1.1.1. Explain the importance of water as a solvent in transport, including its dipole nature.

● Why is ice less dense than water?

● As the temperature of water decreases, the kinetic energy of the individual molecules decreases and the molecules slow down. ◦ This allows each molecule to form the maximum number of hydrogen bonds with other water molecules. ◦ The water molecule spread out or expand to accommodate more bond formation.

WATER PROPERTIES-SURFACE TENSION ● Why does water have high surface tension?

● Between water molecules hydrogen bonds are formed, these bonds pull the molecules down and together. ◦ There is no such attraction between the molecules where the water molecules and air meet. ◦ A water molecule layer holds together, forming a thin surface of skin tension.

WATER PROPERTIES-COHESIVE ● How are water molecules cohesive? ● What's an example of cohesion being a important property?

● Between water molecules, hydrogen bonds are formed, keeping the molecules together. ● For example, water moving up plant xylem. ◦ Long columns of water can be sucked up from roots to leaves without the columns of water breaking. ◦ This is due to hydrogen bonds keeping the water molecules together.

● How is water dipolar? What is the result of this? ● What two molecules make up water? What are their charges? ● Explain how water molecules bond to other water molecules. ● Draw how water molecules join together.

● It is the separation of slightly positive charge (hydrogen atom) and negative charge (oxygen atom) of water molecules which results the formation of hydrogen bonds to each other. ● A water molecule is made of two hydrogen each with a (+) charge and Oxygen with a (-) charge. ● The negative oxygen atom of one water molecule will attract the positive hydrogen atoms of other water molecules in a weak electrostatic attraction (a hydrogen bond). Even though each individual bond is weak, there are a great many of them.

● What makes water important? ● Draw a molecule of water.

● Water is the medium/reactants for reactions to take place (e.g. photosynthesis, reactions in living cells). It is a major habitat for some living organisms.

WATER PROPERTIES-THERMAL ● Why does water have a high melting and boiling point compared to other substances of a similar size? ● How are waters thermal properties crucial to living organisms?

● Water molecules have a high melting and boiling point compared to other substances of a similar size. ◦ It takes more energy to overcome the attractive forces of all the hydrogen bonds between the molecules. ◦ As there are usually many hydrogen bonds the weak bond overall is strong. ● Many living organisms need to maintain particular temperatures in order to optimise enzyme activity. ◦ The high water content of cells and tissues help them to maintain a constant temperature. In this way what are acts as the temperature buffer. ◦ The high melting and boiling point of water makes it useful for storing energy.

WATER PROPERTIES-SOLVENT ● What do ionic substances do in water and why? What are ionic substances? ● What do polar substances do in water and why? What are polar substances? ● What happens when non-polar substances are added to water? What are colloids? ● What are non-polar substances? ● What happens when insoluble substances are added to water? ● What are emulsions? What's an example of emulsions? ● What are suspensions? Give an example. ● What does amphoteric mean? How does water act as an acid? How does water act as a base?

◦ Chemical reactions within cells occur in water, the ability of water to act as a solvent is vitally important for the processes of life. These are due to waters dipole nature. ● For ionic substances, the positive and negative ions separate and become surrounded by water molecules, causing them to dissolve. ◦ Ionic substances: substances that are made up of positive and negative ions. ● Polar substance will not usually dissolve in organic solvents (e.g. Ethanol) but the will dissolve in water. ◦ Polar substances: compounds with covalent bonds, with small charges on parts of the molecule. ● Non-polar substances form colloids in water. ◦ Colloids: when solute particles are larger than the solvents, the solute particles spread through the water but doesn't separate out. ● Non-polar substances: are chemicals that do not form ions and are not charged. ● Insoluble substances in water form emulsions or suspensions. ● Emulsions: Tiny droplets of one liquid suspended in another liquid. ◦ Fats may be transported in the blood as emulsions of tiny fat droplets. They may be broken down for (e.g. digestion) into smaller, soluble molecules to be transported around the body. They are built back into insoluble molecules where these are needed (e.g. cell membrane). ● Suspensions: a solid mixed with a liquid, in which the particles will separate out (sink) if the mixture is not constantly moved/stirred. ◦ E.g blood is a suspension of cells and platelets in plasma. ● Amphoteric: means that water can act as either an acid or an alkali. ◦ Water molecules form H+ ions, is a proton donor. ◦ Water molecules form OH- ions, is a proton acceptor. ◦ The ability of water molecules to both donate and receive protons makes it an ideal medium for biochemical reactions occurring in cells. ◦ Water acts as a buffer, helping to prevent reactions in progress from changing the Ph inside the cell. Any excess H+ or OH- ions are mopped up.