region of the electromagnetic spectrum and reflects or transmits the blue.

Question 14

What do most coloured inorganic compounds contain?

Answer 14

-Transition metal ions

Question 15

What is colour in inorganic chemistry linked to?

Answer 15

The partially filled d-orbitals of transition metal ions.

Question 16

Why is scandium(III) colourless in aqueous solution?

Answer 16

• Scandium(III) has the electronic configuration 1s2 2s2 2p6 3s2 3p6 .
• It is formed from the loss of two 4s electrons and one 3d electron.
• There is no partially filled d-orbital and there is no colour.

Question 17

What is a catalyst?

Answer 17

A substance that changes the rate of a chemical reaction by providing an alternative reaction pathway, with a lower activation energy.

Question 18

How do transition metals act as catalysts by providing a surface area?

Answer 18

• Transition metals provide a surface on which a reaction can take place,
• Reactants are absorbed onto the surface of the metal and held in place while a reaction occurs.
• After the reaction, the products are desorbed and the metal remains unchanged.

Question 19

How do transition metals act as catalysts by changing their oxidation states?

Answer 19

• Transition metal ions have the ability to change their oxidation states by gaining or losing electrons.
• They then bind to reactants, forming intermediates as part of a chemical pathway, often with a lower activation energy, which speeds up the reaction.

Question 20

Why are transition metal catalysts used in industry?

Answer 20

• To improve the profits of an industrial process.

- They can reduce the time it takes to make a product and reduce the amount of energy needed to make the reaction occur.

Question 21

What are the drawbacks of using transition metal catalysts in industry?

Answer 21

• Transition metal compounds can be toxic, they must be handled with care .
• When substances bind to the active site and stop the transition metal catalyst from working, the catalysts can no longer be used.
• The catalyst must be disposed of in such a way as not to cause harm or pollution.

Question 22

What is the Haber process used to do?
What is the balanced symbol equation?
Which catalyst is used and what is its purpose?
What is the product used for?

Answer 22

• Used to make ammonia, NH3, from the reaction of nitrogen and hydrogen.
• N2(g) + 3H2(g) ↔ 2NH3(g)
• Catalyst: Iron metal used to increase rate of reaction and to lower the temp. at which the reaction takes place.
• Much of the ammonia produced in the Haber process is used in manufacturing agricultural fertilisers.

Question 23

What is the contact process used to do?
What is the balances symbol equation?
Which catalyst is used and what is its oxidation state?
-What are the uses of H2SO4?

Answer 23

• To convert sulfer dioxide into sulfer trioxide, which is used manufacture sulfuric acid, H2SO4.
• 2SO2(g) + O2(g) ↔ 2SO3 (g)
• The catalyst used is vanadium(V) oxide, V2O5, in which vanadium has the 5+ oxidation state.
• H2SO4 is an important inorganic chemical with many uses. e.g. production of fertilisers, detergentd, adhesives and explosives and also as the electrolyte in car batteries.

Question 24

What is hydrogenation?
Which catalyst is used and for what purpose?
-What is an industrial use of this process?

Answer 24

• Hydrogen can be added across the C=C double bond in unsaturated compounds to saturate them. This process is called hydrogenation.
• A nickel catalyst is used to lower the temperature and pressure needed to carry out the reaction.
• The process is used in the hydrogenation of unsaturated vegetable oils to make spreadable margarine.

Question 25

What does hydrogen peroxide decompose to form?
Why is a catalyst needed?
Write the balanced symbol equation for the decomposition of hydrogen peroxide.
What would be a suitable catalyst?
What is a use of this reaction?

Answer 25

• Hydrogen peroxide decomposes into water and oxygen. (slowly at RTP)
• A catalyst is needed to increase the reaction rate.
• 2H2O2(aq) → 2H2O(l) + O2(g)
• Manganese(IV) oxide, MnO2, which manganese has the 4+ oxidation state. ( AKA manganese dioxide)
• A catalytic decomposition of hydrogen peroxide is often used in the laboratory as a simple and convenient preparation of oxygen gas.

Question 26

In the laboratory, what is a simple and convenient way to prepare hydrogen gas?
Which catalyst is used?
Write the balanced symbol equation.

Answer 26

-Zinc granules will react dilute sulfuric acid to form hydrogen and zinc sufate.
-When copper(III) sulfate is added, the rate of reaction increases. The transition metal acts as a catalyst.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)