Dilution of a Solution

Summary

In this educational video, Patti demonstrates the process of preparing a concentrated stock solution of Copper II Sulfate and then diluting it to a known concentration. The three-step procedure includes calculating the required amount of compound, preparing the stock solution, and diluting it. Safety measures like lab coats, safety glasses, and gloves are emphasized. Patti uses 6.2 grams of Copper II Sulfate to create a 0.250-liter, 0.100 M stock solution and then dilutes it to a 0.250-liter, 0.004 M solution. The video covers the use of essential lab equipment and provides a hands-on guide to accurately measuring and mixing solutions.

Takeaways

• 🔬 The video demonstrates the process of preparing a concentrated stock solution and diluting it to a known concentration.
• 📝 The procedure is divided into three parts: calculating the amount of compound needed, preparing the stock solution, and preparing the diluted solution.
• 🧪 The example used is the preparation of a 0.250-liter, 0.100 M copper II sulfate stock solution, followed by diluting it to a 0.250-liter, 0.004 M solution.
• 💼 Safety equipment such as lab coats, safety glasses, and gloves are required for this procedure.
• ⚖️ The calculation for the amount of copper II sulfate pentahydrate needed is pre-completed, and 6.2 grams are required.
• 🔑 Accurate weighing is crucial; the script details how to use a scale to measure out the compound.
• 🌡️ The stock solution is prepared by dissolving the compound in distilled water and then diluting to the mark in a volumetric flask.
• 🏺 The diluted solution is prepared by accurately measuring out a specific volume of the stock solution and adding distilled water to the final volume in a volumetric flask.
• 📏 The script emphasizes the importance of careful measurement and technique to avoid errors, such as not exceeding the meniscus when making up to the mark.
• 🔍 The final step includes sealing the flask with parafilm, inverting to mix, and labeling the flask with the solution's name and concentration.
• 📈 The video concludes with a visual comparison of the stock and diluted solutions, noting the difference in color intensity.

Q & A

What is the purpose of preparing a concentrated stock solution in a laboratory?

The purpose of preparing a concentrated stock solution is to have a known, high concentration of a compound that can be diluted to various lower concentrations as needed for different experiments or applications.

Why is it necessary to wear a lab coat, safety glasses, and gloves during the preparation of a stock solution?

Wearing a lab coat, safety glasses, and gloves is necessary to protect the individual from potential hazards such as chemical splashes, inhalation of toxic fumes, and skin contact with chemicals, ensuring safety during the preparation of the stock solution.

What is the molar concentration of the copper II sulfate stock solution being prepared in the script?

The molar concentration of the copper II sulfate stock solution being prepared is 0.100 moles per liter.

How much copper II sulfate pentahydrate is required to prepare 0.250 liters of a 0.100 M stock solution?

6.2 grams of copper II sulfate pentahydrate are required to prepare 0.250 liters of a 0.100 M stock solution.

What is the significance of the meniscus when making up a solution to a specific volume in a volumetric flask?

The meniscus is significant because it represents the curve seen at the top of the liquid in the flask. When making up a solution to a specific volume, the bottom of the meniscus should align with the calibration mark on the flask to ensure the correct volume is achieved.

Why is it important to rinse the weighing boat and funnel after transferring the compound into the volumetric flask?

Rinsing the weighing boat and funnel after transferring the compound ensures that all the compound is transferred into the volumetric flask, preventing loss and ensuring the accuracy of the solution's concentration.

What is the final concentration of the diluted solution prepared from the copper II sulfate stock solution in the script?

The final concentration of the diluted solution prepared from the copper II sulfate stock solution is 0.004 moles per liter.

How is the volume of stock solution required for dilution calculated?

The volume of stock solution required for dilution is calculated using the formula v1 = (c2 * v2) / c1, where c2 is the desired concentration of the diluted solution, v2 is the volume of the diluted solution, and c1 is the concentration of the stock solution.

What is the role of parafilm in the preparation of the stock and diluted solutions?

Parafilm is used to seal the volumetric flasks after preparation, preventing evaporation and contamination of the solutions, ensuring the stability and accuracy of the solution concentrations.

Why is it important to invert the volumetric flask several times after preparing the stock and diluted solutions?

Inverting the volumetric flask several times helps to mix the solution thoroughly, ensuring that the solute is evenly distributed throughout the solvent and that the concentration is uniform.

Outlines

00:00

🧪 Preparing a Concentrated Stock Solution

In this segment, Patti demonstrates the process of preparing a concentrated stock solution of Copper II Sulfate. The goal is to create a 0.250-liter solution with a concentration of 0.100 molar. Patti outlines the three-part procedure: calculating the amount of compound needed, preparing the stock solution, and diluting it. Safety measures such as wearing a lab coat, safety glasses, and gloves are emphasized. Patti calculates the required 6.2 grams of Copper II Sulfate Pentahydrate and uses a scale, weighing boat, and other lab equipment to measure and mix the compound with distilled water in a volumetric flask. The solution is then dissolved and diluted to the correct volume, ensuring accuracy by observing the meniscus level. The flask is sealed, mixed, and labeled before moving on to the next step.

05:01

🌡️ Diluting the Stock Solution

The second part of the video focuses on diluting the prepared stock solution to achieve a more dilute solution with a concentration of 0.004 moles per liter. Patti explains the mathematical calculation required to determine the volume of the stock solution needed for the dilution. Using the formula v1 = c2 × v2 / c1, Patti calculates that 10.0 milliliters of the stock solution is required. She then demonstrates the transfer of the stock solution to an Erlenmeyer flask and the careful measurement using a pipette. The diluted solution is prepared in a 0.250-liter volumetric flask, with distilled water added to reach the correct volume. The flask is sealed, mixed, and labeled, resulting in a lighter-colored solution compared to the stock solution. Patti concludes by encouraging viewers to ask questions and to enjoy the experimental process.

Keywords

💡Stock Solution

A stock solution is a concentrated solution that can be diluted to a lower concentration for practical use. In the video, the stock solution is prepared by dissolving a precise amount of copper (II) sulfate pentahydrate in water to create a solution with a known molarity (0.100 M). This stock solution is later used to prepare a diluted solution.

💡Dilution

Dilution is the process of reducing the concentration of a solute in a solution, usually by adding more solvent. In the video, a stock solution of copper (II) sulfate is diluted to prepare a solution with a lower concentration (0.004 M). This process involves using specific volumes of the stock solution and adding water to achieve the desired concentration.

💡Molarity

Molarity (M) is a unit of concentration that indicates the number of moles of a solute per liter of solution. The video demonstrates the preparation of a stock solution with a molarity of 0.100 M and a diluted solution with a molarity of 0.004 M, emphasizing the importance of accurate measurements to achieve specific concentrations.

💡Copper (II) Sulfate Pentahydrate

Copper (II) sulfate pentahydrate is a blue crystalline compound used in the video as the solute for preparing the stock solution. The video shows the process of weighing out 6.2 grams of this compound, which is then dissolved in water to create the stock solution. It is important for understanding the chemical preparation being demonstrated.

💡Meniscus

The meniscus is the curved surface of a liquid in a container, caused by surface tension. In the video, viewers are instructed to ensure that the bottom of the meniscus is aligned with the graduation line on the volumetric flask when preparing solutions. This precision is crucial for accurate measurement of liquid volumes.

💡Volumetric Flask

A volumetric flask is a type of laboratory glassware used for preparing solutions of precise volumes. In the video, the flask is used to dilute the stock solution to a known final volume (0.250 liters). The shape of the flask allows for accurate measurement when the liquid level reaches the graduation mark on its neck.

💡Pipette

A pipette is a laboratory tool used to measure and transfer small volumes of liquid accurately. The video demonstrates the use of a 10 ml pipette to measure the required volume of stock solution for dilution. Proper pipetting technique is emphasized to ensure accurate delivery of liquid.

💡Tare

Taring is the process of setting a balance to zero to account for the weight of the container, ensuring that only the weight of the substance being measured is recorded. In the video, the weighing dish's weight is tared before measuring the copper (II) sulfate pentahydrate, which ensures accurate mass measurement for the stock solution preparation.

💡Parafilm

Parafilm is a flexible, waxy film used in laboratories to seal containers and prevent contamination or evaporation. In the video, parafilm is used to seal the volumetric flask after the solution is prepared, ensuring that the solution remains uncontaminated and stable for use in further experiments.

💡Graduation Line

The graduation line on laboratory glassware, such as a volumetric flask, indicates a specific volume. The video instructs viewers to ensure that the bottom of the meniscus touches the graduation line when preparing solutions, as this ensures that the solution is of the correct volume and concentration.

Highlights

Introduction to the three-part procedure for preparing a concentrated stock solution and its dilution.

Objective to prepare 0.250 liters of a 0.100 molar copper II sulfate stock solution.

Demonstration of diluting the stock solution to prepare 0.250 liters of a 0.004 molar solution.

Safety measures including lab coat, safety glasses, and gloves are emphasized.

Calculation of 6.2 grams of copper II sulfate pentahydrate needed for the solution.

Use of a scale, weighing dish, and scupula for measuring the compound.

Taring the scale to ensure accurate measurement of the compound.

Transfer of copper II sulfate to a volumetric flask using a funnel to avoid contamination.

Rinsing the weighing boat and funnel with distilled water to transfer all the compound to the flask.

Dissolving the solid by swirling and diluting with distilled water to the mark on the volumetric flask.

Using a disposable pipette to add the last few drops of water to reach the exact volume.

Sealing the flask with parafilm and inverting to mix the solution thoroughly.

Labeling the flask with the name and concentration of the stock solution.

Calculation of the volume of stock solution required for the dilution using the formula.

Preparation of the diluted solution by transferring a measured amount of stock solution to a volumetric flask.

Use of a 10 ml pipette and pipette bulb for accurate transfer of the stock solution.

Adding distilled water to the flask and using a disposable pipette for the final adjustments.

Sealing the diluted solution flask with parafilm and inverting to ensure thorough mixing.

Labeling the diluted solution flask with its concentration and volume.

Visual comparison of the stock and diluted solutions showing the difference in color intensity.

Encouragement for questions and guidance to seek help from instructors or lab assistants.

Transcripts

hi i'm patti today we're going to review

the common procedure and technique for

preparing a concentrated stock solution

then we're going to dilute that stock

solution to a known concentration this

is a three-part procedure part one is

calculating the amount of compound

needed part two is preparing the

concentrated stock solution part 3 is

preparing a diluted solution

for this demonstration we will prepare

0.250 liters of a .100 molar copper ii

sulfate stock solution we will then

dilute the stock solution to prepare

0.250 liter of a

.004 molar solution

for safety purposes a lab coat safety

glasses and gloves are required for this

demonstration let's begin

we need a calculation amount of how much

copper ii sulfate pentahydrate needed to

make the solution i've done the

calculation already and we need 6.2

grams these are the things we're going

to use copper ii sulfate pentahydrate

a scupula

wayne dish

and a scale

first we need to take our copper ii

sulfate and have it ready to start

measuring

put our

weighing dish onto the scale

you will see a value of 2.1 on the scale

we need to tear that which means it

takes away that value and all we'll be

measuring is the product inside the

weighing boat

take the weighing boat off

put your product inside

and place it back on the scale

the reason why we do this step is to

avoid any contamination of the scale or

the product

we have a reading of 4.2 we need to

still add more product

we've reached our value needed 6.2 we

are now ready to make the solution

to complete this step we will use the

following apparatus

100 ml beaker

a volumetric flask

funnel

weighing boat with compound

distilled water

parafilm

disposable pipette

and a marker for labeling

first we will need to pour water into

the volumetric flask until it is about 1

3 full

using a clean dry funnel carefully pour

the compound from the weighing boat into

the volumetric flask

rinse the weighing boat several times

with a small amount of distilled water

from the wash bottle

add the rinse solution to the volumetric

flask with the aid of the funnel

finally rinse the funnel a few times

with water then remove it from the flask

gently swirl the solution until the

solid is dissolved

dilute carefully by adding water from

the 100 ml beaker until the water level

is about one centimeter below the

graduation line on the neck of the flask

use a disposable pipet

to add the last few drops ensuring that

the bottom of the meniscus is at the

graduation line

on this step be careful you don't want

to go over the meniscus line otherwise

you'll have to do it all over again

seal the flask with a small piece of

parafilm

invert the flask several times to ensure

thorough mixing

now label the flask with the name and

concentration of the stock solution

you have now made a stock solution

you can use a stock solution to prepare

a diluted solution

we will now use our stock solution to

prepare

0.250 liters of a diluted solution with

a concentration of 0.004

moles per liter

we will first need to determine the

amount of stock solution required

we want to make a diluted solution with

a concentration of 0.004

moles per liter c2 and a volume of

0.250 liters v2

our stock solution has a concentration

of

0.100 moles per liter c1 the volume of

stock v1 is our unknown quantity to find

the volume of stock required we will

isolate v1 in our equation by dividing

both sides by c1 therefore v1 is equal

to c2 times v2 divided by c1

now substitute in the values of c2 v2

and c1 and solve

the volume of stock required is

0.010 liters or

10.0 milliliters

to prepare the dilution we will need the

following material

stock solution

a 10 ml pipette pipette bulb

erlenmeyer flask

distilled water

disposable pipette

parafilm

and a volumetric flask

here's our stock solution

we do not want to contaminate it by

directly inserting our pipet

so a small amount is first transferred

to an erlenmeyer flask

to use the pipet

place the end in the liquid to be

collected

squeeze the pipet bulb

then securely place over the end of the

pipet

slowly release your grip on the bulb and

allow the liquid to rise up the pipet

you should allow the liquid to rise

above the line marked on the pipet

but stop before the liquid level reaches

the bulb

remove the bulb and quickly cover the

end with your index finger creating a

seal

slowly lift your finger and allow the

liquid to exit until the bottom of the

meniscus is sitting on top of the line

marked on the pipet

if you allow too much to exit simply use

the pipette bulb to draw more liquid in

and try again this takes some practice

so be patient with yourself

once you have the required amount of

liquid pull the pipet out of the

erlenmeyer flask and insert it into a

new

.250 liter volumetric flask

remove your index finger from the end of

the pipet and allow all the liquid to

drain into the flask don't worry if a

few drops remain in the pipet these are

calibrated to deliver the exact amount

of liquid required using the same

procedure as before we now add distilled

water to the flask

monitoring the level and using a

disposable pipette for the last few

drops

once again the bottom of the meniscus

should be sitting on top of the line

marked on the neck of the flask

seal the flask with parafilm

and gently invert to mix thoroughly

label your flask

your diluted solution is now ready for

use

you have now learned how to weigh a

compound prepare a concentrated stock

solution

and prepare a diluted solution

now if you look at them side by side you

can see that

the stock solution is darker

than the diluted solution

if you have any questions about any of

these processes please ask your

instructor or the lab assistant

thanks for watching and happy

experimenting

you