This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Let's go through these chemistry questions step by step. Question 1 1) (i) Calculate the molarity of solution A using the following equations: Given equations: 1. Cr_2O_7^2- + 14H^+ + 6I^- 2Cr^3+ + 7H_2O + 3I_2 2. 2S_2O_3^2- + I_2 2I^- + S_4O_6^2- From your previous work, the mean titre (volume of S_2O_3^2- solution) is 15.65 cm^3. We will assume the concentration of the S_2O_3^2- solution is 0.025 M, as implied by your partial calculation. The volume of solution A used for titration is typically 25.0 cm^3. Step 1: Calculate the moles of S_2O_3^2- used. Moles of S_2O_3^2- = Concentration × Volume Moles of S_2O_3^2- = 0.025 mol dm^-3 × (15.65)/(1000) dm^3 Moles of S_2O_3^2- = 0.00039125 mol Step 2: Calculate the moles of I_2 produced. From equation (2), the mole ratio of S_2O_3^2- to I_2 is 2:1. Moles of I_2 = Moles of S_2O_3^2-2 Moles of I_2 = 0.00039125 mol2 Moles of I_2 = 0.000195625 mol Step 3: Calculate the moles of Cr_2O_7^2- (solution A) reacted. From equation (1), the mole ratio of Cr_2O_7^2- to I_2 is 1:3. Moles of Cr_2O_7^2- = Moles of I_23 Moles of Cr_2O_7^2- = 0.000195625 mol3 Moles of Cr_2O_7^2- = 0.0000652083 mol Step 4: Calculate the molarity of solution A. The volume of solution A used was 25.0 cm^3 (0.025 dm^3). Molarity of A = Moles of Cr_2O_7^2-Volume of A Molarity of A = 0.0000652083 mol0.025 dm^3 Molarity of A = 0.00260833 mol dm^-3 The molarity of solution A is 0.00261 M (to 3 significant figures). 1) (ii) Is the reaction occurring in table 2 exothermic or endothermic? Explain. The reaction is endothermic. The temperature of the water decreased from 27.0^ to 21.5^. This indicates that the reaction absorbed heat from the surroundings (the water), causing the temperature of the water to drop. Question 2 a) (i) Carry out a flame test on a solid sample of E. Observations: Lilac flame Inferences: The presence of potassium ions (K^+). (A lilac flame is characteristic of potassium.) a) (ii) To a solid portion of E in a dry test tube, add 1 cm^3 of conc. H_2SO_4, test for any gas evolved with red and blue litmus paper. Observations: Gas turns blue litmus paper red; red litmus paper shows no observable change. This indicates an acidic gas is evolved. Inferences: The evolution of an acidic gas (likely brown fumes of NO_2) when a solid reacts with concentrated sulfuric acid suggests the presence of nitrite ions (NO_2^-). (Nitrites react with conc. H_2SO_4 to produce acidic brown fumes of nitrogen dioxide.) Last free one today — make it count tomorrow, or type /upgrade for unlimited.