This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Here are the solutions to the organic chemistry questions: 1. Recrystallization as a method of purification relies on the _______. Recrystallization is a purification technique that relies on the difference in solubility of the desired compound and its impurities in a given solvent at different temperatures. The desired compound is typically much more soluble in hot solvent than in cold solvent, while impurities are either much more soluble (remaining in solution upon cooling) or much less soluble (filtered off before cooling). While melting point differences are used to assess purity, the method itself primarily relies on solubility. The correct option is A. 2. All the structures given in the options below exist as isomers except which one? To determine isomers, we need to find the molecular formula for each structure. Isomers have the same molecular formula but different structural formulas. A: This is an alkene with 7 carbons and 1 double bond. Molecular formula: C_7H_14 B: This is an alkene with 7 carbons and 1 double bond. Molecular formula: C_7H_14 C: This is a dimethylcyclohexane. A cyclohexane ring has 6 carbons. With two methyl groups, it has 8 carbons. Cycloalkanes have the general formula C_nH_2n. Molecular formula: C_8H_16 D: This is a branched alkane with 7 carbons. Alkanes have the general formula C_nH_2n+2. Molecular formula: C_7H_16 Comparing the molecular formulas: A: C_7H_14 B: C_7H_14 C: C_8H_16 D: C_7H_16 Structures A and B are isomers of each other. Structure D has a different molecular formula from A and B. Structure C has a different number of carbon atoms (8 carbons) compared to A, B, and D (all 7 carbons). Therefore, C is the structure that is not an isomer of any of the others, as it has a different carbon count. The correct option is C. 3. Pure cinnamic acid has a literature melting point of 132.5 – 133.0 °C. Which of the following melting point data would not be an acceptable observed melting point for pure cinnamic acid in the lab? A pure substance has a sharp melting point that matches its literature value. Impurities typically cause a melting point to be lower and broader. An acceptable observed melting point should be very close to the literature value, possibly slightly lower and/or slightly broader due to minor experimental variations or trace impurities. A. 132.0 – 133.0 °C: This range is very close to the literature value and only slightly broader on the lower end. This is acceptable. B. 132.5 – 133.5 °C: This range is very close to the literature value and only slightly broader on the higher end. This is acceptable. C. 132.0 – 133.5 °C: This range is slightly broader than the literature value but still very close. This is acceptable. D. 128.0 – 137.5 °C: This range is significantly lower than the literature value (starting at 128.0 °C instead of 132.5 °C) and much broader (a 9.5 °C range compared to a 0.5 °C range). This indicates significant impurities and would not be acceptable for pure cinnamic acid. The correct option is D. 4. Liquified petroleum gas is mainly composed of _______. Liquified Petroleum Gas (LPG) is a flammable mixture of hydrocarbon gases used as fuel. Its primary components are propane and butane. Methane and ethane are the main components of natural gas. The correct option is C. 11. Select which option is the correct IUPAC name for the compound shown below. The compound is: ` CH3 | CH3-CH-CH-CH-CH2-CH3 | | CH2 CH3 | CH3 ` Step 1: Identify the longest continuous carbon chain. The longest chain has 6 carbons (hexane). Step 2: Number the chain to give substituents the lowest possible numbers. Numbering from left to right: C_1H_3-C_2H(CH_3)-C_3H(CH_2CH_3)-C_4H(CH_3)-C_5H_2-C_6H_3 Substituents are at positions 2 (methyl), 3 (ethyl), and 4 (methyl). The sum of locants is 2+3+4=9. Numbering from right to left: C_6H_3-C_5H_2-C_4H(CH_3)-C_3H(CH_2CH_3)-C_2H(CH_3)-C_1H_3 Substituents are at positions 2 (methyl), 3 (ethyl), and 4 (methyl). The sum of locants is 2+3+4=9. Both numbering schemes give the same set of locants. Step 3: List the substituents in alphabetical order. Ethyl comes before methyl. There are two methyl groups, so "dimethyl". The name is 3-ethyl-2,4-dimethylhexane. The correct option is A. 12. How many primary carbon atoms are contained in the hydrocarbon chain provided below? A primary carbon atom (1°) is bonded to only one other carbon atom. Let's identify each carbon type in the given structure: ` CH3 (1°) | CH3(1°)-C(4°)-CH2(2°)-CH(3°)-CH2(2°)-CH3(1°) | | CH3(1°) CH3(1°) ` 1. The leftmost CH_3 group: Primary (bonded to one carbon). 2. The top CH_3 group (attached to the quaternary carbon): Primary (bonded to one carbon). 3. The bottom-left CH_3 group (attached to the quaternary carbon): Primary (bonded to one carbon). 4. The bottom-right CH_3 group (attached to the tertiary carbon): Primary (bonded to one carbon). 5. The rightmost CH_3 group: Primary (bonded to one carbon). Counting these, there are 5 primary carbon atoms. Since 5 is not among the given options (A. n=1, B. n=3, C. n=6, D. n=2), there might be an error in the question's options. However, if forced to choose the closest option, 6 is the closest. Given the options, and the clear structure, the most accurate count is 5. If there is a single correct answer among the options, the question or options may be flawed. Assuming there might be a slight misinterpretation or a common error leading to one of the options, let's re-evaluate if any common mistake could lead to 6. If the leftmost carbon was part of a longer chain and the first methyl was not a terminal methyl, it could change. But as drawn, it's 5. Let's assume there's a typo in the question and it meant to ask for the total number of methyl groups, which is 5. Or if one of the secondary carbons was somehow misidentified. Given the options, and the possibility of a slight error in the question, I will state the correct count. There are 5 primary carbon atoms. Since this is not an option, I cannot select one of the provided choices. 13. An Organic compound contains 20% Carbon, 6.66% Hydrogen, 47.33% Nitrogen and the rest was oxygen. Its molar mass is 60 gmol^-1. The molecular formula of the compound is? Step 1: Determine the percentage of Oxygen. Percentage of Oxygen = 100\% - (20\% C + 6.66\% H + 47.33\% N) Percentage of Oxygen = 100\% - 73.99\% = 26.01\% Step 2: Assume a 100 g sample and convert percentages to grams. Carbon (C): 20 g Hydrogen (H): 6.66 g Nitrogen (N): 47.33 g Oxygen (O): 26.01 g Step 3: Convert grams to moles using atomic masses (C=12.01, H=1.008, N=14.01, O=16.00). Moles of C = 20 g12.01 g/mol ≈ 1.665 mol Moles of H = 6.66 g1.008 g/mol ≈ 6.607 mol Moles of N = 47.33 g14.01 g/mol ≈ 3.378 mol Moles of O = 26.01 g16.00 g/mol ≈ 1.626 mol Step 4: Divide by the smallest number of moles to find the empirical formula ratio. Smallest number of moles is approximately 1.626 mol (for Oxygen). C: (1.665)/(1.626) ≈ 1.02 ≈ 1 H: (6.607)/(1.626) ≈ 4.06 ≈ 4 N: (3.378)/(1.626) ≈ 2.07 ≈ 2 O: (1.626)/(1.626) = 1 The empirical formula is CH_4N_2O. Step 5: Calculate the empirical formula mass. Empirical formula mass = (1 × 12.01) + (4 × 1.008) + (2 × 14.01) + (1 × 16.00) Empirical formula mass = 12.01 + 4.032 + 28.02 + 16.00 = 60.062 g/mol Step 6: Compare the empirical formula mass to the given molar mass. Molar mass = 60 g/mol Empirical formula mass ≈ 60 g/mol Since the molar mass is approximately equal to the empirical formula mass, the molecular formula is the same as the empirical formula. The molecular formula is CH_4N_2O. The correct option is B. 14. Which of the following is not an isomeric form of the alkene C_5H_10? An alkene with the formula C_5H_10 has one double bond or is a cycloalkane. We need to check the molecular formula for each given option. A. 3-methyl-2-butene: Butene (4 carbons) + methyl (1 carbon) = 5 carbons. It's an alkene, so C_5H_10. (e.g., CH_3-CH=C(CH_3)-CH_3) This is an isomer of C_5H_10. B. 3-methyl-1-butene: Butene (4 carbons) + methyl (1 carbon) = 5 carbons. It's an alkene, so C_5H_10. (e.g., CH_2=CH-CH(CH_3)-CH_3) This is an isomer of C_5H_10. C. 2-methyl-2-butene: Butene (4 carbons) + methyl (1 carbon) = 5 carbons. It's an alkene, so C_5H_10. (e.g., CH_3-C(CH_3)=CH-CH_3) This is an isomer of C_5H_10. D. 2-methyl-1-butene: Butene (4 carbons) + methyl (1 carbon) = 5 carbons. It's an alkene, so C_5H_10. (e.g., CH_2=C(CH_3)-CH_2-CH_3) This is an isomer of C_5H_10. All the given options are isomers of C_5H_10. This suggests there might be an error in the question or options, as it asks "Which of the following is not an isomeric form". All listed compounds are indeed isomers of C_5H_10 (pentenes). If I must choose one, and assuming there's a subtle error in the question's premise, I would re-examine if any of these names are invalid or refer to a different formula. All names are valid for C_5H_10 isomers. Given that all options are valid isomers of C_5H_10, there is no correct answer among the choices for "not an isomeric form". Drop the next question! 📸