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Solutions. 12.1 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent.

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Presentation on theme: "Solutions. 12.1 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent."— Presentation transcript:

1 Solutions

2 12.1 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount

3 Solutions Solvent: greater quantity (water) Solute: smaller quantity (sugar) Immiscible: two liquids do not mix miscible: two liquids can mix alcohol in water (in any quantities)

4 Parts of a Solution SoluteSolventExample solid liquid gassolid liquid gasliquid gas

5 A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature. A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate. 12.1

6 12.2 Three types of interactions in the solution process: solvent-solvent interaction solute-solute interaction solvent-solute interaction  H soln =  H 1 +  H 2 +  H 3

7 “like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l) 12.2

8 Concentration Units M = moles of solute liters of solution Molarity (M) Molality (m) m = moles of solute mass of solvent (kg) 12.3

9 Temperature and Solubility Solid solubility and temperature solubility increases with increasing temperature solubility decreases with increasing temperature 12.4

10 Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature 12.4

11 Pressure and Solutions P  Solubility  (gas in liquid) Henry’s law

12 Pressure and Solubility of Gases 12.5 The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law). c = kP c is the concentration (M) of the dissolved gas P is the pressure of the gas over the solution k is a constant (mol/Latm) that depends only on temperature low P low c high P high c

13 Calculating the solubility If we want to make an accurate prediction about whether something will dissolve in water or not, we need to know four key factors: 1the type of solute3the volume of solvent 2the mass of solute4the temperature We can say, for example, that the solubility of salt in water at 20 °C is 35 grams per 100 cm3 of water. This means that at 20 °C you can completely dissolve 35g of salt in 100cm3 of water. In general: Solubility = mass of solute / volume of solvent

14 How Much Will Dissolve? The table shows how much potassium nitrate (a type of fertiliser) and potassium chloride (the main ingredient in ‘Lo-Salt’) dissolve in water at different temperatures. The numbers tell you how many grams of solute dissolve in 100 cm3 water. Temperature (°C)Solubility of potassium nitrate Solubility of potassium chloride

15 Graph showing the solubility of potassium nitrate and potassium chloride.

16 Questions 1.How does the solubility of the substances change as the temperature changes? 2.Which substance is the most soluble at 10°C? 3.Which substance is the most soluble at 40°C? 4.Copy and complete this sentence: ‘As the temperature rises, the solubility …’ 5.Which of the two solids dissolves best a at 10 °C b at 40 °C? 6.Use your graph to estimate the solubility of potassium chloride at 55 °C

17 A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance. Colloid versus solution collodial particles are much larger than solute molecules collodial suspension is not as homogeneous as a solution 12.8

18 Suspensions These are mixed, but not dissolved in each other Will settle over time Particles are small Mayo


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