Question 1 – Academy Plus Sample
Acid/Base titration calculation
Molly has a ‘Home Brand’ sample of lemon juice. She wants to find out the concentration and eventually the pH of the lemon juice (HCl) . Molly starts with 60ml of lemon juice, but she decides to dilute it with 190ml of water. Molly then uses a pipette to transfer 25ml solution into the conical flask. She carefully titrates this against a sodium carbonate solution of 2.342g/50ml concentration. The titres used were 10.76ml, 9.78ml, 9.77ml and 9.75 ml respectively.
a) Write the complete balanced reaction of the titration.
(1 mark)
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b) Find the concentration of the sodium carbonate in molarity.
(2marks)
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C(sodium carbonate) = 0.442M
c) Find the mol of HCl in the 25 ml aliquote.
(1 mark)
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n(HCl) = 0.00863mol
d) Find the concentration (in M) of HCl in the original lemon juice sample.
(2marks)
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C(HCl) = 0.144M
e) Find the pH of the lemon juice, given that the only cause of acidity is the HCl.
(2 marks)
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pH = 0.842
