11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
State the relative basicities of ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer. > > most basic least basic The amino acid alanine, H2NCH(CH3)COOH, can act as a buffer. Define a buffer solution. Write two equations to show how an aqueous solution of alanine can act as a buffer solution. Glutamic acid is another amino acid that acts as a buffer. glutamic acid C H2N COOH H CH2CH2COOH Draw the skeletal formula for glutamic acid. Draw the structure for the dipeptide, ala‑glu, formed from one molecule of alanine and one molecule of glutamic acid. The peptide bond formed should be displayed. The isoelectric point of alanine is 6.0 and of glutamic acid is 3.2. A mixture of the dipeptide, ala‑glu, and its two constituent amino acids, alanine and glutamic acid, is analysed by electrophoresis using a buffer at pH 6.0. + – mixture applied here Draw and label three spots on to indicate the predicted position of each of these three species after electrophoresis. Explain your answer. Alanine, H2NCH(CH3)COOH, reacts with methanol to form the ester G under certain conditions. The proton (1H) NMR spectrum of G dissolved in D2O is shown in . G O O chemical shift δ / ppm H2N Table 7.1 environment of proton example chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Complete Table 7.2 for the proton (1H) NMR spectrum of G. Table 7.2 chemical shift (δ) splitting pattern number of 1H atoms responsible for the peak number of protons on adjacent carbon atoms 1.4 3.5 4.0 The proton (1H) NMR spectrum of G dissolved in CDCl3 is obtained. Describe the difference observed between this spectrum and the proton NMR spectrum in D2O shown in Fig 7.3. Explain your answer.
9701_s23_qp_41
THEORY
2023
Paper 4, Variant 1
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State the relative basicities of ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer. > > most basic least basic The amino acid alanine, H2NCH(CH3)COOH, can act as a buffer. Define a buffer solution. Write two equations to show how an aqueous solution of alanine can act as a buffer solution. Glutamic acid is another amino acid that acts as a buffer. glutamic acid C H2N COOH H CH2CH2COOH Draw the skeletal formula for glutamic acid. Draw the structure for the dipeptide, ala‑glu, formed from one molecule of alanine and one molecule of glutamic acid. The peptide bond formed should be displayed. The isoelectric point of alanine is 6.0 and of glutamic acid is 3.2. A mixture of the dipeptide, ala‑glu, and its two constituent amino acids, alanine and glutamic acid, is analysed by electrophoresis using a buffer at pH 6.0. + – mixture applied here Draw and label three spots on to indicate the predicted position of each of these three species after electrophoresis. Explain your answer. Alanine, H2NCH(CH3)COOH, reacts with methanol to form the ester G under certain conditions. The proton (1H) NMR spectrum of G dissolved in D2O is shown in . G O O chemical shift δ / ppm H2N Table 7.1 environment of proton example chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Complete Table 7.2 for the proton (1H) NMR spectrum of G. Table 7.2 chemical shift (δ) splitting pattern number of 1H atoms responsible for the peak number of protons on adjacent carbon atoms 1.4 3.5 4.0 The proton (1H) NMR spectrum of G dissolved in CDCl3 is obtained. Describe the difference observed between this spectrum and the proton NMR spectrum in D2O shown in Fig 7.3. Explain your answer.
9701_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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Define transition element. Explain why transition elements can form complex ions. The 3d orbitals in an isolated Ag+ ion are degenerate. Define degenerate d orbitals. Sketch the shape of a 3dxy orbital in . z y x Tollens’ reagent can be used to distinguish between aldehydes and ketones. Tollens’ reagent contains [Ag(NH3)2]OH, which can be prepared in a two-step process. step 1 Aqueous NaOH is added dropwise to aqueous AgNO3 to form Ag2O as a brown precipitate. step 2 Aqueous NH3 is added dropwise to Ag2O to form a colourless solution containing [Ag(NH3)2]OH. Construct equations for each of the steps in the preparation of [Ag(NH3)2]OH. step 1 step 2 Name the shape of the complex ion [Ag(NH3)2]+. State the bond angle for H-N-Ag and for N-Ag-N. shape bond angle for H-N-Ag = ° bond angle for N-Ag-N = ° An electrochemical cell uses Ag2O as the positive electrode and Zn as the negative electrode immersed in an alkaline electrolyte. The overall cell reaction is shown. Ag2O + Zn + H2O 2Ag + Zn(OH)2 Complete the half-equation for the reaction at each electrode. at the positive electrode Ag2O + at the negative electrode Zn + Coordination polymers are made when a bidentate ligand acts as a bridge between different metal ions. Under certain conditions Ru3+and the bidentate ligand dps can form a coordination polymer containing ([RuCl 4]–)n chains. N N S dps The bidentate ligand dps uses each of the nitrogen atoms to bond to a different Ru3+. Complete by drawing the structure for the coordination polymer ([RuCl 4]–)n. Show two repeat units. The dps ligand can be represented using N N . Ru
9701_s24_qp_41
THEORY
2024
Paper 4, Variant 1
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Explain why transition elements have variable oxidation states. Sketch the shape of a 3dz2 orbital in . z y x Samples of [Cu(H2O)6]2+are reacted separately with an excess of solution A and with an excess of solution B. The reaction of [Cu(H2O)6]2+with solution A is a precipitation reaction. The reaction of [Cu(H2O)6]2+with solution B is a ligand substitution reaction. Suggest a possible identity for solution A and for solution B. Give relevant observations and the formula of the copper‑containing product for each reaction. solution A observations formula of the copper‑containing product solution B observations formula of the copper‑containing product Solutions containing the [Ag(NH3)2]+ complex are colourless. Explain why this complex is colourless. Two bidentate ligands are shown in . en dpys S N N NH2 H2N Explain what is meant by a bidentate ligand. ,   , Ruthenium(ions, Ru3+, form an octahedral complex, +, with the ligands dpys and chloride ions. This complex shows the same kind of stereoisomerism as [Ru(NH3)4Cl2]+ but also shows a different type of stereoisomerism. Complete the three‑dimensional diagrams in to show the three different stereoisomers of +. The dpys ligand can be represented using N N. isomer 1 Ru isomer 2 Ru isomer 3 Ru State the different types of stereoisomerism shown by +. Deduce which stereoisomers in are non-polar. Explain your answer. ,   ,
9701_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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Define transition element. Explain why transition elements can form complex ions. The 3d orbitals in an isolated Ag+ ion are degenerate. Define degenerate d orbitals. Sketch the shape of a 3dxy orbital in . z y x Tollens’ reagent can be used to distinguish between aldehydes and ketones. Tollens’ reagent contains [Ag(NH3)2]OH, which can be prepared in a two-step process. step 1 Aqueous NaOH is added dropwise to aqueous AgNO3 to form Ag2O as a brown precipitate. step 2 Aqueous NH3 is added dropwise to Ag2O to form a colourless solution containing [Ag(NH3)2]OH. Construct equations for each of the steps in the preparation of [Ag(NH3)2]OH. step 1 step 2 Name the shape of the complex ion [Ag(NH3)2]+. State the bond angle for H-N-Ag and for N-Ag-N. shape bond angle for H-N-Ag = ° bond angle for N-Ag-N = ° An electrochemical cell uses Ag2O as the positive electrode and Zn as the negative electrode immersed in an alkaline electrolyte. The overall cell reaction is shown. Ag2O + Zn + H2O 2Ag + Zn(OH)2 Complete the half-equation for the reaction at each electrode. at the positive electrode Ag2O + at the negative electrode Zn + Coordination polymers are made when a bidentate ligand acts as a bridge between different metal ions. Under certain conditions Ru3+and the bidentate ligand dps can form a coordination polymer containing ([RuCl 4]–)n chains. N N S dps The bidentate ligand dps uses each of the nitrogen atoms to bond to a different Ru3+. Complete by drawing the structure for the coordination polymer ([RuCl 4]–)n. Show two repeat units. The dps ligand can be represented using N N . Ru
9701_s24_qp_43
THEORY
2024
Paper 4, Variant 3
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Describe and explain how the basicities of ammonia, ethylamine and phenylamine differ. CH3CH2NH2 NH3 NH2 ammonia ethylamine phenylamine Describe how the use of aqueous silver nitrate and aqueous ammonia can distinguish between aqueous solutions containing chloride, bromide or iodide ions by filling in the following table. halide observation when AgNO3is added observation when dilute NH3is added observation when concentrated NH3is added chloride bromide iodide Silver bromide is sparingly soluble in water. AgBrAg++ Br–Ksp = 5 × 10–13 mol2 dm–6 Calculate [Ag+] in a saturated aqueous solution of AgBr. [Ag+] = mol dm–3 State and explain whether AgBr will be less or more soluble in 0.1 mol dm–3 KBr than it is in pure water. Silver ions form complexes with ammonia and with amines. Ag++ 2RNH2[Ag(RNH2)2]+Write an expression for the Kc for this reaction, and state its units. Kc = units Kc has the numerical value of 1.7 × 107 when R = H. Using your expression for Kc calculate the needed to change the [Ag+] in a 0.10 mol dm–3 solution of silver nitrate to the value that you calculated in . = mol dm–3 Explain whether you would expect the Kc for the reaction where R = C2H5 to be greater or less than that for the reaction where R = H.
9701_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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