** in the $^{13}\\text{C}$ NMR spectrum."},{"type":"text","order":4,"title":"Draw conclusion","content":"Now we compare our results:\n\n- **1,2-dimethylbenzene** has **4 peaks**.\n- **1,3-dimethylbenzene** has **5 peaks**.\n- **1,4-dimethylbenzene** has **3 peaks**.\n\nSince each isomer produces a different, unique number of peaks in its $^{13}\\text{C}$ NMR spectrum, **the student is correct**; $^{13}\\text{C}$ NMR spectroscopy can successfully distinguish between all three isomers."}]}],"generatedAt":"2026-06-11T07:59:52.342Z","modelVersion":"gemini-3.5-flash","explanationVersion":"v2"},"firstAttemptFullMarks":null},{"id":"82eee118-63f3-4785-b13a-acec85fc5d3e","revisionId":"a51890d1-fe31-4d5b-8367-a1f5502bfd28","questionNumber":null,"questionType":"LA","specification":"A sample of peppermint essential oil contains four terpene-derived compounds, **W**, **X**, **Y**, and **Z**, which are analyzed by gas chromatography and mass spectrometry. The results are summarized in the table below:\n\n| Compound | Retention time / minutes | Relative peak area (relative molar proportion) | \$m/z\$ of molecular ion peak |\n| :---: | :---: | :---: | :---: |\n| **W** | 3.4 | 1.6 | 136 |\n| **X** | 5.1 | 3.2 | 154 |\n| **Y** | 6.8 | 4.8 | 196 |\n| **Z** | 7.3 | 2.5 | 154 |\n\nThe concentration of compound **X** in the essential oil is \$8.47 \\times 10^{-2}\\text{ g dm}^{-3}\$.","difficulty":5,"difficultyBand":"medium","totalMarks":4,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"c76e1cf4-0fcd-4fbb-bd7d-a860b7eef3de","label":null,"content":"Using the results, calculate the concentration, in \$\\text{mol dm}^{-3}\$, of compound **Y** in the essential oil.\n\nGive your answer to **two** significant figures.","markscheme":"- Calculates the molar mass of **X** from its molecular ion peak as $154\\text{ g mol}^{-1}$ and sets up the conversion to $\\text{mol dm}^{-3}$: $\\text{Concentration of X} = \\frac{8.47 \\times 10^{-2}}{154}$ M1\n- Obtains $\\text{Concentration of X} = 5.50 \\times 10^{-4}\\text{ mol dm}^{-3}$ A1\n- Sets up the ratio conversion using relative peak areas: $\\text{Concentration of Y} = 5.50 \\times 10^{-4} \\times \\frac{4.8}{3.2}$ M1\n- States the final concentration of **Y** as $8.3 \\times 10^{-4}\\text{ mol dm}^{-3}$ (rounded to 2 s.f.) A1","marks":4,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"molar_ratio_conversion","label":"Molar Ratio Conversion","steps":[{"type":"text","order":0,"title":"Analyze the problem","content":"We need to find the molar concentration (in $\\text{mol dm}^{-3}$) of compound **Y** in the peppermint essential oil.\n\nFrom the given table, we have:\n* The molecular ion peak $m/z$ of **X** is $154$, which corresponds to its molar mass $M = 154\\text{ g mol}^{-1}$.\n* The relative peak area (relative molar proportion) of **X** is $3.2$.\n* The relative peak area (relative molar proportion) of **Y** is $4.8$.\n* The mass concentration of **X** is $8.47 \\times 10^{-2}\\text{ g dm}^{-3}$.","highlights":[{"text":"The concentration of compound X in the essential oil is 8.47 \\times 10^{-2}\\text{ g dm}^{-3}","location":"specification"}]},{"type":"text","order":1,"title":"Calculate molar concentration of X","content":"To convert the mass concentration of **X** to molar concentration, we use its molar mass ($154\\text{ g mol}^{-1}$):\n\n$$\\text{Molar concentration of X} = \\frac{\\text{Mass concentration}}{\\text{Molar mass}}$$\n\nSubstituting the values:\n\n$$\\text{Molar concentration of X} = \\frac{8.47 \\times 10^{-2}\\text{ g dm}^{-3}}{154\\text{ g mol}^{-1}} \\approx 5.50 \\times 10^{-4}\\text{ mol dm}^{-3}$$\n\n*This earns the first two marks (M1, A1) of the question.*","calculator":[{"gdc":{"expression":"(8.47 * 10^-2) / 154","instructions":"Enter (8.47 * 10^-2) / 154 into the main calculation screen and press EXE."},"ti84":{"expression":"(8.47 * 10^-2) / 154","instructions":"Enter (8.47 * 10^-2) / 154 into the main screen and

Analysis

Question 16

Analysis Questions

Analysis

Question 16

Analysis Questions