7. Equilibria
A section of Chemistry, 9701
Listing 10 of 344 questions
The structure of glycolic acid is shown. glycolic acid H H C O C OH OH Complete the table to show what you would observe when an aqueous solution of glycolicacid is added separately to each of the reagents. If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction. reagent observation with glycolic acid does a reaction occur? / functional group Na2CO32,4-DNPH acidified Cr2O7 2–  Two reaction sequences to make glycolic acid are shown. HCHO CH2(OH)CO2H sequence A X HCN and NaCN reaction 1 reaction 2 CH3CO2H CH2BrCO2H CH2(OH)CO2H sequence B Br2 reaction 3 reaction 4 Draw the structure of X.  Name the reagent for reaction2. Name the mechanism of reaction3. Suggest the essential condition for reaction3. Reaction4 occurs via an SN2 mechanism. Complete the diagram for the mechanism for reaction4. Include all relevant charges, partial charges, curly arrows and lone pairs. H H C O C OH –OH Br H H C O C OH OH  Glycolic acid can also be made by reacting glyoxylicacid with NaBH4. H H C O C OH OH C C glyoxylic acid O OH H O NaBH4 glycolic acid State the role of NaBH4 in this reaction. Write an equation for this reaction using molecular formulae. Use to represent NaBH4. When glycolicacid is heated in the presence of a sulfuricacid catalyst, a new compound, Y, C4H4O4, is formed. The equation for the reaction is given. 2CH2(OH)CO2H C4H4O4 + 2H2O glycolic acid Y The infra-red spectrum of Y is shown. transmittance wavenumber / cm–1 State how this spectrum differs from an infra-red spectrum of glycolicacid. Explain your answer with particular reference to the peaks within the range 1500 – 4000 cm–1. Suggest a structure for Y.  
9701_w18_qp_21
THEORY
2018
Paper 2, Variant 1
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The structure of glycolic acid is shown. glycolic acid H H C O C OH OH Complete the table to show what you would observe when an aqueous solution of glycolicacid is added separately to each of the reagents. If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction. reagent observation with glycolic acid does a reaction occur? / functional group Na2CO32,4-DNPH acidified Cr2O7 2–  Two reaction sequences to make glycolic acid are shown. HCHO CH2(OH)CO2H sequence A X HCN and NaCN reaction 1 reaction 2 CH3CO2H CH2BrCO2H CH2(OH)CO2H sequence B Br2 reaction 3 reaction 4 Draw the structure of X.  Name the reagent for reaction2. Name the mechanism of reaction3. Suggest the essential condition for reaction3. Reaction4 occurs via an SN2 mechanism. Complete the diagram for the mechanism for reaction4. Include all relevant charges, partial charges, curly arrows and lone pairs. H H C O C OH –OH Br H H C O C OH OH  Glycolic acid can also be made by reacting glyoxylicacid with NaBH4. H H C O C OH OH C C glyoxylic acid O OH H O NaBH4 glycolic acid State the role of NaBH4 in this reaction. Write an equation for this reaction using molecular formulae. Use to represent NaBH4. When glycolicacid is heated in the presence of a sulfuricacid catalyst, a new compound, Y, C4H4O4, is formed. The equation for the reaction is given. 2CH2(OH)CO2H C4H4O4 + 2H2O glycolic acid Y The infra-red spectrum of Y is shown. transmittance wavenumber / cm–1 State how this spectrum differs from an infra-red spectrum of glycolicacid. Explain your answer with particular reference to the peaks within the range 1500 – 4000 cm–1. Suggest a structure for Y.  
9701_w18_qp_23
THEORY
2018
Paper 2, Variant 3
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Use information from the Data Booklet to draw the structure of the dipeptide glu‑cys.  The isoelectric point is the pH at which an amino acid exists as a zwitterion. The isoelectric point of glutamicacid is 3.2 and of cysteine is 5.0. A mixture of the dipeptide glu-cys and its two constituent amino acids, glutamicacid and cysteine, was analysed by electrophoresis using a buffer at pH5.2. The results obtained are shown. + – E F G mixture applied here Suggest identities for the species responsible for spots E, F and G. Explain your answers. spot identity E F G explanation  
9701_w18_qp_42
THEORY
2018
Paper 4, Variant 2
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Questions Discovered
344