RI Y3 Chem Exercise observations involving acids and bases.pdf

Raffles Institution Raffles Programme Year Three Chemistry Name: _____________________________________ ( ) Class: ________ Date: _____________ Exercise– Observations of Reactions Involving Acids and Bases 1 It is important for science students to learn to record observations correctly so that the scientific community has a common language and understanding. 2 For reactions involving acids and bases, the 4 main types of observations involve: (a) production of a gas (b) production of a solid (precipitate) (c) dissolving of a solid to form a solution (d) colour change of pH indicator 3 The following table gives examples of the correct observations. Reaction Equation Observations dilute hydrochloric acid + zinc carbonate 2HCl (aq) + ZnCO3 (s)  ZnCl2 (aq) + CO2 (g) + H2O (l) Effervescence. The solid dissolves to form a colourless solution. dilute sulfuric acid + magnesium H2SO4 (aq) + Mg (s)  MgSO4 (aq) + H2 (g) Effervescence. The solid dissolves to form a colourless solution. dilute sodium hydroxide + calcium chloride solution 2NaOH (aq) + CaCl2 (aq)  Ca(OH)2 (s) + 2NaCl (aq) A white ppt is formed dilute sodium hydroxide + iron(II) sulfate solution 2NaOH (aq) + FeSO4 (aq)  Fe(OH)2 (s) + Na2SO4 (aq) A green ppt is formed Note: Students must distinguish between observations and inferences 4 Teacher Demonstration Reaction Observations 1. To a few pieces of marble chips (calcium carbonate) add dilute hydrochloric acid. 2. To a small volume of zinc chloride solution add aqueous sodium hydroxide. Divide the mixture into 2 portions. (a) To one portion of the mixture add dilute hydrochloric acid. (b) To the other portion of the mixture add aqueous sodium hydroxide.