Measuring Liquid Volume with a Graduated Cylinder

Summary

This educational video script explains the importance of using graduated cylinders for accurate volume measurements. It highlights the inaccuracy of beakers and emphasizes the correct way to measure liquid volume by reading at the bottom of the meniscus, not the top. The script also demonstrates how to use a pipette for precise addition or subtraction of liquid, ensuring measurements are accurate by maintaining eye level with the liquid's surface.

Takeaways

• 🧪 To measure volume accurately, use a graduated cylinder instead of a beaker, which is less precise.
• 🌀 When water is in a graduated cylinder, it forms a meniscus, a curve at the top of the liquid.
• 🔍 Always measure at the bottom of the meniscus, not the top, for accurate volume readings.
• 👁️ When taking a measurement, ensure your eye level is at the same level as the liquid surface to avoid parallax error.
• 🟡 The yellow piece of plastic at the top of a glass graduated cylinder is a protective measure and should not be used for measuring.
• 📏 Each mark on the graduated cylinder represents a specific volume, often 1 milliliter, which is crucial for accurate counting.
• 💧 If you need to adjust the volume, use a pipette or dropper to add or remove small amounts of liquid.
• 🚫 Avoid submerging the pipette tip into the graduated cylinder when removing liquid, as it can alter the volume measurement.
• 🔼 To increase the volume, add drops from a pipette while observing the bottom of the meniscus until the desired level is reached.
• ⏬ If you need to decrease the volume, remove some liquid and then use a pipette to refill to the correct measurement.

Q & A

What is the purpose of using a graduated cylinder to measure volume?

A graduated cylinder is used to measure volume because it provides a more accurate measurement compared to other containers like beakers, which may have volume marks but are not as precise.

What is a meniscus and why is it important when measuring volume in a graduated cylinder?

A meniscus is the curved surface formed by a liquid when it adheres to the walls of a container. It is important because when measuring volume, one must read the measurement at the bottom of the meniscus to ensure accuracy, rather than at the top of the curve.

Why is it incorrect to measure the volume at the top of the meniscus?

Measuring at the top of the meniscus is incorrect because it does not represent the actual volume of the liquid. The liquid adheres to the walls, creating a curve, and measuring at the top would overestimate the volume.

What is the purpose of the yellow piece of plastic at the top of a glass graduated cylinder?

The yellow piece of plastic at the top of a glass graduated cylinder is not for measuring but serves as a protective feature to prevent the cylinder from breaking if it falls over.

How should one position themselves when measuring volume in a graduated cylinder?

When measuring volume in a graduated cylinder, one should position themselves at eye level with the liquid to ensure an accurate reading of the meniscus.

What is the significance of the longer mark at the 5 mL on the graduated cylinder?

The longer mark at the 5 mL on the graduated cylinder indicates that each subsequent mark represents an increment of 1 mL, making it easier to read the volume in milliliters.

If you need to add a small amount of liquid to reach a specific volume, what tool should you use?

To add a small, precise amount of liquid to reach a specific volume, one should use a pipette, which is essentially a dropper.

How do you add liquid to a graduated cylinder to reach a precise volume?

To add liquid to a graduated cylinder to reach a precise volume, you should use a pipette to drop the liquid into the cylinder while observing the bottom of the meniscus until it aligns with the desired measurement.

What is the recommended method to remove excess liquid from a graduated cylinder if you have added too much?

The recommended method to remove excess liquid from a graduated cylinder is to pour out some of the liquid and then use a pipette to carefully refill to the desired volume, rather than trying to remove liquid directly with the pipette.

Why should you not use the pipette to remove liquid directly from the graduated cylinder?

Using the pipette to remove liquid directly can alter the measurement because the pipette's head can displace the liquid, leading to an inaccurate volume reading.

Outlines

00:00

📏 Measuring Volume with a Graduated Cylinder

This paragraph explains the process of measuring volume using a graduated cylinder, emphasizing the importance of accuracy over using a beaker. It introduces the concept of a meniscus, the curved surface of a liquid in the cylinder, and stresses the need to measure at the bottom of the meniscus for an accurate reading. The paragraph also mentions the yellow plastic piece at the top of the cylinder, which is for protection and not for measuring. The speaker demonstrates how to measure the volume of water by aligning one's eye level with the bottom of the meniscus and counting the milliliter marks on the cylinder.

Keywords

💡Volume

Volume refers to the amount of space that a substance or object occupies. In the context of the video, volume is a critical concept as it is the main property being measured. The video discusses the importance of accurately measuring the volume of liquids, which is essential in scientific experiments and measurements.

💡Graduated Cylinder

A graduated cylinder is a piece of laboratory equipment used to measure the volume of liquids. It is a tall, narrow container marked with lines indicating volume measurements. The video emphasizes the use of graduated cylinders over beakers for more accurate volume measurements due to their precision.

💡Meniscus

The meniscus is the curved surface of a liquid that is in contact with a solid, such as the wall of a container. In the video, the meniscus is highlighted as a key factor to consider when measuring volume. The presenter instructs viewers to measure at the bottom of the meniscus for an accurate reading, as the top of the curve can lead to inaccurate measurements.

💡Inaccuracy

Inaccuracy in this context refers to the lack of precision or correctness in measurements. The video script mentions that beakers, despite having volume marks, are terribly inaccurate for precise volume measurements, which is why graduated cylinders are recommended.

💡Eye Level

Eye level is the height at which a person's eyes are when they are standing upright. The video script stresses the importance of aligning one's eyes with the liquid level in the graduated cylinder to ensure an accurate measurement. This is crucial for avoiding parallax error, which can occur when viewing the meniscus from an angle.

💡Pipet

A pipet, also known as a dropper, is a laboratory tool used for transferring small, measured volumes of liquid. In the video, the presenter uses a pipet to add or remove small amounts of liquid to adjust the volume in the graduated cylinder to the desired measurement.

💡Measurement

Measurement is the process of determining the size, amount, or degree of something. In the script, measurement is the primary action being performed, with a focus on accurately determining the volume of liquids using graduated cylinders and pipets.

💡Beaker

A beaker is a simple container used for mixing, stirring, and heating liquids in a laboratory. The video script mentions beakers as an example of containers that may have volume marks but are not suitable for precise volume measurements, thus highlighting the need for graduated cylinders.

💡Parallax Error

Parallax error is a type of measurement error that occurs when the viewer's line of sight is not perpendicular to the surface being measured, leading to inaccurate readings. The video script advises viewers to be at eye level with the liquid to avoid this error when measuring the volume of liquids.

💡Milliliters (mL)

Milliliters are a unit of volume in the metric system, where 1 milliliter is equivalent to one cubic centimeter. The video script uses milliliters as the unit of measurement for the liquid volume, with the graduated cylinder marked in milliliters, allowing for precise readings.

💡Curve

In the context of the video, 'curve' refers to the shape formed by the meniscus as the liquid adheres to the walls of the graduated cylinder. The script explains that the meniscus curves up the sides, and it is important to measure at the bottom of this curve for an accurate volume reading.

Highlights

Introduction to measuring volume using graduated cylinders.

Inaccuracy of beakers for volume measurement.

Importance of using graduated cylinders for accurate volume measurements.

Explanation of the meniscus phenomenon in graduated cylinders.

How to properly measure volume by reading the bottom of the meniscus.

The function of the yellow piece of plastic at the top of a glass graduated cylinder.

Practical demonstration of measuring volume at eye level with the liquid.

How to read volume measurements on a graduated cylinder.

The significance of each mark on the graduated cylinder representing 1 milliliter.

Correcting a volume measurement using a pipette.

Technique for adding precise amounts of liquid to reach a desired volume.

How to adjust the volume by removing liquid and refilling with a pipette.

The importance of not submerging the pipette tip to avoid measurement errors.

Summary of the correct procedure for measuring and adjusting liquid volumes in a graduated cylinder.

Transcripts

okay now we're going to talk about

finding volume or measuring volume and

to find volume we use graduated

cylinders which are these tall looking

containers here okay you may notice that

a beaker has volume marks on it but it's

terribly inaccurate so to order to find

uh volume correctly we need to use a

graduated cylinder okay all right so the

really important thing to to know about

finding volume in a graduated cylinder

okay when water is poured into a

graduated

cylinder it forms what's called a

meniscus in other words you see how in

this picture here I've shown that water

kind of Curves up the edges all right if

you measure at the top of the curve that

is not an accurate measurement you must

measure at the bottom of the curve or

the bottom of the meniscus

okay water kind of sticks to the edges

and forms a little curve and we'll look

at that in just if you're using a glass

graduated cylinder notice it has this

yellow piece of plastic at the top of it

okay that's not to use to measure that

actually protects it if it falls

over it keeps it from breaking okay so

that needs to stay at the top always

stay at the top okay so let's practice

measuring now okay so let's say you have

an amount of water and you pour it into

the graduated

cylinder now how much water do we have

okay first thing never look at it from

up here okay if you're going to measure

using a graduated cylinder you always

need to get down eye level with the

water or whatever liquid you're

measuring okay and then once I get close

to it here you can see the meniscus you

see how the liquid curves up the sides

okay you're you're not measuring at the

top of the meniscus you need to measure

at the bottom of the meniscus okay let's

see how much water we have in here okay

it's colored water okay notice right

here the big line is 70 milliliters okay

notice below there is 60 there's 10

marks in between 1 2 3 4 five the five

is the longer one 6 7 8 9 and 10 70 okay

so that means each Mark is 1 ml all

right so let's count starting at

70 all right 1 2 3 4 5 so that's

75 okay the top of the meniscus is

actually at

76 but we always read the bottom of the

meniscus so this is 75 mL of water okay

if you're from up here you might get a

wrong measurement if you look from down

here again you might get a wrong

measurement cuz that looks more like 76

you you have to be exactly at eye level

what do I do if I want a little bit more

let's say I want 77 M instead of 75 okay

I'm going to use a

pipet which is an fancy word for a

dropper okay so I've gotten some more

liquid in my dropper and my pipet and

I'm going to hold it over here

above hold it in the uh graduated

cylinder and then I need to look as I'm

dropping drops in to see when it gets up

to the appropriate place all right

remember we want to look at the bottom

of the meniscus only not the top okay so

now I'm going to add drops with my

dropper with my uh

pipette I'm going to keep dropping them

in okay now I'm up to notice the bottom

of the meniscus now is at 76 the top is

at 77 so I need a little bit more so I

keep

dropping until the bottom of my meniscus

now is at 77 so that's how you add water

okay or add a liquid to to bring it up

to the correct

measurement all right so if you need to

remove some water or liquid the way to

do it is to dump some of it out and then

fill back up with the pipet again okay

if you try to stick the pipet down in

there to take some out well when you P

the pipe head in it actually changes the

measurement just a little bit so it's

best just to dump it out and then fill

it back up with the pipe B