Question #6a5d8

1 Answer
Nov 29, 2015

Answer:

#"364 g " -> " lactose"#
#"196 g " -> " water"#

Explanation:

So, you know that your target solution has a total mass of #"560 g"#, and that its percent concentration by mass is equal to #65%#.

What that means is that every #"100 g"# of solution must contain #"65 g"# of solute. In your case, the target solution needs to contain #"65 g"# of lactose per #"100 g"#.

So, you know that

#color(blue)("% w/w" = "mass of solute"/"mass of solution" xx 100)#

If #x# represents the mass of lactose needed to make this solution, you can say that you have

# ( x )/"560 g" xx 100 = 65%#

The value of #x# will come out to be

#x = (65 * "560 g")/100 = "364 g"#

Since the total mas of the solution is equal to #"560 g"#, it follows that the mass of water needed to make this solution will be

#m_"sol" = m_"solute" + m_"solvent"#

#m_"water" = "560 g" - "364 g" = "196 g"#

Therefore, if you mix #"196 g"# of water with #"364 g"# of lactose, you will get a final solution that is #"65% w/w"# lactose.