Copy of SCSS Prelim 2024 Chem P3 MS

1 SWISS COTTAGE SECONDARY SCHOOL SECONDARY 4 CHEMISTRY 6092 PRELIMINARY EXAMINATION 2024 PAPER 3 MARK SCHEME Question Skill MS Mark Total 1(a) PDO MMO all temperature readings recorded to 0.5 C temperature changes correctly calculated (to 1 d.p.) and ‘+’ sign is included full set of data + correct trend (rise in temperature decreases with deceasing volume of P used) temperature rise for first reading is greater than 10 C 1 1 1 1 [4] 1(b) PDO correct axis labels and units appropriate scale + size of plotted area covers at least 50% of the graph paper all points correctly plotted correct line of best fit, allow ecf from wrongly plotted points accept both straight line and curved line as long as the line is the best fit anomalous points must be circled 1 1 1 1 [4] 1(c) ACE rise in temperature decreases as the volume of P decreases / rise in temperature increases as the volume of P increases greater volume of P used means greater number of moles of aci d to react with the magnesium, leading to more energy given off 1 1 [2] 1(d) ACE volume of P = 0.0065 1.000 = 6.5 cm3 correct calculation and unit temperature change correctly read with unit and shown clearly on the graph 1 1 [2] 1(e) ACE Answer 1 His prediction was correct. As the amount of magnesium ribbon that reacted with the acid doubled, the amount of energy produced would also be doubled. Thus, the rise in temperature also doubled. The prediction is only correct if it is assumed that the acid is not used up in the reaction. / there is no heat loss to the surroundings. / the pieces of magnesium ribbon have exactly the same length. 1 1 [2]

2 Answer 2 His prediction was not correct. Although the amount of magnesium ribbon added to the acid doubled, there may not be sufficient acid to react completely with the magnesium. / the acid could be the limiting reagent. / the magnesium ribbon s could be added in excess. Thus, amount of energy produced may not be doubled. Thus, the rise in temperature may not be doubled. He assumed that there is excess acid present to react completely with the magnesium ribbons. / the acid is not used up in the reaction. / magnesium ribbons reacted completely with the acid. R: the pieces of magnesium ribbon have exactly the same length. 1 1 1(f) MMO ACE any two observations with relevant explanation observation: Effervescence is seen. / Bubbles are seen. explanation: The reaction produces hydrogen gas. observation: Magnesium dissolves to form a colourless solution. explanation: Soluble magnesium chloride is formed. 1 1 1 1 max [4] 1(g) ACE error: A measuring cylinder was used to measure the volumes of P and water. This was not accurate / precise as it can only measure up to 0.1 cm3. improvement: A burette should be used inste