What is the observation indicating that matter moved when ethanol was burned?

The observation that indicates matter moved when ethanol was burned is that the BTB (bromothymol blue) gained mass. When ethanol combusts, it reacts with oxygen to produce carbon dioxide and water as products. This chemical reaction signifies a transformation of matter, as the original substances (ethanol and oxygen) are converted into different substances (carbon dioxide and water).

In a controlled experiment, the gained mass can often be attributed to the combustion products that are contained or absorbed within a system, such as a solution indicated by BTB. If the BTB solution shows an increase in mass, it suggests that matter has entered the solution, possibly through the absorption of carbon dioxide, which can form carbonic acid and lead to changes in pH. Thus, the gain in mass of the BTB is a direct measure of the movement of matter resulting from the combustion of ethanol, validating the observation of matter movement during this process.