Question

Define the following term: Invert sugar.

Hint:

Invert sugar is the mixture of glucose and fructose obtained when sucrose is hydrolysed (broken down by water, usually with acid or the enzyme invertase).

Answer 1

Step 1: Start with sucrose.
Sucrose is a disaccharide made of one glucose unit and one fructose unit joined together. It is dextrorotatory (rotates light to the right, \(+66.5^\circ\)).

Step 2: Hydrolyse it.
When sucrose is broken down by water (using acid or the enzyme invertase), it splits into equal amounts of glucose and fructose.

Step 3: Watch the rotation flip.
Glucose is \(+52^\circ\) and fructose is \(-92^\circ\). The mixture is overall negative (laevorotatory), so the sign of rotation changes from \(+\) to \(-\).

Step 4: See why the name.
Because the optical rotation is inverted (reversed) during this reaction, the product mixture is called invert sugar.

Step 5: State what it contains.
Invert sugar is the equimolar mixture of glucose and fructose formed in this hydrolysis.

Answer: Invert sugar is the equal mixture of glucose and fructose obtained on hydrolysis of sucrose, so called because the optical rotation inverts from \(+\) to \(-\).