Solutions, Acids, and Bases Ch 21 & 22

What is a solution? A solution is a mixture that has the same composition, color, density, and even taste throughout.

Solutes and Solvents To describe a solution, you may say that one substance is dissolved in another. The substance being dissolved is the solute, and the substance doing the dissolving is the solvent. When a solid dissolves in a liquid, the solid is the solute and the liquid is the solvent.

How Substances Dissolve Like the particles of any substance, water molecules are constantly moving. Also, water molecules are polar which means they have a positive area and a negative area. Molecules of sugar are also polar.

How Sugar Dissolves Moving water molecules cluster around the sugar molecules as their negative ends are attracted to the positive ends of the sugar molecules.

Water molecules pull the sugar molecules into solution.

Water molecules and sugar molecules spread out to form a homogeneous mixture.

Dissolving Gases Shaking or pouring a solution of a gas in a liquid causes gas to come out of the solution. An example of a solution of a gas dissolved in a liquid is a soft drink. Pressure and temperature affect how much gas is dissolved in the solution.

What affects the rate of solubility? Stirring – Stirring a solution speeds up dissolving because it brings more fresh solvent into contact with more solute. – The fresh solvent attracts the particles of solute, causing the solid solute to dissolve faster.

What affects the rate of solubility? Surface Area – Another way to speed the dissolving of a solid in a liquid is to grind large crystals into smaller ones. – Large crystals dissolve in water slowly because the amount of surface area is limited. – Increasing the amount of surface area by creating smaller particles increases the rate of dissolving.

What affects the rate of solubility? Temperature – Increasing the temperature of a solvent speeds up the movement of its particles. – This increase causes more solvent particles to bump into the solute. As a result, solute particles break loose and dissolve faster

How much can dissolve? If you continue adding sugar to lemonade, eventually the point is reached when no more sugar dissolves and the excess granules sink to the bottom of the glass.

How much can dissolve? Solubility is the maximum amount of a solute that can be dissolved in a given amount of solvent at a given temperature. The amount of a substance that can dissolve in a solvent depends on the nature of these substances.

Concentration A concentrated solution is one in which a large amount of solute is dissolved in the solvent. A dilute solution is one that has a small amount of solute in the solvent.

Types of Solutions A saturated solution is a solution that contains all the solute it can hold at a given temperature.

Types of Solutions An unsaturated solution is any solution that can dissolve more solute at a given temperature.

Types of Solutions A supersaturated solution is one that contains more solute than a saturated solution at the same temperature.

Particles in Solution Substances that dissolve in water to produce solutions that conduct electricity are called electrolytes. All ionic compounds are electrolytes when they are in a liquid state, or dissolved in water.

Dissolving Without Water Water cannot dissolve all solutes. Nonpolar solvents are needed to dissolve nonpolar solutes. Nonpolar materials have no separated positive and negative areas.

Vinegar-and-oil salad dressing has two distinct layers  the bottom layer is vinegar, which is a solution of acetic acid in water, and the top layer is salad oil.

Remember that water is polar, which means that the positive areas of the water molecules are attracted to the negative chloride ions. The water surrounds the charged ions with the oppositely charged end to separate the ion from the rest of the solute.

Solubility Curves Each line on the graph is called a solubility curve for a particular substance. You can use a solubility curve to figure out how much solute will dissolve at any temperature given on the graph. You need to know how to read a graph like this.

Solubility Curves According to the graph, in 100 g of water: a. at what temperature will 140 g of sodium chlorate dissolve? b. how many grams of potassium nitrate will dissolve at 60 °C

Acids Although some acids can burn and are dangerous to handle, most acids in foods are safe to eat. What acids have in common, however, is that they contain at least one hydrogen atom that can be removed when the acid is dissolved in water.

Properties of Acids An acid is a substance that produces hydrogen ions in a water solution. It is the ability to produce these ions that gives acids their characteristic properties.

Properties of Acids Acids have several common properties. All acids taste sour. Taste never should be used to test for the presence of acids. Acids are corrosive.

Bases You do not consume many bases. Some foods, such as egg whites, are slightly basic. Medicines, such as milk of magnesia and antacids, are basic, too.

Properties of Bases One characteristic of bases is that they feel slippery, like soapy water. Bases are important in many types of cleaning materials.

Properties of Bases Any substance that forms hydroxide ions, OH , in a water solution is a base. In addition, a base is any substance that accepts H + from acids.

Strong bases are corrosive, and contact with skin can result in severe burns. Therefore, taste and touch never should be used to test for the presence of a base.

Common Bases Some drain cleaners contain NaOH, which dissolves grease and small pieces of aluminum. The aluminum reacts with NaOH, producing hydrogen and dislodging solids, such as hair.

Strength and Concentration The terms strong and weak are used to classify acids and bases. The terms refer to the ease with which an acid ionizes or base dissociates in solution. Strong acids and bases ionize or dissociate completely; weak acids and bases ionize or dissociate only partially.

Strength and Concentration In contrast, the terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.

pH of a Solution The pH of a solution is a measure of the concentration of H + ions in it. The greater the H + concentration is, the lower the pH is and the more acidic the solution is. The pH measures how acidic or basic a solution is.

pH of a Solution Solutions with a pH lower than 7 are described as acidic.

pH of a Solution Solutions with a pH greater than 7 are basic.

Basic or Acidic or Neutral? pH of: – 8 – 14 – 9 – 2 pH of: – 3 – 6.9 – 1 – 7 Acidic Basic Neutral

Indicating pH An indicator is an organic compound that changes color in acid and base. For example, the indicator litmus paper turns red in acid. Bases react with indicators to produce changes in color. The indicator litmus turns blue in bases.