Answer is: A. 1.81 mol.
Balanced chemical reaction: FeCl₂ + 2KOH → Fe(OH)₂ + 2KCl.
n(FeCl₂) = 4.15 mol; amount of iron(II) chloride.
n(KOH) = 3.62 mol; amount of potassium hydroxide, limiting reactant.
From chemical reaction: n(KOH) : n(Fe(OH)₂) = 2 : 1.
n(Fe(OH)₂) = n(KOH) ÷ 2.
n(Fe(OH)₂) = 3.62 mol ÷ 2.
n(Fe(OH)₂) = 1.81 mol; amount of iron(II) hydroxide.
This method of quantitative determination of percent purity is titrimetric reactions. These reactions most commonly involve neutralization reactions between an acid and a base. Then, we look at the neutralization reaction:
H₂C₂O₄ + 2 NaOH ⇒ Na₂C₂O₄ + 2 H₂O
So, we do the stoichiometric calculations. The important data we should know is the molar mass of oxalic acid which is equal to 90 g/mol.
(0.2283 mol/L NaOH * 0.3798 L * 1 mol H₂C₂O₄/ 2mol NaOH * 90 g/mol H₂C₂O₄) ÷ 0.7984 g *100%
= 488%
This is impossible. The purity can't be more than 100%. Looking at our calculations and the balance reaction, all steps were done correctly. So, I think there is some typographical error in the given. The mass of the sample should be 7.984 g. Then, the answer would be 48.87% purity.
We are given that the balanced chemical reaction is:
cacl2⋅2h2o(aq) +
k2c2o4⋅h2o(aq) --->
cac2o4⋅h2o(s) +
2kcl(aq) + 2h2o(l)
We known that
the product was oven dried, therefore the mass of 0.333 g pertains only to that
of the substance cac2o4⋅h2o(s). So what we will do first is to convert this
into moles by dividing the mass with the molar mass. The molar mass of cac2o4⋅h2o(s) is
molar mass of cac2o4 plus the
molar mass of h2o.
molar mass cac2o4⋅h2o(s) = 128.10
+ 18 = 146.10 g /mole
moles cac2o4⋅h2o(s) =
0.333 / 146.10 = 2.28 x 10^-3 moles
Looking at
the balanced chemical reaction, the ratio of cac2o4⋅h2o(s) and k2c2o4⋅h2o(aq) is
1:1, therefore:
moles k2c2o4⋅h2o(aq) = 2.28
x 10^-3 moles
Converting
this to mass:
mass k2c2o4⋅h2o(aq) = 2.28
x 10^-3 moles (184.24 g /mol) = 0.419931006 g
Therefore:
The mass of k2c2o4⋅<span>h2o(aq) in
the salt mixture is about 0.420 g</span>
I am attempting the problem for phosphonium Ion rather than its chloride salt. The chemical equation is shown below along with molar masses in mg.
First of all we will calculate the amounts of reactants required for the synthesis of 220 mg of phophonium ion. Calculations for both reactants is as follow,
For
Benzyl chloride,
=
Solving for X,
X =
X = 78.79 mg
For PPh₃:
=
Solving for X,
X =
X = 163.27 mg
Now, Assuming these values as for 95 % conversion, we can calculate 100 % yield as follow,
when
=
Solving for X,
X =
= 231.57 mg
Now, calculate reactants mass with respect to 231.57 mg
when
=
Solving for ,
X =
=
82.93 mg of Benzyl chloride
when
=
Solving for ,
X =
=
171.85 mg of PPh3
So, reaction was started with reacting
82.93 mg of Benzyl Chloride and
171.85 mg of Triphenyl Phosphine.
The trick for this problem is to understand atomic mass: the fact that different atoms have different masses. What we need to do is add up all the atomic masses of the compound and work out the ratio of mass of water to the mass of sodium carbonate. Atomic masses are often given for each atom in the periodic table, but you can look them up on google too.
You can do this by adding up individual atoms for each molecule, or you can shortcut and lookup the molar mass of the compound (i.e.the task already done for you).
The molar mass of water is 18.01g/mole so for 10 moles of water we have a mass of 180.1g.
The molar mass of sodium carbonate is 106g/mole (google).
So the total mass of the sodium carbonate decahydrate compound is 180.1+106 = 286.1g, of which water would make up 180.1g, so the percentage of water is is 180.1/286.1 = 0.629, so we can round this to 63%
:)
