When two substances are mixed and light is produced is it a chemical or physical change?

You find that the unknown powder contains the illegal drug cocaine. If someone where to ask you to determine the purity of the substance, what would they mean? Why is purity important in crime investigations?

Which type of organism can experience a mutation?

What is the mass of exactly 500 molecules of chloral hydrate?

If you drop. the soap in the shower is It still dirty

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).

What is the term for the amount of salts in water? Evaporation Evaporation Salinity Thermocline Density

In an acid-base titration, of 20 ml of a m HCI solution with 1 m NaOH. How many ml of NaOH are needed

Which of the following is not a source of air pollution related to human activities

Objects and substances in motion is I

If you were to remove an electron from a sodium atom that has eleven protons, what would be the electrical charge of the ion?