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How to mix a Standard Solution

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1 How to mix a Standard Solution
Use a VOLUMETRIC FLASK to make a standard solution of known concentration Step 1> add the weighed amount of solute in the volumetric flask Step 2> add distilled water (about half of final volume) Step 3> cap volumetric flask, and shake to dissolve solute completely Step 4> add distilled water to volume marker (calibration mark) The solution process may be exothermic (release heat). This may cause the liquid to show a larger volume than is real. Allow the solution to return to ambient (room) temperature and check volume again. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 480

2 Process of Making a Standard Solution from Liquids
Solutions can be made using liquids or solids (or gases). To make a 5% solution v/v (volume to volume) This means to add 5 mL of solute in 95 mL of solvent. The total is 5 mL / 100 mL or 5%. For the diagram add 25 mL of liquid solute and add water to bring volume to 500 mL (about 475 mL water). Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 483

3 Markings on Glassware Beaker 500 mL + 5% Range = 500 mL + 25 mL
Graduated Cylinder Volumetric Flask 500 mL mL Range = – mL TC 20oC “to contain at a temperature of 20 oC” 22 TD “to deliver” T s “time in seconds”

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

5 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 mol L M D. molality (m) = moles of solute kg of solvent

6 WRONG 7.85 kg KCl are dissolved in 2.38 L of solution. Find molality. 24.8 g table sugar (i.e., sucrose, C12H22O11) are mixed into 450 g water. Find molality.

7 What mass of CaF2 must be added to 1,000 L of water
so that fluoride atoms are present at a conc. of 1.5 ppm? = 3.34 x 1028 m’cules H2O

8 mol L M How many moles solute are required to make 1.35 L of 2.50 M solution? mol = M L = 2.50 M (1.35 L) = 3.38 mol A. What mass sodium hydroxide is this? B. What mass magnesium phosphate is this?

9 Find molarity if 58.6 g barium hydroxide are in 5.65 L solution.

10 You have 10.8 g potassium nitrate.
How many mL of solution will make this a 0.14 M solution? convert to mL

11 Concentration The amount of solute in a solution.
Describing Concentration % by mass - medicated creams % by volume - rubbing alcohol ppm, ppb - water contaminants molarity - used by chemists molality - used by chemists

12 SAWS Water Quality Report - June 2000
Concentration SAWS Water Quality Report - June 2000

13 Molality mass of solvent only 1 kg water = 1 L water

14 Molality Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

15 Molality How many grams of NaCl are req’d to make a 1.54m solution using kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

16 Molarity of Solutions Molarity of Solutions Molarity of Solutions

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