Chapter 8 Section 2 Solubility 2 WaterThe Universal

Chapter 8 Section 2

Solubility 2 Water—The Universal Solvent • A solution in which water is the solvent is called an aqueous (A kwee us) solution. • Because water can dissolve so many different solutes, chemists often call it the universal solvent.

Solubility 2 Molecular Compounds • When certain atoms form compounds, they share electrons. Sharing electrons is called covalent bonding. • Compounds that contain covalent bonds are called molecular compounds, or molecules.

Solubility 2 Molecular Compounds • If a molecule has an even distribution of electrons it is called nonpolar. • In a water molecule, the electrons spend more time around the oxygen atom than the hydrogen atoms. • Such a molecule is polar.

Solubility 2 Ionic Bonds • Atoms with a charge are called ions. • Bonds between ions that are formed by the transfer of electrons are called ionic bonds, and the compound that is formed is called and ionic compound. • Table salt is an ionic compound that is made of sodium ions and chloride ions.

Solubility 2 How Water Dissolves Ionic Compounds • Because water molecules are polar, they attract positive and negative ions. • The more positive part of a water molecule— where the hydrogen atoms are—is attracted to negatively charged ions.

Solubility 2 How Water Dissolves Ionic Compounds

Solubility 2 How Water Dissolves Ionic Compounds • The more negative part of a water molecule— where the oxygen atom is—attracts positive ions. • When an ionic compound is mixed with water, the different ions of the compound are pulled apart by the water molecules.

Solubility 2 How Water Dissolves Molecular Compounds • Water does dissolve molecular compounds, such as sugar, although it doesn’t break each sugar molecule apart. • Water simply moves between different molecules of sugar, separating them.

Solubility 2 What will dissolve? • When you stir a spoonful of sugar into iced tea, all of the sugar dissolves but none of the metal in the spoon does. • A substance that dissolves in another is said to be soluble in that substance. • You would say that the sugar is soluble in water but the metal of the spoon is insoluble in water.

Solubility 2 Like Dissolves Like • When trying to predict which solvents can dissolve which solutes, chemists use the rule of “like dissolves like. ” • Polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.

Solubility 2 Like Dissolves Like • On the other hand, if a solvent and a solute are not similar, the solute won’t dissolve. • For example, oil and water do not mix. • Oil molecules are nonpolar, so polar water molecules are not attracted to them.

Solubility 2 How much will dissolve? • Solubility (sahl yuh BIH luh tee) is a measurement that describes how much solute dissolves in a given amount of solvent. • The solubility of a material has been described as the amount of the material that can dissolve in 100 g of solvent at a given temperature. • When a substance has an extremely low solubility, it usually is considered insoluble.

Solubility 2 Solubility in Liquid-Solid Solutions • The solubility of many solutes changes if you change the temperature of the solvent. • For example, if you heat water, not only does the sugar dissolve at a faster rate, but more sugar can dissolve in it.

Solubility 2 Solubility in Liquid-Solid Solutions • This graph shows how the temperature of the solvent affects the solubility of some solutes.

Solubility 2 Solubility in Liquid-Gas Solutions • Unlike liquid-solid solutions, an increase in temperature decreases the solubility of a gas in a liquid-gas solution. • You might notice this if you have ever opened a warm carbonated beverage and it bubbled up out of control while a chilled one barely fizzed. • Carbon dioxide is less soluble in a warm solution.

Solubility 2 Saturated Solutions • A solution that contains all of the solute that it can hold under the given conditions is called a saturated solution. • If a solution is a liquid-solid solution, the extra solute that is added will settle to the bottom of the container. • It’s possible to make solutions that have less solute than they would need to become saturated. Such solutions are unsaturated.

Solubility 2 Saturated Solutions • A hot solvent usually can hold more solute than a cool solvent can. • If a saturated solution is cooled slowly, sometimes the excess solute remains dissolved for a period of time. • Such a solution is said to be supersaturated, because it contains more than the normal amount of solute.

Solubility 2 Rate of Dissolving • Some solutes dissolve quickly, but others take a long time to dissolve. • A solute dissolves faster when the solution is stirred or shaken or when the temperature of the solution is increased.

Solubility 2 Rate of Dissolving • These methods increase the rate at which the surfaces of the solute come into contact with the solvent.

Solubility 2 Concentration • The concentration of a solution tells you how much solute is present compared to the amount of solvent. • You can give a simple description of a solution’s concentration by calling it either concentrated or dilute. • A concentrated solution has more solute per given amount of solvent than a dilute solution.

Solubility 2 Measuring Concentrations • One way of giving the exact concentration is to state the percentage of the volume of the solution that is made up of solute.

Solubility 2 Measuring Concentrations • Labels on fruit drinks show their concentration. • Another way to describe the concentration of a solution is to give a percentage of the total mass that is made up of solute.

Solubility 2 Effects of Solute Particles • The effect that a solute has on the freezing or boiling point of a solvent depends on the number of solute particles. • When a solvent such as water begins to freeze, its molecules arrange themselves in a particular pattern.

Solubility 2 Effects of Solute Particles • Adding a solute such as sodium chloride to this solvent changes the way the molecules arrange themselves. • To overcome this interference of the solute, a lower temperature is needed to freeze the solvent.

Section Check 2 Question 1 Bonds between ions formed by the transfer of electrons are known as _______. Answer The answer is ionic bonds. “Ions” are atoms with a net charge, either positive or negative.

Section Check 2 Question 2 How does water dissolve ionic compounds? Answer When an ionic compound is mixed with water, the different ions of the compound are pulled apart by the water molecules.

Section Check 2 Question 3 The measure of how much solute will dissolve in a given amount of solvent is its _______. Answer The answer is solubility. If you have ever stirred too much sugar into a glass of water and had some left on the bottom, you have observed solubility.