Homework Practice

Printable assignment

Physical and Chemical Changes: Crystals, Burning and Reasoning

Crystallisation and Burning

Question 1mcq

Crystallisation is useful because it helps:

A.turn every metal into rust

B.make all changes irreversible

C.obtain pure crystals of a substance from its solution

D.identify acids by litmus only

Question 2mcq

Burning of magnesium ribbon is a chemical change mainly because:

A.the ribbon only changes shape

B.the ribbon only melts and returns unchanged

C.no heat or light is seen

D.magnesium oxide, a new substance, is formed

Question 3mcq

Which comparison is correct?

A.Melting wax is physical if only state changes; burning wax is chemical because new substances form.

B.Both are always chemical because wax is involved.

C.Both are always physical because wax is involved.

D.Burning wax forms no new substances.

Question 4mcq

A white powder is heated and gives off a gas, leaving a different solid. What is the best classification?

A.Physical change, because heating always means physical change.

B.Chemical change, because new substances are likely formed.

C.No change, because powder is still visible.

D.Physical change, because gas is never a product.

Question 5mcq

In a crystallisation activity, why is a hot saturated solution often allowed to cool slowly?

A.To make the solute disappear permanently.

B.To turn the beaker into salt.

C.To let well-formed crystals separate from the solution.

D.To prevent any solid from forming.

Reversibility and Evidence

Question 6mcq

Cooking food is usually considered a chemical change because:

A.the food only changes place

B.no heat is ever used

C.raw food can always be restored exactly

D.new substances with different taste, smell and properties are formed

Question 7mcq

Which example best shows why “irreversible” does not automatically mean “chemical”?

A.Breaking a glass changes shape but does not form a new substance.

B.Burning paper forms ash and gases.

C.Rusting forms iron oxide.

D.Curdling milk forms new substances.

Question 8mcq

A student observes: “The material changed colour, became warm, and cannot be changed back easily.” What should the student do before concluding?

A.Conclude physical change only because colour changed.

B.Check whether a new substance formed using all observations.

C.Ignore the warmth because heat is not evidence.

D.Classify it only by whether it is reversible.

Question 9mcq

Which sequence best represents crystallisation of copper sulphate in a school activity?

A.Burn copper sulphate until ash forms, then add oil.

B.Freeze dry powder directly without water.

C.Dissolve in hot water, filter if needed, cool to form crystals.

D.Mix with litmus and call it neutralisation.

Question 10mcq

A nail rusts in a wet garden but another nail kept dry in a sealed packet does not. What conclusion is best?

A.Dry air always causes faster rusting.

B.Rusting needs no oxygen or water.

C.Paint causes rusting.

D.Moisture is important for rusting.