Solutions Mathematicians have Problems, But Chemists have Solutions! Ionic Solvation Covalent Solvation

Objectives   To compare and contrast solute and solvents   To determine if a molecule is ionic, polar covalent, non-polar covalent, or metallic   To describe how a non-polar solute will dissolve in a non-polar solvent.

What is a solution?   A solution is a mixture of 2 things, the solute and the solvent. Another word for a solution is a homogenous mixture. A homogenous mixture is when 2 or more things are mixed, but you only see one thing.   A solute is what dissolves or disappears, like salt or sugar.   A solvent is what does the dissolving. It is what you see when you look at a solution. Water is called the universal solvent.   You will always have more solvent than solute.   Solvation is the scientific way of saying “dissolving.” solvent solute solution

Solvation Examples  Example: Salt water What is the solute?___________ What is the solute?___________ What is the solvent?___________ What is the solvent?___________  Example – 70% ethanol solution. Solute _______________ Solute _______________ Solvent________________ Solvent________________ Why? Why? Salt water Water ethanol If 70% is ethanol, then it must be the solvent. The remaining 30% is water, the solute.

Studying Solvation   We want to predict what solutes will dissolve in which solvents.   In order to do this, we need to know what type of molecule the solute and solvent are.   The type of molecule and the IMFs that form will help us to determine if solvation will occur. Like molecules will hang out with each other to form a solution Molecules that are not alike will separate from each other. Heterogeneous Mixture: Different Bond Types Homogeneous Mixture: Same Bond Types Solvent: H 2 O (polar) Solute: any non-polar Solvent: H 2 O (polar) Solute: any polar or ionic

Bond Review   How can you tell if a molecule is ionic, polar covalent, non-polar covalent, or metallic?   Ionic: Electronegativity difference of 1.8 or more 1 st element in groups 1-3, metals, 2 nd element is in groups 5-7 non-metals strongest IMF   Metallic: two metals combining electrons   Covalent: Polar has un-bonded pair of e- on central element (usually grps 5 or 6) or Polar will have 2 different elements bonded to central element (usually groups 3 or 4) Solvent: Water molecules Solute: Na+ or Cl-

Determine what type of bond hold the molecule together   KCl H2OH2O   CaCO 3   CO 2   Sugar   BenzeneIonic Non-polar covalent Polar covalent: memorize Non-polar covalent Ionic (polyatomic) Polar covalent

Water  Water is a polar molecule. Why? Because oxygen has 2 unbonded pairs Because oxygen has 2 unbonded pairs  This means the oxygen is negatively charged and both hydrogens are positively charged. Why? Because oxygen hogs the e- Because oxygen hogs the e-  What type of IMFs will water have? Polar molecules can have dipole-dipole or hydrogen bonds. Water has both H & O, so molecules are held together by hydrogen bonding, the strongest IMF. Polar molecules can have dipole-dipole or hydrogen bonds. Water has both H & O, so molecules are held together by hydrogen bonding, the strongest IMF. H H O

Ionic Solubility Rules We can predict if a solute will dissolve in a solvent by using looking at the bonds of each molecule. “Like Dissolves Like”  Ionic or Polar solutes will dissolve in ionic or polar solvents  Alcohols (ending in –ol or OH) will dissolve anything BUT polar covalent solids. Ethanol, methanol, isopopanol are alcohols and will dissolve anything except polar covalent solids like sugar. Ethanol, methanol, isopopanol are alcohols and will dissolve anything except polar covalent solids like sugar.  Water is considered a universal solvent because it can dissolve both ionic and polar covalent compounds

Ionic Compounds & Water  In an aqueous solution, water is the solvent. HCl (aq), NaCl(aq), CuSO 4 (aq)  Ionic solutes will dissociate into its ions when dissolved in water. Why? Because the charged parts of ionic bonds are heavily attracted to the charged parts of water. Because the charged parts of ionic bonds are heavily attracted to the charged parts of water.   NaCl (in water)    K 2 SO 4 (in water )  Na + + Cl - 2K + + SO 4 2-

Ionic Solvation: NaCl & H 2 O 1. Salt solute is added to water. 2. Salt randomly moves around until it bumps into or “hits on” the water molecules. The Na+ part of the salt is very attracted to the bad boy Oxygen and his negative charge. The Cl- part of the salt is very attracted to the good little girl Hydrogen and her positive charge 3. Salt dissociates or breaks up into Na+ and Cl-. 4. Each ion is completely surrounded by water molecules “groupies!”. When the ion can no longer be seen, it is said to be dissolved.

Ionic Solvation + O H H O H H O H H Na O H H O H H O H H Cl Cl Na O H H O H H That Hydrogen is a cutie! Look at the charge on the Oxygen!

Solvation Animation Ionic Solvation Animation Ionic Solvation Animation #1

Polar Covalent Solvation: Sugar Water 1. Sugar is added to water. 2. Sugar will randomly move around until it bumps into the water molecules 3. The partially charged part of sugar is very attracted to part of the oppositely charged part of water. 4. The covalent solute (the sugar) DOES NOT break up. 5. Instead, the sugar becomes a cheater by staying bonded and forming a partial relationship with the water. 6. When the sugar is completely surrounded by solute “groupies,” we say it has been dissolved. Ions that are completely surrounded by water molecules form hydration spheres and are said to be “hydrated”.

Polar Solvation   Polar molecules will dissolve in water because of the attractions of the charges   The charged parts of the sugar are attracted to partial charged areas of water   Water surrounds the sugar

Solubility Rules   We can predict if a solute will dissolve in a solvent by using looking at the bonds of each moelcule. “Like Dissolves Like”  Ionic or Polar substances will dissolve in ionic or polar solvents  Non-polar substances will only dissolve in non-polar substances.  Alcohols (ending in –ol or OH) will dissolve anything BUT polar solids.  Water is considered a universal solvent because it can dissolve both ionic and polar covalent compounds

Like Dissolves Like You must first identify if the molecule is ionic, polar, or non-polar. Will NaCl dissolve in water? Will CO 2 dissolve in water? Will oil dissolve in vinegar? Will sugar dissolve in water? Ionic Solid +Polar solvent =Solution YES! Non-polar +Polar solvent =No solution NO! Ionic Solid +Polar solvent =Solution YES! Polar Solid +Polar solvent =Solution YES!

Solvation Stories What happens when molecules face temptation! AKA: Celebrity Marriage… TMZ Style

Objectives  When given a solute, determine if it is ionic polar covalent, or non-polar covalent  To describe what happens to an ionic solute when it dissolves in a solvent  To describe what happens to a polar covalent solute when it dissolves in a solvent  To identify 4 ways to increase the solubility of a solute  To interpret a solubility curve

Solvation Animation Ionic Solvation Animation Ionic Solvation Animation #1

Factors that Affect Solvation We can speed up the process in a couple of ways: Shake or stir the mixture Increase the temp (solids or liquids only) Increase the surface area of solute Increase the pressure (gases only) Why does each of the above work? Because it will increase the number of collisions!

Solubility Curves   Solubility depends on the molecule and the temp   Graph allows us to predict the solubility under different temps   Which one is the only molecule where solubility decreases as you increase temp? Why?   Because it is a gas.

Solubility Curves Questions 1. What is the solubility of KCl at 70°C? 2. How many grams of KClO 3 will dissolve in 100 grams of water at 40°C ? 3. How many grams of KClO 3 will dissolve in 50 grams of water? 47 g 15 g 15 g KClO 3 = x 100 g H 2 O 50 g H 2 O