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 H2O is attracted to

a partially negative O atom of another H2O 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