If an unknown solid is either #"NaOH"# or #"Ba"("OH")_2#, and it is reacted with excess #37%"w/w"# stock #"HCl"# (#rho = "1.19 g/mL"#), can you still determine which base is the limiting reagent?
1 Answer
I believe it's a valid test. The reactions would be
#"NaOH"(aq) + "HCl"(aq) -> "NaCl"(aq) + "H"_2"O"(l)#
and
#"Ba"("OH")_2(aq) + 2"HCl"(aq) -> "BaCl"_2(aq) + 2"H"_2"O"(l)#
Unfortunately, none of the products are sufficiently insoluble to form a precipitate in a laboratory setting, as far as I can tell.
You can indeed find a limiting reagent for this.
- Start from the mass of the base, and suppose you have one or the other.
- Then, note the density of
#37%# w/w stock#"HCl"# is#"1.19 g/mL"# and solve for its mass in grams. You only need an estimate, I suppose, so if your HCl is dilute, it's OK to assume the density is#"1.00 g/mL"# as an approximation since the density of dilute aqueous HCl has to be between#1.00# and#"1.49 g/mL"# . - Convert both masses to
#"mol"# s, and compare to see which one is the limiting reagent. - Then, convert to
#"mol"# s of either#"NaCl"# or#"BaCl"_2# from the#"mol"# s of limiting reagent.
If you have the experimental mass of the product, then you should be able to see two clearly different results for the theoretical mass from solving either reaction 1 or reaction 2.
Suppose you had
#"0.1" cancel("g NaOH") xx "1 mol"/(39.9959 cancel("g")) = color(blue)(2.5xx10^(-3) "mols NaOH")#
#"0.1" cancel("g Ba"("OH")_2) xx "1 mol"/(171.3138 cancel("g")) = color(blue)(5.8xx10^(-4) "mols Ba"("OH")_2)#
If you had barium hydroxide at room temperature, a reasonable amount of water to dissolve it is
So let's just say we had
That gives us
Thus, the base can easily be the limiting reagent.
Since for the same mass of base, the
A factor of