CHM 003 Assignment

QUESTION 1

Strontium, ₃₆Sr, is an element in Group II of the periodic table

1. State the full electronic configuration of an atom of strontium.
2. Strontium nitrate, Sr(NO₃)₂ undergoes thermal decomposition.
   1. State one observation you would make during this reaction
   2. Write a balanced equation for this reaction (3 marks)
3. Samples of magnesium and calcium are placed separately in cold water and left for some time. In each case, describe what you would see and write a balanced equation for each reaction.
   1. Magnesium
      Observation;
      Equation;
   2. Calcium
      Observations;
      Equation; (6 marks)

QUESTION 2

The melting points of some oxides of Group iv elements are given below

Oxide Melting point/^OC

CO₂ -78

SiO₂ 1610

SnO₂ 1630

1. Describe the bonding in each oxide, and how it related to its melting point
   CO₂ (ii) SiO₂ (iii) SnO₂ (3 marks)
2. Writing balanced equations where appropriate, describe how the above three oxides differ in their reactions with
   1. NaOH (aq)
   2. HCl (_aq) (4marks)

3. Going down Group IV there is a variation in the relative stabilities of the higher and lower oxidation states of the elements in their oxides.

   Illustrating your answers with balanced equations, in each of the following cases suggest one piece of chemical evidence to show that

   1. CO is less stable than CO₂
   2. PbO is more stable than PbO₂

QUESTION 3

1. i. Write an equation for the reaction between chlorine and hydrogen
   ii. Describe and explain the trend observed in the reactions of the elements chlorine, bromine and iodine with hydrogen (5 marks)
2. i. Describe what you would see when aqueous silver nitrate aqueous sodium bromide and aqueous sodium iodide.
   ii. Describe and explain the effect of adding aqueous ammonal to each of the resulting mixtures (5 marks)

QUESTION 4

1. State the electronic configuration of the chromium atom and predict two of the likely oxidation states of chromium (2 marks)
2. Anhydrous copper sulphate, CuSO₄(s) is a white powder that readily dissolves in water.
   1. Describe and explain what is seen when CuSO₄(s) is stirred with water.
   2. Describe and explain the final colour change seen when an excess of NH_3(aq) is added to CuSO_4(aq) (4 marks)
3. i. Explain why so many transition element complexes are coloured
   ii. Give the IUPAC name of each of the following coordination compounds.
   1. [Pt (NH₃)₂Cl]₂
   2. [PtCl₄]^2-

QUESTION 5

Nitrogen, which makes up about 80% of the Earth’s atmosphere, is very unreactive .

1. i. Explain the lack of reactivity of nitrogen
   ii. Nitrogen does, however, undergo some reactions. Write an equation for one reaction of nitrogen, stating the conditions under which it occurs.
   iii. Suggest why nitrogen does react in the example you have chosen.
2. i. Explain with equations ONLY how hydrogen can behave as a metal and as a non-metal (2 marks)
   ii. Mention two(2) uses of hydrogen (2 marks)

QUESTION 6

Sulphur and its compounds are found in volcanoes, in organic matter and in minerals. Sulphuric acid, an important industrial chemical, is manufactured from sulphur by the contact process. There are three conceptive reactions in the contact process which are essential.

1. Write a balanced equation (using where appropriate) for each of these reactions in the correct sequence (4 marks).
2. What catalyst is used? (1 mark)

   Hydrogen sulphide burns with a blue flame in an excess of oxygen to form sulphur dioxide and water.

3. i. Write a balanced equation for the complete combustion of H₂S
   ii. What is the change in the oxidation number of sulphur in this reaction? From_____ to____
   iii. What volume of oxygen, measured at room temperature and pressure is required for the complete combustion of 8.65g of H₂S? Give your answer to two decimal places (5 marks).