Trick to Calculate Molarity | Molarity practice problems

Summary

This educational video script offers an easy method to calculate molarity, a measure of solute concentration in a solution. It explains the basic formula, m = n/V, where m is molarity, n is moles of solute, and V is volume in liters. The script provides step-by-step examples, including converting mass to moles and milliliters to liters, to find molarity for various solutions like HCl, NaCl, and HNO3. It also emphasizes the importance of understanding volume conversions and molar mass to solve complex molarity problems efficiently.

Takeaways

• 🧪 Molarity is defined as the number of moles of solute dissolved in 1 liter of solution.
• 📝 The formula for molarity is M = n/V, where M is molarity, n is moles of solute, and V is volume in liters.
• 🌟 An example given is dissolving 6 moles of HCL in 1 liter of water, resulting in a 6 M molar solution.
• 📏 Conversion of volume units is crucial; 1 liter is equal to 1000 cm³ or 1 dm³.
• 🔢 To convert from mL to liters, move the decimal point three places to the left.
• 🧪 For problems involving mass, first convert the mass of the solute to moles using its molar mass.
• 📐 The molar mass of a compound is the sum of the molar masses of its constituent elements.
• 🌡️ Example calculations include converting 2 grams of sodium hydroxide to moles and then calculating its molarity in a 600 cm³ solution.
• 📉 When given mass, always remember to perform the conversion to moles before applying the molarity formula.
• 💡 The script provides a step-by-step guide for calculating molarity, even when the solute's mass is provided instead of moles.
• 📚 Practice is encouraged with a final problem to calculate the molarity of a solution with a given mass of HCL.

Q & A

What is molarity and how is it defined?

Molarity is defined as the number of moles of solute dissolved in 1 liter of solution. It measures the concentration of a solute in a solution.

What is the formula used to calculate molarity?

The formula to calculate molarity is m = n/V, where 'm' stands for molarity, 'n' is the number of moles of solute, and 'V' is the volume of the solution in liters.

If 6 moles of HCL are dissolved in a solution that is marked to 1 liter, what is the molarity of the solution?

The molarity of the solution would be 6 M, as 6 moles of HCL are dissolved in 1 liter of solution.

What is the relationship between liters, cubic decimeters (dm³), and milliliters?

One liter is equal to 1 cubic decimeter (dm³), which is also equal to 1000 cubic centimeters (cm³) or 1000 milliliters.

How do you convert the volume of a solution from milliliters to liters?

To convert milliliters to liters, you move the decimal point three places to the left or divide the volume in milliliters by 1000.

What is the molarity of a solution if 0.5 moles of sodium chloride are dissolved in 400 ml of water?

The molarity of the solution would be 1.25 M, after converting 400 ml to 0.4 liters and using the molarity formula m = n/V.

How do you calculate the molarity of a solution when the volume is given in cubic centimeters?

First, convert the volume from cubic centimeters to liters by moving the decimal point three places to the left. Then, use the molarity formula m = n/V.

If the mass of a solute is given instead of moles, how do you find the number of moles?

To find the number of moles when the mass of a solute is given, you divide the mass by the molar mass of the solute.

What is the molar mass of sodium hydroxide (NaOH), and how do you calculate the number of moles from a given mass?

The molar mass of NaOH is 40 grams (23 for sodium + 16 for oxygen + 1 for hydrogen). To find the number of moles, divide the given mass of NaOH by 40.

How do you calculate the molarity of a solution when the mass of HNO3 is given as 4 grams and the volume of the solution is 80 milliliters?

First, find the molar mass of HNO3 (63 grams). Calculate the number of moles (4 grams / 63 grams/mole). Convert the volume to liters (80 ml / 1000 = 0.08 liters). Then, use the molarity formula m = n/V to find the molarity, which would be 0.75 M.

What is the molarity of a solution with 20 grams of HCL in a 0.5 DM³ volume?

First, find the molar mass of HCL (36.5 grams). Calculate the number of moles (20 grams / 36.5 grams/mole). Since 0.5 DM³ is equal to 0.5 liters, use the molarity formula m = n/V to find the molarity, which would be 1.1 M.

Outlines

00:00

🧪 Understanding Molarity: Calculation and Conversion

This paragraph introduces the concept of molarity, defined as the number of moles of solute per liter of solution, with the formula m = n/V, where 'm' is molarity, 'n' is moles of solute, and 'V' is the volume in liters. It demonstrates how to calculate molarity with examples, emphasizing the importance of converting volumes from milliliters or cubic centimeters to liters by moving the decimal point three places to the left. The paragraph also explains how to handle more complex problems where the mass of the solute is given, requiring the calculation of moles from mass using molar mass before applying the molarity formula.

05:02

📚 Advanced Molarity Calculations with Solute Mass

The second paragraph delves into more advanced molarity problems where the mass of the solute is provided instead of the number of moles. It outlines the steps to find the molar mass of different substances, such as sodium hydroxide (NaOH) and nitric acid (HNO3), and then convert the given mass to moles. The summary explains how to convert the volume of the solution from cubic centimeters to liters for the molarity calculation, using the formula m = n/V. The paragraph includes examples with calculations to illustrate the process clearly, showing how to arrive at the molarity of solutions with different solutes and volumes.

Keywords

💡Molarity

Molarity is defined as the number of moles of solute dissolved in one liter of solution. It is a measure of concentration that indicates how much solute is present per unit volume of solution. In the video, molarity is the central theme, as it is used to explain how to calculate the concentration of different solutions, such as HCL and sodium hydroxide.

💡Moles

Moles represent a quantity in chemistry, which is the amount of a chemical substance that contains as many elementary entities (such as atoms, molecules, ions, etc.) as there are atoms in 12 grams of carbon-12. In the script, moles are used to quantify the amount of solute in various solutions, which is essential for calculating molarity.

💡Solute

A solute is the substance that is dissolved in a solvent to form a solution. In the context of the video, solutes such as HCL, sodium chloride, and sodium hydroxide are mentioned, and their moles are calculated to determine the molarity of the solutions they are dissolved in.

💡Solution

A solution is a homogeneous mixture of two or more substances. In the video, the term 'solution' is repeatedly used to describe the mixture where a solute is dissolved in a solvent, like water, and the goal is to calculate the molarity of these solutions.

💡Volume

Volume in the context of the video refers to the space occupied by the solution, which is crucial for calculating molarity. The script mentions converting volumes from milliliters to liters, which is necessary because molarity is expressed in terms of liters.

💡Conversion

Conversion in the script refers to the process of changing the units of measurement, particularly from milliliters to liters, to match the units required for the molarity formula. This is a key step in the calculations presented in the video.

💡Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. In the video, molar mass is used to convert the mass of a solute into moles, which is a prerequisite for calculating molarity when only the mass of the solute is given.

💡Numerical Problems

Numerical problems in the script are practical examples or exercises that demonstrate the calculation of molarity using different scenarios. These problems help illustrate the application of the molarity formula in various situations.

💡Decimal Point

The decimal point is mentioned in the script as a tool for unit conversion, specifically when converting from milliliters to liters by moving the decimal point three places to the left. This is a simple arithmetic technique used in the molarity calculations.

💡Formula

The formula in the context of the video is the molarity equation, M = n/V, where M is molarity, n is the number of moles of solute, and V is the volume of the solution in liters. The formula is central to all the calculations and examples provided in the script.

💡Calculation

Calculation refers to the arithmetic operations performed to determine the molarity of a solution. The script provides step-by-step calculations for various substances, emphasizing the process of computing molarity based on the given amounts of solute and solution volumes.

Highlights

Molarity is defined as the number of moles of solute dissolved in 1 liter of solution.

The formula for molarity is M = n/V, where M is molarity, n is moles of solute, and V is volume of solution in liters.

An example calculation shows 6 moles of HCL in 1 liter of solution results in a 6 M molarity.

One liter is equivalent to 1 cubic decimeter (dm³), 1000 cubic centimeters (cm³), or 1000 milliliters.

To calculate molarity, convert the volume from milliliters to liters by moving the decimal point three places to the left.

A 0.5 mole of sodium chloride in 400 ml of water results in a 1.25 M molarity when converted to liters.

0.9 mole of HCL in 500 cm³ of water has a molarity of 1.8 M when the volume is converted to liters.

0.2 moles of HNO₃ in 200 ml of water yield a molarity of 1 M after converting volume to liters.

In molarity problems involving mass, convert the mass of the solute to moles using the molar mass.

2 grams of sodium hydroxide with a molar mass of 40 grams/mol results in 0.05 moles.

The molarity of a solution with 0.05 moles of sodium hydroxide in 600 cm³ of water is 0.083 M.

4 grams of HNO₃ with a molar mass of 63 grams/mol equates to 0.06 moles.

A solution with 0.06 moles of HNO₃ in 80 ml of water has a molarity of 0.75 M when converted to liters.

20 grams of HCL with a molar mass of 36.5 grams/mol results in 0.55 moles.

A 0.55 mole of HCL in 0.5 DM³ of water equates to a molarity of 1.1 M.

The video provides a simple trick for calculating molarity of any solution using basic arithmetic and unit conversions.

Transcripts

easy trick to calculate molarity firstly

let me quickly revise the concept of

molarity we Define molarity as the

number of moles of solute dissolved and

1 liter solution the formula of molarity

is m equals n upon V where m is the

molarity of a solution n is the number

of moles of a solute V is the volume of

a solution for example consider that I

take 6 moles of HCL in this speaker now

I add water to this Beaker until the

water level reads to 1 liter Mark here

in this speaker the volume of a solution

is 1 liter we know that we have

dissolved 6 moles of HCL in this one

liter solution so the molarity of this

solution is 6 M therefore remember that

molarity measures the number of moles

that of a solute dissolved and 1 liter

solution

also note you down that one liter is

equal to 1 DM Cube one dm cube is equal

to 1000 CM Cube or thousand milliliter

hence remember all these important

points

now how can we calculate molarity using

super easy trach well consider these

numerical problems of molarity here in

this question 0.5 moles of sodium

chloride is dissolved so the number of

moles of solute n equals 0.5 mole

secondly the volume of solute is 400 ml

remember that a volume of a solute is

given in milliliter or centimeter Cube

we have to convert it to liter let me

repeat it a volume of a solute is given

in milliliter or centimeter Cube we have

to convert it to liter now to do so the

easy trick is to move the decimal point

three times to the left are dividing

milliliter by thousand after moving

decimal point three times to the left I

get 0.4 liter

we already know that molarity m equals n

upon V here n equals 0.5 mole and V is

0.4 liter I plug in these two values in

this equation after calculation I get

1.25 mole per liter are just 1.25 M thus

the molarity of this solution is 1.25 M

now in this question

0.9 mole of HCL is dissolved so the

number of moles of a solution is 0.9

mole secondly the volume of a solution

is 500 cm Cube I convert it to liter to

do so I move the decimal point three

times to the left I get 0.5 liter we

already know that molarity of a solution

is m equals n upon v e the value of n is

0.9 mole and the value of e is 0.5 mole

I plug in these two values in this

equation after calculation I get 1.8

mole per liter are just 1.8 m so the

molarity of this solution is 1.8 m now

in this question 0.2 moles of hno3 is

dissolved so the number of moles of a

solute is 0.2 mole secondly the volume

of a solute is 200 mL I move the decimal

point 3 3 times to the left I get 0.2

liter we know that the formula of

molarity is m equals n upon V here n is

0.2 mole and V is 0.2 liter I plug in

these values in this equation after

calculation I get 1 mole per liter or

just 1 M this is the molarity of this

solution is 1 M now let me teach you

some hard level questions of molarity

consider these numerical problems of

molarity here in this question instead

of moles of a solute mass of a solute is

given like 2 gram of sodium hydroxide

remember that in such type of numericals

we have to convert the mass of a solute

the number of moles of a solute

firstly I find the molar mass of sodium

hydroxide I write sodium plus oxygen

plus hydrogen the molar mass of sodium

is 23 gram the molar mass of oxygen is

16 gram and the molar mass of hydrogen

is one gram after addition I get 40 gram

so the number of moles of sodium

hydroxide is 40 Gram now to find the

number of moles of sodium hydroxide I

divide the given mass of sodium

hydroxide by its molar mass the given

mass of sodium hydroxide is 2 gram and

the molar mass of sodium hydroxide is 40

gram after calculation I get 0.05 mole

hence the number of moles of a solute n

equals 0.05 mole

secondly the volume of a solution is 600

cm Cube I convert it to liter I move the

decimal point three times to the left I

get 0.6 liter we know that molarity of a

solution is m equals n upon V the value

of n is 0.05 mole and the value of V is

0.6 liter I plug in these two values in

this equation after calculation I get

0.0 at 3 mole per liter are just

0.083 m so the molarity of this solution

is

0.083 M now in this problem only mass of

a solute hno3 is given firstly I find

the molar mass of hno3 I write h plus n

plus 3 oxygen because there are three

atoms of oxygen we know that the molar

mass of hydrogen is one gram the molar

mass of nitrogen is 14 gram there are

three atoms of oxygen and the molar mass

of oxygen is 16 gram after addition I

get 63 gram so the molar mass of hno3 is

63 Gram now to find the number of moles

of hno3 I divide given mass of hno3 by

its molar mass the given mass of hno3 is

4 gram and its molar mass is 63 gram

after calculation I get

0.06 small secondly the volume of a

solution is 80 milliliter I convert it

to liter to do so I move the decimal

point three times to the left I get

0.08 liter we already know that molar

TFA solution is m equals n upon V the

value of n is 0.06 mole and the value of

V is 0.08 liter I plug in these two

values in this equation after

calculation I get

0.75 mole per liter or just 0.75 m so

the molarity of this solution is 0.75 m

lastly pause the video and try to solve

this numerical problem

firstly I find the molar mass of HCL I

write hydrogen plus chlorine the molar

mass of hydrogen is 1 gram and that of

chlorine is 35.5 gram after addition I

get 36.5 Gram now to find the number of

moles of a solute I divide given mass of

HCL by its molar mass the given mass is

20 gram and the molar mass is 36.5 gram

after calculation I get 0.55 mole

secondly the volume of a solution is 0.5

DM Cube we already know that 1 liter is

equal to 1 DM Cube so 0.5 DM cube is

equal to 0.5 liter also we know that

molarity is equal to n upon V I plug in

these two values in this equation after

calculation I get 1.1 mole per liter are

just 1.1 M thus the molarity of this

solution is 1.1 M therefore using this

simple trick we can easily calculate the

molarity of any solution