Question #ec7e1

1 Answer
Apr 29, 2016

Answer:

Here's how you can do that.

Explanation:

All you have to do here is use the given weight by volume percent concentration, #"% w/v"#, as a conversion factor to help you determine how many milliliters of solution would contain #"2.5 mg"# of solute.

A solution's weight by volume percent concentration tells you how many grams of solute you get for every #"100 mL"# of solution.

In your case, the solution is said to be #"0.80% w/v"#, which means that you get #"0.80 g"# of solute for every #"100 mL"# of solution.

Now, the problem tells you that you have a mass of solute of #"2.5 mg"#. Before doing anything else, convert this from milligrams to grams by using

#color(purple)(|bar(ul(color(white)(a/a)color(black)("1 g" = 10^3"mg")color(white)(a/a)|)))#

You will have

#2.5 color(red)(cancel(color(black)("mg"))) * "1 g"/(10^3color(red)(cancel(color(black)("mg")))) = "0.0025 g"#

So, you know that the solution contains #"0.80 g"# of solute per #100 mL"# of solution. Use this as a conversion factor to find the volume of the solution that would contain #"0.0025 g"# of solute

#0.0025 color(red)(cancel(color(black)("g solute"))) * overbrace("100 mL solution"/(0.80color(red)(cancel(color(black)("g solute")))))^(color(blue)("= 0.80% w/v")) = "0.3125 mL solution"#

Rounded to two sig figs, the answer will be

#"volume of solution" = color(green)(|bar(ul(color(white)(a/a)"0.31 mL"color(white)(a/a)|)))#