Question 16

Both cups should have contained the same mass of water at the same temperature.

To draw a valid conclusion from the experiment, it is essential that both cups start with the same mass of water at the same temperature. This ensures that any differences observed in the melting of the ice cubes can be attributed solely to the type of solution used, rather than variations in initial conditions.

A) Salt water should have been used to make the ice cubes for the cup of salt water.

This option is incorrect because using salt water to make the ice cubes would not provide a fair comparison with the fresh water. It would introduce an additional variable that could skew the results, rather than isolating the effect of the salt water on the melting rate of the ice.

B) The time for ice cubes to melt should have been measured in minutes.

While measuring the time in minutes may provide more detailed data, it does not address the fundamental requirement of controlled initial conditions. Therefore, this change alone would not significantly enhance the validity of the experiment's conclusions.

C) At the beginning, both cups should have contained the same mass of water at the same temperature.

This change is crucial as it ensures that the experiment controls for variables that could affect the melting rate of the ice cubes. By having equal mass and temperature, any differences observed can be attributed to the type of solution rather than other factors.

D) The energy released should have been measured, not calculated.

Measuring the energy released could provide additional insights into the melting process; however, it does not directly address the need for controlled conditions at the start of the experiment. Thus, this suggestion does not rectify the primary flaw affecting the validity of the conclusions drawn.

Conclusion

The necessity for both cups to contain the same mass of water at the same temperature is fundamental to ensuring a fair and valid comparison in the experiment. This requirement eliminates confounding variables and allows for a clear interpretation of the effects of salt water on ice melting. All other options fail to address this critical aspect of experimental design, making option C the only viable choice for improving the experiment's validity.