Concentration of solutions Chemistry

Summary

This video script offers a comprehensive guide on calculating the number of moles in a solution, given the volume of the solvent and the solution's concentration. It explains the concept of a solution, the definition of concentration, and the formulae for calculating molar concentration. The script provides step-by-step examples, including converting units from cubic centimeters to cubic decimeters, using molar mass from the periodic table, and solving for moles and concentration. It emphasizes the importance of units and formula application in stoichiometry, with additional resources available for further chemistry and physics topics.

Takeaways

• 🧪 A solution is a mixture where a solute is dissolved in a solvent.
• 📏 Concentration is defined as the number of moles of solute per unit volume.
• 🔄 The formula for concentration is C = n/V, where C is concentration, n is the number of moles, and V is volume.
• 🔢 The formula n = mass / molar mass can be used to find the number of moles when mass and molar mass are known.
• ⚖️ Molar mass is calculated using atomic mass numbers found on the periodic table.
• 📐 Volume must be measured in cubic decimeters for concentration calculations.
• 🔄 Conversion between cubic centimeters and cubic decimeters is necessary, with 1 cubic decimeter equal to 1 liter.
• 🌡️ Standard temperature and pressure (STP) calculations for gases are not covered by the concentration formula.
• 📝 Units are crucial for correct calculations and must be included in the answer.
• 🔍 The choice of formula depends on the information given in the problem.
• 📚 Examples in the script illustrate how to calculate the number of moles and concentration given different variables.

Q & A

What is a solution in chemistry?

A solution is a homogeneous mixture composed of a solute, which is the substance dissolved, and a solvent, which is the substance doing the dissolving.

How is the concentration of a solution defined?

Concentration is defined as the number of moles of solute per unit volume, typically measured in moles per cubic decimeter.

What is the formula to calculate the concentration of a solution?

The formula to calculate the concentration of a solution is C = n/V, where C is the concentration, n is the number of moles, and V is the volume of the solution.

How can you calculate the number of moles of solute in a solution if you know the concentration and volume?

You can calculate the number of moles using the formula n = C * V, where C is the concentration and V is the volume of the solution.

What is the relationship between mass, molar mass, and the number of moles?

The relationship is given by the formula n = mass / molar mass, where the mass is the amount of solute in grams and the molar mass is the mass of one mole of the solute.

Why is it important to use the correct units when calculating concentration?

Using the correct units ensures the accuracy of the calculation. For concentration, the volume must be in cubic decimeters, and the mass must be in grams, with the result in moles per cubic decimeter.

How do you convert cubic centimeters to cubic decimeters for concentration calculations?

To convert cubic centimeters to cubic decimeters, you divide the number of cubic centimeters by 1000, since 1 cubic decimeter is equal to 1000 cubic centimeters.

What is the molar mass of sodium chloride (NaCl)?

The molar mass of sodium chloride is approximately 58.5 g/mol, calculated by adding the atomic mass of sodium (23 g/mol) and chlorine (35.5 g/mol).

How can you calculate the concentration of a solution if you know the mass of the solute and the volume of the solvent?

First, calculate the number of moles using the formula n = mass / molar mass. Then, use the formula C = n/V to find the concentration, where V is the volume of the solvent.

What is the significance of the SI unit for concentration in chemistry?

The SI unit for concentration is moles per cubic decimeter (mol/dm³), which is significant because it standardizes the measurement of solute concentration in a solution regardless of the size of the volume.

Can the formula for concentration be used to calculate the volume of a gas at standard temperature and pressure?

No, the formula for concentration of solutions is not used for calculating the volume of a gas at standard temperature and pressure. A different formula is required for that purpose.

Outlines

00:00

🧪 Understanding Solutions and Calculating Moles

This paragraph introduces the concept of a solution, which is a mixture of a solute dissolved in a solvent. It explains the importance of concentration, defined as the number of moles of solute per unit volume, and how to calculate it using the formula C = n/V, where C is concentration, n is the number of moles, and V is volume. The paragraph emphasizes the need to use the correct formula based on the given information, such as mass, molar mass, and volume, and to pay attention to units, especially when converting from cubic centimeters to cubic decimeters. It also clarifies that the formula for gas volume at standard temperature and pressure is different and not to be confused with the concentration formula.

05:02

📚 Applying Formulas to Calculate Concentration and Moles

The second paragraph delves into the application of the formulas for calculating the concentration of a solution and the number of moles of solute. It provides step-by-step instructions on how to use the formulas, emphasizing the importance of knowing the mass, molar mass, and volume of the solution. The paragraph includes examples to illustrate the process, such as calculating the number of moles in a solution with a given concentration and volume, and determining the concentration of a solution with a known mass of solute and volume of solvent. It also discusses alternative methods to calculate concentration directly using mass, molar mass, and volume, and the importance of units in ensuring accurate results.

Keywords

💡Solution

A solution is a homogeneous mixture composed of a solute and a solvent. In the context of the video, it refers to the process of dissolving a solute in a solvent to create a uniform mixture. The script uses the term to explain the basis of calculating the concentration of a solution, emphasizing that the concentration is the ratio of the amount of solute to the volume of the solution.

💡Concentration

Concentration in chemistry is defined as the amount of solute per unit volume of solution. The video script explains that it can be expressed in moles per cubic decimeter, which is the SI unit for molar concentration. The concept is central to the video's theme, as it discusses how to calculate the concentration of a solution given the volume of the solvent and the amount of solute.

💡Moles

Moles represent the amount of a substance, typically measured in terms of the number of atoms, molecules, or other elementary entities. In the script, moles are used to quantify the solute in a solution, with the formula n = mass / molar mass, where n is the number of moles, mass is the weight of the solute, and molar mass is the mass of one mole of the solute.

💡Molar Mass

Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). The script explains that molar mass is calculated using the atomic masses from the periodic table and is essential for determining the number of moles of a solute in a solution.

💡Volume

Volume in the context of the video refers to the space occupied by the solvent in a solution, measured in cubic decimeters (dm³), which is the SI unit for volume. The script emphasizes the importance of using the correct units for volume when calculating the concentration of a solution.

💡Solute

A solute is the substance that is dissolved in a solvent to form a solution. The video script discusses how the solute's mass and molar mass are used to calculate the number of moles, which is then used to determine the solution's concentration.

💡Solvent

A solvent is a substance, usually a liquid, capable of dissolving other substances to form a solution. In the script, water is mentioned as a common solvent, and the volume of the solvent is a key factor in calculating the concentration of a solution.

💡Formula

In chemistry, a formula represents the composition of a substance or the relationship between variables. The script introduces several formulas, such as n = mass / molar mass and C = n / V, to calculate the number of moles and the concentration of a solution, respectively.

💡Cubic Centimeters

Cubic centimeters (cm³) is a unit of volume measurement. The script mentions that 500 cubic centimeters is equivalent to 500 milliliters and that to convert to cubic decimeters, one must divide by a thousand, highlighting the importance of unit conversion in calculations.

💡Sodium Chloride

Sodium chloride, commonly known as table salt, is used in the script as an example of a solute. Its molar mass is calculated as part of an example to demonstrate how to find the concentration of a solution when given the mass of the solute and the volume of the solvent.

💡Stoichiometry

Stoichiometry is the quantitative relationship between the amounts of reactants and products in chemical reactions. Although not explicitly mentioned in the script, the principles of stoichiometry are applied in calculating the concentration of solutions, as it involves the relationships between mass, moles, and volume.

Highlights

Definition of a solution as a mixture of solute and solvent.

Concentration is the number of moles of solute per unit volume.

Formula for calculating concentration: C = n/V, where C is concentration, n is moles, and V is volume.

Formula for calculating moles: n = mass/molar mass.

Combining formulas to find concentration: C = (mass / molar mass) * volume.

The importance of using the correct units for volume in concentration calculations.

Conversion of volume units: 1 cubic decimeter equals 1 liter, and 1 cubic centimeter equals 1 milliliter.

Example calculation of moles in a solution given concentration and volume.

How to handle volume units in calculations: converting cubic centimeters to cubic decimeters.

Example calculation of solution concentration given mass of solute and volume of solvent.

Use of the periodic table to determine molar mass for concentration calculations.

Alternative approach to calculating concentration by combining moles and volume directly.

The significance of including units in the calculation results for accuracy.

Different scenarios for using the concentration formula, including calculating mass and volume.

The potential to identify compounds by calculating molar mass from given concentration, volume, and mass.

Emphasis on starting with a blank formula, substituting variables, and performing mathematical operations correctly.

Transcripts

in this video we will be looking at how

to calculate the number of moles if you

are dealing with Solutions and you're

given the volume of the solvent and the

concentration of the solution how do you

calculate the concentration of a

solution now remember let's first look

at what a solution is a solution is if I

take a solute and I dissolve it within a

solvent that outcome that mixture is

what we call a solution and I can

calculate the concentration of that

solution concentration can be defined as

the number of moles of solute per unit

volume or per cubic decimeter volume so

we will use the following formula or

this variation of the formula in order

to work out either concentration of a

solution or the number of moles if I am

given concentration of a solution and

the volume of the solvent so just to

recap this is a solution we take a

solute and we can work out the moles of

the solute by using this formula and we

dissolve it in a solvent of a particular

volume that will get us the

concentration of the solution because we

can combine these two formulas together

n is equal to mass over molar mass and C

is equal to n divided by V if I

substitute mass divided by molar mass in

the place of n in this formula I get the

second formula C is equal to mass

divided by molar mass multiplied by

volume so when working out the

concentration of a solution I can work

with either of these formulas they will

ultimately get the same answer and I

choose which one to use depending on the

information that I'm given it's very

important to note that if you are asked

to work out the volume of a gas at

standard temperature and pressure they

are not wanting you to use this formula

remember this is the formula that we use

for the concentration of solutions so

when we're dealing with a solute

dissolved in a solvent Solutions if I

want to work with gases and I want to

work out the volume of a gas I know

there's a v there and V is for volume

but we will use this formula this is the

one in order to calculate volume of a

gas if you want to see a video of me

going over this formula I will link it

in the description description below but

calculating this volume will get you the

volume of the solvent in a solution

looking at this version of the formula

concentration is equal to number of

moles divided by volume this matches up

with our definition for concentration

and our definition for concentration is

it is the number of moles per unit

volume the number of moles of solvents

per unit volume or per cubic decimeter

which is our unit of volume

concentration measured in moles per

cubic decimeter and in meaning moles it

makes sense why our unit for

concentration is moles per cubic

decimeter because as I mentioned unit

for in

is mole

divided by our unit for V which is cubic

decimeters

and if I move this up to the top we know

we have to make that a negative exponent

so mole per cubic decimeter that's why

it has an exponent of negative three

just remember that volume must be

measured in cubic decimeters it's often

given in cubic centimeters in order to

convert from cubic centimeters to cubic

decimeters we must divide by a thousand

the reason why it must be in cubic

decimeters by uniform volume is because

my unit for concentration the SI unit is

moles per cubic decimeter if I look at

this version of the formula again

concentration C in moles per cubic

decimeter again we've got volume in

cubic decimeters here at the bottom V

Big M is molar mass and we use our

periodic table to help us calculate

molar mass of our compound and Baby M is

mass in grams now please just remember

that MV is molar mass multiplied by our

volume another thing to note when

calculating the concentration of a

solution is that our volume is not

always given in cubic decimeters or

cubic centimeters but it can be given in

liters or milliliters which is another

familiar unit for volume heaters now one

cubic decimeter is equal to one liter

this is something that you can memorize

and one cubic centimeter is equal to one

milliliter first example says calculate

the number of moles of solute in 500

cubic centimeters of a solution of

concentration two mole per cubic

decimeter now the first thing to note is

that they don't say that this is the

volume so you need to look at the units

and no cubic centimeters that's a

measure of volume they do tell me

concentration is two moles per cubic

decimeter but again even if the word

concentration isn't there you need to

rely on the units in order to know this

is a representation of concentration now

which formula we decide to use depends

on the given information and as you can

see from the question I'm given volume

and I'm given concentration and I'm

looking for number of moles

if I look at that given information and

the information I'm looking for it

doesn't make sense to use this formula I

don't know the mass I don't know the

molar mass I don't even know the

compound so this one's out of the

question we're going to use this one so

you write your Formula First which I'll

be doing over there

then we substitute in our variables

in the place of concentration I'm going

to put two two moles per cubic decimeter

I'm looking for the number of moles so n

is my variable it's my unknown and I

divide that by the volume of the

solution now take note how the volume is

given us 500 cubic centimeters just note

that 500 cubic centimeters is equal to

500 milliliters but they don't ask for

that in this question it's just

something to keep in the back of your

mind but as I mentioned my unit for

volume needs to be cubic decimeters so

to get it to cubic decimeters what I can

do is I divide by a thousand so the five

500 by a thousand and I'm going to get 0

comma five cubic decimeters and that is

what I need to substitute into my

formula I can therefore work out that my

number of moles is one

remember your unit if you don't give me

a unit you're not getting your mark and

if you don't write your formula you

won't get the formula Mark so this over

here represents my written out formula

substitution onto width unit let's do

another example calculate the

concentration of a solution containing

11 comma 7 grams of sodium chloride in

500 cubic centimeters of water the first

thing that I like to do is list my

variables and then I can decide which

formula makes sense to use calculate the

concentration I'm looking for

concentration then they give me mass

measured in grams they tell me that the

compound is sodium chloride as soon as

you know your compound you can work out

the molar mass using the atomic mass

numbers 23 for sodium plus 35 comma 5

for chlorine which is 58 comma 5 for my

molar mass and they give me volume which

I converted to cubic decimeters now

there's two ways that we can answer this

question

I know that ultimately I am looking for

the concentration which means I can

think to use this formula I'm looking

for concentration I have the volume but

do I have the number of moles at the

moment I don't however I can first use

this formula to calculate the number of

moles using my mass and my molar mass so

I use maths and molar mass to get number

of moles and then once I know number of

moles I put that in the place of in and

I put in my volume to get my

concentration or what you can do instead

is you can use the formula that combines

these two into one and that is this

formula

I'm looking for concentration I have

mass I have molar mass I have volume so

I'm going to use this one I write my

Formula First let this represent my

written out formula just so that I don't

have to rewrite it then I substitute

into the formulas you take your

variables you plug them in Remember at

the bottom this means molar mass

multiplied by volume and I get 0 comma

four and remember your units mole per

cubic decimeter that is your unit for

concentration

now we can also use this formula to work

backwards in order to calculate mass if

this is the case we would substitute in

our concentration our molar mass and our

volume and we would work backwards we

would do inverse operations in order to

work out our Mass

in the same way we can use this formula

to calculate volume of a solution and

maybe even they ask you to identify the

compound by calculating the molar mass

if they give you the concentration

volume and mass just always start with

your blank Formula First substitute your

variables in the correct places and if

you do your mathematical operations in

the correct order you should get the

correct answer provided that you give

the correct units in the other videos in

my playlist we look at how to calculate

number of moles as well as things like

volume at STP remember to check out the

links in my description below for more

Stoichiometry videos more chemistry and

more physics videos