A list of five metals is shown.
(a) All metals form positive ions.
(i) Describe how atoms form positive ions.
(ii) State which of the five metals in the list has the greatest tendency to form positive ions.
(iii) Suggest one of the five metals in the list which is not likely to show catalytic properties.
(iv) State which of the five metals in the list is a major component of stainless steel.
(b) A student adds a sample of a metal to an aqueous metal salt in a beaker to see if a displacement reaction takes place. Complete Table 2.1 to show the colour of the solution in the beaker at the start and at the end of the experiment. 
(c) Most Group II metals form a gas when placed into cold water. An alkaline solution is also formed.
(i) Name the gas formed when strontium is added to cold water.
(ii) Name the alkaline solution formed when strontium is added to cold water.
(iii) One Group II metal reacts very slowly when placed in cold water. When heated, the metal reacts with steam to form a white solid. Identify this metal and name the white solid formed.
(d) Under certain conditions, iron will react with steam to form an oxide of iron with the formula \(Fe_3O_4\). \(Fe_3O_4\) reacts with dilute hydrochloric acid to form a mixture of iron(II) and iron(III) salts and water. Deduce the symbol equation for the reaction between \(Fe_3O_4\) and dilute hydrochloric acid.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 2.2 — Atomic structure and the Periodic Table (Part (a)(i))
• Topic 9.4 — Reactivity series (Part (a)(ii))
• Topic 8.4 — Transition elements (Part (a)(iii))
• Topic 9.3 — Alloys and their properties (Part (a)(iv))
• Topic 9.4 — Displacement reactions (Part (b))
• Topic 9.1 — Properties of metals / Group II properties (Part (c))
• Topic 6.4 — Redox and equations (Part (d))
(a)(i) Atoms form positive ions by losing one or more electrons from their outer shell. This loss reduces the number of negative charges, resulting in a net positive charge.
(a)(ii) Potassium has the greatest tendency to form positive ions because it is the most reactive metal in the list, lying at the top of the reactivity series.
(a)(iii) Magnesium (or potassium) is not likely to show catalytic properties, as these metals are not transition elements; catalytic activity is a common characteristic of transition metals like iron and copper.
(a)(iv) Iron is a major component of stainless steel, which is an alloy of iron with other elements such as chromium, nickel, and carbon.
(b) Completed Table 2.1:
Explanation: Zinc displaces iron from iron(II) sulfate, removing the pale green Fe²⁺(aq) ions. Copper displaces silver from silver nitrate, forming blue Cu²⁺(aq) ions.
(c)(i) Hydrogen is the gas formed when strontium is added to cold water, as Group II metals react to produce hydrogen gas and the metal hydroxide.
(c)(ii) Strontium hydroxide is the alkaline solution formed when strontium reacts with cold water (Sr + 2H₂O → Sr(OH)₂ + H₂).
(c)(iii) M1: Magnesium (Mg). M2: Magnesium oxide (MgO) is the white solid formed when magnesium reacts with steam (Mg + H₂O → MgO + H₂).
(d) The balanced symbol equation is: Fe₃O₄ + 8HCl → 2FeCl₃ + FeCl₂ + 4H₂O
Explanation: Fe₃O₄ contains iron in both +2 and +3 oxidation states. It reacts with 8 moles of HCl to produce one mole of iron(II) chloride, two moles of iron(III) chloride, and four moles of water, balancing all atoms and charges.
