WAEC Chemistry Past Questions & Answers

In chemical change a new substance is formed while in physical change no new substance is formed. Options A,B,C are all properties of a physical change

Biodegradable because the straight hydrocarbons are natural and slightly soluble in water. Options A,C,D do not have strength hydrocarbon chains and they could harm the environment if they are made with the detergent

There is no disorderliness so no entropy change.

Na, Mg, S and Ar is the set of elements that belong to third period of the periodic table. Option A,B,C have elements which belong to the other period in the periodic table included in them.

The oxidation state of K2Cr2O7 is +6. option A,C,D are the oxidation state of other elements like O7,C14, etc.

\(+2 + 2x + (-2\times7) =0\)

\(2x=12\)

\(x = +6\)

C = 40%, 40/12 = 3.33
H = 6.7%, 6.7/1 = 6.7
O = 53.3%, 53.3/16 = 3.33
C = 3.33/3.33 = 1
H = 6.7/3.33 = 2
O = 3.33/3.33 = 1
(CH2O)n = 180
(12 + 2 + 16)n = 180
30n = 180
n = 6
= C6H12O6

Fractionating column contains petrol with different densities.

Salt is a chemical used for varieties of purposes, so it’s not part of matter, Atom being the smallest part of molecule and ion are charge which are part of matter

The number of isomers C6H14 cm is 5. it will not form options A,C, D

The oxidation number is from +1 to O as a result of the release of sulphur. Options B, C, and D are not the actual oxidation number for copper