You work for a dairy that produces specialty butters. You use the Mohr titration

Question

You work for a dairy that produces specialty butters. You use the Mohr titration to measure the salt content of the butter. You titrate 288.2 mg KCl in 100 mL ddH2O with aqueous AgNO3 (28.11 mL). The blank (100 mL ddH2O) with no KCl registers the endpoint when 1.77 mL AgNO3 is added. You then disperse 3.78 g butter in 100 mL boiling ddH2O and titrate to equivalence (31.9 mL AgNO3). The serving size for butter is 1 tablespoon (14 g).

What is the Cl? content (mg/serving) of the butter? (ONE QUESTION, ALL INFORMATION IS GIVEN!)

Explanation / Answer

standardisation of AgNO3

M1xV1=M2xV2

V2=28.11-1.77ml=26.34ml

M1=(mass/molarmass)/volume in L=(0.2882g/74.5513 g/mol)/0.1L=0.0386M

V1=100ml

M2=0.0386Mx100ml/26.34ml=0.1465M

calculation for unknown

Atomic mass of Cl- = 35.45 g/mole

moles of Cl- =M2xV3

V3=31.9ml-1.77ml=30.13ml=0.03013L

moles of Cl- =0.1465Mx0.03013L=0.004415mol

mass of Cl- =0.004415molx35.45 g/mole=0.1565g

3.78 g of butter contains 0.1565g of Cl- then 1 serving (14g) contains Cl- =14gx0.1565g/3.78g=0.5797g

Cl- content=579.72mg/serving of the butter

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