Calcium and Magnesium ion concentration determination with EDTA titration

Summary

This 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

00:00

🔬 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.

Keywords

💡EDTA

Ethylenediaminetetraacetic acid (EDTA) is a strong chelating agent that forms stable complexes with metal ions in a 1:1 ratio. In the video, EDTA is used to determine the concentration of calcium and magnesium ions by titrating them. Its role is crucial because it binds to these metal ions, making the titration process possible.

💡Calcium and Magnesium Ions

Calcium and magnesium are metal ions present in the limestone sample, whose concentrations are being determined in the experiment. They react with EDTA in a 1:1 ratio, allowing their total amount in the solution to be measured. These ions are the primary focus of the titration process discussed in the video.

💡Titration

Titration is a method used to determine the concentration of a substance in a solution by adding a reagent of known concentration. In this experiment, the titration process involves gradually adding EDTA to bind with calcium and magnesium ions until a color change indicates the endpoint. It is the central method used to measure ion concentration.

💡Buffer

A buffer is a solution that maintains a stable pH during chemical reactions. In this experiment, a buffer is added to keep the solution basic, as acidic conditions could interfere with the reaction by forming toxic HCN gas. The buffer ensures that the titration process is safe and effective.

💡Potassium Cyanide

Potassium cyanide is used as an auxiliary complexing agent in the experiment. It binds with metal ions other than calcium and magnesium, preventing them from interfering with the titration. However, it must be used in a basic environment to avoid the production of toxic HCN gas.

💡Indicator

The indicator, calmagite, is a substance that changes color to signal the completion of the titration. It initially forms a wine-red complex with magnesium ions, and as EDTA binds the magnesium, the color changes to purple and finally blue, indicating the endpoint of the titration.

💡Aliquot

An aliquot is a measured portion of a solution. In this experiment, a 50-milliliter aliquot of the limestone sample is taken for titration. Using an aliquot ensures accuracy and consistency in the experiment, allowing the calculation of ion concentrations based on the specific volume titrated.

💡Complex

A complex is a structure formed when metal ions bond with other molecules or ions. In this experiment, calcium and magnesium ions form complexes with EDTA, which allows their concentrations to be measured. The concept of complex formation is key to understanding how the titration works.

💡Concentration

Concentration refers to the amount of a substance in a given volume of solution. The aim of the experiment is to determine the concentration of calcium and magnesium ions in the limestone sample. This is done by calculating the moles of EDTA used to titrate the sample and dividing by the volume of the aliquot.

💡Endpoint

The endpoint is the point at which the titration is complete, signaled by a change in color. In this experiment, the color changes from wine-red to blue, indicating that all magnesium and calcium ions have reacted with EDTA. Reaching the endpoint allows the calculation of ion concentrations in the sample.

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