Chapter 6 3

Chapter 6-3 NWRC BIO 30

Water’s Polarity • Water is a "polar" molecule, meaning that there is an uneven distribution of electron density. Water has a partial negative charge near the oxygen atom due the unshared pairs of electrons, and partial positive charges near the hydrogen atoms.

Water’s Polarity • An attraction between the partial positive charge near the hydrogen atoms and the partial negative charge near the oxygen results in the formation of a hydrogen bond as shown

Mixtures with Water • A Solution is a homogenous mixture (homo means same so a homogenous mixture is uniform throughout ) • 2 components of a mixture are the SOLVENT and the SOLUTE

Mixtures with Water • Heterogeneous Mixtures are not the same throughout – hetero means different • A suspension is a type of heterogeneous mixture – where one substance is suspended in another

Mixtures with Water • Another type of Heterogeneous Mixtures is a colloid • are mixtures with characteristics part way between a solution and a suspension. Colloidal dispersions may appear homogeneous but are actually heterogeneous. Colloidal dispersions do not settle when left standing undisturbed for a period of time. Paint is a colloid because it is made of tiny particles of color that float in a liquid instead of dissolving in it.

What’s the Solution? Acid or Base Understanding pH

Chemistry • Chemicals can be grouped by their properties. • One of these properties is pH, which tells you whether a substance is an acid, a base, or between an acid and a base called a neutral.

What is pH? • The p stands for potential, or power. • The H stands for the chemical symbol for hydrogen. • The pH of a solution is how acidic or basic it is.

Acids and Bases • Acids: – Acids are a group of sour chemicals. They contain hydrogen. When a food tastes sour, it usually contains an acid.

• Bases: – Bases are the opposite of acids. They contain a hydroxide ion, and feel slippery or soapy. Bases in food have no strong taste.

Neutralization • All acids release H+ into solution (and all bases release OH-). acids and bases counteract each other. This idea, that a base can make an acid weaker, and vice versa, is called neutralization. • Neutralization: acids release H+ into solution and bases release OH-. If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water: • H+(aq)+ OH-(aq) H2O • The neutralization reaction of an acid with a base will always produce water and a salt.

Water and pH •

All substances are made up of millions of tiny atoms. These atoms form small groups called molecules. In water, for example, each molecule is made up of two hydrogen atoms and one oxygen atom. The formula for a molecule of water is H2O. "H" means hydrogen, "2" means 2 hydrogen atoms, and the "O" means oxygen.

Acids and Bases in Water •

When an acid is poured into water, it gives up H (hydrogen) to the water. When a base is poured into water, it gives up OH (hydroxide) to the water.

The pH scale • pH is measured On a scale from 014. • pH levels from 0-6 is acidic. • pH levels from 8-14 is basic. • pH of 7 is neutral.

pH Facts: • As acids get stronger, pH gets lower. A pH of 1 is a very strong acid. • As bases get stronger, pH gets higher. A pH of 14 is a very strong base. • Can you think of some foods that might be a base or an acid? (remember, acids taste sour, bases don’t have much of a taste)

Why is pH important? • Both humans and aquatic (water) organisms depend on water. • The pH of water must be within a range of 5 to 9 in order for organisms to survive. • Waters with a pH less than about 5 are too acidic for humans to drink and cannot allow most aquatic life to survive. Low pH can also cause the pipes our water comes out of to wear away. • Waters that are too basic can also harm humans, plants, and animals. Water with a pH of greater that 9 can dissolve materials such as animal scales and skin.

Why do pH levels change? • pH can be affected by the chemicals in the water. • The pH of water affects organisms living in the water. A changing pH in water can mean that there is an increase of pollution or some other environmental factor. • Things such as burning fossil fuels (like with cars), mining, chemical spills, runoff (washing cars and farming), and sewage cause pH levels to change.

• It’s very important that the pH levels of water don’t increase or decrease too much out of a certain range. • This change could affect food chains and the survival of species.

Examples of pH levels • Water: should be between 5 and 9 for most aquatic organisms to live. • Algae: grow best between 7.5 and 8.4. • Acid Rain: 1-3, battery acid: 0 • Aquatic bacteria can live in a pH level between 2 and 13 and plants between 6 and 13. Organisms such as carp, catfish, bass, bluegill, snails, clams, mussels and trout can be found in pH levels between 6 and 9.

Page 165 - Assessment • 1. Water’s ability to increase and decrease hydrogen ions helps maintain PH

Page 164 - Assessment • 2. As a polar molecule electrons in hydrogen atom bonds are closest to the oxygen atom creating a negative charge that attracts positive ions in solutions

Page 164 - Assessment • 3. Hydrochloric acid – acidic pH2. • Water –neutral ph7 • Sodium hydroxide – basic – ph14

Page 165 - Assessment • A solution is a liquid that contains a dissolved substance -- a solid, liquid, or gas. The solvent is the liquid in which the substance is dissolved. The solute is the substance dissolved in the liquid. Solutions do not have to be liquid. There are solid solutions, such as glass, and gaseous solutions, such as air.