Laura could use a few different methods to determine which beakers contain pure water and which contain solutions. One method is to test the boiling point of each liquid. Pure water boils at 100 degrees Celsius at standard pressure. If the liquid in a beaker boils at a temperature higher than 100 degrees Celsius, it is likely a solution and not pure water. Another method is to test the freezing point of each liquid. Pure water freezes at 0 degrees Celsius at standard pressure. If the liquid in a beaker freezes at a temperature other than 0 degrees Celsius, it is likely a solution and not pure water.
Another method is through density test. Pure water has a density of 1g/cm³ at 4°C. Laura can use a hydrometer, which is an instrument that measures the density of a liquid to check if the density of the liquids in the beakers is equal to 1g/cm³. If it is not, then it is not pure water.
Additionally, Laura could also test the conductivity of the liquids. Pure water is a poor conductor of electricity, whereas solutions can conduct electricity. Laura could use a conductivity meter to check the conductivity of the liquids. If a liquid conducts electricity, then it is likely a solution and not pure water.
Finally, Laura could also use a refractometer, which measures the refractive index of the liquid. The refractive index of pure water is 1.333 and any deviation from this value indicates the presence of dissolved solutes.
It's important to notice that no single test can confirm that a liquid is pure water, but a combination of tests can give us a strong indication of it.