PROPERTIES OF WATER Chapter 2.2

The Meniscus Effect Water molecules have the ability to stick to each other and their containers in a way that creates a concave or convex shape. WHY????

The Molecule…H 2 O In theory the water molecule is neutral. WHY Is It NOT???

The Characteristics of the Water Molecule Water has… –2 Hydrogen atoms attached to 1 Oxygen atom. –Two covalent bonds each one joining the 2 Hydrogen atoms to the oxygen atom –Good solubility properties –Good adhesion and cohesion abilities –Strong polarity

Hydrogen Bonds Because of waters partially positive and partially negative charges, polar molecules such as water can ATTRACT each other. The squiggly shape indicates partially (-) and partially (+) charges

Hydrogen Bonds Hydrogen bonds are not as strong as covalent or ionic bonds Hydrogen bonds are the strongest bonds that can form between two or more molecules. A single water molecule can have four hydrogen bonds

Water molecule = 4 H bonds

Polarity of H 2 O Oxygen has a stronger attraction for electrons compared to hydrogen. –WHY??? Oxygen will have the greater chance to have paired electrons around the atom. This gives H 2 O a bent shape. The oxygen side is partially negative and the hydrogen side is partially positive.

Bent Water Molecule

Polar Molecule A molecule in which the charges are unevenly distributed is called a Polar molecule. A polar molecule acts like a magnet with two opposite poles.

Is Water Polar? If yes why, If no why. A water molecule is Polar –There is an uneven distribution of electrons between the oxygen and hydrogen atoms. Which atom is negative Which atom is positive? The oxygen atom is partially negative and the hydrogen atoms are partially positive

Cohesion An attraction between molecules of the same substance. Because of hydrogen bonding water is extremely cohesive. Water’s cohesion causes molecules on the surface of water to be drawn inward. Reason why water beads on smooth surfaces.

Can Animals Walk on Water? If you're a little bug with big waxy feet (like the water strider in the figure), walking on water is a snap because the water acts like a taut elastic sheet. Water behaves this way because of surface tension or cohesion: the surface's tendency to contract. Water Strider

Adhesion An attraction between molecules of different substances. In a glass container, water will dip down in the center when you look at it eye level. –This happens because the adhesion between water molecules and glass molecules is stronger then the cohesion between 2 water molecules.

Adhesion and Cohesion

Adhesion & Capillary Action Capillary Action: Adhesion between water and glass also causes water to rise in a narrow tube against the force of gravity.

Mixture A material composed of two or more elements or compounds that are physically mixed together but NOT chemically combined. –Water is typically not pure, it is often found as part of a mixture. –Salt and pepper combined constitute a mixture –Earth’s atmospheric gases are constituted as a mixture

Solutions Mixture of two or more substances in which the mlcls. of the substances are evenly distributed. –Ex: Salt water mixture is a type of solution Solute- the substance that is dissolved Solvent- the substance in which the solute is dissolved into

Suspensions Mixture of water and non-dissolved particles –Ex: materials do not dissolve when placed in water but separate into pieces so small that they do no settle out. The movement of water mlcls keeps the small particles suspended.

Acids, Bases and pH Water molecules can react to form IONS. H 2 O  H + + OH -  Water  Hydrogen + Hydroxide  Ion Ion 1.1 water molecule in 550 million will form ions. 2.The number of positive hydrogen ions produced is equal to the number of hydroxide ions produced 3. Therefore water is neutral.

The pH Scale Used to indicate the concentration of hydrogen ions (H + ) in solution

Acids Any compounds that forms hydrogen ions (H + ) in solutions. Acidic solutions contain higher concentrations of H + ions than pure water and have pH values below 7. Strong acids between 1-3 –Ex: hydrochloric acid produced in the stomach

Bases Is a compound that produces hydroxide ions (OH - ) in solutions Basic solutions contain lower concentrations of H + ions than pure water and have pH values above 7. Strong bases have a pH range from 11-14

pH SCALE

Buffers They are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH. –pH fluid of most human cells must be kept between 6.5 and 7.5. –To maintain homeostasis human cells perform chemical reactions that produce buffers.

EXPLAIN: ACIDS-BASES Write a paragraph that explains how the concentration of hydrogen ions determines the acid-base properties of a solution.