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How can I convert moles to milliliters?

There are at least three different mole-to-volume conversions you'll encounter in general chemistry. Before you can make the conversion, ask: moles of what ? Milliliters of what?

Converting moles of a substance to milliliters of the same substance. You must know the substance's atomic or molecular weight and its density to do this conversion. Here's the basic strategy:
 moles molecular weight grams density milliliters

For example, to find the number of milliliters that 10.0 moles of NaCl would occupy, you must find the molecular weight (58.45 g/mol) and look up the density (2.17 g/mL):
 10.0 mol NaCl ( 58.45 g NaCl1 mol NaCl ) ( 1 mL NaCl2.17 g NaCl ) = 269 mL NaCl

Converting moles of solute to milliliters of solution. You'll need to know the concentration of the solute in the solution to do this conversion. For example, to find the number of milliliters of 0.123 M AgNO3 solution that contains 1.00 mol of AgNO3, convert moles of AgNO3 to liters of solution using the molarity:
 1.00 mol AgNO3 ( 1 L solution0.123 mol AgNO3 ) ( 1000 mL solution1 L solution ) = 8.13×103 mL

Converting moles of gas to milliliters of gas. If you know the density of the gas, you can use the first conversion method to do this type of problem. But if you don't know the density, and the gas can be treated as ideal, you can calculate the molar volume of the gas from the ideal gas law and use it to convert moles to liters directly. Since PV=nRT, V/n = RT/P. For example, to find the number of milliliters that 1.00 mol of helium would occupy at 298 K and 1.00 atm, compute the molar volume
 Vn = RTP = ( 0.0821 L atm mol-1 K-1× 298 K1.00 atm ) = 24.4658 L/mol
where nonsignificant figures are grey. Now do the conversion directly:
 1.00 mol gas ( 24.4658 L gasmol gas ) ( 1000 mL gas1 L gas ) = 2.45×104 mL gas

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How can I convert moles to milliliters?