NECO 2003 Chemistry · Question 38

Which statement is NOT true about the composition of starch?

Options

A.It contains only the atoms of carbon, hydrogen oxygen
B.It is a polysaccharide
C.Its empirical formula is C2H20.
D.It is made from the monomerC6H12O6.
E.The hydrogen and oxygen atoms are in the ratio 2:1.

Answer: C. Its empirical formula is C2H20.

Explanation written with AI and checked against the answer key

Analyze the question: We need the statement that is NOT true about starch.

Concept: Starch is a polysaccharide, a polymer of glucose (C6H12O6) units joined by glycosidic links with loss of water. Its general formula is (C6H10O5)n. Its empirical formula is often given as CH2O for carbohydrates in general (Cn(H2O)m), where H:O is 2:1 in the carbohydrate family.

Check each option:

A. Only C, H, O: True. Starch is made of carbon, hydrogen and oxygen only.
B. It is a polysaccharide: True. It consists of many glucose units.
C. Empirical formula is C2H20 (read as C₂H₂O or C₂H₂₀): False. Starch's formula is (C6H10O5)n, so its empirical formula is C6H10O5. Even in the simplified carbohydrate form, it is CH2O. C2H20 (or C2H2O) matches neither. A formula like C2H20 would also be an impossible compound (20 hydrogens on 2 carbons).
D. Made from monomer C6H12O6: True. The monomer is glucose.
E. H and O in ratio 2:1: Broadly true. This is the "hydrate of carbon" idea, Cx(H2O)y. Strictly, starch (C6H10O5)n has H:O = 2:1 as well (10:5). So this is true.

Answer: Option C is the statement that is not true.

Tip: For carbohydrates, remember "Cx(H2O)y", so H:O is always 2:1. The empirical formula of simple sugars is CH2O, and for starch, (C6H10O5)n. If a formula has a strange H count like C2H20, it is almost certainly the false option.

AI can make mistakes. Report anything that looks wrong.