How do you calculate the number of moles from volume?

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    It depends on the substance whose volume you know.
    If you have a pure liquid or a solid you use its to calculate its mass and then divide the mass by the molar mass.
    If you have a solution you multiply the by the volume in litres.
    MOLES FROM VOLUME OF PURE LIQUID OR SOLID
    There are two steps:
    Example
    How many moles are in 10.00 mL of acetic anhydride? The molar mass of acetic anhydride is 102.1 g/mol and its density is 1.080 g/mL?
    Solution
    The formula for density is
    ##color(blue)(|bar(ul(color(white)(a/a) = m/V color(white)(a/a)|))) ##
    where #### is the density ##m## is the mass and ##V## is the volume of the sample.
    We can rearrange the formula to get
    ##m = V ##
    ##mass = 10.00 color(red)(cancel(color(black)(mL))) 1.080 g/(1 color(red)(cancel(color(black)(mL)))) = 10.80 g##
    ##n = 10.80 color(red)(cancel(color(black)(g))) 1 mol/(102.1color(red)(cancel(color(black)(g)))) = 0.1058 mol##
    MOLES FROM VOLUME OF SOLUTION
    Molarity is the number of moles of a substance in one litre of solution.
    ##color(blue)(|bar(ul(color(white)(a/a) M = n/Vcolor(white)(a/a)|))) ##
    where ##n## is the number of moles and ##V## is the volume in litres.
    We can rearrange this equation to get the number of moles:
    ##n = M V##
    Example
    How many moles of ##NaCl## are contained in 0.300 L of 0.400 mol/L ##NaCl## solution?
    Solution
    ##n = 0.300 color(red)(cancel(color(black)(L soln))) 0.400 mol NaCl/(1 color(red)(cancel(color(black)(L soln)))) = 0.120 mol NaCl##

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