Dilution of Solutions Don’t be dilutional… This isn’t as tough as it seems

Concentration = # of fish volume (L) Concentration = V = 1 L n = 2 fish Concentration = 2 “fishar” V = 1 L n = 4 fish [ ] = 4 “fishar” V = 5 L n = 20 fish [ ] = 4 “fishar” 1 fish 1 (L) Concentration = 1 “fishar”

V = 1 L n = 2 moles Concentration = 2 molar V = 1 L n = 4 moles [ ] = 4 molar V = 5 L n = 20 moles [ ] = 4 molar Concentration = # of moles volume (L) V = 250 mL n = 8 moles [ ] = 32 molar

Making Molar Solutions …from liquids (More accurately, from stock solutions)

Concentration… …a measure of solute-to-solvent ratio concentrated vs. dilute “lots of solute” “not much solute” “watery” Add water to dilute a solution; boil water off to concentrate it.

Making a Dilute Solution Timberlake, Chemistry 7 th Edition, page 344 initial solution remove sample diluted solution same number of moles of solute in a larger volume mix moles of solute

Concentration “The amount of solute in a solution” mol L M A. mass % = mass of solute mass of sol’n B. parts per million (ppm)  also, ppb and ppt – commonly used for minerals or contaminants in water supplies C. molarity (M) = moles of solute L of sol’n – used most often in this class D. molality (m) = moles of solute kg of solvent M = mol L % by mass – medicated creams % by volume – rubbing alcohol

Want to see what taking in a milligram per kilogram of your body weight amounts to? It’s the equivalent of 726 people, each weighing 150 pounds, sharing a chocolate bar (~50 grams). A part per million may be hard to comprehend or visualize. Want to see how much it is? A step in a journey of 568 miles. Or one minute in two years. Taking that further, a part per trillion is a million times smaller than that credit card on the football field, for example, or 6 feet out of a journey of six round trips to the sun (95 million miles one way to the sun). It’s a credit card lying in the middle of a football field.

How do you read volume? ~ ~ ~ ~ ~ ~ ~ ~ water in grad. cyl. mercury in grad. cyl. Measure to part of meniscus w/zero slope. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

How to mix a Standard Solution Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 480 Wash bottle Volume marker (calibration mark) Weighed amount of solute

How to mix a Standard Solution

Process of Making a Standard Solution from Liquids Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 483

How to mix a dilute solution from a concentrated stock solution Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Identify each volume to two decimal places (values tell you how much you have expelled) mL mL5.00 mL Reading a pipette

One mole, in solution. What do you call a tooth in a glass of water? - A one molar solution.

Dilution Math C = concentrate D = dilute Dilutions of Solutions  Dilution Equation: Concentrated H 3 PO 4 is 14.8 M. What volume of concentrate is required to make L of M H 3 PO 4 ? V C = L = 845 mL Acids (and sometimes bases) are purchased in concentrated form (“concentrate”) and are easily diluted to any desired concentration. **Safety Tip: When diluting, add acid or base to water.**

14.8M (0.845L) = 0.500M (25.00L) safety glasses Be sure to wear your safety glasses! 1. Measure out L of concentrated H 3 PO In separate container, obtain ~20 L of cold H 2 O. 3. In fume hood, slowly pour [H 3 PO 4 ] into cold H 2 O. 4. Add enough H 2 O until L of solution is obtained. How would you mix the above solution?

Yes; we’re OK. You have 75 mL of conc. HF (28.9 M); you need 15.0 L of M HF. Do you have enough to do the experiment? > mol HAVE1.50 mol NEED M C V C = M D V D 28.9 M (0.075 L) = M (15.0 L)

Dilution Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same.

Dilution What volume of 15.8M HNO 3 is required to make 250 mL of a 6.0M solution? GIVEN: M 1 = 15.8M V 1 = ? M 2 = 6.0M V 2 = 250 mL WORK: M 1 V 1 = M 2 V 2 (15.8M) V 1 = (6.0M)(250mL) V 1 = 95 mL of 15.8M HNO 3

Preparing Solutions How to prepare 500 mL of 1.54 M NaCl solution –mass 45.0 g of NaCl –add water until total volume is 500 mL 500 mL volumetric flask 500 mL mark 45.0 g NaCl solute

500 mL volumetric flask Preparing Solutions 500 mL of 1.54M NaCl 500 mL water 45.0 g NaCl –mass 45.0 g of NaCl –add water until total volume is 500 mL –mass 45.0 g of NaCl –add kg of water –1 kg = 1 L or 1000mL 500 mL mark 1.54m NaCl in kg of water molality molarity

Using Sucrose…C 12 H 22 O 11 How Many Grams in… 1.1 mole? 2.1M in 1L? 3.1M in 50mL? 4.2M in 50mL? 5.1.5M in 50mL? 342g 17.12g 34.24g 25.86g