OCR AS Level Chemistry A H032-02 Depth in Chemistry A Question Paper Oct 2021

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1 This question is about compounds of sulfur. (a) Potassium sulfide, K2S, shows ionic bonding. (i) Explain what is meant by ionic bonding (ii) Draw a ‘dot-and-cross’ diagram to show the bonding... in K2S. Show outer electrons only. (b) Sulfur difluoride, SF2, shows covalent bonding. Draw a ‘dot-and-cross’ diagram to show the bonding in SF2. Show outer electrons only. (c) At room temperature, K2S is a solid, but SF2 is a gas. Use ideas about structure and bonding to explain this difference (d) Sulfur hexafluoride, SF6, is used in medical ultrasound imaging because SF6 is unreactive. (i) State the shape of, and F—S—F bond angle in, an SF6 molecule. 3 Glutaric acid is used in the production of polymers. The formula of glutaric acid can be represented as HOOC(CH2)nCOOH, where n is a whole number. A student carries out a titration to find the value of n. 1. The student dissolves 2.891 g of glutaric acid in water and makes up the solution to 250.0 cm3 in a volumetric flask. 2. The student transfers 25.0 cm3 of this solution into a conical flask. 3. The student titrates the solution with 0.240 mol dm–3 NaOH(aq) in the burette. Equation: HOOC(CH2)nCOOH(aq) + 2NaOH(aq) NaOOC(CH2)nCOONa(aq) + 2H2O(l) The student uses phenolphthalein as the indicator. Phenolphthalein is colourless in acid and pink in alkali. (a) State the colour change observed at the end point of the titration. Colour from ....................................................... to ....................................................... [1] (b) The student carries out a trial titration followed by three further titrations, 1, 2 and 3 [Show More]

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