BIOLOGY 111 1st Edition Lecture 4 Outline of Last Lecture I Continue Chemistry Review II Bonds III Chemical Reactions IV Properties of water Outline of Current Lecture I Moles II Molarity III Acids and Bases IV Organic Chemistry V Carbon VI Isomers Current Lecture Moles one mole is equal to 6 02 X 10 23 Avogadro s number For an Element a mole is the atomic weight expressed in grams For a Compound a mole is the formula or molecular weight in grams this is a standardized ratio of the number of molecules atoms per unit of weight that Represents an exact number of objects standardized in the same form that a dozen is a dozen regardless of what i e people tables chairs although 12 people are not equal in weight to 12 tables or 12 chairs the moles of one substance doesn t equal the moles of another substance in terms of weight grams Conversion to and from moles given the grams of a substance and knowing molar mass we can find the moles of a substance with the moles of a substance we use avogadro s number to find the number of atoms or molecules this process can be done in the reverse order as well knowing number of atoms molecules to find grams of a substance the practical advantage of measuring a quantity of chemicals in moles is that a mole of one substance has exactly the same number of molecules as a mole of any other substance It makes These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute it much more convenient for scientists working in a laboratory to combine substances in fixed ratios of molecules Ex say you have 5 5 moles of water To find the exact number of molecules you would multiply 5 5moles by avogadro s number 5 5moles X 6 02 X 10 23 molecules moles 3 31 X 10 24 molecules of water Ex 2 Suppose you have 25 grams of water You can find the number of moles for a similar situation as the first example by dividing the grams of water by the formula weight of the water compound weight of 2 hydrogens and 1 oxygen 25 grams water 18 015 grams water 1 39 moles water Know the molecular weight of hydrogen carbon oxygen and nitrogen for the test Molarity concentration is described as the number of moles of solute in a volume of solution Conc Mole Liter a solution has a concentration of 1 molar 1M if there is 1 mole of substance in 1 Liter of solution given glucose 180g and 1 Liter of solution how do you make 5M and 1M glucose o Since Concentration 5M moles Liter and you want to find moles you will multiply 5M by 1Liter to find discover there are 5 moles of glucose To find grams we need to convert the 5 moles by multiplying it by molar mass 180g So that 5mol X 180g 90 grams of glucose that was used o do the same steps above to make 1M glucose You should get 180 grams of glucose Water is composed of a ration between Hydrogen and Oxygen 2 grams of Hydrogen and 16 grams of Oxygen to equal roughly 18 grams of water if the proportion is changed you will not make the desired molecule for example 12 grams of Hydrogen and 4 grams of Oxygen will produce 18 grams but it will not be of water Occasionally water molecules dissociate and the hydrogen bond between two water molecules shift and cause the hydrogen atom to transfer with the product temporarily existing as Hydrogen ions a single proton with a charge of 1 H this will never exist on its own it will be represented as a hydronium ion Hydronium ions where there is an extra H on the water H2O molecule making H3O due these are acidic and also have a charge of 1 Hydroxide ions where there is one less H on the water H2O molecule making it OH these are basic and have a charge of 1 H and OH are very reactive and play a huge role Acid vs Base Acids a substance that increases the hydrogen ion concentration of a solution donate their extra H in aqueous solution Bases a substance that reduces the hydrogen ion concentration of a solution accept the H sometimes they donate themselves as OH in aqueous solution concentration Acidic H OH pH between 0 7 Neutral H OH pH around 7 Basic H OH pH between 7 14 pH affects many things including shapes and functions of molecules rates of chemical reactions molecules ability to bind to each other ions ability to dissolve in water pH log H s concentration if H concentration is 10 5 then log 10 5 will give you the pH value of 5 if pH is 5 then the H value is 10 5 M and the OH value 10 9 M Increasing Hydrogen will increase acidity Increasing Hydroxide will increase basicity decrease acidity Buffers a substance that minimizes changes in the concentration of H or OH in solution weak acids or weak bases that help solutions resist changes in pH this is important to prevent even the slightest deviation in our blood which could be lethal strong acids dissociate easily but hard to come back together weak acids don t dissociate easily but if they do can come back together easily to rise in pH will donate a proton hydrogen called a proton donor to drop in pH will accept a proton hydrogen called a proton acceptor For every change in pH by one unit the acidity changes by 10X Ex pH around 7 4 is dropped to 6 4 the 1 pH difference represents 10 times as many H ions Ex 2 pH of 3 and pH of 6 differ in acidity by a thousand 10 X 10 X 10 Acidification Ocean acidification When CO2 from the air dissolves in seawater it reacts to form carbonic acid which lowers ocean pH As seawater acidifies the extra hydrogen ions combine with carbonate ions to form bicarbonate ions reducing carbonate concentration Acid precipitation rain snow or fog with pH lower more acidic than 5 2 Chapter 4 Organic Chemistry study of molecules and compounds containing carbon abundant in all living things Urea is one of the most abundant b c discreted waste by living organisms Miller Urey experiment stimulated real atmosphere through a laboratory apparatus where they found the first few organic molecules CARBON can make 4 bonds with 4 valence electrons allowing formation of complex molecules usually single or double bonds can form non polar poorly water soluble and polar bonds more water soluble simplest being hydrocarbons hydrogen carbon o ex CH4 C2H6 o hydrocarbons can also have several complex structures because of carbons versatility o simple rearrangement of the same number and type of atoms will give you very different molecules o the molecular formula can provide several different molecular structures Nitrogen is also another common partner with carbon Isomers same