How would you calculate the pH of a substance after a titration of 10.19mL 0.10M HCl with 10.99mL 0.093M NaOH?
1 Answer
Explanation:
You're mixing hydrochloric acid,
The balanced chemical equation for this neutralization reaction looks like this
"HCl"_text((aq]) + "NaOH"_text((aq]) -> "NaCl"_text((aq]) + "H"_2"O"_text((l])HCl(aq]+NaOH(aq]→NaCl(aq]+H2O(l]
In order to have a complete neutralization, you need to add equal numbers of moles of strong acid and weak base.
If you have more acid than base, the resulting solution will be acidic, since it will contain an excess of hydronium ions,
Likewise, if you have more base than acid, the resulting solution will be basic, since it will contain an excess of hydroxide anions,
Use the molarities and volumes of the two solutions to determine how many moles of each you;'re adding together
color(blue)(c = n/V implies n = c * V)c=nV⇒n=c⋅V
n_(HCl) = "0.10 M" * 10.19 * 10^(-3)"L" = "0.001019 moles HCl"nHCl=0.10 M⋅10.19⋅10−3L=0.001019 moles HCl
n_(NaOH) = "0.093 M" * 10.99 * 10^(-3)"L" = "0.001022 moles NaOH"nNaOH=0.093 M⋅10.99⋅10−3L=0.001022 moles NaOH
Notice that you have more moles of sodium hydroxide than you do of hydrochloric acid. This tells you that the reaction will completely consume the acid and leave you with
n_(NaOH) = 0.001022 - 0.001019 = "0.0000030 moles NaOH"nNaOH=0.001022−0.001019=0.0000030 moles NaOH
Sodium hydroxide dissociates completely in aqueous solution, so you can say that
n_(OH^(-)) = n_(NaOH) = "0.0000030 moles OH"^(-)nOH−=nNaOH=0.0000030 moles OH−
The total volume of the resulting solution will be
V_"total" = "10.19 mL" + "10.99 mL" = "21.18 mL"Vtotal=10.19 mL+10.99 mL=21.18 mL
The molarity of the hydroxide anions will be
c = "0.0000030 moles"/(21.18 * 10^(-3)"L") = 1.42 * 10^(-4)"M"c=0.0000030 moles21.18⋅10−3L=1.42⋅10−4M
As you know, a solution's pOH is equal to
"pOH" = - log( ["OH"^(-)])pOH=−log([OH−])
In this case.
"pOH" = - log(1.42 * 10^(-4)) = 3.85pOH=−log(1.42⋅10−4)=3.85
The pH of the solution will thus be
"pH" + "pOH" = 14pH+pOH=14
"pH" = 14 - 3.85 = color(green)(10.15)pH=14−3.85=10.15
