Final answer:
To identify whether a liquid is water or methanol, perform a boiling point test. Water boils at 100°C, while methanol boils at around 65°C. Record the temperatures at which each liquid boils to differentiate them.
Step-by-step explanation:
To identify which liquid is water and which is methanol, you would perform the boiling point test, option a: Heat the liquids; water boils at a higher temperature. This is because water has a boiling point of 100°C, while methanol boils at around 65°C. When heating both liquids, you would expect water to boil at a higher temperature compared to methanol. This difference in boiling points is due to the intermolecular forces present in the compounds. Water molecules are held together by strong hydrogen bonds, which require more energy (in the form of heat) to break compared to the hydrogen bonds in methanol.
After heating the liquids, record your observations of the temperatures at which they begin to boil. Water's boiling point will signal its presence when the liquid reaches 100°C. Options b, c, and d provided in the question are not accurate tests for differentiating water from methanol. Adding litmus paper, mixing the liquids, or igniting them will not distinguish them as effectively as utilizing their different boiling points.
Therefore, identifying each liquid based on boiling point is a direct method with clear, observable results that can be recorded and verified. Learning the various boiling points of substances is crucial for handling chemicals safely in a laboratory setting, and it also provides an understanding of the polar nature of water and methanol and their resulting physical properties.