\text{O}_2 + 6\\text{O}_2 \\rightarrow 5\\text{CO}_2 + 4\\text{H}_2\\text{O}$ B1\n- Calculates the volume of $\\text{CO}_2$ produced: $V = 365 - 125 = 240\\text{ cm}^3$ or $2.40 \\times 10^{-4}\\text{ m}^3$ M1\n- Calculates the amount in moles of $\\text{CO}_2$ using $n = \\frac{pV}{RT}$ with temperature in $\\text{K}$ and pressure in $\\text{Pa}$: $n(\\text{CO}_2) = \\frac{102 \\times 10^3 \\times 240 \\times 10^{-6}}{8.31 \\times 293} = 1.01 \\times 10^{-2}\\text{ mol}$ M1\n- Determines the moles of $\\text{Y}$ using the $1:5$ stoichiometric ratio: $n(\\text{Y}) = 2.01 \\times 10^{-3}\\text{ mol}$ M1\n- Calculates the mass of $\\text{Y}$ using $M_r = 100.0\\text{ g mol}^{-1}$ to give $201\\text{ mg}$ (or $200\\text{ mg}$ to 2 s.f.) A1","marks":5,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"ideal_gas_stoichiometry","label":"Ideal Gas Law and Stoichiometry","steps":[{"type":"text","order":0,"title":"Write balanced combustion equation","content":"First, we write a balanced chemical equation for the complete combustion of $\\text{Y}$ ($\\text{C}_5\\text{H}_8\text{O}_2$) in oxygen to produce carbon dioxide ($\\text{CO}_2$) and water ($\\text{H}_2\text{O}$):\n\n$$\\text{C}_5\\text{H}_8\\text{O}_2 + 6\\text{O}_2 \\rightarrow 5\\text{CO}_2 + 4\\text{H}_2\\text{O}$$\n\n*Award 1 mark (B1) for the correct balanced equation.*","highlights":[{"text":"C_5H_8O_2","location":"specification"}]},{"type":"text","order":1,"title":"Find carbon dioxide volume","content":"When the gaseous mixture is passed through aqueous sodium hydroxide ($\\text{NaOH}$), the acidic carbon dioxide gas is absorbed. The reduction in the total gas volume is equal to the volume of $\\text{CO}_2$ produced.\n\n$$V(\\text{CO}_2) = 365\\text{ cm}^3 - 125\\text{ cm}^3 = 240\\text{ cm}^3$$\n\nTo use this in the ideal gas equation, we convert it to cubic meters ($\\text{m}^3$):\n\n$$V = 240 \\times 10^{-6}\\text{ m}^3 = 2.40 \\times 10^{-4}\\text{ m}^3$$\n\n*Award 1 mark (M1) for calculating this volume.*","highlights":[{"text":"total volume of gas remaining was 365 cm^3","location":"specification"},{"text":"volume of gas decreased to 125 cm^3","location":"specification"}]},{"type":"text","order":2,"title":"Calculate moles of CO₂","content":"Next, we calculate the moles of $\\text{CO}_2$ produced using the ideal gas equation:\n\n$$pV = nRT \\implies n = \\frac{pV}{RT}$$\n\nFirst, convert temperature and pressure to SI units:\n- Temperature ($T$): $20\\text{ }^\\circ\\text{C} + 273.15 = 293\\text{ K}$ (using $293\\text{ K}$)\n- Pressure ($p$): $102\\text{ kPa} = 102 \\times 10^3\\text{ Pa}$\n\nSubstitute these values into the formula:\n\n$$n(\\text{CO}_2) = \\frac{(102 \\times 10^3\\text{ Pa}) \\times (2.40 \\times 10^{-4}\\text{ m}^3)}{8.31\\text{ J K}^{-1}\\text{ mol}^{-1} \\times 293\\text{ K}} \\approx 0.01006\\text{ mol}$$\n\n*Award 1 mark (M1) for calculating the moles of $\\text{CO}_2$.*","highlights":[{"text":"20 ^∘C and 102 kPa","location":"specification"},{"text":"R = 8.31 J K^{-1} mol^{-1}","location":"specification"}]},{"type":"text","order":3,"title":"Determine moles of Y","content":"From our balanced equation in Step 1, the molar ratio of $\\text{Y}$ to $\\text{CO}_2$ is $1:5$. Thus:\n\n$$n(\\text{Y}) = \\frac{n(\\text{CO}_2)}{5} = \\frac{0.01006\\text{ mol}}{5} \\approx 2.01 \\times 10^{-3}\\text{ mol}$$\n\n*Award 1 mark (M1) for using the stoichiometric ratio to find the moles of $\\text{Y}$.*"},{"type":"text","order":4,"title":"Calculate mass of Y","content":"Now we determine the molar mass ($M_r$) of $\\text{Y}$ ($\\text{C}_5\\text{H}_8\text{O}_2$):\n\n$$M_r = (5 \\times 12.0) + (8 \\times 1.0) + (2 \\times 16.0) = 100.0\\text{ g mol}^{-1}$$\n\nNow, calculate the mass of $\\text{Y}$:\n\n$$\\text{mass of Y} = n \\times M_r = (2.012 \\times 10^{-3}\\text{ mol}) \\times 100.0\\text{ g mol}^{-1} = 0.201\\text{ g}$$\n\nConvert this mass to milligrams ($\\text{mg}$):\n\n$$\\text{mass of Y} = 0.201\\text{ g} \\times 1000 = 201\\text{ mg}$$\n\n*(Accept $200\\text

Amount of substance

Question 25

Amount of substance Questions

Amount of substance

Question 25

Amount of substance Questions