Comparing the Rates of Hydrolysis Reactions
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why can silver nitrate solution be used in a test for halide ions
• because the silver ions in silver nitrate react with the halide ions formed in the hydrolysis (with water in the solution) • to give a precipitate
what is the general formula for this occurring
Ag+ + X- = AgX
how could we use this to determine how quickly the hydrolysis reaction occurs
be observing how quickly the precipitate of AgX forms
why couldnt you tell the rate of the reactions without the percipitate
because both reagents and the products are colourless
what are the three things the comparison of the rates of reaction involves
• using ethanol as the solvent for the mixture • controlling variables like temperature and the concentration and quantity of the halogenoalkanes • timing the appearance of the precipitate
why does ethanol need to be used as a solvent for the mixture
• because halogenoalkanes and aqueous silver nitrate dont mix • but from separate layers • ethanol is needed to prevent this
why is difficult to time the appearance of the precipitate
because a precipitate may appear faint but become thicker over time
what is the general trend you should observe about how much precipitate is formed as you go down group 7
• more and thicker precipitates are formed as you go down the group • due to the halogenoalkanes being less reactive as you go down group 7
why would you expect the halogens at the top of the group to form the precipitates the quickest regarding their bonds
• the electronegativity of the elements in group 7 increase as you go up the group • meaning the o+ charge on the carbon atom would also increase • so the attacking nucleophile should be attracted more strongly
despite that prediction, why do the elements down the group experience the fastest results when reacted with silver nitrate in the same conditions
• the bond energies between the carbon atom and the halogen decrease as you do down the group • weaker bonds break more easily than stronger bonds, so the bonds between the carbon atom the halogen as you go down the group require less energy to break • this means that for the same conditions, the C-X bond breaks most easily as you go down the group, so the precipitate forms more quickly
what is the trend in how quickly precipitates are formed regarding what the classification of halogenoalkane is
• tertiary halogenoalkanes react the quickest with the silver nitrate to form the precipitate the quickest • primary halogenoalkanes are the slowest • with secondary ones being in between