Solubility and Solutions

CHEMISTRY Unit 5: Solubility and Solutions Many chemical compounds are stored, measured, and used in reactions as solutions. Recall the definition of a solution: Types of solutions: Solid solute Liquid solute Gas solute Consider: SOLUTION A homogenous mixture of solute and solvent. Common examples: eg. NaCl (aq) (salt in water) eg. H3PO4 (aq) (acid and water) eg. CO2 (aq) (carbonated water) Note: CO2 (g) + H2O (l) à H2CO3 (aq) (carbonic acid). This makes “pop” acidic. 5% alcohol solution SOLUTE alcohol SOLVENT water 90% alcohol solution water alcohol Recall the definition of concentration: The amount of solute in a given amount of solution. One of the most useful measurements of concentration is MOLARITY = MOLARITY number of moles of solute One litre of solution Or…a concentration unit giving the number of moles of solute in one litre of a solution. eg. 1 mole of HCl in 1 L of solution. NOTATION: [HCl] = 1 M. “A molar solution of HCl” Important note It is correct to say “the molarity is one molar” since: MOLARITY is a QUANTITY and MOLAR is the UNIT of Molarity. CHEMISTRY Unit 5: Solubility and Solutions Many chemical compounds are stored, measured, and used in reactions as solutions. Recall the definition of a solution: Types of solutions: Common examples: Solid solute Liquid solute Gas solute Note: CO2 (g) + H2O (l) à H2CO3 (aq) (________________________). Consider: SOLUTION SOLUTE SOLVENT 5% alcohol solution 90% alcohol solution Recall the definition of concentration: One of the most useful measurements of concentration is _____________________ MOLARITY = number of moles of solute One litre of solution Or…“a concentration unit giving the number of moles of solute in one litre of a solution”. eg. 1 mole of HCl in 1 L of solution. NOTATION: _______________________ “A (one) molar solution of HCl” Important note It is correct to say “the molarity is one molar” since: MOLARITY is a ___________ and MOLAR is the UNIT of ________. Sample MOLARITY calculations 1) What is the molarity of the solution produced by dissolving 4.0 moles of solute in enough water to make 2.0 L of solution? 2) How many moles of solute are contained in 2.0 L of a 5.0 M (“5 Molar”) solution? 3) Consider 3.0 L of a solution. Now imagine being able to look at the number of molecules contained in each litre of the solution: If the solution is a “7.0 M” solution, then each 1.0 L of of dissolved solute molecules. solution contains _______moles 4) What volume of a 1.2 M solution contains 4.8 moles of solute? 5) What is the molarity of a solution prepared by dissolving 117 g of NaCl in enough water to make 500. mL of solution? IMPORTANT LABORATORY TECHNIQUE: When preparing a solution, dissolve the solute COMPLETELY in a small amount of solvent first, by slowly adding solute in small quantities and continually swirling the mixture, and then “top off” with solvent until you have achieved the accurate final volume and molarity. 6) What is the concentration of a solution containing 6.35 mmoles in 10.00 ml? 7) A 655 mL solution of NaF contains 29.0 g of NaF. Find [NaF]. 8) How many grams of LiF are in 1.00L of a 2.00 M solution? 9) How much water is added to 6.0 moles of solute to make 2.0 L of a 3.00 M solution? CHEMISTRY Unit 5: Solubility and Solutions Many chemical compounds are stored, measured, and used in reactions as solutions. Recall the definition of a solution: A homogenous mixture of solute and solvent. Types of solutions: Common examples: Solid solute eg. NaCl (aq) (salt in water) Liquid solute eg. H3PO4 (aq) (acid and water) Gas solute eg. CO2 (aq) (carbonated water) Note: CO2 (g) + H2O (l) à H2CO3 (aq) (carbonic acid). This makes “pop” acidic. Consider: SOLUTION 5% alcohol solution 90% alcohol solution SOLUTE alcohol water SOLVENT water alcohol Recall the definition of The amount of solute in a given amount of solution. concentration: One of the most useful measurements of concentration is MOLARITY MOLARITY = number of moles of solute 1 litre of solution Or…a concentration unit giving the number of moles of solute in one litre of a solution. eg. 1 mole of HCl in 1 L of solution. NOTATION: [HCl] = 1 M. “A molar solution of HCl” Important note It is correct to say “the molarity is one molar” since: MOLARITY is a QUANTITY and MOLAR is the UNIT of Molarity. ANSWER to #9: We have no way of knowing how much water was added (if you refer back to the IMPORTANT LAB TECHNIQUE, you should know why). We know the final volume of the solution, but not the accurate volume of the solvent that the solute is added to. When water is added to a solution, the volume increases, but the number of moles of the solute(s) does not change. As water is added to the solution, however, the molarity of the solution decreases. In other words, you are DILUTING the solution when you add water (or any other suitable solvent). Solvents are suitable, if the polarity of the solvent matches the polarity of the solute.