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:
Dilution of Solutions
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
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
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 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
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.
ppm 1 inch in 16 miles ppb 1 inch in 16,000 miles ppt 1 sec = 32,000 years
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:
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
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
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
Identify each volume to two decimal places (values tell you how much you have expelled) mL mL5.00 mL Reading a pipette
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
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.**
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; 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)
One mole, in solution. What do you call a tooth in a glass of water? - A one molar solution.
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 500 mL mark 1.54m NaCl in kg of water molality molarity
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!
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.