CHE 104 Chapter 13 Dr. Mark Shuman
Solutions • A solution is a homogeneous mixture of two or more substances. – If I look at any microscopic portion of the solution, it will have the same composition as any other portion. • A solution contains a solvent and one or more solutes. • The solvent determines the state of the solution. – If the solvent is a gas, the solution is a gas. – If the solvent is a liquid, the solution is a liquid. – If the solvent is a solid, the solution is a solid.
Solutions (cont.) • The solvent can be a gas, a liquid or a solid. • The solute(s) can be gaseous, liquid or solid.
Solutions (cont.) • It is necessary to specify the solution composition. – i.e. we must specify the relative amounts of solvent and solute in a solution. • There are many ways to specify solution composition – Molarity (M) – Molality (c m ) – Mole fraction ( ) – Mass % – And others
Molarity (M) • Molarity of a solute, A • M A = n soluteA /V solution • “moles of solute per liter of solution” – Solution volume typically depends on temperature so molarity should be specified for a given temperature.
Molality (c m ) • Molality of a solute, A – c mA = n soluteA /kg of solvent – “moles of solute per kilogram of solvent” – Moles of solute and mass of solvent are temperature independent so molality is temperature independent.
Mole Fraction ( ) • Mole Fraction of a solute, A – A = n soluteA /n total here n total = total moles of solution. – Moles are temperature independent so mole fraction is temperature independent.
Mass Percent • Mass % of a solute, A – % A = (mass A /mass solution ) * 100 – Mass is temperature independent so mass % is temperature independent.
Problem • Assume you add 1.2 kg of ethylene glycol, HOCH 2 CH 2 OH, as an antifreeze to 4.0 kg of water in the radiator of your car. What are the mole fraction, molality and weight percent of the ethylene glycol?
Problem • You dissolve 1.0 mol of urea, H 2 NCONH 2 , in 270 g of water. What are the mole fraction and molality of the urea?
Problem • Suppose you dissolve 2.56 g of succinic acid, C 2 H 4 (CO 2 H) 2 , in 500. mL of water. Calculate the molality, mole fraction and weight percent of acid in the solution.
Problem • What mass of Na 2 CO 3 must you add to 125 g of water to prepare 0.200 m (molal) Na 2 CO 3 ?What is the mole fraction of Na 2 CO 3 in the resulting solution?
Problem • Concentrated sulfuric acid has a density of 1.84 g/mL and is 95% by weight H 2 SO 4 . What are the molality and molarity of this solution?
Solubility • If a solute is soluble in a solvent at any composition. – The solute and solvent are said to be miscible . • If a solute is not soluble in a solvent at any composition. – The solute is said to be insoluble in that solvent.