ACSI 2020 Y6 Prelim Paper 3 QP

Anglo-Chinese School (Independent) YEAR 6 PRELIMINARY EXAMINATION 2020 INTERNATIONAL BACCALAUREATE DIPLOMA PROGRAMME CHEMISTRY HIGHER LEVEL Paper 3 Tuesday 15 September 2020 1 hours 15 minutes INSTRUCTIONS TO CANDIDATES • Write your candidate number in the box above. • Do not open this examination paper until instructed to do so. • Answer all questions • A calculator is required for this paper. • A copy of the Chemistry Data Booklet is required for this paper. • Write your answers in the boxes provided. • The maximum marks for this examination paper is 45 marks. ________________________________________________________________________ This question paper consists of 14 printed pages including this cover page. For examiner’s use Section A Qn 1 /7 Qn 2 /8 Section B Qn 3 /6 Qn 4 /6 Qn 5 /8 Qn 6 /10 Total /45 Candidate Number Candidate Full Name

2 Section A Answer all questions. Answers must be written in the answer boxes provided. 1. "Lethal Dose", LD, is a means of measuring toxicity. LD50 is the amount of a material which causes the death of 50% of a group of test animals. Its value is expressed as the mass of a chemical administered per kg body mass of a test animal. "Lethal Concentration", LC, is another means of measuring toxicity. The value of LC 50 is the concentration of a chemical in the air that kills 50% of the test animals during the observation period. The table below shows the values for the LD50 and LC50 along with the toxicity ratings. Toxicity rating Commonly used term LD50: Oral (mg kg–1) LC50: Inhalation (ppm) 1 Extremely Toxic 1 or less 10 or less 2 Highly Toxic 1 – 50 10 – 100 3 Moderately Toxic 50 – 500 100 – 1000 4 Slightly Toxic 500 – 5000 1000 – 10 000 5 Practically Non-toxic 5000 – 15 000 10 000 – 100 000 6 Relatively Harmless 15 000 or more 100 000 or more (a) 9.90 × 10–4 mol of a toxic compound, C 4H5NO, was found to cause death in 50% of test animals weighing 1 kg. Calculate the LD50 of the compound and state its toxicity rating. [2] ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... (This question continues on the following page)

3 (Question 1 continued) (b) Phosphine, PH 3, is a gas widely used in the semiconductor industries as a dopant and a precursor for the deposition of compound semiconductors. For safety considerations, the permissible limits of phosphine must not exceed 10 1 of the LC50 value expressed in terms of ppm. When expressing the concentration of a small quantity of gas, parts per million (ppm) can be used. The unit ‘ppm’ is usually used for volume of gases and is expressed as shown in the equation below: The concentration of gas (in ppm) = volume of gas volume of air × 106 (i) Given that the LC 50 for phosphine is 55 mg m –3 at standard temperature and pressure, convert the LC50 to ppm and determine its toxicity rating. [3] ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... (This question continues on the following page)

4 (Question 1 continued) (ii) A factory in the semiconductor industries attempts to assess the polluting rating based on the air emitted from its factory daily. The semiconductor factory releases 24.0 dm3 of phosphine in a day. Using your value in (b)(i), determine the minimum volume of air emitted that will allow the volume of phosphine to be within permissible limits. (You may assume that the LC50 value is 30.0 ppm if you did not obtain an answer in (b)(i).) [2] ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................

5 2. Calcium iodate(V), Ca(IO3)2, is sparingly soluble in water. It has a solubility of approximately 4.6 g dm‒3 at 25 °C. A student would like to investigate the effect of increasing temperature on the solubility of the salt. He decided to measure the solubility of Ca( IO3)2 using gravimetric analysis. The steps of the experiment were outlined as follows. Step 1: Dissolve 1.0 g of calcium iodate(V) salt into a 100 cm3 distilled water at room temperature. Filter the resulting mixture immediately to separate the undissolved solid from the filtrate. Step 2: Pipette 25 cm3 of the filtrate into a petri dish. Place the petri dish into a drying oven to evaporate the water at 100 oC. Step 3: Remove the petri dish and its content from the oven when the water is completely evaporated. Record the mass of the petri dish and its content. Step 4: Repeat steps 1 to 3 to determine the solubility of the salt at four other temperatures, namely 35, 45, 55 and 65 oC using a Bunsen burner. (a) (a) The solubility of calcium iodate( V) is represented by the following chemical equation. Ca(IO3)2 (s) ⇌ Ca2+ (aq) + 2IO3 − (aq) Hsol > 0 Predict and explain how the solubility of calcium iodate( V) in water changes as the temperature is increased. [3] ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ..................................................................................................