E6
ANALYSIS OF SALT IN FOOD PRODUCTS
You are required to submit ONE report from the group 4, 5 and 6. A report includes results,
calculations and questions.
PURPOSE
To determine the salt content (as chloride) in food items by potentiometric titration with silver nitrate.
PROCEDURE
I.. Soy sauce
1.
Pipette a 5 mL aliquot of soy sauce into a 250 mL volumetric flask and make up the mark with
water.
2.
Set up apparatus suitable for the potentiometric titration.
3.
Titrate a 25 mL aliquot of the diluted sample with 0.05 M AgNO3.
4.
Repeat with a duplicate aliquot.
II. Beef stock concentrate
1.
Tare a 150 mL beaker, and squeeze the contents of one sachet into the beaker. Record the mass.
2.
Dissolve the stock in 50 mL of water.
3.
Quantitatively transfer to a 100 mL volumetric flask, and make up to the mark with water.
4.
Pipette 10 mL of this solution into another 100 mL volumetric flask, and make up to the mark
with water.
5.
Titrate a 25 mL aliquot of the diluted sample (from step 4) with 0.05 M AgNO3.
6.
Repeat with a duplicate aliquot.
CALCULATIONS
I. Soy sauce
•
calculate the average titration volume
•
calculate moles of silver nitrate in the titration (this is equal to the moles of chloride)
•
calculate the mass of sodium chloride (assuming all chloride is present as NaCl)
•
calculate the concentration of NaCl as g/100 mL in the diluted solution
•
multiply this by 50 to calculate the concentration of salt in the soy sauce
II. Beef stock
•
calculate the average titration volume
•
calculate moles of silver nitrate in the titration (this is equal to the moles of chloride)
•
calculate the mass of sodium chloride (assuming all chloride is present as NaCl)
•
multiply this mass by 40 to determine the mass of NaCl in the beef stock
•
calculate the concentration of NaCl in the beef stock as %w/w
QUESTIONS
1.
Compare your results with those expected for the samples. Suggest reasons for any differences.
2.
What health problems are associated with too much salt in the diet?
3.
Is it accurate to assume that all chloride is present in the samples as NaCl? How could a true
value of NaCl be obtained?
4.
In the beef stock calculation, there is a multiplication factor of 40 that converts from the mass of
NaCl in the titrated aliquot to the mass of NaCl in the beef stock. Explain where it comes from.
E6. ANALYSIS OF SALT IN FOOD PRODUCTS
RESULTS SHEET
Soy sauce ID
Brand
Barcode
Expiry date
Beef stock ID
Brand
Barcode
Expiry date
Analysis data
Molarity silver nitrate
Mass of beef stock (g)
Titres (mL)
Tester’s signature ________________________________
Date _______________
Supervisor’s signature ______________________________
Date ______________