When testing for alcohol content, how is the sample prepared in the 100mL container?

When testing for alcohol content in fuel, the preparation of the sample is crucial for accurate results. Filling the container with fuel to 90mL and then adding water to bring the total volume up to 100mL is the correct method because it allows for the separation of alcohol from the hydrocarbon components of the fuel.

In many instances, water is used in combination with fuel to create a mixture where the alcohol, which is usually soluble in water, can effectively dissociate. This dilution ensures that the alcohol content can be assessed without interference from the fuel components. As a result, this preparation method provides a clearer understanding of the proportion of alcohol in the sample.

Other options would not yield the same clarity or effectiveness in the testing process. For instance, simply filling the container with fuel could underestimate the alcohol content. Filling with water first and then adding fuel might not accurately reflect the intended concentration of alcohol, and mixing fuel and water at a 50/50 ratio could lead to an imprecise measurement, as the standard method typically requires a known one-third ratio of water to fuel. Thus, the specified method of filling to 90mL with fuel and topping off with water is essential for precision in testing alcohol content.