Gravimetric Analysis (4.3.3)

Question 1

• Gravimetric analysis is a technique for quantifying an unknown substance by converting the substance to a known product that can be isolated and weighed.

Answer 1

• Gravimetric analysis is a technique for quantifying an unknown substance by converting the substance to a known product that can be isolated and weighed.

Question 2

Gravimetric analysis is a technique for quantifying
an unknown substance by converting the substance
to a known product that can be isolated and
weighed.
Precipitation reactions are often used in
gravimetric analysis.
For example, an unknown metal chloride can be
identified using gravimetric analysis. The chloride
ion can be precipitated with silver ions. This
precipitate can then be dried and weighed, and the
mass can be used to determine the moles of
chloride ions present. This can be used to
determine the moles of unknown. This data can be
used, for example, to determine the molar mass of
the unknown.
First, the mass of silver chloride is converted to
moles of silver chloride. This is equal to the moles
of chloride ion. Multiplying by the molar mass of
chloride ion yields the mass of chloride in the
unknown sample.
Next, the percent by mass of chloride ion in the
unknown is determined. The mass of chloride ion is
divided by the mass of the compound, and
multiplied by 100%.
The percent by mass of chloride ion in the original
unknown is equal to the mass of chloride ion divided
by the total mass of the compound. The total mass
of the compound is the mass of chloride ion plus the
mass of the unknown metal cation. Substituting the
molar mass of chloride ion into this equation allows
for the determination of the molar mass of the metal
cation.
The molar mass of the metal cation is found to be
39.1 g/mol. By referencing a periodic table, the
metal cation is identified as potassium ion. The
unknown compound is potassium chloride, a table
salt substitute.

Answer 2

Gravimetric analysis is a technique for quantifying
an unknown substance by converting the substance
to a known product that can be isolated and
weighed.
Precipitation reactions are often used in
gravimetric analysis.
For example, an unknown metal chloride can be
identified using gravimetric analysis. The chloride
ion can be precipitated with silver ions. This
precipitate can then be dried and weighed, and the
mass can be used to determine the moles of
chloride ions present. This can be used to
determine the moles of unknown. This data can be
used, for example, to determine the molar mass of
the unknown.
First, the mass of silver chloride is converted to
moles of silver chloride. This is equal to the moles
of chloride ion. Multiplying by the molar mass of
chloride ion yields the mass of chloride in the
unknown sample.
Next, the percent by mass of chloride ion in the
unknown is determined. The mass of chloride ion is
divided by the mass of the compound, and
multiplied by 100%.
The percent by mass of chloride ion in the original
unknown is equal to the mass of chloride ion divided
by the total mass of the compound. The total mass
of the compound is the mass of chloride ion plus the
mass of the unknown metal cation. Substituting the
molar mass of chloride ion into this equation allows
for the determination of the molar mass of the metal
cation.
The molar mass of the metal cation is found to be
39.1 g/mol. By referencing a periodic table, the
metal cation is identified as potassium ion. The
unknown compound is potassium chloride, a table
salt substitute.