Chapter 3 Study Guide Dr. Joseph Silver

this chapter deals with - structure of water - the molecules which make up water - the properties of water - the uniqueness of water - acids, bases, pH, and buffers

WATER liquid at room temperature ¾ of earth’s surface covered by water polar covalent bond (see page 45 fig 3.2) water has 2 single covalent bonds water molecules bond to each other by hydrogen bonds water becomes or has cohesive – adhesive – high specific heat high heat of vaporization – low density of ice - high surface tension - universal solvent

each water molecule has 2 weak positive and 2 weak negative charges these charges attract water molecules and form weak hydrogen bonds – trillions of them – actually more - causing all water molecules to be attached to all of the other water molecules allowing water to have a high surface tension – a pin gently placed on water will float – a lizard can run across a pond – and insects can walk on water

the weak polar charges of water are attracted to other polar charges water makes polar surfaces wet meaning they interact with each other – they dissolve unlike non polar oils which form a ball and do not interact with water these charges allow water to climb up a capillary tube see fig 3.3

a gram of water can hold more heat (specific heat) than any other biologically active compound if the heat generated by the chemical processes which keep you alive were not removed your body would literally go up in flames water in your blood and sweat picks up this heat and brings it to the surface where it leaves through your skin and lungs

it takes more heat to evaporate 1 gram of water (high heat of vaporization) than any other biologically active molecule so water is able to remove large amounts of heat as sweat is evaporated from your body and blood vessels bring heat to your skin

a gallon of water weighs more than a gallon of ice ice is less dense than water that is why ice floats this is very important think about this

you live in upper Michigan it is 20 below zero the ice on the lake is really thick now what will happen if the ice gets thicker and thicker and sinks to the bottom of the lake YES all plants and animals in the lake just got crushed to death

as you walk on the ice covering the lake the air temperature is 20 below zero what is the temperature of the water under the ice? Since water freezes at 0 C or 32 F then the water below the ice is much warmer than the temperature of the air in the middle of winter the water can be 50, 60, 70 degrees warmer than the air the insulation of the ice preserves life in the lake

water is a universal solvent more things dissolve or get wet in water than any other molecule think of all the chemicals and molecules that are in your body which dissolve in water

here is a new word mole a mole is the weight of any substance in grams that corresponds to the atomic masses of all of the atoms in that molecule of that substance 1 mole of any substance contains 6.02 x molecules scientists use this information to know how much reactant and product are present

a calorie = the amount of heat needed to raise the temperature of 1 gram of water 1 degree Celsius at normal atmospheric pressure

temperature is the average kinetic energy of the molecules in a substance the faster they move the greater the temperature

molecular mass the sum of all of the atoms that make up a molecule H20 = 18 HCl = 18 H2SO4 = 48 C12H22O11 = mole of sucrose = 342 grams = 6.02 X10 23 = molar mass

in the lab we will use 1M sucrose and 1M HCl 1M sucrose is 342 grams of sucrose and enough water added until 1 liter is reached 1M HCl is 18 grams of HCl and enough water added until 1 liter is reached

molarity the number of moles of solute per liter of solution 3M HCl would be 18 x 3 = 54 grams of HCl and enough water added to equal 1 liter

if we have a glass of pure water what do we have in the glass?

if you said pure water that is a logical answer but it is not the correct answer

Look on page 51 and read the section under the drawing

In pure water, only one water molecule in every 10 million is dissociated; the concentration of each ion (H+ and OH-) in pure water is this means that there is 1/10,000,000 th of a mole of H + per liter of water and 1/10,000,000 th of a mole of OH - per liter of water 6.02 x x = 60,000 trillion

water can spontaneously split to form ions H 2 O splits to form H + and OH - H = a positive hydrogen ion (a proton) OH = a negative hydroxyl ion for every 10 million molecules of water 1 molecule splits into H and OH

1 out of 10 million is 1/10,000,000 or scientifically 10 -7

thus in pure water the concentration of H is and the concentration of OH is they are equal

what is an acid? a substance which adds H + ions to a solution if there are more H ions in a solution than OH ions then it is an acid

what is a base? a substance which add OH ions to a solution if there are more OH ions than H ions then it is a base

in pure water the H ions and the OH ions are equal so water is not a base nor is it an acid so pure water is neutral

because most people do not want to be speaking in scientific terminology like negative 6 or negative 12 scientists removed the negative attributes and called pure water where did the 7 come from from 1 part in 10 million

look at fig 3.10 the pH scale goes from 0 to 14 the amount of H and OH always adds up to 14 so at a pH of 4 the concentration of H is and the concentration of OH is remember minus 4 is more than minus 10

at a pH of the concentration of H is and the concentration of OH is minus 2 is much greater than minus 12

so an acid has more H than OH and a base has more OH and H and the farther away from 7 the more concentrated an acid or base becomes

pH is calculated on a log scale as you move 1 number (from 7 to 6 or 7 to 8) the concentration increased 10 times and as you move 2 numbers the concentration increases 10 x 10 or 100 times think back to math class and working with exponents

in your body you have many chemical processes which produce acids and bases your body in order to work efficiently must keep the pH of your body around 7.35 this is done by a series of chemicals known as buffers

buffers are compounds which when reacted with a base release an acid and when reacted with an acid release a base the goal is to keep the pH of the body optimum

HCl + NaOH  HOH + NaCl acid + base  water + salt a buffer releases H ions when a base is added or releases OH ions when an acid is added

the action of a buffer is to resist a change in pH in our bodies there are 2 important buffers carbonic acid and bicarbonate