Chapter 23 Solutions

How Solutions Form What is a solution? A solution is a mixture that has the same composition, color, density, and even taste throughout. To describe a solution, you can say that one substance is dissolved in another. – Solute: The substance being dissolved. – Solvent: The substance doing the dissolving. Examples: – Salt water – salt is the solute and water is the solvent. – Carbonated drinks – carbon dioxide gas is one of the solutes and water is the solvent. When a solid dissolved in a liquid, the solid is the solute and the liquid is the solvent. When a liquid dissolved in another liquid, the substance present in the larger amount is usually the solvent.

How Solutions Form Solutions can also be gaseous or even solid. – Ex: Air – 78% nitrogen, 21% oxygen, 1% other gases. – Ex: Sterling silver: 92.5% silver, 7.5% copper. Solid solutions are known as alloys. – Alloys are made by melting a metal solute and solvent together.

How Solutions Form The dissolving of a solid in a liquid occurs at the surface of the solid. How do water solutions form? Two reasons: 1.Water molecules are constantly moving. 2.Water molecules are polar. – Polar: Having separate positive and negative areas; polar materials attract water molecules and dissolve easily in water (i.e. salt and water).

How Solutions Form There are several things you can do to speed up the rate of dissolving: – Stirring: Speeds up the process because it brings more fresh solvent into contact with more solute. – Reducing Crystal Size: Breaking the solid into smaller pieces greatly increases its surface area. And since dissolving takes place at the surface of the solid, more surface area allows more solvent to contact more solute. Surface Area of a Cube = 2(h × w) + 2(h × l) + 2(w × l) – Increasing the 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.

How Solutions Form Can these factors combine to further increase the rate or perhaps control the rate of dissolving? Yes – when two or more techniques are combined, the rate of dissolving is even faster.

Solubility and Concentration 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. – Expressed in grams of solute per 100 grams of solvent or grams per liter of solution. The amount of solute that can dissolve depends on the nature of the substances. The amount of solute that is dissolved in a given quantity of solvent is called concentration. – Concentrated Solution: A large amount of solute is dissolved in the solvent. – Diluted Solution: A small amount of solute is dissolved in the solvent. Concentrations are typically given in percent by volume of the solute. – Ex: Fruit-Flavored Drinks – Range from 10% to 100% fruit juice.

Solubility and Concentration There are three basic types of solutions: – Saturated Solutions: A solution that contains all the solute it can hold at a given temperature. In general, as the temperature of a liquid solvent increases, the amount of solid solute that can dissolve also increases (Solubility Curve). – Unsaturated Solutions: Any solution that can dissolve more solute at a given temperature. Each time a saturated solution is heated to a higher temperature, it becomes unsaturated. – Supersaturated Solutions: A solution that contains more solute than a saturated solution at the same temperature. Supersaturated solutions are unstable (Ex: Rock Candy).

Solubility and Concentration Some liquids are infinitely soluble in each other. – Ex: Water and Ethanol Pairs of liquids such as these are said to be completely miscible. – Miscible: Describes liquids that dissolve in one another in all proportions. – The liquid present in the larger amount is usually considered the solvent. Liquids that are insoluble in one another are immiscible. – Ex: Oil and water.

Solubility and Concentration Solutions of gases behave differently from those of solids or liquids. Increasing the pressure of a gas over a liquid can increase the amount of gas that dissolves into the liquid. – Ex: Carbonated drinks. Another way to increase the amount of gas that dissolves in a liquid it to cool the liquid. – This is why you refrigerate carbonated beverages after opening – to keep the CO 2 in the beverage.

Particles in Solution What is an atom with a positive or negative charge called? Ion: Charged particle that either has more or fewer electrons than protons. Ions in your body help transmit messages. Compounds that produce solutions of ions that conduct electricity in water are known as electrolytes. – Strong electrolytes conduct a strong electric current (sodium chloride). – Weak electrolytes conduct a weak electric current (vinegar). When you drink Gatorade, Powerade, etc., you are replacing the vital electrolytes that your body loses through sweat during exercise. – Without electrolytes, your body cannot transmit messages, which leads to cramping, fatigue, etc. – Electrolytes in Gatorade = Sodium, Potassium, Chloride Should you always drink Gatorade during/after exercise? No – For most athletes, water is just fine. Gatorade is really only useful in replenishing electrolytes in athletes that exercise longer than 60 to 90 minutes. Why? Sodium and potassium are plentiful in your diet.

Particles in Solution Substances that form no ions in water and cannot conduct electricity are called nonelectrolytes. – Ex: Sucrose and Ethyl Alcohol. Ionic solutions form in two ways: – Ionization: Process by which electrolytes dissolve in water and separate into charged particles. Ex: Hydrogen Chloride and Water. – Dissociation: Process in which an ionic compound separates into its positive and negative ions. Ex: Sodium Chloride and Water.

Particles in Solution All solute particles – polar and nonpolar, electrolyte and nonelectrolyte – affect the physical properties (i.e. freezing/boiling point) of the solvent. Adding a solute to a solvent lowers the freezing point of the solvent. – This works because as the substance freezes, the particles arrange themselves in an orderly pattern. With solute particles interfering with the formation of this pattern, the solvent freezes at a lower temperature. – Ex: Antifreeze, adding salt to the roads in the winter, animals (Caribou/Fish/Insects).

Particles in Solution Adding a solute to a solvent also raises the boiling point of the solvent. – This occurs because the particles of the solute interfere with the evaporation of the solvent particles, thus more energy is needed for the solvent particles to escape from the liquid surface. – Ex: Antifreeze, adding salt to water when cooking.

Dissolving without Water Water if often referred to as the universal solvent because it can dissolve many things. – Water is polar = it has positive and negative ends. Nonpolar substances have no separated positive and negative and do not dissolve in water. – Nonpolar substances share their electrons equally. – Ex: Oil, mineral oil, gasoline, turpentine, etc. Polar and nonpolar substances do not mix. Some substances form solutions with polar as well as nonpolar solutes because their molecules have polar and nonpolar ends. – Ex: Ethanol (alcohol) General Rule = Likes dissolve Likes

Dissolving without Water Nonpolar substances have many drawbacks: – Ex: Flammable and toxic. Soaps are substances that have polar and nonpolar properties. – They are salts of fatty acids, which are long hydrocarbon molecules with a carboxylic acid group –COOH at one end. Soap has an ionic end that will dissolve in water and a long hydrocarbon portion that will dissolve in oily dirt.

Dissolving without Water Vitamins can be polar or nonpolar. – Nonpolar vitamins can dissolve in fat and do not wash away with the water that is present in the cells throughout your body, so they can accumulate in your tissues. Some fat-soluble vitamins are toxic in high concentrations. Ex: Vitamin A, vitamin D, vitamen E, and niacin. – Polar vitamins dissolve in water and do not accumulate in tissue because any excess vitamin is washed away with the water in the body. Ex: Vitamin B and C