SME
Analytical Chemistry · Problem type
Two chlorides from one AgCl mass
Use this for “A 0.6000 g mixture of NaCl and KCl, dissolved and treated with excess AgNO₃, gives 1.3250 g of AgCl. What percent of the mixture is NaCl?”
Chart
NaCl: 0.2279 g
KCl: 0.2721 g
This is an example. Type your own values to start a new problem.
mNaCl (g)
MNaCl (g/mol)
+
m (g)
−
mNaCl (g)
MKCl (g/mol)
=
mAgCl (g)
143.32
g/mol
mKCl
Mass of KCl
worked out (not typed) · g
wNaCl
Percent NaCl in the mixture
calculated · %
Formulas
mNaCl
MNaCl
+
m
− mNaCl
MKCl
=
mAgCl
143.32
0.2279
58.44
+
0.5 − 0.2279
74.55
=
1.082
143.32
mKCl
=
m
−
mNaCl
0.2721 = 0.5 − 0.2279
wNaCl
=
100
×
mNaCl
m
45.58
=
100
×
0.2279
0.5
Assumptions
•
The mixture is only NaCl and KCl, and every chloride ion ends up in the AgCl (143.32 g/mol).
•
Each salt gives one AgCl per formula, so the moles of AgCl are the moles of NaCl plus the moles of KCl.
•
The AgCl mass must lie between what pure KCl and pure NaCl would give.
Step-by-step
WE KNOW
m = 0.5 g, mAgCl = 1.082 g, MNaCl = 58.44 g/mol, MKCl = 74.55 g/mol
FIND
mass of NaCl (mNaCl), mass of KCl (mKCl), percent NaCl in the mixture (wNaCl)
Step 1 · Find mass of NaCl (mNaCl)
Use mNaCl ÷ MNaCl + (m − mNaCl) ÷ MKCl = mAgCl ÷ 143.32
The moles of AgCl are the moles of chloride from both salts. Put the KCl as the mixture less the NaCl, and solve for the NaCl mass.
mNaCl
=
MNaCl
×
(mAgCl
×
MKCl
−
143.32
×
m
)
÷
(143.32
×
(MKCl
−
MNaCl))
mNaCl = 58.44 × (1.082 × 74.55 − 143.32 × 0.5) ÷ (143.32 × (74.55 − 58.44))
mNaCl = 58.44 × (1.082 × 74.55 − 143.32 × 0.5) ÷ (143.32 × 16.11)
mNaCl
=
58.44
×
80.6631 − 71.66
2,308.8852
mNaCl
=
58.44
×
9.0031
2,308.8852
mNaCl
=
526.1
2,308.8852
mNaCl = 0.2279 g
Step 2 · Find mass of KCl (mKCl)
Use mKCl = m − mNaCl
The rest of the mixture is the KCl.
mKCl = 0.5 − 0.2279
mKCl = 0.2721 g
Step 3 · Find percent NaCl in the mixture (wNaCl)
Use wNaCl = 100 × mNaCl ÷ m
The NaCl’s grams over the mixture’s grams, as a percent.
wNaCl
=
100
×
0.2279
0.5
wNaCl
=
22.79
0.5
wNaCl = 45.58%
Check
Put the numbers back in. Both sides should match.
0.2279
58.44
+
0.5 − 0.2279
74.55
=
1.082
143.32
✓
0.2721 = 0.5 − 0.2279 ✓
45.58
=
100
×
0.2279
0.5
✓
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