A student has a stock solution of 30.0% w/v hydrogen peroxide, #H_2O_2#, solution. How should the student prepare 250 mL of a 0.25% w/v #H_2O_2# solution?

Question

Avery Adams · Accepted Answer

Here's how you could do that.

Your strategy here will be to figure out exactly how many grams of hydrogen peroxide are needed to make the target solution, then figure out what volume of the stock solution would contain that many grams. Weight by volume percent concentration is defined as mass of solute, which in your case is hydrogen peroxide, divided by volume of solution, and multiplied by #100#. #color(blue)("% w/v" = "mass of solute"/"volume of solution" xx 100)# So, a #"0.25% w/v"# hydrogen peroxide solution will contain #"0.25 g"# of solute for every #"100m0 mL"# of solution. This means that your #"250-mL"# target solution will contain #250 color(red)(cancel(color(black)("mL solution"))) * ("0.25 g H"_2"O"_2)/(100color(red)(cancel(color(black)("mL solution")))) = "0.625 g H"_2"O"_2# Your focus now should shift to the stock solution. More specifically, you need to figure out what volume of the stock solution will contain this many grams of hydrogen peroxide #"% w/v" = m_"solute"/V_"sol" xx 100 implies V_"sol" = m_"solute"/"%w/v" xx 100# In your case, you will get #V_"sol" = (0.625 color(red)(cancel(color(black)("g"))))/(30.0 color(red)(cancel(color(black)("g")))/"mL") xx 100 = "2.0833 mL"# Rounded to two sig figs, the volume will be #V = color(green)("2.1 mL")# So, in order to prepare your solution, you need to take #"2.1 mL"# of stock solution and add enough water to get the final volume of the solution to #"250 mL"#.

Serenity Allen · Answer

undefined To prepare 250 mL of a 0.25% w/v hydrogen peroxide (H2O2) solution from a 30.0% w/v stock solution, the student would need to dilute the stock solution with water. The dilution equation can be used to calculate the volume of the stock solution needed.

First, let's determine the amount of H2O2 in the desired solution:

0.25% of 250 mL = (0.25/100) * 250 = 0.625 grams

Next, we'll set up a proportion to find out how much of the stock solution is needed:

(0.625 grams) / (30.0 grams) = (x mL) / (250 mL)

Solving for x:

x = (0.625 grams * 250 mL) / 30.0 grams
x ≈ 5.21 mL

So, the student should mix approximately 5.21 mL of the 30.0% w/v hydrogen peroxide solution with enough water to make a total volume of 250 mL to obtain a 0.25% w/v H2O2 solution.