Calcium and Magnesium ion concentration determination with EDTA titration
Summary
TLDRThis video explains how to experimentally determine the concentration of calcium and magnesium ions using EDTA titration. EDTA, a strong compound, forms a 1:1 complex with metal ions. The experiment involves titrating a 50 mL aliquot of a dissolved limestone sample containing unknown calcium and magnesium concentrations. A buffer, potassium cyanide, and an indicator (calmagite) are added. EDTA binds with calcium and magnesium, causing a color change from wine red to blue, signaling the titration's end. The volume of EDTA used is calculated to determine the cumulative concentration of calcium and magnesium ions.
Takeaways
- 🧪 EDTA (ethylenediaminetetraacetic acid) forms a 1:1 complex with most metal ions, including calcium and magnesium.
- ⚖️ The experiment involves titrating calcium and magnesium ions in a limestone sample using EDTA.
- 📏 A 50-milliliter aliquot of the sample is used for each titration, measured with a burette for accuracy.
- 🧴 A buffer is added to make the solution basic before the titration process.
- 🔗 Potassium cyanide is used as a complexing agent to prevent interference from other metal ions.
- 🚫 It is important to maintain a basic pH to avoid the formation of toxic HCN gas in acidic conditions.
- 🎨 An indicator, calmagite, is added, which turns wine red when it binds with magnesium ions.
- 🔄 During titration, EDTA binds with free calcium and magnesium ions, causing a color change from wine red to purple and then to blue, signaling the endpoint.
- 📐 The amount of EDTA used in the titration allows calculation of the cumulative concentration of calcium and magnesium in the sample.
- 🧮 The total concentration is determined by multiplying the volume of EDTA used by its concentration and dividing by the volume of the aliquot.
Q & A
What is EDTA and how does it interact with metal ions?
-EDTA, or ethylenediaminetetraacetic acid, is a strong compound that forms a one-to-one complex with most metal ions by binding its carboxyl groups to the positive charge of the metal ions.
What ions are being measured in this experiment?
-The experiment measures the concentrations of calcium and magnesium ions.
What sample is used in this titration experiment?
-A 250 milliliter sample of limestone dissolved in acid is used in the experiment.
What is the purpose of using a buffer in this experiment?
-A buffer is used to maintain a basic pH in the solution, which is important for preventing interference from protons that could bind and form toxic HCN gas.
Why is potassium cyanide added to the aliquot?
-Potassium cyanide is added as an auxiliary complexing agent to bind ions other than magnesium and calcium so they don't interfere with the titration.
What indicator is used, and how does it behave in the titration?
-The indicator used is Calmagite (referred to as 'kaga mine' in the transcript). It binds with magnesium to form a wine-red color, and during titration, the solution changes color from wine-red to purple and then blue, indicating the endpoint.
What is the purpose of titrating the solution with EDTA?
-The purpose of titration with EDTA is to form complexes with the free calcium and magnesium ions, eventually displacing magnesium from the Calmagite indicator until the solution turns blue, signaling the end of the titration.
How is the concentration of calcium and magnesium ions determined?
-The concentration is determined by multiplying the volume of EDTA used by its molar concentration, giving the moles of EDTA. Since the reaction is in a one-to-one ratio, this also represents the total moles of calcium and magnesium ions. The cumulative concentration is then calculated by dividing the moles by the volume of the aliquot.
Why is maintaining a basic pH crucial in this experiment?
-Maintaining a basic pH prevents the formation of HCN gas, which is toxic and could result from protons binding to cyanide in an acidic environment.
What volume of EDTA was used in the example provided?
-In the example, an average volume of 38.5 milliliters of 0.01 molar EDTA was used to titrate the aliquot.
Outlines
🔬 Understanding Calcium and Magnesium Determination via EDTA Titrations
This paragraph introduces the process of determining the concentration of calcium and magnesium ions using EDTA titration. EDTA (ethylenediaminetetraacetic acid) forms a 1:1 complex with metal ions, particularly calcium and magnesium in this experiment. The paragraph provides an overview of how a sample of limestone dissolved in acid is prepared and measured for titration, and outlines the critical use of a 50 mL aliquot for the analysis.
🧪 Buffer and Potassium Cyanide in Titration
Here, the paragraph explains the addition of three essential components to the 50 mL aliquot for the titration: a buffer to maintain basic conditions, potassium cyanide as a complexing agent for other ions, and an indicator. The role of potassium cyanide is emphasized to prevent interference from other metal ions. It also highlights the importance of keeping the pH basic to avoid the formation of toxic HCN gas.
🔵 Role of the Indicator and Titration Procedure
The indicator, calmagite, is introduced as a blue compound that forms a red complex when it binds to magnesium ions. The paragraph then explains the titration process, where EDTA pulls magnesium from the indicator complex, leading to color changes that signal the endpoint of the titration—first from red to purple and finally to blue.
📏 Calculating Calcium and Magnesium Concentrations
In this final section, the paragraph explains the calculation of calcium and magnesium concentrations. It walks through an example where 38.5 mL of 0.01 M EDTA is used to titrate the aliquot. The number of moles of EDTA is calculated, which corresponds to the total moles of calcium and magnesium ions present. The final concentration is determined by dividing the total moles by the aliquot volume.
Mindmap
Keywords
💡EDTA
💡Calcium and Magnesium Ions
💡Titration
💡Buffer
💡Potassium Cyanide
💡Indicator
💡Aliquot
💡Complex
💡Concentration
💡Endpoint
Highlights
EDTA (ethylenediaminetetraacetic acid) forms a one-to-one ratio complex with most metal ions.
In this experiment, EDTA reacts in a one-to-one ratio with both calcium and magnesium ions.
The experiment uses a 250 mL sample of limestone dissolved in acid containing an unknown concentration of calcium and magnesium ions.
A 50 mL aliquot is measured for each titration using a burette for accuracy.
A buffer is added to the aliquot to maintain a basic pH during the experiment.
Potassium cyanide is used as an auxiliary complexing agent to bind ions other than magnesium and calcium.
Maintaining a basic pH is crucial to prevent the formation of toxic HCN gas in the presence of acidic conditions.
An indicator called Calmagite, which is blue, is added to the aliquot. It forms a wine-red color when it binds with magnesium.
The titration is carried out using a 0.01 molar solution of EDTA.
Initially, the solution in the Erlenmeyer flask has a mixture of free calcium and magnesium ions and Calmagite-indicator complex with magnesium.
During titration, EDTA complexes with free calcium and magnesium ions, pulling magnesium ions away from the indicator complex.
The endpoint of the titration is indicated by the solution turning from wine-red to first purple, then blue.
The volume of EDTA used is measured; in the example, an average volume of 38.5 mL of 0.01 molar EDTA is used.
The amount of EDTA used is calculated by multiplying its volume by its concentration, giving the total moles of EDTA.
Since the EDTA reacts in a one-to-one ratio with calcium and magnesium ions, the total moles of EDTA correspond to the total moles of calcium and magnesium ions in the aliquot.
Transcripts
this video is about how to
experimentally determine calcium
magnesium ions concentration by EDTA
titrations ethylenediaminetetraacetic
acid better known as EDTA is a strong
compound that forms one-to-one ratio
complex with most metal ions when a
metal ion inserted to EDTA they form a
complex in which the carboxyl groups
negative charges form bonds with the
positive charge metal ions for the
purpose of this experiment this reaction
happens in a one-to-one ratio with both
calcium and magnesium ions so in this
example we have 250 milliliters of a
sample of limestone dissolved in acid
which contains an unknown concentration
of calcium and magnesium ions so for
each titration we will measure out a 50
milliliter aliquot using a burette for
accuracy - this 15 milliliter aliquot we
are going to add three more things we
first are going to add a buffer in order
to make this alcohol basic then
potassium cyanide and indicator
potassium cyanide is an auxiliary
complexing agent that binds ions other
than magnesium and calcium in the
experiment it has the purpose to complex
with any other ions so they don't
interfere with the titration however
before adding potassium cyanide is
necessary for us to add basic buffer it
is important for us to keep a basic pH
in this experiment since if we have an
acidic environment protons would bind to
Zn forming HCN gas which is very toxic
we're also going to add an indicator
which is kaga mine which is color blue
the indicator once it binds magnesium it
forms a white red color which we can see
F right after we add the indicator to
our a liquid to titrate our aliquot we
will be using a solution of 0.01 more
in 1 millimolar magnesium chloride
before we start the titration the
Erlenmeyer flask contains a mixture of
free calcium and magnesium ions and
calumet indicator complex with magnesium
which give it a wine red color once we
start the titration the free calcium and
magnesium ions will complex with the
added aid ETA then the EDTA will pull
away magnesium ions from the calmate
indicator until the color of the
solution goes to first purple then blue
which indicates the end of the titration
at this point we measure that a volume
of EDTA used in our example we use an
average volume of 38.5 milliliters of
the 0.01 molar EDTA to titrate our
aliquot this is equal to 0.03 8 5 liters
this multiplied by the concentration of
EDTA 0.01 moles per liter gives us the
number of moles of EDTA used since the
reaction between both calcium and
magnesium ions and EDTA happens in a
one-to-one ratio this is also the total
number of moles of calcium and magnesium
in our aliquot this divided by the
volume of the alcot 50 milliliters which
is 0.05 liters gives us the cumulative
concentration of our unknown for
magnesium and calcium ions
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