Aneeqa Haider, Ariel Tsang, Carrie Fan, Fabiha Nuzhat

Chloride ion
○ Cl + e−  Cl−

Chloride
○ Results from the
combination of Cl2
with a metal (e.g.
NaCl)

Chloride Ion
Reactants: NaCl,
AgNO3

Gravimetric analysis
○ The set of procedures to determine the quantity of
a substance present in the mass of a solid

Seven steps
1.
2.
3.
4.
5.
6.
7.
Drying and measuring the masses of samples to
be analysed
Dissolving the sample in distilled water.
Precipitating the substance by adding a reagent.
Separating the precipitate from the solution by
filtration.
Washing precipitate free of impurities.
Drying precipitate to obtain mass.
Determine the amount of the original ion based
on the known mass and composition of the
precipitate.
Objective: Determine the amount of
chloride ions present in a given
solution of NaCl using AgNO3 as a
reagent.
 Problem: What is the amount of
chloride ions present in 0.2 g of
Sodium Chloride (NaCl)?
 Hypothesis: The number of chloride
ions present in 0.2 g of NaCl is
approximately 2.06 x 10²¹.





Erlenmeyer Flask
(2)

Beaker (1)
Funnel (1)
Ashless Filter
Paper (1)
3 g of Silver
Nitrate AgNO3 (aq)

Retort Stand

Ring Clamp

Distilled Water

Clay Triangle

Dropper

Safety Goggles

Test Tubes (2)

Spatula
Stirring Rod

Paper Clips (4)

Bunsen Burner


Balance

Crucible and lid


Crucible tongs

0.2 g of Sodium
Chloride -NaCl
Graduated
Cylinder
1.
Formation of the precipitate
2.
Filtration of the solution containing
the precipitate
3.
Measurement of the mass of AgCl by
drying the filter paper
4.
Measurement of the mass of AgCl by
burning the ashless filter paper
0.2 g of NaCl was
dissolved in Distilled
Water in Erlenmeyer
Flask
 3.4 g of AgNO3 (aq)
was poured into
Erlenmeyer Flask
containing NaCl (aq).
 Solution was put into
rest until all the
precipitate formed.

Filter paper, funnel and Erlenmeyer
flask were set up
 The solution containing the
precipitate was poured through the
filter paper
 Washed periodically with Distilled
water



Filter paper and precipitate were
completely dried
Mass of the precipitate:
○ Mass of the filter paper with precipitate -
Mass of the filter paper
Retort stand, ring clamp, clay triangle,
and Bunsen burner were set up
 Filter paper was carefully folded with
the precipitate inside, and placed in the
crucible
 Crucible was heated until no more
filter paper was left
 Mass of Precipitate:

○ Mass of crucible, lid & precipitate –
Mass of crucible & lid


General Safety
Precautions
Safety precautions
specific for this
experiment:
○ Avoiding contact with Silver Chloride (AgCl)
○ Safety precautions while using the Bunsen
burner

Formation of the Precipitate
Objects
Mass (g)
Filter paper
1.04 g
Filter paper with NaCl
1.24 g
NaCl
0.2 g
Graduated cylinder
22.48 g
Graduated cylinder with
AgNO3
27.08 g
AgNO3
3.4 g
Calculation
(1.24 g - 1.0 g)
(27.48 g - 22.48 g)

Measurement of the mass of AgCl by
drying the filter paper
Objects
Filter paper
Filter paper with
AgCl
AgCl
Mass (g)
1.04 g
1.43 g
0.39 g
Calculation
(1.43 g - 1.04 g)

Measurement of the mass of AgCl by
drying the filter paper
Objects
Crucible and lid
Crucible, lid and
contents (AgCl)
AgCl
Mass (g)
32.13 g
32.64 g
Calculation
0.51 g (32.64 g - 32.13 g)

Mass used of Sodium Chloride (NaCl):
○ 0.2 g

Molar mass of NaCl:
○ 35.45 g/mol

Percentage composition by mass of
Silver Chloride (AgCl):
○ Silver (Ag) = 75%
○ Chloride (Cl) = 25%

Mass of filter paper:
○ 1.04g

Mass of filter paper + AgCl:
○ 1.43g

AgCl:
○ (1.43g – 1.04g) = 0.39g

Mass of chloride ions present:
○ 0.25 x 0.39g = 0.0975g

Number of moles of chloride ions:
=
Mass of Cl
Molar Mass of Cl
= 0.0975g
35.45g
= 0.00275 mol

Mole = Avogadro's number
○ 6.022 x 1023

Number of chloride ions:
= (# of moles) x (Avogadro's number)
= (0.00275) x (6.022 x 1023)
= 1.656 x 1021 chloride ions present
in 0.2 g of NaCl by drying filter paper

Mass of crucible + lid + filter paper:
○ 32.13g

Mass of crucible + lid + filter paper +
AgCl
○ 32.64g

AgCl
○ (32.64g – 32.13g) = 0.51g

Mass of chloride ions present:
○ 0.25 x 0.51g = 0.1275g

Number of moles of chloride ions:
= Mass of Cl
Molar Mass of Cl
= 0.1275g
35.45g
= 0.00360 mol

Mole = Avogadro's number:
○ 6.022 x 1023

Number of chloride ions:
○ (# of moles) x (Avogadro's number)
○ (0.00360) x (6.022 x 1023)
○ 2.167 x 1021 chloride ions present in 0.2 g of
NaCl by burning filter paper

Law of Conservation of Mass
○ Mass of the reactants = Mass of the
products
Mass of Cl ions in NaCl (reactant)
= Mass of Cl ion is AgCl (product)


Double displacement reaction:
AB + CD
AgNO3 (aq) + NaCl
(aq)
→
AD + CB
→ AgCl
(s)
+ NaNO3 (aq)
Hydration
provides
greater stability
than lattice
energy
 Hydration shell

Water – dipole moment
More stable as a solid precipitate
than separate ions
 Hydration energy provided is less
than lattice energy released when
compound forms

White crystalline solid
 Light sensitive

○ Purple  black
Change colour when AgCl  Ag + Cl
 Dry powder, doesn’t draw moisture
from the air
 Very low solubility
 MP: 455°C BP: 1550°C

AgNO3 is the excess reagent
Amount of chloride ions = product
In this double displacement reaction all of
the NaCl must be used up
 LR = NaCl : limits amount of AgNO3 used
limits amount of products
 An excess of AgNO3 will not react since all
the NaCl is used up already



Otherwise, mass of the impurities
would be included in the mass of the
AgCl precipitate
 Causes an inaccurate measurement
of mass of AgCl
 Causes inaccurate determination of
the number of Cl ions

Contents: AgCl and ashless filter
paper
 Ashless filter paper turned into CO2
 Remaining content: AgCl
 AgCl is a white coloured powder at
SATP
 Upon heating, AgCl undergoes
decomposition to yield Ag and Cl


Percentage Yield
=
Actual Yield
x 100
Theoretical Yield
= 80%

Percentage Error
= (Theoretical Yield – Actual Yield) x 100
Theoretical Yield
= 20%

By drying filter paper:
○ Number of chloride ions in 0.2g of NaCl is
1.656 x 1021

By burning ashless filter paper:
○ Number of chloride ions in 0.2g of NaCl is
2.167 x 1021

Amount of ions present in NaCl =
amount of ions present in AgCl
○ Law of Conservation of Mass

The reading on the electrical balance
was observed to change constantly
○ Due to slight air currents
○ Contents being weighted were extremely
light
○ Measured multiple times

Small amounts of AgCl were stuck in
the flask after attempts to remove it
○ Caused alterations in final mass
○ Inaccurate percentage yield

Ashless filter paper not burned away
completely
○ final mass greater than expected

Crucible was placed on counter to
allow for cooling
○ picked up unwanted particles on the
counter
Use of better quality ashless filter
paper that will completely burn away
without leaving any unwanted
residue
 Use of clean crucible and lid
 Minimum transfer of the samples
from container to container
