7.2. Brønsted–Lowry theory of acids and bases
A subsection of Chemistry, 9701, through 7. Equilibria
Listing 10 of 133 questions
The hydrogen halides HCl, HBr and HI are all colourless gases at room temperature. The hydrogen halides can be formed by reacting the halogens with hydrogen. Describe and explain the relative reactivity of the halogens down the group when they react with hydrogen to form HCl, HBr and HI. HCl is a product of several different reactions. Some of these are shown in Fig.3.1. SiCl 4 NaCl HCl reaction 1 H2O reaction 2 concentrated H2SO4 Write an equation for reaction1. In reaction2, NaCl reacts with concentrated H2SO4 to form HCl and NaHSO4. When NaBr reacts with concentrated H2SO4, the products include Br2 and SO2. Identify the typeof reaction that occur in each case by completing Table3.1. Explain the difference in these reactions. Table 3.1 reactants typeof reaction NaCl and concentrated H2SO4 NaBr and concentrated H2SO4 explanation  When heated with a Bunsen burner, HCl does not decompose, whereas HI forms H2 and I2. Explain the difference in the effect of heating on HCl and HI. The hydrogen halides dissolve in water to form strong Brønsted–Lowry acids. The concentration of a strong acid can be determined by titration. State what is meant by strong Brønsted–Lowry acid. On Fig.3.2, sketch the pH titration curves produced when: ● 0.1 mol dm–3 NaOHis added to 25 cm3 of 0.1 mol dm–3 HBr, to excess ● 0.1 mol dm–3 NH3is added to 25 cm3 of 0.1 mol dm–3 HBr, to excess. pH volume of NaOH / cm3 reaction of NaOHand HBr14 pH volume of NH3 / cm3 reaction of NH3and HBr0 10 15 20 25 30 35 40 45 10 15 20 25 30 35 40 45  HBr reacts with propene to form two bromoalkanes, CH3CH2CH2Br and (CH3)2CHBr. Complete the diagram to show the mechanism of the reaction of HBr and propene to form the major organic product. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Draw the structures of the intermediate and the major organic product. H Br C C C H H H H H H  Explain why the two bromoalkanes are not produced in equal amounts by this reaction. The reaction of CH3CH2CH2Br and NaOH is different depending on whether water or ethanol is used as a solvent. Complete Table 3.2 to identify the organic and inorganic products of the reaction of CH3CH2CH2Br and NaOH in each solvent. Table 3.2 solvent organic productinorganic productwater ethanol  
9701_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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Give an expression for Ka as applied to the weak acid RCO2H. The Ka values for three carboxylic acids are listed in the table below. Describe and explain the trend in acid strength illustrated by these values. Calculate the pH of a 0.100 mol dm–3 solution of ClCH2CO2H. Calculate the pKa value for Cl 2CHCO2H. Use acid Ka/ mol dm–3 CH3CO2H 1.8 × 10–5 ClCH2CO2H 1.4 × 10–3 Cl2CHCO2H 5.5 × 10–2 The acid ClCH2CO2H features in the industrial synthesis of the important weedkiller 2,4-D. Suggest a possible reagent for reaction I. What type of reaction is reaction I, reaction II? Describe a test (reagents and observations) that would distinguish phenol from compound A. reagents observation with phenol observation with compound A CH2OH compound A OH OH Cl Cl OCH2CO2H Cl Cl phenol + NaOH + ClCH2CO2H I II 2,4-D Examiner's Use
9701_s05_qp_4
THEORY
2005
Paper 4, Variant 0
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Explain what is meant by the Bronsted-Lowry theory of acids and bases. The Ka values for some organic acids are listed below. acid Ka /mol dm−3 CH3CO2H 1.7  10−5 Cl CH2CO2H 1.3  10−3 Cl 2CHCO2H 5.0  10−2 Explain the trend in Ka values in terms of the structures of these acids. Calculate the pH of a 0.10 mol dm−3 solution of Cl CH2CO2H. pH = Use the following axes to sketch the titration curve you would obtain when 20 cm3 of 0.10 mol dm−3 NaOH is added gradually to 10 cm3 of 0.10 mol dm−3 Cl CH2CO2H. pH volume of NaOH added / cm Write suitable equations to show how a mixture of ethanoic acid, CH3CO2H, and sodium ethanoate acts as a buffer solution to control the pH when either an acid or an alkali is added. Calculate the pH of a buffer solution containing 0.10 mol dm−3 ethanoic acid and 0.20 mol dm−3 sodium ethanoate. pH =
9701_s09_qp_4
THEORY
2009
Paper 4, Variant 0
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