Objectives: 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) Unit: Solutions Topic: Molarity

Solutions Most of the important chemistry that keeps plants animals and humans alive takes place in aqueous solutions Even water that comes our of your faucet is a solution because it has dissolved minerals in it If you recall, a solution is a homogeneous mixture 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 Solutions are not just made of liquids Solutions can be solids and gases as well Consider brass, brass is a solution made up of copper and zinc A gaseous solution would be air Air is made up of mostly nitrogen(80%) and oxygen (20%)

What is a Solution? a ______ mixture of ___or more substances (usually liquid) Ex: "he used a solution of sugar and water" Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Solutions The substance present in the largest amount is called the solvent (usually water) The other substance in lesser amounts is called the solute

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 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 SolventSolute Coffee solution made up of 98.75% water and the rest consists1.25% of other chemicals Cola is a solution made up of about 11 % sugar and roughly 88% water Vinegar is a solution made up of 3.5 % acetic acid and 96.5% water.

Water Polarity 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 + - +

When a compound such as salt dissolves in water we call this solvation

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

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What is Solvation (dissolution)? The process by which a compound such as salt _____in water NaCl  Na +1 + Cl -1 Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

Polar vs. Nonpolar H 2 O = polar electrons shared unequally resulting in a slight positive charge and a slight negative charge asymetrical geometry CH 4 methane = nonpolar electrons shared equally No charge symetrical geometry

H 2 O = polar electrons shared unequally resulting in a slight positive charge and a slight negative charge asymetrical geometry CH 4 methane = nonpolar electrons shared equally No charge symetrical geometry What’s the difference between polar and non-polar molecules?

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 Polar molecules can dissolve other polar molecules Hydrogen Bond

Solubility of Polar Molecules Because sugar and alcohol are both polar molecules they are soluble (will dissolve in water) Polar molecules will dissolve in another polar liquid like water We say “like dissolves like” That is, polar molecules will dissolve other polar molecules

Substances Insoluble in Water But what about molecules or substances that are nonpolar? Why do nonpolar molecules not dissolve in in polar water molecules? Methane is a nonpolar molecule and has no overall charge to it. It has a symetrical geometry an the electrons are equally distributed Therefore, there is no attraction between the two molecules which prevent it from being soluble (dissolving)

Substances Insoluble in Water Many substances do not dissolve in water For example oil does not mix with water because it is made up of nonpolar molecules The C—H bond has a low negativity and the electrons are shared equally The result are nonpolar bonds that do no mix with the polar water molecule

How Substances Dissolve One rule of thumb that chemists use and worth remembering is “like dissolves like” In other words, polar molecules will dissolve polar molecules Nonpolar molecules will dissolve nonpolar molecules

What’s the difference between polar and non-polar substances? Polar substances will ______(soluble) in _____substances (alcohol & water) Non-polar substances (methane, oil) will not _____(insoluble) in ____substances (think oil and water or vinegar and water) “like dissolves like!” Answer Bank Largest concentration dissolve(s) Homogeneous Lesser Polar Higher Surface Crystal Temperature Two

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

Factors Affecting the Rate of Dissolution 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

Molarity When dealing with aqueous solutions, chemists often describe a solution in terms of concentration We define the concentration of a solution as the amount of solute in a given volume of solution The most commonly used expression of concentration when dealing with aqueous solutions is Molarity (M)

Molarity Molarity describes the amount of solute in moles in the volume in liters Molarity is describes the amount of solute in moles and volume of the solution 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

What is Molarity (M)? The number of _____ of solute per _____of solution in liters, or…. M = Molarity = moles of solute liters of solution Answer Bank liters concentrated moles Molarity(M) volume solute

11.5 g NaOH 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 We are given the following information: Mass of solute = 11.5 grams Volume of Solution = 1.5 Liters Remember the definition of Molarity: M = moles of solute liters of 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 1 mol NaOH 40.0 g NaOH = mol NaOH Now that we have mols we can solve for Molarity M= moles of solute = mol NaOH = M NaOH liters of solution 1.50 L of solution

1.56 g HCl Practice: Calculate the Molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8mL of solution Remember the definition of Molarity: M = moles of solute liters of 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 1 mol HCl 36.5 g HCl = mol HCl We are given the following information: Mass of solute = 1.56 grams Volume of Solution = 28.6 mL 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

18 mol MgCl 2 Practice: How many grams of magnesium chloride MgCl 2 are needed to make 6.0 L of a 3.0 M solution? Remember the definition of Molarity: M = moles of solute liters of solution Since we have molarity and we have liters, we To solve for moles and then convert to grams M = moles of solute liters of solution 95.3 g MgCl 2 1 mol MgCl 2 = 1,715 g mol MgCl 2 We are given the following information: Molarity of solution = 3.0 M Volume of Solution = 6.0 L Molarity only deal in Moles, so solving for moles we get: 3.0M = mol MgCl 2 6 L of solution moles MgCl 2 = (3.0 M)(6.0 L) = 18 mol MgCl 2

Demo: I am going to make a 1M solution of CuSO 4 Can anyone tell how to make it? Why don’t we make things easy. I have a 1000ml beaker (1.0 liter) And grams (molar mass) which is equal to 1 mole of CuSO 4 By dissolving grams of CuSO 4 in water, a made a 2M solution of CuSO 4 Molarity (M) = 1 moles of solute = 2M 0.5 liters of solution

Summarize: Answer Bank liters concentrated moles Molarity(M) volume Solute Oxygen Nitrogen polarity Gases can be solutions. Air contains 21%O 2 and 79% N 2, so oxygen is the solute and ___________is the solvent In the expression like dissolves like, the word like refers to similarity in molecular ___________. Molarity is equal to ______ divided _____ The more _________ a solution is, the higher the ________ Molarity describes the amount of ____in moles in the volume in liters