N/10 Sodium Thiosulfate Solution Preparation and Standardization with K2Cr2O7 | Iodometric titration

Summary

This video tutorial demonstrates the preparation and standardization of sodium thiosulphate solution using potassium dichromate. The process involves weighing 2.48 grams of sodium thiosulphate and diluting it to 100 ml, followed by preparing a potassium dichromate solution with 0.49 grams in 100 ml. The video then details the titration process, including the addition of potassium iodide and HCl, and the use of starch indicator to determine the endpoint. The final step shows how to calculate the normality of the sodium thiosulphate solution and prepare an n by 80 hypo solution by dilution.

Takeaways

• 🧪 Sodium thiosulfate solution is prepared by weighing 2.48 grams of pentahydrated sodium thiosulfate and dissolving it in 100 ml of distilled water.
• 🔬 The prepared sodium thiosulfate solution is standardized using potassium dichromate, with 0.49 grams of potassium dichromate dissolved in 100 ml of distilled water.
• 🧼 All glassware, including burets and conical flasks, must be thoroughly rinsed before use to ensure accurate results.
• 📏 The titration process involves filling the buret with sodium thiosulfate solution and transferring 25 ml of potassium dichromate to a conical flask.
• 🧴 Potassium iodide and concentrated HCl are added to the potassium dichromate solution, which liberates iodine and changes the solution's color.
• 🧫 The titration continues by adding sodium thiosulfate to the flask until the dark brown color fades, followed by starch solution to form a starch-iodine complex.
• ⚗️ The titration is complete when the iodine's blue color disappears, and a pale color appears due to chromium ions.
• 📊 Observations include an initial buret reading of 0 ml and a final reading of 25 ml, indicating that 25 ml of sodium thiosulfate was consumed.
• 📝 The normality equation (N1V1 = N2V2) is used to calculate the normality of sodium thiosulfate, confirming it as N/10.
• 🌡️ To prepare N/80 sodium thiosulfate, 12.5 ml of N/10 sodium thiosulfate is diluted in a 100 ml measuring flask using distilled water.

Q & A

What is the purpose of preparing a sodium thiosulphate solution in the video?

The purpose is to prepare a sodium thiosulphate solution and standardize it using potassium dichromate.

How much sodium thiosulphate is used to prepare the solution in the video?

2.48 grams of sodium thiosulphate pentahydrate is used.

What is the final volume of the sodium thiosulphate solution prepared in the video?

The final volume of the sodium thiosulphate solution is 100 ml.

How is the sodium thiosulphate dissolved in the video?

It is dissolved by transferring the weighed amount to a measuring flask, rinsing the beaker properly, and shaking well to dissolve it into distilled water.

What is the concentration of the prepared sodium thiosulphate solution in the video?

The concentration of the prepared sodium thiosulphate solution is n by 10.

How much potassium dichromate is used to prepare its solution in the video?

0.49 grams of potassium dichromate is used.

What is the volume of the potassium dichromate solution prepared in the video?

The volume of the potassium dichromate solution is 100 ml.

Why is it necessary to rinse the glassware before standardizing the solution in the video?

Rinsing the glassware is necessary to ensure that there is no contamination that could affect the accuracy of the standardization process.

What is the initial reading of the burette when potassium dichromate is added in the video?

The initial reading of the burette is zero.

How much potassium iodide is added to the conical flask in the video?

0.5 grams of potassium iodide is added to the conical flask.

What color change is observed after adding concentrated HCl to the conical flask in the video?

After adding concentrated HCl, the color changes to indicate the liberation of iodine.

How is the endpoint of the titration determined in the video?

The endpoint of the titration is determined by the disappearance of the color of the starch-iodine complex after adding a few drops of starch solution.

What is the final reading of the burette after the titration in the video?

The final reading of the burette is about 25 ml.

How is the normality of the sodium thiosulphate solution calculated in the video?

The normality is calculated using the normality equation N1V1 = N2V2, where N1 and V1 are the normality and volume of potassium dichromate, and N2 and V2 are the normality and volume of sodium thiosulphate.

What is the normality of the hypo solution prepared by dilution in the video?

The normality of the hypo solution prepared by dilution is n by 80.

How much volume of n by 10 sodium thiosulphate solution is taken to prepare n by 80 hypo solution in the video?

12.5 ml of n by 10 sodium thiosulphate solution is taken to prepare 100 ml of n by 80 hypo solution.

Outlines

00:00

🧪 Preparation of Sodium Thiosulphate Solution

In this section, the process of preparing sodium thiosulphate solution is explained. The speaker weighs 2.48 grams of sodium thiosulphate, transfers it to a measuring flask, and dissolves it in distilled water. After ensuring it is well mixed, the solution is made up to 100 mL. The prepared solution is of n/10 concentration, and the sodium thiosulphate used is pentahydrated.

05:01

🔬 Preparation of Potassium Dichromate Solution

This paragraph details the preparation of potassium dichromate solution. The speaker uses 0.49 grams of potassium dichromate, dissolves it similarly by rinsing a funnel, and transfers the dissolved solution into a flask. After dissolving it fully, the solution is made up to 100 mL and shaken well to ensure homogeneity.

🧴 Preparing the Equipment for Standardization

Before starting the titration, the speaker stresses the importance of thoroughly rinsing the glassware, including the buret and conical flask, to ensure accuracy. Sodium thiosulphate solution is used to rinse the buret, and potassium dichromate is used to rinse the conical flask, following which 25 mL of potassium dichromate solution is added to the flask.

⚗️ Adding Reagents for Titration

After preparing the potassium dichromate solution, the speaker adds 0.5 grams of potassium iodide to the conical flask, followed by 1 mL of concentrated hydrochloric acid (HCl). This results in the liberation of iodine, indicated by a change in color. The flask is then covered with brown paper to prevent exposure to sunlight, which could oxidize the iodine.

🧪 Conducting the Titration Process

The speaker begins the titration by adding sodium thiosulphate solution from the buret into the conical flask containing the iodine. After the solution turns light brown, a starch solution is added, creating a blue-black iodine-starch complex. As titration continues, the color disappears, marking the endpoint. The speaker notes that the remaining slight color is due to chromium ions.

📊 Observation and Normality Calculation

This part describes the observation table, with the initial buret reading at 0 mL and the final reading at 25 mL, indicating 25 mL of sodium thiosulphate was used. Using the normality equation (N1V1 = N2V2), the speaker calculates the normality of the sodium thiosulphate solution. Since both solutions are of n/10 concentration, the normality of the sodium thiosulphate is confirmed to be n/10.

📏 Preparation of n/80 Sodium Thiosulphate Solution

In this paragraph, the speaker explains how to prepare an n/80 sodium thiosulphate solution using the dilution method. They take 12.5 mL of the standardized n/10 sodium thiosulphate solution and dilute it to 100 mL with distilled water. This produces an n/80 solution, which is achieved through careful measurement and calculation.

👍 Conclusion and Final Remarks

The speaker concludes the video by summarizing the successful preparation of n/10 and n/80 sodium thiosulphate solutions. They encourage viewers to like, share, and subscribe if they found the content helpful, offering thanks for watching the video.

Keywords

💡Sodium Thiosulphate

Sodium thiosulphate is a chemical compound often used in titration experiments. In the video, it is prepared by dissolving 2.48 grams in distilled water to make a 100 mL solution. The compound is described as pentahydrated, meaning it contains five water molecules in its crystalline structure, and it is standardized using potassium dichromate.

💡Standardization

Standardization refers to the process of determining the exact concentration of a solution. In the video, the sodium thiosulphate solution is standardized using potassium dichromate to ensure its concentration is accurate for further use in titration experiments. This step is essential for obtaining precise results in chemical analysis.

💡Potassium Dichromate

Potassium dichromate is a strong oxidizing agent used in the video for the standardization of sodium thiosulphate. It is dissolved to prepare a 100 mL solution with a specific normality (N/10). This compound plays a key role in redox reactions during titration, where it reacts with sodium thiosulphate.

💡Titration

Titration is a method used to determine the concentration of a solution by reacting it with a solution of known concentration. In the video, titration is performed between potassium dichromate and sodium thiosulphate, where the color change helps indicate the end point of the reaction. It helps calculate the normality of sodium thiosulphate.

💡Normality

Normality is a unit of concentration, often used in titration to express the concentration of a solution. In the video, both potassium dichromate and sodium thiosulphate are prepared and standardized to N/10 concentration, which means 1/10th of the equivalent weight per liter of solution. Normality is crucial for accurate chemical reactions and calculations.

💡Potassium Iodide

Potassium iodide is added to the potassium dichromate solution in the conical flask during the titration process. It acts as a source of iodide ions, which are oxidized by potassium dichromate to release iodine. The release of iodine is indicated by the dark brown color in the solution, signaling the progress of the reaction.

💡Concentrated Hydrochloric Acid (HCl)

Concentrated HCl is added to the titration mixture after potassium iodide to further assist in the liberation of iodine. In the video, the addition of 1 mL of concentrated HCl turns the solution a dark brown color, showing the presence of iodine. This step is important for completing the redox reaction in the titration.

💡Starch Solution

Starch solution is used as an indicator in iodine titrations. When added to the titration mixture, the starch reacts with iodine to form a blue-black starch-iodine complex. In the video, after the addition of starch solution, the titration continues until the blue color disappears, indicating the completion of the titration.

💡N/80 Hypo Solution

The N/80 hypo solution is a diluted form of sodium thiosulphate prepared in the video using a dilution method. To prepare this solution, 12.5 mL of the N/10 sodium thiosulphate is diluted to 100 mL. This lower concentration is used in experiments requiring more precise control of reactions, such as in titrations.

💡Chromium (III) Ions

Chromium (III) ions are a byproduct of the titration reaction involving potassium dichromate. In the video, after the titration is completed, the chromium (III) ions in the solution cause a residual color that may lead to confusion about whether the titration has finished. This phenomenon is important for understanding the visual cues during titration.

Highlights

Preparation of sodium thiosulphate solution by weighing 2.48 grams of sodium thiosulphate pentahydrate.

Solution made by transferring the sodium thiosulphate into a 100 mL measuring flask and dissolving it in distilled water.

Potassium dichromate solution preparation by dissolving 0.49 grams of potassium dichromate in 100 mL of distilled water.

Importance of rinsing all glassware thoroughly before use to ensure accuracy during standardization.

Filling the buret with sodium thiosulphate solution after rinsing it multiple times to avoid contamination.

Potassium dichromate solution transferred into the conical flask for titration, starting with 25 mL.

Addition of 0.5 grams of potassium iodide to the conical flask, followed by 1 mL of concentrated HCl to liberate iodine.

Titration process with sodium thiosulphate to reduce iodine until the dark brown color fades.

Addition of starch solution during titration, creating a starch-iodine complex and a visible color change.

Completion of titration when the blue-black color of the starch-iodine complex disappears.

Observing final titration reading of 25 mL, equating to full consumption of sodium thiosulphate solution.

Calculation of the normality of sodium thiosulphate solution using the equation N1V1 = N2V2.

Preparation of N/80 sodium thiosulphate solution by dilution method from standardized N/10 solution.

Using 12.5 mL of N/10 sodium thiosulphate solution and diluting it to 100 mL to achieve N/80 concentration.

Reiterating the process of solution preparation and standardization, ensuring proper methodology and accurate results.

Transcripts

everyone welcome back to Spectrum

classes

today in this video we are going to

prepare sodium thiosulphate solution

as well as its standardization with the

help of potassium dichromate so here I

am going to prepare the sodium

thiosulphate solution for that I have

taken 2.48 grams of

sodium thiosulphate now I am preparing

the solution so the weight amount you

have to transfer to the

measuring flask

now rinse your final properly

and shake it well

to dissolve the sodium thiosulphate

into the distilled water and now once it

is dissolved you make up the solution up

to the mark which is given over there

and the solution is 100 ml the

calculation which we have done is 400 ml

so this is how we can prepare

sodium thiosulphate solution

here it is as weighed and calculated n

by 10 sodium thiosulphate

and this sodium thiosulphate is

pentahydrated now we are going to

prepare potassium dichromate solution

and for that purpose I have taken 0.49

grams of potassium dichromate

now I transferred it again in the same

way and now I am going to rinse this

funnel properly

and thoroughly

now I am going to dissolve this

potassium dichromate

so you see it is not completely

dissolved so you have to dissolve it

first

once it is dissolved you make up the

solution up to the mark and this

solution is 100 ml

after

making it up up to the mark you shake it

well

before use

now we are going to rinse the glass

layers because we are standardizing so

every glassware should be washed

thoroughly and it is rinsed before using

so in the buret I am going to fill the

sodium thiosulphate solution so I am

rinsing it with the help of sodium

thiosulphate solution

now I fill it after rinsing two three

times you take

little more amount in the buried just to

fill this nodule now I am going to rinse

conical flask also

with the potassium dichromate as I am

going to take potassium dichromate in

the conical flask

and now I am going to transfer 25 mL of

potassium dichromate

in the conical flask and this potassium

dichromate solution is of n by 10

concentration

initial reading of the buret is zero

we are going to add this

potassium dichromate solution in the

conical flask now I am going to add

potassium iodide

to this

0.5 grams to the conical flask

and now I am shaking it you see no color

changes visible now I am going to add

one ml of concentrated HCl solution to

this conical flask and you see the color

iodine is liberated now let this conical

flask with the help of a petri dish I am

showing you the color but before doing

the titration you keep it with a wrapped

brown paper just to avoid the exposure

of this conical flask

from the direct sunlight because that

can oxidize this iodine

now titrating it against the sodium

thiosulphate solution

and we first do this titration until

this dark brown color get it painted

now we are going to add

starch solution to this two three drops

I'm adding three four drops actually so

you see the color

of starch iodine complex now we are

again titrating it and on titration you

see

the color disappears this I am shaking

it just to ensure that the iodine is

titrated and see later on you will see

this type of color so you may get

confused

titration is completed or not actually

this is because of the chromium 3 plus

ions

now take the final reading of the buret

which is about 25

M now calculate the concentration

now coming to the observation table here

in observation table

I have kept the volume taken for k2cr207

is 25 ml which is taken in the conical

flask initial reading of the buret is 0

and final reading of the view rate is 25

ml

so on subtracting this final to initial

we get 25 mL of sodium thiosulphate is

consumed

now calculation using the normality

equation so N1 V1 is equal to n2b2 here

this side I have chosen k2cr2o7 and on

this side I have chosen sodium types

on putting the values of these N1 V1

normality and volume

on each sides so N1 is

n by 10 for k 2 cr207 which I have

prepared by calculation and since it is

a primary standard so it is suppose that

the weight we have taken is exactly at

the same normal solution and against

this 25 mL of n by 10 K to cr207 25 mL

of two sodium thiosulfate is consumed

now calculating the normality of sodium

thiosulphate which we have prepared this

will be canceled out by this so

normality of sodium thiosulphate is n by

10 which we prepared

baby this is the result now coming to

the preparation of n by 80 hypo solution

so this n by 80 hyper solution will be

prepared by dilution method and here we

are again using this normality equation

so I want to prepare n by 80 sodium

thiosulphate solution and in 100 ml so

whatever volume you want to prepare you

can put that volume here this equal to

stock solution so stock solution is n by

10 now which we have standardized Now

volume of this is standardized

hypersolution taken to prepare this

solution in 100 ml so on calculation I

will get that 12.5 mlo hyper solution of

n by 10 normality is taken in 100 ml to

prepare n by 80 hypo Solution by this

dilution method so we come to know that

the sodium thiosulphate solution which

we have prepared by being is about n by

10 normality so we are going to prepare

and by 80 Solution by dilution method so

for that purpose I am going to take 12.5

ml of sodium thiosulphate which is

already filled in the buried to this

measuring flask

on adding 12.5 mL of and by 10 sodium

thiosulphate solution to this measuring

plus I will stop this

and

you see the reading so I after

calculation I have done this

and this is 12.5 ml in this measuring

class now I am going to make up the

solution up to the mark by distilled

water

this measuring flask is of 100 ml

so this is how we can prepare n by 80

sodium thiosulfate Solution by dilution

method from The Strand rice n by 10

sodium thiosulphate solution

if you find this video useful please

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thanks for watching