Question

Post-lab questions:
1. Provide the chemical structure of KHP, indicating the acidic hydrogen.  

2. Why is the solubility of KHP in water greater than many fatty acids with six or more carbons?

3. What is the chemical difference between saturated and unsaturated fats?   

4. How many moles of NaOH are in 26.7 mL of a 0.100 M NaOH solution?  

5. If the above volume of NaOH was required to titrate a fatty acid solution containing 0.753 g of an unknown fatty acid, what is the molar mass of the fatty acid?

Answer 1

1)

2) KHP means Postassium Hydrogen phthalate, which is monopotassium salt of phthalic acid. KHP dissociates completely in water giving potassium salt and hydrogen phthalate anion (HP-).
Molecules which are soluble in water, they must have either polar groups or ionic groups. In the KHP we have two ionizable
carboxylic groups, therefore, it is readily soluble in water.
Fatty acids also contain one carboxylic group which can be ionized, however, it also contains long hydrocarbon chain which is a
non-polar group and dominates the small polar carboxylic acid group. Longer the fatty acid chain the lower the solubility.
Therefore, the solubulity of fatty acid is lower than the KHP.

3) Saturated fats means, their is no double bond in their hydrocarbon chain.
Unsaturated fats means, there is one or more doubles in their hydrocarbon chain.
4) no. moles of NaOH = molarity x volume in L
                   = (0.1 mol/L) x 0.0267 L
                   = 0.00267 moles
5) we have used 0.00267 moles of NaOH to neutralize unknow fatty acid,
therefore, the no. moles of unknow fatty acid = 0.00267 moles
we know, the mass of fatty acid = 0.753 g
Therefore, no. moles = mass/ mol.wt
mol.wt of fatty acid = mass of fatty acid/no.moles
                   = 0.753 g/ 0.00267 moles
                   = 282 g/mol
Hence, the mol.wt of fatty acid = 282 g/mol