1	Solubility Factors Science TAKS 9(D) What factors influence the solubility of a substance? C. Johannesson Communications Arts High School
2	Index Click on the headings below to jump to a specific section. Click on the home button in the lower-right corner of the screen to return to this page. TAKS Objective The Solution Process Factors Affecting Solubility Factors Affecting Rate of Dissolution
3	TAKS Objective Integrated Physics and Chemistry (9) Science Concepts. The student knows how solution chemistry is a part of everyday life. The student is expected to: (D) demonstrate how various factors influence solubility including temperature, pressure, and nature of the solute and solvent.
4	What is a solution? A solution is defined as… a homogeneous mixture of two or more substances in a single phase. Homogeneous means that… the mixture appears uniform because the particles of both substances are evenly interspersed. The phase of a solution may be… solid, liquid, or gas.
5	Components of a solution To keep these terms straight, remember the phrase, “The solute dissolves in the solvent.”
6	The Process of Dissolving The process of dissolving is called solvation, or when water is the solvent, hydration. STEP 1: Solvent is attracted to the solute. STEP 2: Solvent particles surround the solute particles and pull them into solution.
7	Dissociation vs. Decomposition Dissociation is the separation of ions that occurs when an ionic compound dissolves in water. It is a physical change. Note that this is not the same thing as decomposition, which occurs when a compound chemically breaks down into simpler substances.
8	What is Solubility? Solubility is defined as… the maximum amount of solute that can dissolve in a specific amount of solvent at a specific temperature. Example: 85 grams of KNO₃ will dissolve in 100 grams of water at 50°C.
9	Degree of Saturation A saturated solution contains the maximum amount of solute. Additional solute won’t dissolve. An unsaturated solution contains less than the maximum amount of solute. Additional solute will dissolve. A supersaturated solution contains more than the maximum amount of solute and is unstable. Additional solute causes rapid crystallization.
10	Factors Affecting Solubility TEMPERATURE Solubility curves show how the solubility of a solute changes with temperature. At high temperatures… solids are more soluble gases are less soluble Everyday Example Warm sodas fizz more than cold sodas when you open them because CO₂ gas is less soluble at higher temperatures.
11	Factors Affecting Solubility PRESSURE Henry’s Law - Gases become more soluble as the pressure above the solution increases. Everyday Example Opening a bottle of soda decreases the pressure inside the bottle. This decreases the solubility of CO₂ in the soda and results in the formation of bubbles, or fizz.
12	Factors Affecting Solubility NATURE OF SOLUTE AND SOLVENT Polar solutes dissolve well in polar solvents. Nonpolar solutes dissolve well in nonpolar solvents. Polar solutes do not dissolve well in nonpolar solvents and vice versa. This relationship is often expressed as, “Like dissolves like.” The solute and solvent must be alike in terms of polarity.
13	Like Dissolves Like “Like dissolves like,” but why? Polar molecules have positive and negative regions. Solute and solvent are both polar - The opposite charges help attract the particles to each other and solvation occurs. One polar, one nonpolar - There is no attraction between the particles and solvation does not occur. These substances are described as insoluble or immiscible.
14	“Like Dissolves Like” Everyday Example Water and grease are insoluble because water is polar and grease is nonpolar. Soap helps dissolve greasy stains because it contains a polar head and a long, nonpolar tail. The nonpolar tail mixes with the grease while the polar head mixes with the water…goodbye greasy stain!
15	Factors Affecting Rate of Dissolution Just as different factors affect the amount of solute that dissolves, there are also various factors that influence how quickly a solute dissolves. The factors affecting the rate of dissolution are… Temperature Agitation Surface area
16	Factors Affecting Rate of Dissolution TEMPERATURE Solutes dissolve faster at high temperatures. At high temperatures, solvent particles move faster and solvation occurs more quickly. Everyday Example When making sweetened iced tea, it is much easier to add the sugar while the tea is still hot. The hot temperature helps the sugar dissolve more quickly.
17	Factors Affecting Rate of Dissolution AGITATION Solutes dissolve faster when the solution is agitated by stirring or shaking. The solvent immediately surrounding the solute can quickly become saturated. Agitation helps bring fresh solvent into contact with the surface of the solute so that more solute can dissolve. Everyday Example When adding sugar to coffee, stirring helps the sugar dissolve faster.
18	Factors Affecting Rate of Dissolution SURFACE AREA Solutes dissolve faster when the surface area of the solute is increased by crushing it into smaller pieces. Solvation occurs at the surface of the solute. The greater the surface area, the more opportunities there are for the solvent to attack the solute. Everyday Example A sugar cube takes longer to dissolve in a cup of tea than an equal amount of granulated sugar.
19	Image Credits Solubility Curve "Solubility Curve" North Carolina Department of Public Instruction. 20 Jan. 2003 <http://www.ncpublicschools.org/curriculum/science/ Chemistry/solubil.htm> Henry’s Law Diagram, Soap Dissolving Grease Brucat, PJ. "CHM2041 Fall '97, Lecture 9, Solutions" University of Florida. 20 Jan. 2003 <http://itl.chem.ufl.edu/2041_f97/lectures/ lec_i.html> Saltwater Solution, Hydration of LiCl, Water Molecule, Soluble, Insoluble, Surface Area Davis, Raymond E., H. Clark Metcalfe, John E. Williams, and Joseph F. Castka. Modern Chemistry: Annotated Teacher's Edition. Austin: Holt, Reinhart and Winston, 2002.