18.1. Carboxylic acids
A subsection of Chemistry, 9701, through 18. Carboxylic acids and derivatives
Listing 10 of 132 questions
Ethanedioic acid, C2O4H2, occurs in many vegetables. The amount that occurs in spinach can be estimated as follows. • 40.0 g of spinach leaves are crushed and mixed with distilled water, using a mortar and pestle. • The mixture is filtered, and the leaves are washed with a little more water. • The combined filtrate and washings are made up to 100.0 cm3 with water. • A 25.0 cm3 portion of the resulting solution is added to a conical flask, along with an excess of dilute sulfuric acid. • The acidified solution is warmed, and then titrated with 0.0200 mol dm–3 KMnO4. The equation for the reaction between ethanedioic acid and acidified manganate(ions is shown. 2MnO4 – + 6H+ + 5C2O4H2 → 2Mn2+ + 10CO2 + 8H2O In the titration, 15.20 cm3 of KMnO4 was required to reach the end-point. Calculate the percentage by mass of ethanedioic acid in the spinach leaves. percentage of ethanedioic acid = % Ethanedioic acid can be converted into ethanedioyl chloride: HO2CCO2H → Cl OCCOCl State a suitable reagent for this reaction. For the reactions of ethanedioyl chloride below, suggest the structures of compounds J and K and draw them in the boxes. CH3OH H2NCH2CH2NH2 K (C4H6N2O2) J (C4H6O4) COCl COCl When ethanedioyl chloride is reacted with silver ethanedioate, AgO2CCO2Ag, in ethoxyethane at –30 °C, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has molecular formula C4O6. The carbon-13 NMR spectrum of a solution of L in ethoxyethane, CH3CH2OCH2CH3, is shown below. δ Use the Data Booklet to state in the boxes below the δ values for the peaks in the spectrum which are due to the carbon atoms in ethoxyethane. CH3 CH3 CH2 CH2 O δ values Explain what the rest of the carbon-13 NMR spectrum indicates about the structure of L. When pure L is reacted with an excess of CH3OH, a mixture of three compounds is formed. L and CH3OH → M and N and O (C4O6) (C2H2O4) (C3H4O4) (C4H6O4) M is formed as one of the products when either N or O is heated with aqueous acid. The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O. compound peaks recorded in carbon-13 NMR spectrum M δ 162 N δ 53 δ 160 δ 162 O δ 53 δ 160 Suggest the structures of M, N and O. M, (C2H2O4) N, (C3H4O4) O, (C4H6O4) Suggest a structure for L that fits all the data given in and . L, (C4O6)
9701_s16_qp_41
THEORY
2016
Paper 4, Variant 1
View
Ethanedioic acid, C2O4H2, occurs in many vegetables. The amount that occurs in spinach can be estimated as follows. • 40.0 g of spinach leaves are crushed and mixed with distilled water, using a mortar and pestle. • The mixture is filtered, and the leaves are washed with a little more water. • The combined filtrate and washings are made up to 100.0 cm3 with water. • A 25.0 cm3 portion of the resulting solution is added to a conical flask, along with an excess of dilute sulfuric acid. • The acidified solution is warmed, and then titrated with 0.0200 mol dm–3 KMnO4. The equation for the reaction between ethanedioic acid and acidified manganate(ions is shown. 2MnO4 – + 6H+ + 5C2O4H2 → 2Mn2+ + 10CO2 + 8H2O In the titration, 15.20 cm3 of KMnO4 was required to reach the end-point. Calculate the percentage by mass of ethanedioic acid in the spinach leaves. percentage of ethanedioic acid = % Ethanedioic acid can be converted into ethanedioyl chloride: HO2CCO2H → Cl OCCOCl State a suitable reagent for this reaction. For the reactions of ethanedioyl chloride below, suggest the structures of compounds J and K and draw them in the boxes. CH3OH H2NCH2CH2NH2 K (C4H6N2O2) J (C4H6O4) COCl COCl When ethanedioyl chloride is reacted with silver ethanedioate, AgO2CCO2Ag, in ethoxyethane at –30 °C, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has molecular formula C4O6. The carbon-13 NMR spectrum of a solution of L in ethoxyethane, CH3CH2OCH2CH3, is shown below. δ Use the Data Booklet to state in the boxes below the δ values for the peaks in the spectrum which are due to the carbon atoms in ethoxyethane. CH3 CH3 CH2 CH2 O δ values Explain what the rest of the carbon-13 NMR spectrum indicates about the structure of L. When pure L is reacted with an excess of CH3OH, a mixture of three compounds is formed. L and CH3OH → M and N and O (C4O6) (C2H2O4) (C3H4O4) (C4H6O4) M is formed as one of the products when either N or O is heated with aqueous acid. The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O. compound peaks recorded in carbon-13 NMR spectrum M δ 162 N δ 53 δ 160 δ 162 O δ 53 δ 160 Suggest the structures of M, N and O. M, (C2H2O4) N, (C3H4O4) O, (C4H6O4) Suggest a structure for L that fits all the data given in and . L, (C4O6)
9701_s16_qp_43
THEORY
2016
Paper 4, Variant 3
View
Questions Discovered
132