8/17/2015 Miss Kennedy Properties of Water Section 2-2 pgs 40-43 The Water Molecule ● Like all molecules, a water molecules is neutral, because it has 10 protons and 10 ____________________ which balance each other out ● An ______________________ atom has a much stronger attraction for electrons than the hydrogen atom ● This is because it has a greater number of protons. ● Therefore, there’s a higher chance of finding shared electrons near the oxygen atom than near the hydrogen atom. ● The water molecule has a _____________ shape, meaning the oxygen atom is on one end of the molecule and the hydrogen atoms are at the other. ● As a result, the oxygen end of the molecule has a slight _________________________ charge and the hydrogen end of the molecule has a slight ___________________________ charge. ● A molecule in which the charges are unevenly distributed is called a ______________________ molecule because it’s like a magnet with poles. ● The water molecule is polar because, due to the difference in the number of protons, there is an uneven distribution of electrons between the oxygen and hydrogen atoms. ● The __________________________________________ is near the oxygen atom, and the ____________________________________________ is near the hydrogen atoms. ● Because they have partial positive and negative charges, polar molecules such as water can attract each other. ● The attraction between the hydrogen atom on one water molecule and the oxygen atom on another is an example of a ______________________________________________. ● Hydrogen bonds aren’t as strong as covalent or ionic bonds, but water’s ability to form as many as _____________________ hydrogen bonds at one time is responsible for many of its special properties. ● Two of these properties are called __________________________ and _________________________. 8/17/2015 Miss Kennedy ● _____________________________ is an attraction between molecules of the same substance. ● Because of hydrogen bonding, water is extremely cohesive, causing molecules on the surface of water to be drawn inward. ● This is why water forms beads on surfaces and also why many insects can walk on water. ● ___________________________________ is an attraction between molecules of different substances. ● If you’ve ever looked at water in a narrow tube, the surface of the water dips slightly in the middle. ● This is because the adhesion between the water molecules and _____________________ ___ __ _ _ _ _______________________ is stronger than the cohesion between water molecules. ● Adhesion can also cause water to rise in a narrow tube against the force of gravity. ● That effect is called __________________________________________________ and is one of the forces that draw water out of the roots of a plant and into its stems and leaves. ● Cohesion is also a part of capillary action, as it holds the column of water together as it rises. Solutions and Suspensions ● Water isn’t always pure, but is often found as part of a mixture. ● A _____________________________________ is a material composed of two or more elements that are physically mixed together but not chemically combined. ● Salt and pepper stirred together is an example of a mixture. ● Living things are in part composed of mixtures involving water. ● Two types of mixtures that can be made with water are ______________________________ and ___________________________________________. ● If a crystal of table salt is placed in a glass of water, sodium and chloride ions on the surface of the crystal are attracted to the polar water molecules. ● Ions then break away from the crystal and are surrounded by water molecules. 8/17/2015 Miss Kennedy ● The ions gradually become dispersed in the water, forming a type of mixture called a ________________________________________. ● In a saltwater solution, the table salt is the ________________________________, or substance that is dissolved, and the water is the ________________________________, or the substance in which the solute dissolves. ● Water’s polarity gives it the ability to dissolve both ionic compounds and other polar molecules, like sugar, making water the greatest solvent on Earth. ● However, some materials don’t dissolve when placed in water. ● Instead, these materials separate into pieces so small that they don’t settle out, and the movement of water molecules keeps the small particles suspended. ● The mixtures of water and nondissolved material are known as ___________________________. ● Some of the most important biological fluids are both solutions and suspensions. ● The ________________________ that circulates through your body is mostly water, which contains many ___________________________________________________________. ● However, blood also contains ________________________ and other _____________________ __________________________________ that remain in suspension as the blood moves through the body. Acids, Bases, and pH ● A water molecule can react to form both positive __________________________ (H+) and negative ______________________________ (OH-) ions. ● This happens with 1 molecule out of 550 million in pure water. ● Since the numbers of positive hydrogen ions produced is equal to the number of negative hydroxide ions, water remains neutral. ● With other solutions, this isn’t always the case. ● Chemists devised a measurement system called the __________________________________ to indicate the concentration of H+ ions in a solution. ● This scale ranges from 0 to 14, where 7 is a neutral solution. 8/17/2015 Miss Kennedy ● Solutions with a pH below 7 are called ____________________________ because they have more H+ ions than OH- ions. ● Solutions with a pH above 7 are called ____________________________ because they have more OH- ions than H+ ions. ● Each step on the pH scale represents a factor of __________. ● For example, a liter of solution with a pH of 4 has 10 times as many H+ ions as a liter of solution with a pH of 5. ● An ________________________ is any compound that forms H+ ions in a solutions. ● Acidic solutions contain higher concentrations of H+ ions than pure water and have pH values below 7. ● Strong acids, like hydrochloric acid, have pH values that range from ______________________. ● A ___________________ is a compound that produces hydroxide (OH-) ions in solution. ● Basic, or ________________________________, solutions contain lower concentrations of H+ ions than pure water and have pH values above 7. ● Strong bases, such as lye, tend to have pH values ranging from __________________________. ● If the pH in the human body goes lower than 6.5 or higher than 7.5, it will affect the chemical reactions that take place within the cells. ● Therefore, controlling pH is important for maintaining homeostasis. ● One of the ways that the body controls pH is through dissolved compounds called ________________________________. ● Buffers are ____________________ acids or bases that can react with ____________________ acids or bases to prevent sharp, sudden changes in pH.