Oils Fats and Soaps Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the decisive advantage. Soap forms insoluble calcium and magnesium salts with the hardness in water, so it is consumed before it can clean and leaves a scum on the fabric and the machine. Synthetic detergents, particularly the sulphonates, have soluble calcium and magnesium salts, so they work in hard water without that loss.

Answer: B

Correct answer: True

Both processes cleave the triglyceride and release its glycerol backbone. In soap making the fat is saponified with caustic and the glycerine is recovered from the spent lye; in biodiesel manufacture the oil is transesterified with methanol and the glycerine separates as the denser layer. The very large expansion of biodiesel production consequently depressed the glycerine market for years.

Answer: C

The glycerol of the triglyceride is replaced by methyl groups, giving methyl esters of low viscosity. Glycerine is released and is the principal by-product of the process. Methanol is recovered and recycled to the reactor.

Answer: D

The first two are correct and name the two distinct mechanisms. The third overstates the case, since refining can remove the products of rancidity but cannot restore what has already been destroyed. Peroxide value tracks the first of the two.

Answer: A

They donate a hydrogen atom to the propagating radical and stop the chain, which extends the induction period considerably. They cannot reverse oxidation that has already occurred. Their effect is measured as an induction period.

Answer: B

Correct answer: about 2.8 per cent

Convert the potassium hydroxide to moles and then to oleic acid: \[ \frac{5.6\ \mathrm{mg}}{56.1\ \mathrm{g/mol}} = 9.98\times10^{-5}\ \mathrm{mol}, \qquad 9.98\times10^{-5} \times 282 = 0.0282\ \mathrm{g}, \] so 2.8 per cent by mass. The useful shortcut is that the free fatty acid percentage is about half the acid value for oleic acid, since \( 282/(2\times56.1) \approx 2.5 \) - and quoting the acid value itself as a percentage gives the 5.6 offered.