 Compounds can be mixed together to create solutions ◦ Solutions are mixtures in which one or more substances are uniformly distributed in another substance ◦ Made from two major components:  Solute: what is dissolved  Solvent: liquid doing the dissolving

 How can we measure the strength of solutions?  Concentration of a solution = the amount of solute dissolved in a solution 100mL 100mL 100mL 100mL 100mL 10g 20g 30g 40g 50g

 pH scale measures the acidity or basicity of a solution  0-14

 Acids: ◦ pH < 7 ◦ Has many H+ions ◦ Ex: HCl (stomach acid), milk  Bases: ◦ pH > 7 ◦ Has many OH- ions (less H+ ions) ◦ Ex: Blood (7.4), Ammonia (11.5)  Neutral: pH = 7 (water)

 Oxygen and hydrogen are held together by covalent bonds  But electrons are NOT shared equally ◦ Oxygen has 8 protons to attract the electrons shared by H & O ◦ Hydrogen only has 1 proton to attract the electrons  Oxygen hogs electrons!

 Water is a POLAR molecule ◦ All characteristics of water are due to its polarity  What does “polar” mean? ◦ A polar molecule has a partially negative end and a partially positive end ◦ From unequal sharing of electrons in covalent bond  Oxygen is partially negative because hog electrons  Hydrogen is partially positive because usually without any electrons

 Remember: opposites attract!  Hydrogen bond ◦ Type of van der Waals force ◦ Partially positive H atom of one H 2 O is attracted to a partially negative O atom of another H 2 O  Between two DIFFERENT water molecules ◦ Weak bond ◦ Occurs between water molecules and between water molecules and other polar molecules

 Creates cohesion of particles ◦ Like particles attract each other (water to water)

 Surface tension: ◦ Created by cohesion ◦ Prevents the surface of water from breaking

 Creates adhesion ◦ Attractive forces between different substances ◦ Ex: water sticking to the sides of a graduated cylinder

 Allows for capillary action ◦ Combination of adhesion & cohesion ◦ Water is pulled up through narrow tubes

 Moderate temperature ◦ Water must gain or lose large amounts of energy (heat) to break/form the hydrogen bonds for any temperature change. ◦ Why is this important?  Helps organisms maintain homeostasis  Helps moderate climate/ocean water temperature

 Ice is less dense than water  Atoms slow down when cold ◦ Allow for more H bonds to form ◦ H bonds separate water molecules

 This means that ice floats!  Why is this helpful to living organisms? ◦ Does not freeze solid – allow creatures to live under ice ◦ Insulates water – maintains stable temperature

 Bozeman Water Bozeman Water