G4

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G4
Group 4 chemistry Project
Name of students Kate Chan, Kim Cheung
Jacky Wong , Philip Kong
Chinese YMCA Secondary School Address Area 102
Tin Shui Wai Yuen Long, NT Tel No. 24488071,
25408650
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Title
Determination of the amount of Ca2 ions Mg2
ions in a bottle of Pierval Natural Spring Water
.
Objective
To find out whether the amount of Ca2 ions
Mg2 ions in a bottle of Pierval Natural Spring
Water reach to the amount that the manufacturer
announced.
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Introduction
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Drink healthily

• A trend that people regard Pierval Natural Spring
  
• Water as a healthy drinking.
• Mg2(aq) and Ca2(aq) can be lost from human body
  easily after exercise.
• They are the essential components of the human
  beings.

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• The manufacturer of Pierval Natural Spring Water
• claimed that it has 4mg/L of Mg2(aq) and
  104mg/L of
• Ca2(aq) .
• Investigate the content of the Mg2(aq) and
  Ca2(aq) inside
• the Pierval Natural Spring Water.
• To find out whether it has enough Mg2(aq) and
  Ca2(aq)
• that the manufacturer claimed .

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Methodology
1.EDTA titration 2.Precipitation of Na2SO4(aq)
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How does EDTA work ?

• EDTA stands for ethylenediaminetetraacetic acid
  and possesses six potential sites for bonding
  with a metal ion.
• The four COOH groups in EDTA are capable of acid
  dissociation while the two tertiary amines can be
  protonated to become quarterly ammonium ions.

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• The relative abundance of the various forms of
  EDTA in solution is controlled by pH. For
  example, H2Y2- predominates at moderately acidic
  pH (pH 3 6), while Y4- predominates at pH gt 10.

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• EDTA forms 11 chelates with metal ions
  regardless of their charge
• Mg2 Y4- MgY2-
• Ca2 Y4- CaY2-
• Mn Y4- MY(n-4)
• Equilibrium of the formation of MY(n-4) is
  affected by pH of the titration medium. Thus, all
  EDTA complex-formation titrations have to be
  performed in buffer of known pH.

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• Minimum pH needed for satisfactory titration of
  various cations with EDTA

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• For example, NH3 and NH4Cl is usually used as pH
  buffer in the EDTA titration of Zn(II). In such
  system, Zn(II) exists in zinc(II) ammine
  complexes which are soluble even at high pH

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Indicator Eriochrome Black T

• Over 200 organic dyes can be used as indicators
  for EDTA complex-formation titration.
• These indicator dyes to form coloured metal
  chelates and are discernible to the eye at
  concentrations in the range of 10-6 to 10-7 M.
• Eriochrome Black T is a very commonly adopted
  colour indicator for EDTA titration

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• Metal chelates of Eriochrome Black T are usually
  red in colour.
• Thus, in order to obtain a sharp colour change
  for end-point detection, pH of the EDTA titration
  is needed to adjust to pH 7 or above so that the
  blue-colour form, HIn2-, species of Eriochrome
  Black T predominates in the absence of a metal
  ion.
• Thus, before the equivalent point, the
  Eriochrome Black T dye is chelating with the
  metal ion to give a red colour solution.
  Immediately passing the equivalent point, as no
  metal ion is available (all chelated by EDTA),
  the blue colour of HIn2- appears to mark the
  end-point
• Min- HY3- HIn2- MY2-
• (red) (blue)

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Precipitation
Only the calcium ions but not magnesium ions are
able to form the precipitates with the sodium
sulphate solution.
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Procedure
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(A)
1)
Transfer 20.0cm3 the Pierval Natural Spring
Water into a conical flask.
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2)
Add a little amount of Eriochrome Black T
(EBT) solid into the Pierval Natural
Spring Water as indicator.
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3)
Add 20.0cm3 of NH3-NH4Cl solution in pH10
as buffer solution into the 20.0cm3
Pierval Natural Spring Water.
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4)
Titrate the Pierval Natural Spring Water
with 0.01M EDTA solution until reach to the
end point. Mark down the EDTA solution used
in the titration.
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(B)
1)
Transfer another 20.0cm3 Pierval Natural
Spring Water into a beaker.
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2)
Add excess 3.0M Na2SO4 solution into the
Pierval Natural Spring Water. Wait
to form some white precipitate (CaSO4(s)) in the
beaker.
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3)
Filtrate out the white precipitate.
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4)
Titrate the filtrated solution against EDTA
solution. Mark down the EDTA solution used
in the titration.
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Data Calculation
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The table below show our result
Average vol. of EDTA used (32.530.533.0)(1/3)
32.00cm3
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Formula Ca2 EDTA4- ? Ca(EDTA)2- Mg2
EDTA4-? Mg(EDTA)2-

• Total vol. of EDTA used 32.0cm3

• Total no. of moles of (Ca2 Mg2)
• 32.0/1000 0.01
• 3.2 x 10-4 mol

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Difficulties Solutions
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Difficulties
The amount of Mg2(aq) are not enough
in the 20cm3 Pierval Natural Spring Water.
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• Solution
• boil 100cm3 Pierval Natural Spring Water
• until there are 20cm3 liquid remain in the
  beaker
• a more concentrated Pierval Natural Spring
• Water can be obtained

• could prepare a more concentrated Na2SO4(aq)

• Double the concentration of the Na2SO4(aq)

• add 17.04g Na2SO4(s) into the 20cm3 distilled
  water to make
• up 6.0M Na2SO4 solution

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Suggested Method

• According to the trying experiment we had , we
  had
• to change some parts of our methodology in
• procedure,
• 1. Weigh the clean filter paper (1).
• 2. Desiccate the filter paper that contain the
  calcium sulphate
• precipitate.
• Weigh the desiccated filter paper (2).
• Get the difference of (1) and (2) .
• The difference will be the amount of calcium
  ions.

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Conclusion
Although we cannot determine the calcium and
magnesium ions in Pierval Natural Spring Water ,
we learned how to master to use EDTA.In fact ,
the learning process is the most important part
in this project.
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Acknowledgement