Presentation on theme: "How to mix a Standard Solution"— Presentation transcript:
1How to mix a Standard Solution Use a VOLUMETRIC FLASK to make a standard solution of known concentrationStep 1> add the weighed amount of solute in the volumetric flaskStep 2> add distilled water (about half of final volume)Step 3> cap volumetric flask, and shake to dissolve solute completelyStep 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
2Process 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
3Markings on Glassware Beaker 500 mL + 5% Range = 500 mL + 25 mL Graduated CylinderVolumetric Flask500 mL mLRange = – mLTC 20oC “to contain at a temperature of 20 oC”22TD “to deliver”Ts“time in seconds”
4Concentration…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.
5A. mass % = mass of solutemass of sol’nB. parts per million (ppm) also, ppb and ppt-- commonly used for minerals orcontaminants in water suppliesC. molarity (M) = moles of soluteL of sol’n-- used most often in this classmolLMD. molality (m) = moles of solutekg of solvent
6WRONG7.85 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.
7What 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
8molLMHow 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 molA. What mass sodium hydroxide is this?B. What mass magnesium phosphate is this?
9Find molarity if 58.6 g barium hydroxide are in 5.65 L solution.
10You have 10.8 g potassium nitrate. How many mL of solution will make this a 0.14 M solution?convert to mL
11Concentration The amount of solute in a solution. Describing Concentration% by mass - medicated creams% by volume - rubbing alcoholppm, ppb - water contaminantsmolarity - used by chemistsmolality - used by chemists
12SAWS Water Quality Report - June 2000 ConcentrationSAWS Water Quality Report - June 2000
13Molalitymass of solvent only1 kg water = 1 L water
14MolalityFind the molality of a solution containing 75 g of MgCl2 in 250 mL of water.75 g MgCl21 mol MgCl295.21 g MgCl20.25 kg water= 3.2m MgCl2
15MolalityHow many grams of NaCl are req’d to make a 1.54m solution using kg of water?0.500 kg water1.54 mol NaCl1 kg water58.44 g NaCl1 mol NaCl= 45.0 g NaCl
16Molarity of Solutions Molarity of Solutions Molarity of Solutions