Solutions.

Solutions

Unit: Solutions Topic: Molarity Objectives: Day 1 of 3
To understand the difference between a solvent and solute To understand the process of dissolution To understand how polar and nonpoloar substances dissolve To understand Molarity in terms of solution concentration To understand how to calculate Molarity given moles, volume or molarity (M)

Quickwrite Please answer any of the questions below in 1-2 sentences:
Why do you solids such as salt and sugar disappears when the are added to water??? As these substances dissolve, what do you think is happening on a molecular level???? What do you think is more concentrated, a 1 liter glass of water with 1 cup of sugar dissolved in it, or a 1 liter glass of water with 2 cups of sugar dissolved in t??

Solutions If you recall, a solution is a homogeneous mixture of two or more substances in which the components are uniformly intermingled Salt water is homogeneous mixture in which the first sip will be the same as the last sip Solutions can be solids and gases as well Consider brass, brass is a solution made up of evenly mixed parts of copper and zinc An example of a gaseous homogeneous solution would be the air we breathe Air is made up of mostly nitrogen(79%) and oxygen(21%), and as you know, every breadth of air you take is identical to the one before it In this unit we will study only liquid solutions = N2 = O2

What is a Solution? A ______ mixture of ___or more substances (usually liquid) which the components are uniformly mixed Ex: solution of sugar and water Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Salt (Solute) Solutions The substance present in the largest amount is called the solvent (usually water) The other substance in lesser amounts is called the solute Together, the solvent and the solute make a solution Water (Solvent) Salt Solution

What is the difference between a solvent and a solute?
The substance present in the _____amount is called the solvent (usually water) The other substance dissolved in ____amounts is called the solute Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Practice: Complete the table by identifying the solvent and solute for each solution:
In the solution below, determine Solvent Solute 1. Coffee solution made up of 98.75% water and the rest consists1.25% of other chemicals 2. Cola is a solution made up of about 11 % sugar and roughly 88% water 3. Vinegar is a solution made up of 3.5 % acetic acid and 96.5% water.

Water Polarity And Dissolution
When Salt (NaCl) is added to water, it dissolves and disappears We call this process Dissolution Remember, a water molecule has a negative and positive dipole or charge to it The oxygen atom gives it a slight negative charge while the two hydrogen atoms give it a slight positive charge These strong charges rip and remove sodium and chlorine atoms individually + -

Let’s see what happens when salt dissolves in water……

Positive charges of water surround the negative Chlorine atom and remove it
+ + + + - + + + +

Eventually the salt will dissolve and disappear
Negative charges of water surround the Positive Sodium atom and remove it - + - - - Eventually the salt will dissolve and disappear We call this process Dissolution

What is Dissolution? The process by which a compound such as salt _____in water Positive and negative charges of water surround and rip apart ions and molecules NaCl  Na Cl-1 Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

O H H H C H H H Polar vs. Nonpolar H2O = polar CH4 methane = nonpolar
electrons shared unequally resulting in a slight positive charge and a slight negative charge asymmetrical geometry H H H CH4 methane = nonpolar electrons shared equally No charge symmetrical geometry C H H H

Solubility of Polar Molecules
Because water is a polar molecule it can dissolve ions such as chlorine and sodium But water can also dissolve other nonionic molecules such as ethanol, more commonly known as alcohol Like water, Ethanol has a polar O—H end to it with a positive and negative charge to it - + + - +

Solubility of Polar Molecules
Ethanol dissolves in water because it is polar molecule The negative charge on water forms a hydrogen bond with the slight positive charge on ethanol Therefore Polar molecules can, and will dissolve other polar molecules Hydrogen Bond + - + - We say “like dissolves like” That is, polar molecules will dissolve polar molecules, and nonpolar molecules will dissolve nonpolar molecules - +

What’s the difference between polar and non-polar substances?
Polar substances will dissolve in _____substances Ex: (NaCl & water) Non-polar substances will dissolve non- _____ substances Ex: Because oil is non-polar, it will not dissolve in a polar substance like water “like dissolves like!” Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Molarity M = Molarity = moles of solute liters of solution
The most commonly used expression of concentration when dealing with aqueous solutions is Molarity (M) Molarity describes the amount of solute in moles in the volume in liters Molarity is define as the number of moles of solute per volume of solution in liters, or…. M = Molarity = moles of solute liters of solution

Molarity - 1 Molar Solution
1.0 mole KCl (74.55g) Let’s make a 1Molar 1M KCl solution!!!! First we will add 1Liter of water Then we will add 1mole of KCl (74.55 grams = molar mass of KCl) Then stir to dissolve the solute 1000 800 600 400 200 Dissolution 1M KCl Solution 1.0 mole KCl (74.55g) 1.0 L solution (1000mL)

Molarity - 3 Molar Solution
3.0 mole KCl (3 x 74.55g) Let’s make a Molar 3M KCl solution!!!! First we will add 1Liter of water Then we will add 3 moles of KCl (3 x grams = molar mass of KCl) Then stir to dissolve the solute 1000 800 600 400 More Concentrated 200 Dissolution 3M KCl Solution 3.0 mole KCl (3 x 74.55g) 1.0 L solution (1000mL)

1M Solution Versus 3M Solution
1000 1000 800 800 600 600 400 400 More Concentrated Less Concentrated 200 200 1M KCl Solution 1.0 mole KCl (74.55g) 1.0 L solution (1000mL) 3M KCl Solution 3.0 mole KCl (3 x 74.55g) 1.0 L solution (1000mL)

What is Molarity (M)? The ratio that compares the number of _____ of solute per _____of solution It measures solution _______ M = Molarity = Answer Bank liters concentrated Moles concentration Molarity(M) volume solute moles of solute liters of solution

Practice: How many grams of magnesium chloride MgCl2 are needed to make 6.0Liter of a 3.0M solution? 18 mol MgCl2 We are given the following information: Molarity of solution = 3.0 M Volume of Solution = 6.0 L 95.3 g MgCl2 = 1,715 g MgCl2 Remember the definition of Molarity: M = moles of solute liters of solution 1 mol MgCl2 Since we have molarity and we have liters, we Need to solve for moles and then convert to grams M = moles of solute liters of solution Molarity only deal in Moles, so solving for moles we get: 3.0M = mol MgCl2 6 L of solution moles MgCl2 = (3.0 M)(6.0 L) = 18 mol MgCl2

Practice: Calculate the molarity of a solution prepared by dissolving 11.5 grams of solid NaOH in enough water to make 1.5 Liter solution Since the molarity requires mole and we are given gram, we need to convert grams to mols M = moles of solute liters of solution Remember the definition of Molarity: M = moles of solute liters of solution We are given the following information: Mass of solute = 11.5 grams Volume of Solution = 1.5 Liters 11.5 g NaOH 1 mol NaOH = mol NaOH 40.0 g NaOH Now that we have mols we can solve for Molarity M= moles of solute = mol NaOH = M NaOH liters of solution L of solution

Practice: #10 homework Calculate the Molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8mL of solution Since the molarity requires moles and we are given grams, we need to convert grams to mols M = moles of solute liters of solution We are given the following information: Mass of solute = 1.56 grams Volume of Solution = 28.6 mL Remember the definition of Molarity: M = moles of solute liters of solution 1.56 g HCl 1 mol HCl = mol HCl 36.5 g HCl Now that we have mol we can solve for Molarity Don’t forget to convert millileters into liters! M= moles of solute = mol HCl = 1.59 M HCl liters of solution Lof solution

Summarize: Try to come up with some different solutions we use in everyday life….if you can’t use my examples….. In your own words, describe the process of dissolution…… Explain why oil and water DO NOT mix…… Write the equation for Molarity and describe what Molarity measures…..

Topic: Unsaturated, Saturated, and Supersaturated Solutions
Unit: Solutions Topic: Unsaturated, Saturated, and Supersaturated Solutions Objectives: Day 2 of 3 To understand what factors increase the rate of dissolution (dissolve) To understand the difference between a Unsaturated, Saturated, and Supersaturated solution To learn how to calculate stoichiometry problems that involve solutions

If you wanted increase the rate at which sugar will dissolve in your tea, what are some things you could do to increase this rate of dissolution (dissolve)???? What do you think effects how fast salt will dissolve in water? What do you think will dissolve faster in a cup of water, a cube of sugar, or a spoon full of sugar??? Do you think there is a limit to how much salt can dissolve in a given amount of water?

Factors Affecting the Rate of Dissolution
Temperature causes the molecules to move faster increasing the rate of dissolution, dissolving the solid faster Stirring removes newly dissolved particles from the solid surface and continuously exposes the surface to fresh solvent (water molecules) When considering surface are, smaller salt crystals will dissolve faster than larger salt crystals Solid Solid Solid Solid

What factors affect the rate of dissolution?
3 things: _____ area stirring, and __________ Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Unsaturated Solutions
Salt (Solute) Unsaturated Solutions A solution that has not reached the limit of solute that will dissolve in it is said to be “Unsaturated” In other words, it is a solution that is able to dissolve more solute at that temperature If we were to add more solute (salt), it would continue to dissolve because the solution is unsaturated Water (Solvent)

Saturated Solutions Solid (Solute)
Salt (Solute) Saturated Solutions At a particular temperature, there is a limit to how much solute or salt that can dissolve in a solution The solvent, water in this case can only dissolve so much solute Let’s add more salt or solute to our Unsaturated solution and see what happens Eventually it would stop dissolving and solid would form at the bottom When a solution can no longer dissolve the solute at a particular temperature, we say the solution is “saturated” That is, the solute (salt) will no longer dissolve at a certain temperature Water (Solvent) Solid

Supersaturated Solutions
Consider our previous Saturated solution What would happen if we heated it up? Let’ find out…. The solute or salt will dissolve and become aqueous If we let the solution slowly cool, back to it’s original temperature, the solute will remain dissolved in solution This type of solution is called a Supersaturated Solution It contains more dissolved solute than a saturated solution will hold at a particular temperature A supersaturated solution is very unstable, adding a crystal of the solid will often cause immediate precipitation of a solid Water (Solvent) Solid

What is the difference between an Unsaturated, Saturated, & Supersaturated Solution?
An UNSTATURATED solution is a solution that is able to ______more solute at that _______ A SATURATED solution occurs when the solvent can _____ longer dissolve more of a solute at a particular temperature A SUPERSATURATED solution is an unstable solution that contains more dissolved solute than a saturated solution at an elevated temperature. A _____ added will cause the solution to precipitate out Answer Bank dissolve(s) Homogeneous NO Higher Surface Crystal Temperature

Molarity Stoichiometry
Because so many important reactions take place in solutions, it is important to be able to do stoichiometric calculations for solution reactions Remember, molarity deals with moles, so if you are given Molarity (M), and liters, you should solve for moles A common mistake is to convert moles to grams DO NOT DO THIS!!!!

Practice: NaHCO3 + HCl  NaCl + H2O + CO2
Sodium bicarbonate is used to neutralize an acid spill. If there was 2.5L of 0.1M HCl , how many grams of sodium bicarbonate would be needed? 2.5L 0.1M HCl Step1: Calculate the moles of HCl Plugging in our values into the molarity equation we get…. Molarity = moles solute Liters of solution moles of HCl Solving for Moles of HCl, the molarity expression becomes: moles HCl = (0.1M)(2.5 L) = 0.25 moles HCl 0.25 moles HCl Step2: Set up the problem and solve for grams of NaHCO3 84.0 g of NaHCO3 1 mol NaHCO3 = 22.0 grams of NaHCO3 1 mol HCl 1 mol NaHCO3

Practice: Convert mLL Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
If 500mL of a 2M HCl solution reacts with excess magnesium at STP, what volume of hydrogen gas can be produced? 500mL 2M HCl Step1: Calculate the moles of HCl Plugging in our values into the molarity equation we get…. Molarity = moles solute Liters of solution moles of HCl 0.5L Convert mLL Solving for Moles of HCl, the molarity expression becomes: moles HCl = (2M)(0.5 L) = 1.0 mole HCl 1.0 mole HCl Step2: Set up the problem and solve for grams of NaHCO3 22.4 L H2 1 mol H2 = L of H2 2 mols HCl 1 mol H2

Summarize: You are given cubes of sugar, what are 3 things you could do to speed up the dissolving or dissolution process? In your own words, describe how you would create a UNSATURATED solution, a SATURATED solution, and a SUPERSATURATED solution

Topic: Factors that effect concentration
Unit: Solutions Topic: Factors that effect concentration Objectives: Day 3 of 3 To learn what factors effect Molarity or concentration To understand the concept of dilution and calculations that involve dilution

If you added water, or diluted a glass of sweet Kool Aid, how do you think this would affect it’s Molarity? If you left a glass of salty water out, and half of the water evaporated, how do you think this affects concentration or Molarity?

Standard Solutions 1.0 mole KCl (74.55g) A standard solution is a solution whose concentration is accurately known For example, if we filled up a beaker with 1L of water (1000mL) then weighed out grams of KCl (1mole) and mixed it with our solvent, a 1M standard solution is created 1000 800 600 400 200 1M KCl Solution 1.0 mole KCl (74.55g) 1.0 L solution (1000mL)

What is a standard solution?
A solution whose________ is accurately known Ex: 3M HCl acid solution Answer Bank liters concentrated moles Molarity(M) volume solute

Evaporation: Increases Concentration
Let’s say we have a 1M KCl Solution and we would like to make a 2M KCl What would happen if the solution was left outside to evaporate??? 1000 800 By evaporating the solution, more solute KCl remains in solution resulting in a greater concentration 600 400 200

Evaporation: Increases Concentration
Let’s say we have a 1M KCl Solution and we would like to make a 2M KCl What would happen if the solution was left outside to evaporate??? 400 1000 600 800 200 By evaporating the solution, more solute KCl remains in solution resulting in a greater concentration

Adding Solute: Increases Concentration
Salt (Solute) Let’s say we have a 1M KCl Solution and we would like to make a 3M KCl Solution In order to make a stronger more concentrated solution, we need to add more solute, in this case KCl Water (Solvent)

What are two ways to increase Concentration or Molarty?
By adding more ______ to a solution Ex: I added more salt to a 1M solution to make a 3M solution By letting the solution _____ Answer Bank after volume concentration solvent before Dilution evaporate solute

Dilution: Decreases Concentration
Let’s say we have a 12M HCL solution and we would like to make a 3M HCl Solution In order to make a weaker solution and decrease the concentration of a 12M HCl Solution, we need to add more water (solvent) That is, we need to dilute it!! 3 M HCl Acid Solution Weaker Acid 12 M HCl Acid Solution Very Strong Acid!!!!

Dilution: Decreases Concentration
Let’s say we have a 12M HCL solution and we would like to make a 3M HCl Solution In order to make a weaker solution and decrease the concentration of a 12M HCl Solution, we need to add more water (solvent) That is, we need to dilute it!! 1000 800 3M HCl Acid Solution Weaker Acid 600 400 200 12M HCl Acid Solution Very Strong Acid!!!!

How do we decrease Concentration or Molarty?
By adding more ______ or water to a solution Dilution _______ the concentration or Molarity (M) Ex: I diluted the 12M solution in order to make a 3M solution Answer Bank after volume concentration Solvent decreases before Dilution increases

Dilution Calculations
A typical dilution calculation involves determining how much water must be added to an amount of known stock solution The key to doing these calculations is to remember that only water (solvent) is added to the solution The amount of solute in the final more dilute solution is the same amount of solute in the original concentrated stock solution That is, Moles of solute after solution = Moles of solute before dilution

M1V1 = M2V2 Dilution Equation
Recall that a standard solution is a solution in which the concentration is accurately known Chemist’s use a dilution equation to create standard solutions Volume before dilution Volume after dilution M1V1 = M2V2 Molarity before dilution Molarity after dilution

What is the dilution equation?
M1V1 = M2V2 M1 = Molarity before______ V1 = Volume _____ dilution M2 = Molarity ______dilution V2 = ______after dilution Answer Bank after volume concentration solvent before dilution

Demo: I have standard solution of 500ml of a 2M CuSO4 solution. What will my molarity be if I add 500mL Use your dilution equation to help me out…. Volume before dilution Volume after dilution M1V1 = M2V2 Molarity before dilution Molarity after dilution

By adding more water, the molarity or
Demo: I have standard solution of 500ml of a 2M CuSO4 solution. What will my molarity be if I add 500mL??? Plugging in our values we get: (2.0M)(500mL) = M2 (1000mL) Solving for M2 we get….. M2 = (2.0M)(500mL) (1000mL) M2 = 1.0 M By adding more water, the molarity or concentration decreased Volume before dilution = 500mL Volume after Dilution = = 1000 mL M1V1 = M2V2 Concentration before dilution = 2.0M Molarity after dilution = ????

Practice: # 6 Dilutions Worksheet
If I have 40 mL of a 12 M HCl solution, what will the concentration be if I add 960 mL more water to it? Plugging in our values we get: (12.0M)(40.0mL) = M2 (960+40mL) Solving for M2 we get….. M2 = (12.0M)(40.0mL) (1000mL) M2 = 0.5 M If we add more water, the molarity or concentration should decrease Volume before dilution = 40mL Volume after dilution = 1000 mL M1V1 = M2V2 Concentration before dilution = 12.0M Molarity after dilution = ????

If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it? Plugging in our values we get: (0.5M)(340mL) = M2 (900mL) Solving for M2 we get….. M2 = (0.5M)(340mL) (900mL) M2 = 0.19 M If we add more water, the molarity or concentration should decrease Volume before dilution = 340mL Volume after Dilution = = 900 mL M1V1 = M2V2 Concentration before dilution = 0.5M Molarity after dilution = ????

To what volume must 1.0 L of a 6.0 M solution of HCl be diluted in order to prepare a 0.2 M solution? Plugging in our values we get: (6.0M)(1.0L) = (0.2M) V2 Solving for V2 we get….. V2 = (6.0M)(1.0L) (0.2M) V2 = 30 Liters If we add more 30 liters water, the molarity or concentration decreased Volume before dilution = 1.0L Volume after Dilution = ????? M1V1 = M2V2 Concentration before dilution = 6.0M Molarity after dilution = 0.2M

Summarize: Molarity is equal to _______ of solute divided by _________of solution To increase molarity or concentration, we add more _______. To dilute a solution and decrease Molarity or Concentration, we add only more _______. The amount of _______ doesn’t change. In the equation, M1 x V1 = M2 x V2, M1 is the molarity of a solution before ______ and V2 is the _______of a solution ______ dilution. Answer Bank Solute(2) liters concentration solvent moles Dilution after

Dilution Solutions We can check our calculations from our previous problem using the dilution equation M1 = 17.5 M V1 = ???? M2 = 1.0 M V2 = 2.0 L (17.5M)(V1) = (1.0M)(2.0) V1 = (1.0M)(2.0) 17.5M V1 = 0.11L

The number of moles of solute stays the same but more water is added increasing the volume, so the molarity(M) decreases Let’s review our definition of molarity: Molarity (M) = What happens when add more water? Moles remain constant moles of solute liters of solution Molarity Decreases Volume Increases

For example, suppose we want to prepare 2.0L of a1M acetic acid (vinegar) from a 17.5 M stock solution of acetic acid. What volume of stock solution is required? We have a 17.5M of a stock solution of acetic acid available We need to prepare a 2.0L 1M acetic acid solution 17.5 M Acetic Acid 1.5L

To solve the problem, we need to determine the number of moles of acetic acid (solute) needed in the final solution: Now we need to find the volume of our 17.5 M solution (stock solution) that contains 2.0 mol of HC2H3O2 2.0L solution 1 mol HC2H3O2 = 2.0 mol HC2H3O2 1L HC2H3O2

Remember: Molarity = Solving for Liters (V), the expression becomes…… V = moles of solute liters of solution moles of solute Molarity = 0.11 L of solution 2.0 mol HC2H3O2 17.5 mol/L

Therefore to make 2. 0L of a 1 M acetic solution we take 0
Therefore to make 2.0L of a 1 M acetic solution we take 0.11 Liters of our 17.5M stock solution of acetic acid and dilute it to a total volume of 0.5 liters Then we add 2.0 liters of water The resulting Solution is 1M Acetic acid First we add 0.11 liters of our stock 17.5 solution

Moles of solute = (Molarity)(Liters of solution) We do this because the moles of solute in the stock solution = moles of solute in our new solution were trying to make 0.5L solution 1 mol HC2H3O2 = 0.5 mol HC2H3O2 1L HC2H3O2

Visulaize: 1 mol NaOH = mol NaOH 40.0 g NaOH

Solubility What happens when you put a salt in water?
Why does the salt disappear? What is really happening when something dissolves? Earlier, we saw that when sodium chloride dissolves in water, the resulting solution conducts electricity

Unsaturated Solutions
A solution that has not reached the limit of solute that will dissolve in it is said to be “Unsaturated” In other words, it is a solution that is able to dissolve more solute at that temperature If we were to add more solute (salt), it would continue to dissolve because the solution is unsaturated

What is a Unsaturated Solution?
A solution that is able to ____more solute at that_______ Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Saturated Solutions If you were to keep adding salt to water, eventually it would stop dissolving There is a limit to how much solute can be dissolved in a solvent (water) When a solution can no longer dissolve the solute, we say the solution is “saturated” That is, the solute (salt) will no longer dissolve at a certain temperature

What is a Saturated Solution?
A solution in which the solvent can ____no more of a specific solute at a particular _______ Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Supersaturated Solutions
Sometimes when a solid is dissolved to the saturation level at an elevated temperature and then allowed to cool, all of the solid may remain dissolved This type of solution is called a supersaturated solution It contains more dissolved solid than a saturated solution will hold at that temperature A supersaturated solution is very unstable, adding a crystal of the solid will cause immediate precipitation of a solid

What do you think effects how fast salt will dissolve in water? 3 things to consider is surface area, stirring, and temperature

When considering surface are, smaller salt crystals will dissolve faster than larger salt crystals Temperature causes the molecules to move faster increasing te rate of dissolution Finally, stirring removes newly dissolved particles from the solid surface and continuously exposes the surface to fresh solvent (water molecules)

What factors affect the rate of dissolution?
3 things: _____ area stirring, and __________ Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

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