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Dilution of Solutions. Concentration = # of fish volume (L) Concentration = V = 1000 mL n = 2 fish Concentration = 2 fishar V = 1000 mL n = 4 fish [ ]

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Presentation on theme: "Dilution of Solutions. Concentration = # of fish volume (L) Concentration = V = 1000 mL n = 2 fish Concentration = 2 fishar V = 1000 mL n = 4 fish [ ]"— Presentation transcript:

1 Dilution of Solutions

2 Concentration = # of fish volume (L) Concentration = V = 1000 mL n = 2 fish Concentration = 2 fishar V = 1000 mL n = 4 fish [ ] = 4 fishar V = 5000 mL n = 20 fish [ ] = 4 fishar 1 fish 1 (L) Concentration = 1 fishar

3 V = 1000 mL n = 2 moles Concentration = 2 molar V = 1000 mL n = 4 moles [ ] = 4 molar V = 5000 mL n = 20 moles [ ] = 4 molar Concentration = # of moles volume (L) V = 250 mL n = 8 moles [ ] = 32 molar

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

5 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.

6 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

7 Concentration The amount of solute in a solution mol L M A. mass % = mass of solute mass of soln 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 soln – 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

8 Want to see what taking in a milligram per kilogram of your body weight amounts to? Its 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 (Editor's note: 95 million miles one way to the sun). Its a credit card lying in the middle of a football field.

9 ppm 1 inch in 16 miles ppb 1 inch in 16,000 miles ppt 1 sec = 32,000 years

10 Glassware

11 precise; expensive Range: Glassware – Precision and Cost beakervs.volumetric flask When filled to 1000 mL line, how much liquid is present? beaker 5% of 1000 mL = 50 mL volumetric flask 1000 mL mL 950 mL – 1050 mL mL– mL imprecise; cheap Range:

12 Markings on Glassware TC 20 o C to contain at a temperature of 20 o C TD to deliver T s time in seconds mL + 5%Range = 500 mL + 25 mL 475 – 525 mL Beaker Graduated Cylinder Volumetric Flask 500 mL mLRange = – mL 1000 mL + 5 mLRange = 1000 mL + 5 mL 475 – 525 mL

13 ~ ~ ~ ~ ~ ~ ~ ~ water in grad. cyl. mercury in grad. cyl. Measure to part of meniscus w/zero slope. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

14 How to mix solid chemicals Lets mix chemicals for the upcoming soap lab. We will need 1000 mL of 3 M NaOH per class. How much sodium hydroxide will I need, for five classes, for this lab? M = mol L 3 M = ? mol 1 L ? = 3 mol NaOH/class How much will this weigh? 1 23g/mol + 16g/mol g/mol MM NaOH = 40g/mol 40.0 g NaOH 1 mol NaOH X g NaOH = 15.0 mol NaOH = To mix this, add 120 g NaOH into 1L volumetric flask with ~750 mL cold H 2 O. Mix, allow to return to room temperature – bring volume to 1 L. FOR EACH CLASS: x 5 classes 15 mol NaOH 600 g NaOH

15 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

16 How to mix a Standard Solution

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

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

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

20 Dilution of Solutions Solution Guide Formula Weight Specific Gravity Molarity Reagent Percent To Prepare 1 Liter of one molar Solution Acetic Acid Glacial (CH 3 COOH) %57.3 mL Ammonium Hydroxide (NH 4 OH) %69.0 mL Formic Acid (HCOOH) %42.5 mL Hydrochloric Acid (HCl) %82.5 mL Hydrofluoric Acid (HF) %34.5 mL Nitric Acid (HNO 3 ) %63.0 mL Perchloric Acid 60% (HClO 4 ) %110 mL Perchloric Acid 70% (HClO 4 ) %85.5 mL Phosphoric Acid (H 3 PO4) %67.5 mL Potassium Hydroxide (KOH) %57.3 mL Sodium Hydroxide (NaOH) %85.5 mL Sulfuric Acid (H 2 SO 4 ) %51.5 mL M Conc. V Conc. = M Dilute V Dilute

21 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.**

22 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?

23 Yes; were 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)

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

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

26 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

27 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

28 500 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 500 mL mark 1.54m NaCl in kg of water molality molarity

29 Preparing Solutions 250 mL of 6.0M HNO 3 by dilution measure 95 mL of 15.8M HNO 3 95 mL of 15.8M HNO 3 water for safety 250 mL mark combine with water until total volume is 250 mL Safety: Do as you oughtta, add the acid to the watta!

30 Solution Preparation Lab Turn in one paper per team. Complete the following steps: A) Show the necessary calculations. B) Write out directions for preparing the solution. C) Prepare the solution. For each of the following solutions: 1) mL of 0.50M NaCl 2) 0.25m NaCl in mL of water 3) mL of 3.0M HCl from 12.1M concentrate.

31 Textbook Problems KeysKeys Textbook problems


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