Question #724b9
2 Answers
The answer is B 13 mL of
Explanation:
The equation for the reaction is
1. Calculate the moles of
2. Calculate the moles of
3. Calculate the volume of
Here's what I got.
Explanation:
Here's how you can solve this problem by using a more intuitive approach.
Look at the chemical equation given to you
#"H"_ 3"PO"_ (4(aq)) + color(red)(3)"NaOH"_ ((aq)) -> "Na"_ 3"PO"_ (4(aq)) + 3"H"_ 2"O"_ ((l))#
Notice that it takes
This tells you that when you're working with solutions of sodium hydroxide and phosphoric acid of equal volumes, the sodium hydroxide solution must be
Now, let's assume that you have
#["NaOH"] = color(red)(3) xx "0.25 M" = "0.75 M"#
However, the concentration of sodium hydroxide solution is
This means that you must have a volume of phosphoric acid solution that is approximately
#"100 mL"/8 = "12.5 mL"#
is
ALTERNATIVELY
You can prove that this is the answer by using the molarity and volume of the sodium hydroxide solution to figure out how many moles it contains
#color(purple)(|bar(ul(color(white)(a/a)color(black)(c = n_"solute"/V_"solution" implies n_"solute" = c * V_"solution")color(white)(a/a)|)))#
You will have
#n_"NaOH" = "0.1 mol" color(red)(cancel(color(black)("L"^(-1)))) * overbrace(100 * 10^(-3)color(red)(cancel(color(black)("L"))))^(color(blue)("volume in liters"))#
#n_"NaOH" = "0.010 moles NaOH"#
This many moles of sodium hydroxide would require
#0.010 color(red)(cancel(color(black)("moles NaOH"))) * ("1 mole H"_3"PO"_4)/(color(red)(3)color(red)(cancel(color(black)("moles NaOH")))) = "0.00333 moles H"_3"PO"_4#
The volume of
#V_("H"_3"O"_4) = (0.00333 color(red)(cancel(color(black)("moles"))))/(0.25 color(red)(cancel(color(black)("mol"))) "L"^(-1)) = "0.01333 L"#
Expressed in milliliters, the answer will once again be
#V_("H"_3"PO"_4) = color(green)(|bar(ul(color(white)(a/a)color(black)("13.33 mL")color(white)(a/a)|)))#
I won't bother with sig figs, but keep in mind that you don't have four sig figs for the values given to you by the problem.