The concept you're referring to relates to the principles of buoyancy and evaporation in an open system. When several liquids are mixed in an open flask, there are a few factors that can lead to the combined weight of the liquid mixture being less than the total weight of the individual liquid components. However, it cannot be more than the sum of their weights. Here's why:
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Buoyancy: When liquids are mixed, they can create a buoyant force which can cause a slight reduction in the effective weight measured. If you use a scale to weigh the flask, the buoyancy effect in the air or in another denser medium could create an apparent decrease in weight.
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Volatile Components: If any of the liquids are volatile (able to evaporate), some of their mass may escape into the air. Since the flask is open, any vapor that escapes will reduce the total mass of the liquid left in the flask. This would account for a situation where the measured weight of the mixture is less than the sum of the weights of the individual components.
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Measurement Errors: In physical experiments, measurement errors can also occur. For instance, when pouring liquids, there might be drips that are not captured, leading to an apparent decrease in mass.
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Chemical Reactions: In some cases, if the liquids mix and undergo a chemical reaction, products formed may be in the gas phase, which can also lead to a loss in weight compared to the original reactants.
However, the reason the combined weight can never exceed the sum of all the individual weights is based on the law of conservation of mass. The mass of a closed system must be conserved, meaning that in an open system with regard to weight, it can only lose mass (due to evaporation, for instance) but cannot gain mass unless an external factor contributes additional weight.
In summary: The combined weight of liquids in an open flask can be less than the sum due to evaporation and measurement distractions, but it cannot exceed the sum because of the conservation of mass principle.
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