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Solubility and Concentration. Chemistry Mrs. Coyle. Part I Solubility:. The ability of a solute to dissolve in a solvent. Expressed as g solute/100g H 2 O or g solute/100mL H 2 O. Soluble. • Soluble: a solute that has appreciable solubility. Miscible.
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Solubility and Concentration ChemistryMrs. Coyle
Part I Solubility: • The ability of a solute to dissolve in a solvent. • Expressed as g solute/100g H2O or g solute/100mL H2O
Soluble • Soluble: a solute that has appreciable solubility.
Miscible • Substances that dissolve in each other.
Types of Solutions • Saturated contains the maximum amount of solute that can be dissolved at the given conditions of T and P. • Unsaturated contains less than the saturated amount of solute. • Supersaturated contains more than the saturated amount of solute by dissolving at higher temp and then cooling.
A supersaturated solution crystallizes after a seed crystal is introduced. http://www.chem.ufl.edu/~itl/2045/change/C12F11.GIF
Rates of Solution • Does every candy you eat take the same time to dissolve?
Factors affecting the rate of dissolving: • Surface Area • Stirring • Temperature (average kinetic energy)
Factors Affecting Solubility • Temperature (affects solid, liquid and gaseous solutes) • Pressure (affects gaseous solutes)
Effect of temperature on solubility of gases. Example:Compare the amount of oxygen dissolved in the waters of the arctic ocean to the amount of oxygen dissolved in warm tropical waters.
Effect of temperature on solubility of solids. • Example: Can you dissolve more sugar in warm water or in cold water?
Effect of Pressure on solubility of solids. • Negligible.
Effect of Pressure on solubility of gases. • Henry’s Law: the amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution. • The higher the pressure the higher the solubility of the gas.
Effect of Pressure on solubility of gases. http://www.chem.ufl.edu/~itl/2045/lectures/lec_i.html
Example An unopened bottle of soda has a pressure of 5atm above the liquid, so the concentration of CO2 in the soda is high. Compare that to a pressure of 1 atm above the liquid when the bottle has been opened.
Part II Concentration: • A measure of the amount of solute dissolved in the solution. • Molarity (M) • Molality (m) • Mole Fraction (x) • Percent by Mass (%)
Part II • Concentration
Molarity • A unit of concentration of a solution expressed in moles solute per liter of solution. (Note: 1L = 1 dm3) Moles of Solute Molarity (M) = Liters of Solution
Why Molarity ? http://www.chem.ucla.edu/~gchemlab/volumetric_soln_conc.jpg
Steps involved in the preparation of a standard aqueous solution
Ex. 1 Molarity • What is the molarity of a solution of 8g NaOH in 100mL of solution? • Answer: 2M NaOH
Ex. 2 Molarity • How many grams of NaOH are contained in 2L of a 3M NaOH solution? • Answer: 240g NaOH
Making Dilutions • Moles Solute=M1V1=M2V2 • M molarity • V volume
Ex. 3 Dilutions • How many milliliters of 2.00M MgSO4 solution must be diluted with water to prepare 100.00 mL of 0.400M MgSO4? • Answer: 20.0mL
Percent by Mass % by mass= Mass of solute x 100 % Mass of solution
Percent by Volume % by volume= Volume of solute x 100 % Volume of solution
Molality • Moles of Solute per kilogram of Solvent Molality (m) = moles solute kg solvent
Mole Fraction xsolute = Moles of solute Moles of solution xsolvent = Moles of solvent Moles of solution xsolute + xsolvent= 1