Molality, Colloids, Suspensions

Evaluation/Assessment: Objective: Today I will be able to: Explain why suspensions and colloids are not solutions Calculate the concentration of a solution using the equation for molality and mole fractions Evaluation/Assessment: Informal assessment – monitoring student progress as they complete the practice Formal assessment – analyzing student responses to the classwork and exit ticket. Common Core Connection Build Strong Content Knowledge Make sense of problem and persevere in solving them Look for and express regularity in repeated reasoning

Lesson Sequence Evaluate: Warm – Up Explain: Molality, Suspensions and Colloid Notes Elaborate: Molality Calculations Explain: Mole Fraction Elaborate: Mole Fraction Calculations Evaluate: Exit Ticket

Warm - Up What is the proper lab technique for preparing a solution? What is the difference between an unsaturated, saturated and supersaturated solution?

Objective Today I will be able to: Explain why suspensions and colloids are not solutions Calculate the concentration of a solution using the equation for molality

Homework Finish Molality/Mole Fraction Calculations Wear closed toe shoes Friday for Dilutions lab

Agenda Warm-Up Molality, Suspensions and Colloids Notes Molality Calculations Mole Fraction Notes Mole Fraction Calculations Exit Ticket

Molality, Suspensions and Colloids Notes

Molality (m) = moles of solute/kg of solvent Molality is used for vapor pressure and temperature change Used because it does not change with change in temperature

Things that Remind Mr. Klotz of Solutions (but are not) Suspension - a mixture from which some particles will slowly settle when left alone for a period of time (muddy water) - Particles that settle can be filtered out

Things that Remind Mr. Klotz of Solutions (but are not) Colloid – heterogeneous mixture of two or more substances that appears to be a solution Smoke (solid in gas), marshmallow (gas in a solid), whipped cream (gas in a liquid)

Things that Remind Mr. Klotz of Solutions (but are not) Tyndal Effect – allows you to distinguish between a true solution and a colloid Shine a light on a true solution, and the light is invisible Shine a light on a colloid, and you will be able to see the light beam as it reflects off the relatively large solute particles (headlights in fog)

Molality Calculations

Mole Fraction

Mole Fraction Χi = moles of i total moles

Mole Fraction Example 0.100 mole of NaCl is dissolved into 100.0 grams of pure H2O. What is the mole fraction of NaCl? Steps to solve the problem Convert mass of H2O  moles of H20 Add the moles of H2O and NaCl together to get the total number of moles in the solution Divide the moles of NaCl by the total number of moles Answer: 0.982 No units because it is a ratio!

Mole Fraction Practice Complete the practice at your desk. The problems you do not finish will become your homework.

Exit Ticket How would you prepare 1.5 L a 2.0 M solution from a stock solution of 6.0M HCl?