![]() Accounting for sig figs the answer is properly reported as 0.28 grams of beryllium chloride. So we can take our mole number from before and multiply it by the molar mass: 0.00625 mol x (45.4622 g/1 mol) = 0.27788875 g. Again the molar mass of a chemical says how many grams are contained within 1 mole of that chemical. We can get this number by adding the relative atomic masses of both elements on the periodic table: 9.0122 (Be) + 35.45 (Cl) = 45.4622 g/mol. To convert moles of a chemical to grams we need a conversion ratio which uses moles and grams: the molar mass of beryllium chloride. Again see how the units cross cancel to give us a new unit. Now this volume can be multiplied by the molarity to yield us moles of beryllium chloride: 0.125 L x (0.050 mol/ 1 L) = 0.00625 mol. So I divided by 1000 essentially which is the same as multiplying by its reciprocal 1/1000. ![]() So for the mL units to cancel and give us liters as the unit we need to do: 125 mL x (1 L/1000 mL) = 0.125 L. We know there are 1000 mL in 1 liter so the conversion ratio is 1: 1000. In order for the units to cancel we need the volume to be in liters instead of milliliters. Molarity is a unit of concentration defined as moles/liter. If we look at just the units we know which to do. So we're going to either multiply or divide the volume and the molarity to get grams. We begin with volume of a solution in milliliters and its concentration in molarity, and we ultimately want the mass in grams. Essentially it amounts to performing multiple multiplications/divisions where every step you are cross canceling units until you arrive at the desired unit.įor the first question involving beryllium chloride we can use dimensional analysis to quickly solve the problem. Dimensional analysis is a way of converting quantities from one unit to another and takes all the guess work out of it. For these problems it is invaluable to be well acquainted with something called dimensional analysis. ![]() So this is a stoichiometry problem where we have figure out amounts of chemicals. You would observe solid salt particles just falling to the bottom of the water in a saturated solution. The solid form does not add to the molarity since molarity only measures aqueous species in solution. Eventually you run out of free water molecules to surround the ions and the salt can no longer dissolve so it stays in its unaltered solid. If you keep adding more salt you need more and more water molecules to surround those ions to actually make them dissolve. When you dissolve something like salt, sodium chloride or NaCl, into water, the water molecules surround each individual sodium and chloride ion thereby turning them into aqueous ions and increasing the molarity. If you can no longer dissolve any more solute into the solvent, your solution has become saturated therefore essentially capping the molarity of the solute. When you dissolve a solute into a solvent you create a solution where the solute has a concentration measured in molarity.
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