Gold and iron extraction are important mining processes in South Africa. Refining takesplace according to the following reactions: Gold is dissolved using cyanide ions (CN–) to extract it from the ore: 4Au(s) + 8NaCN(aq) + 2H2O(ℓ) + O2(g) → 4NaAu(CN)2(aq) + 4NaOH(aq) Iron(lll)oxide is burned in a furnace in the presence of CO: Fe2O3(s) + … Read more
MnO4 (aq) + H+(aq) + H2S(g) → Mn2+(aq) + S(s) + H2O(ℓ) 9.1 Define reduction in terms of oxidation numbers. (2) 9.2 Determine the oxidation number of manganese in the permanganate ion. (1) 9.3 Write down the FORMULA of the substance that undergoes oxidation. (1) 9.4 Explain the answer to QUESTION 9.3 in terms of … Read more
Ammonia can readily dissolve in water according to the equation below: 8.1 Explain why a hydroxide ion is regarded as a Lowry-Brønsted base. (2) 8.2 Identify the type of bond responsible for the formation of the ammonium ion inthe above equation. (1) 8.3 Write a balanced equation to show how the ampholyte in the above … Read more
The following reaction between ammonia and oxygen takes place in a closed systemat constant pressure and temperature: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) 7.1 Define the term activation energy. (2) 7.2 Give a reason why this reaction is exothermic. (1) 7.3 Calculate the heat of reaction. (3) 7.4 Redraw the graph and indicate with … Read more
6.1 In an experiment, a learner added 1,5 g of sodium carbonate (Na2CO3) tohydrochloric acid (HCℓ). A volume of 306 cm3 of carbon dioxide gas wasformed and collected under standard pressure at room temperature. Take themolar gas volume at room temperature (Vm) as 24,45 dm3. The unbalanced equation for the reaction is: Na2CO3(s) + HCℓ(aq) … Read more
A balloon is filled with 160 g of argon gas (Ar). The pressure of the gas is 120 kPa ata temperature of 15 ºC. 5.1 Calculate the volume of the balloon. (4) 5.2 The temperature of the gas is now increased BY 20 ºC and the initial pressureis doubled. Calculate the new volume of the … Read more
A certain amount of gas is sealed in a container of which the volume can change.The relationship between the pressure and volume of the gas at 20 ºC is investigated.The results of the experiment are given in the table below. 4.1 Name the gas law that is represented by the results of the experiment. (1) … Read more
The reaction below is used in the Haber process to manufacture ammonia N2(g) + 3H2(g) → 2NH3(g) The boiling points of the substances in the reaction are as follows: 3.1 Refer to the intermolecular forces and explain the difference in boiling pointbetween NH3 and N2. (3) 3.2 Write down the FORMULA of the substance in … Read more
Hydrogen cyanide (HCN) is a very poisonous compound used in the manufacturing ofplastics, mining of gold and as a poison. 2.1 Define the term chemical bond. (2) 2.2 Draw Lewis structures for: 2.2.1 HCN (2) 2.2.2 H2O (2) 2.3 What is the shape of the HCN molecule? (1) 2.4 Calculate the electronegativity difference for the … Read more
2.1 Determine the: 2.1.1 Length of PQ. Leave your answer in surd form. (2) 2.1.2 Gradient of PQ (2) 2.1.3 Coordinates of T (2) 2.2 Calculate the: 2.2.1 Area of ΔAQTR (3) 2.2.2 Size of θ, with reasons (2) 2.2.3 Coordinates of S (3) 2.3 Determine, with reasons, the gradient of the line through T … Read more