An empirical formula is a formula for a chemical compound found by direct laboratory examination. Laboratory procedures allow the chemist to find the simplest whole number ratio of elements within the compound. In order to find the true molecular formula, the chemist also needs to know the compound’s molecular mass.
The general procedure is to use laboratory techniques to determine the mass of each element in the compound. In this lab, we will react a known quantity of magnesium metal to form chloride product. We then mass the final product and subtract to find the mass of chlorine in the product. Once we know the masses of elements in the compounds, we can convert to moles and determine the simplest whole number mole ratio.
The objective of this lab is to determine the empirical formula of magnesium chloride.
Measure the mass of an evaporating dish with its watch glass lid.
Obtain a strip of magnesium metal approximately 2 cm long. Sand the surface until it is shiny, measure its mass, and place it into the evaporating dish.
Using a dropper, slowly add 6 M HCl to the magnesium. Keep the watch glass lid on the evaporating dish to prevent splashing. Continue adding acid until the reaction ceases.
Heat the product gently to evaporate the water from the dish. Keep the lid on the dish at all times to avoid loss of sample by splashing.
Mass the product, then reheat and mass again until the last two masses agree within 0.02 g. This is called heating to a constant mass.
To find the mass of magnesium chloride, you must subtract the mass of the dish and lid from the final mass. Then, subtract the mass of magnesium to find the mass of chlorine in the product. You now know the mass of magnesium and chlorine in the product. Convert both masses to moles. The moles of magnesium should be the smaller number, so divide both numbers by the moles of magnesium. Round...
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