Question

class is learning about the physical properties of substances and wants to investigate how impurities affect the melting point of ice.


They prepare two samples:

Sample A: pure water
Sample B: water with salt added


Both are frozen and then heated until they melt. The students record the temperature at which each sample begins to melt.

Which variable should the students control to ensure the results of this investigation are valid?

Responses

A The temperature at which the ice meltsThe temperature at which the ice melts

B The size and shape of each ice sampleThe size and shape of each ice sample

C The amount of salt that dissolves in the waterThe amount of salt that dissolves in the water

D The time it takes to collect data

Answer 1

B — The size and shape of each ice sample.

Reason: size and shape affect how quickly heat is absorbed and the energy needed to melt (surface area and mass). Keeping them the same ensures any difference in melting temperature is due to the impurity (salt) rather than sample geometry.