Download - GRAVIMETRIC ESTIMATION OF CHLORIDE IONS
GRAVIMETRIC ESTIMATION OF CHLORIDE
IONSAneeqa Haider, Ariel Tsang, Carrie Fan, Fabiha Nuzhat
Introduction Chloride ion
○ Cl + e− Cl− Chloride
○ Results from the combination of Cl2 with a metal (e.g. NaCl)
Reactants: NaCl, AgNO3 Chloride Ion
Introduction Gravimetric analysis
○ The set of procedures to determine the quantity of a substance present in the mass of a solid
Seven steps1. Drying and measuring the masses of samples to
be analysed2. Dissolving the sample in distilled water.3. Precipitating the substance by adding a reagent.4. Separating the precipitate from the solution by
filtration.5. Washing precipitate free of impurities.6. Drying precipitate to obtain mass.7. Determine the amount of the original ion based
on the known mass and composition of the precipitate.
Introduction 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.
Materials Erlenmeyer Flask
(2) Beaker (1) Funnel (1) Ashless Filter
Paper (1) Paper Clips (4) Balance 0.2 g of Sodium
Chloride -NaCl
3 g of Silver Nitrate - AgNO3 (aq)
Distilled Water Dropper Test Tubes (2) Bunsen Burner Crucible and lid Crucible tongs
Retort Stand Ring Clamp Clay Triangle Safety Goggles Spatula Stirring Rod Graduated
Cylinder
Procedure1. 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
Formation of the Precipitate 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.
Filtration of the Solution containing the Precipitate 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
Measurement of the Mass of AgCl by drying the filter paper Filter paper and precipitate were
completely dried
Mass of the precipitate:○ Mass of the filter paper with precipitate -Mass of the filter paper
Measurement of the Mass of AgCl by burning the ashless 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
Safety Precautions General Safety
Precautions
Safety precautions specific for this experiment:○ Avoiding contact with Silver Chloride (AgCl)○ Safety precautions while using the Bunsen
burner
Observations Formation of the PrecipitateObjects Mass (g) CalculationFilter paper 1.04 gFilter paper with NaCl 1.24 gNaCl 0.2 g (1.24 g - 1.0 g)Graduated cylinder 22.48 gGraduated cylinder with AgNO3
27.08 g
AgNO3 3.4 g (27.48 g - 22.48 g)
Observations Measurement of the mass of AgCl
by drying the filter paper
Objects Mass (g) CalculationFilter paper 1.04 gFilter paper with AgCl
1.43 g
AgCl 0.39 g (1.43 g - 1.04 g)
Observations Measurement of the mass of AgCl
by drying the filter paperObjects Mass (g) Calculation
Crucible and lid 32.13 gCrucible, lid and contents (AgCl)
32.64 g
AgCl 0.51 g (32.64 g - 32.13 g)
Calculations – Known Information 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%
Calculations – By Drying Filter Paper 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
Calculations – By Drying Filter Paper
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
Calculations – 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
Calculations – By Burning Ashless Paper
Number of moles of chloride ions: = Mass of Cl
Molar Mass of Cl = 0.1275g
35.45g = 0.00360 mol
Calculations – By Burning Ashless Paper
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
Calculations – By Burning Ashless Paper
How did the Law of Conservation of Mass help predict the amount of Cl ions in AgCl?
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)
What type of chemical reaction is taking place in this experiment? Double displacement reaction:
AB + CD → AD + CB
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
Why does NaCl dissolve in water? Hydration
provides greater stability than lattice energy
Hydration shell
Water – dipole moment
Why doesn’t AgCl dissolve in water? More stable as a solid precipitate
than separate ions Hydration energy provided is less
than lattice energy released when compound forms
What are some properties of AgCl? 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
Why doesn’t an excess amount of AgNO3 affect the chemical reaction in the experiment? 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
Why was it necessary to wash off all the impurities from the AgCl precipitate? 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
Why were the contents of the crucible slightly gray in colour after heating? 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 and Error Percentage Yield
= Actual Yield x 100 Theoretical Yield= 80%
Percentage Error= (Theoretical Yield – Actual Yield) x 100
Theoretical Yield= 20%
Conclusion 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
Sources of Error 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
Sources of Error 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
Suggestions 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
THE END.Thank you for listening to our presentation.