Chemistry Help

This question is from the June 2005 AQA Unit 4 Module (Further Physical and Organic Chemistry), question 7c.

Write an equation for the reaction of propanoyl chloride with water. An excess of water is added to 1.48g of propanoyl chloride. Aqueous sodium hydroxide is then added from a burette to the resulting solution. Calculate the volume of 0.42 mol dm-3 aqueous sodium hydroxide needed to react exactly withe the mixture formed.

This is the markscheme
M1 CH3CH2COCl + H2O → CH3CH2COOH + HCl 1
(penalise wrong alkyl group once at first error)
M2 Mr of CH3CH2COCl = 92.5 1
(if Mr wrong, penalise M2 only)
M3 moles of CH3CH2COCl = 1.48/92.5 = 0.016 1
M4 moles NaOH = 2 × 0.016 = 0.032 1
(allow for × 2 conseq to wrong no of moles)

Why is there 2 moles of NaOH?

M5 volume of NaOH = 0.032/0.42 = 0.0762 dm3 or 76.2 cm3 1
(with correct units)
(if ×2 missed in M4 lose M5 also)

Reply 1

*BCM*

1 mole to react with the HCl, and 1 mole to react with the propanoic acid - coz u get two moles of acid (1 of each) when u react with propanoyl chloride and the water

Reply 2

username872714

Ha I know this was yeaaarss ago, but you are a life saver, that question has just had me confused for AGES! As if I didn't notice that! thanks! :biggrin:

xxxx