Difference between Molarity and Molality

Summary

This educational script introduces the concepts of molarity and molality, two methods for measuring solution concentration. Molarity is defined as the number of moles of solute per liter of solution, disregarding the solvent's volume. Molality, however, is the number of moles of solute per kilogram of solvent. The script provides examples of how to calculate each, emphasizing the importance of understanding these terms for accurate chemical analysis.

Takeaways

• 🔍 Concentration is defined as the amount of solute dissolved in a given amount of solvent.
• 📝 The difference between molarity and molality is crucial for understanding how to measure the concentration of a solution.
• 🔬 Molarity (denoted by M) measures the number of moles of solute per liter of solution, not considering the solvent.
• 📦 Molality (denoted by m) measures the number of moles of solute per kilogram of solvent.
• 🧪 To prepare a molar solution, dissolve a specific number of moles of solute in water until the total volume reaches one liter.
• 🧊 To prepare a molal solution, dissolve a specific number of moles of solute in one kilogram of solvent.
• 📈 Molarity is expressed in moles per liter (e.g., 5 M means 5 moles per liter).
• 📉 Molality is expressed in moles per kilogram (e.g., 5 m means 5 moles per kilogram of solvent).
• 📚 The formula for molarity is the number of moles of solute divided by the volume of the solution.
• 📏 The formula for molality is the number of moles of solute divided by the mass of the solvent.
• 🔑 Understanding molarity and molality is essential for various chemical calculations and experiments.

Q & A

What is concentration in the context of solutions?

Concentration is defined as the amount of solute dissolved in a given amount of solvent, which indicates the amount of substance present in a solution.

How is the concentration of a solution measured?

The concentration of a solution is typically measured using molarity or molality, which are terms that quantify the amount of solute in a solution.

What is molarity and how is it denoted?

Molarity measures the number of moles of solute dissolved in one liter of solution and is denoted by the capital letter 'M'.

What is the formula for calculating molarity?

The formula for calculating molarity is the number of moles of solute divided by the volume of the solution in liters.

How would you prepare a solution with a molarity of 5 M of HCl?

To prepare a 5 M HCl solution, you would dissolve 5 moles of HCl in enough water to make the total volume of the solution one liter.

What does the 'M' in molarity signify?

The 'M' in molarity signifies 'moles per liter', indicating the number of moles of solute per liter of solution.

What is molality and how is it denoted?

Molality measures the number of moles of solute dissolved in 1 kg of solvent and is denoted by the lowercase letter 'm'.

What is the formula for calculating molality?

The formula for calculating molality is the number of moles of solute divided by the mass of the solvent in kilograms.

How would you prepare a solution with a molality of 5 m of HCl?

To prepare a 5 m HCl solution, you would dissolve 5 moles of HCl in 1 kg of water.

What does the 'm' in molality signify?

The 'm' in molality signifies 'moles per kilogram', indicating the number of moles of solute per kilogram of solvent.

What is the main difference between molarity and molality?

The main difference between molarity and molality is that molarity is based on the volume of the solution (in liters), while molality is based on the mass of the solvent (in kilograms).

Why might someone choose to use molality instead of molarity?

Molality might be chosen over molarity when the solution's density changes with concentration, as molality is independent of the solution's volume and is a more stable measure of concentration in such cases.

Outlines

00:00

🧪 Understanding Molarity and Molality

This paragraph introduces the concepts of molarity and molality, two methods for measuring the concentration of a solution. It explains that concentration is the amount of solute in a given volume of solvent, using the example of sugar dissolved in water. The paragraph then defines molarity as the number of moles of solute per liter of solution, emphasizing that the volume of the solvent is not considered. It also introduces molality, which is the number of moles of solute per kilogram of solvent. The paragraph provides an example of preparing an HCl solution with specific molarity and molality values, illustrating the process of calculation for both terms.

Keywords

💡Concentration

Concentration in the context of the video refers to the amount of solute that is dissolved in a given amount of solvent. It is a fundamental concept in chemistry that helps to describe the composition of a solution. For instance, the script mentions solutions with different amounts of sugar dissolved in equal volumes of water to illustrate the difference in concentration, with the higher amount indicating a more concentrated solution.

💡Molarity

Molarity is a measure of the concentration of a solute in a solution, expressed in moles per liter of solution. It is denoted by the symbol 'M' and is calculated by dividing the number of moles of solute by the volume of the solution in liters. The video script uses the example of preparing a 5M HCl solution, where 5 moles of HCl are dissolved in enough water to make the total volume one liter, to explain the concept of molarity.

💡Molality

Molality is another measure of concentration, defined as the number of moles of solute per kilogram of solvent. It is represented by the lowercase 'm' and is calculated by dividing the moles of solute by the mass of the solvent in kilograms. The script illustrates molality with the preparation of a solution where 5 moles of HCl are added to 1 kg of water, emphasizing that the solvent's mass is considered in this measurement.

💡Solute

A solute is the substance that is dissolved in a solvent to form a solution. In the video script, sugar and HCl are examples of solutes that are dissolved in water to create different concentrations of solutions. The solute's role is crucial in determining the properties and the concentration of the solution.

💡Solvent

A solvent is the substance that dissolves the solute to form a solution. Water is commonly used as a solvent, as mentioned in the script when preparing sugar and HCl solutions. The solvent's volume or mass is essential in calculating the molarity or molality of a solution.

💡Solution

A solution is a homogeneous mixture of two or more substances. In the context of the video, solutions are formed by dissolving solutes like sugar or HCl in a solvent like water. The script discusses solutions to explain the differences in concentration and how molarity and molality are used to measure these concentrations.

💡Moles

Moles are a unit of measurement used in chemistry to express amounts of a chemical substance, defined as the number of particles (atoms, molecules, etc.) in one mole, which is Avogadro's number (approximately 6.022 x 10^23). The script refers to moles when discussing the preparation of solutions with specific molarities and molalities, such as 5 moles of HCl.

💡Volume

Volume is the measure of the space occupied by a substance. In the context of molarity, the script specifies that the volume of the solution is considered when calculating the concentration, with the example of making a solution with a volume of one liter.

💡Mass

Mass is the measure of the amount of matter in an object, typically measured in kilograms or grams. In the context of molality, the script emphasizes the importance of the mass of the solvent when calculating the concentration of a solution, as seen in the example where 1 kg of water is used.

💡Concentrated Solution

A concentrated solution is one that has a high amount of solute relative to the solvent. The script contrasts concentrated solutions with less concentrated ones by using the example of sugar dissolved in water, where more sugar indicates a higher concentration.

💡Dissolved

To dissolve means to mix a solute with a solvent to form a solution. The script describes the process of dissolving substances like sugar and HCl in water to create solutions of varying concentrations.

Highlights

Concentration is defined as the amount of solute dissolved in a given amount of solvent.

Molarity and molality are terms used to measure the concentration of a solution.

Molarity measures the number of moles of solute dissolved in one liter of solution, excluding the solvent.

Molarity is denoted by 'M' and is calculated as the number of moles of solute per volume of the solution.

An example of preparing a 5 molarity HCl solution involves dissolving 5 moles of HCl in one liter of water.

Molarity is expressed in 'moles per liter' (e.g., 5 M means 5 moles per liter).

Molality measures the number of moles of solute dissolved in 1 kg of solution, including the solvent.

Molality is denoted by 'm' and is calculated as the number of moles of solute per mass of solvent.

An example of preparing a 5 molality HCl solution involves adding 5 moles of HCl to 1 kg of water.

Molality is expressed in 'moles per kilogram' (e.g., 5 m means 5 moles per kilogram of solvent).

The difference between molarity and molality lies in the units used for the volume of the solution and the mass of the solvent.

Molarity is affected by the volume of the solution, which can change with temperature.

Molality is less affected by temperature changes because it is based on the mass of the solvent.

Understanding the difference between molarity and molality is crucial for accurately measuring solution concentrations.

The transcript provides a clear explanation of how to calculate both molarity and molality.

An upcoming lecture will teach an easy trick to calculate molarity and molality.

The transcript emphasizes the importance of remembering the formulas and units for molarity and molality.

The practical examples given in the transcript help in understanding the application of molarity and molality.

Transcripts

what is the difference between molarity

and molality well to learn about

molarity and molality we have to learn

about the concentration now what is

concentration well concentration is

defined as

how much solute is dissolved in a given

amount of solvent for example consider

one liter water in this object and one

liter water in this object

and this one liter water i dissolved 10

grams sugar to form a solution

while in this one liter water i

dissolved 20 grams sugar to form a

solution

we know that this solution contain less

amount of sugar while this solution

contains more amount of sugar so we say

that this is less concentrated solution

and this is more concentrated solution

now let me ask you

how can we measure the concentration of

a solution

well to measure the concentration of a

solution we always use the two terms

molarity and molality

just remember that molarity and molality

is used to measure the concentration of

any solution

now what is molarity and molality

well molarity measures the number of

moles of solute dissolved in one liter

solution

remember that

solvent is not considered and molarity

molarity is denoted by capital m and its

formula is equal to

number of moles of solute

upon volume of a solution

for example

i want to prepare solution of hcl having

5 molarity

firstly i take 5 moles hcl in the beaker

secondly i slowly add water to it

until the water level reads to one liter

mark

let me repeat it

i slowly add water to it

until the water level reads to one liter

mark

now as a whole the volume of the

solution is one little

i have dissolved five moles of solute

does the molarity of this solution are

the molarity of hcl is 5 m

therefore

wherever you see 5 m it means 5 moles

per liter

if you see 6 m it means

6 moles per liter

thus noted down these important points

about molarity

secondly

molality measures the number of moles of

solute dissolved in 1 kg solution

remember that solvent is considered and

the molarity

molality is denoted by small m

and its formula is equal to number of

moles of solute

upon mass of solvent

for example

i want to prepare solution of hcl

having 5m molality

firstly i take 1 kg water in the beaker

secondly i add 5 moles hcl to 1 kg water

let me repeat it i add 5 moles hcl to 1

kg water

now of the solvent is 1 kg and i have

dissolved 5 moles of solute thus the

molality of hcl is 5 m

therefore wherever you see 5 m it means

that 5 mole solute is dissolved in 1 kg

solvent

secondly if you see 6 m

it means that

6 moles solute is dissolved in 1 kg

solvent

thus noted down these important points

about molality

in the next lecture

we will learn the easy trick to

calculate molarity and molality