Question 1: Metal hydroxides are compounds formed when metals react with water or oxygen, producing solutions that are typically alkaline. They are important in various industrial processes and are characterised by their chemical formulae and solubility properties.

Answer: Metal hydroxides are compounds consisting of metal cations and hydroxide anions, often formed by the reaction of metals with water or oxygen, and usually exhibit alkaline properties.

Question 1: Define a metal hydroxide and give two examples commonly encountered in the laboratory.

Answer: A metal hydroxide is a compound made of a metal ion and hydroxide ions, such as sodium hydroxide (NaOH) and aluminium hydroxide (Al(OH)₃).

Question 2: Explain why most metal hydroxides are insoluble in water, and name one exception.

Answer: Most metal hydroxides are insoluble because their lattice energy exceeds the hydration energy, but sodium hydroxide (NaOH) is soluble due to its ionic nature and smaller lattice energy.

Question 1: Calculate the number of moles of NaOH in 250 cm³ of a 0.2 mol/dm³ solution.

Answer: n = C × V = 0.2 mol/dm³ × 0.25 dm = 0.05 mol

Question 2: A sample of aluminium hydroxide, Al(OH)₃, weighs 4.8 grams. Calculate the number of moles of Al(OH)₃ present. (Atomic masses: Al = 27, O = 16, H = 1)

Answer: Molar mass = 27 + (3 × 16) + (3 × 1) = 78 g/mol; Moles = 4.8 g / 78 g/mol ≈ 0.0615 mol

Question 1: Describe a safe method to prepare a dilute solution of sodium hydroxide in the laboratory, including safety precautions.

Answer: To prepare a dilute NaOH solution safely, wear eye protection and gloves, add small pieces of NaOH solid to water in a beaker while stirring gently, and add acid-resistant gloves and eye protection to prevent chemical burns. Use a fume cupboard if necessary and label the solution clearly.

Question 1: A student titrates a hydrochloric acid solution with a sodium hydroxide solution. The initial volume of NaOH used is 25.0 cm³, and the concentration of NaOH is 0.1 mol/dm³. Calculate the moles of NaOH used and explain how this relates to the amount of HCl in the original solution.

Answer: Moles of NaOH = 0.1 mol/dm³ × 0.025 dm³ = 0.0025 mol. Since NaOH and HCl react in a 1:1 ratio, the moles of HCl in the original solution are also 0.0025 mol, allowing calculation of its concentration if the volume of HCl was known.

Question 1: Explain how metal hydroxides are used in water treatment processes.

Answer: Metal hydroxides, like aluminium hydroxide, are used to remove impurities by precipitating out unwanted substances, such as sulphur compounds and heavy metals, through coagulation and flocculation.

Question 2: Describe one industrial application of metal hydroxides in the production of paper or textiles.

Answer: Metal hydroxides are used to neutralise acids in the paper and textile industries, and aluminium hydroxide is employed as a filler or to control pH levels.