hello everyone and welcome back to your online video lecture in this video we will be focusing on water and why it's so crucial and beneficial to life we'll touch on the four emergent properties of water solutions and concentrations and will finish off with acid-base chemistry for this chapter's objectives students will model and categorize the fundamentals of molecular structure and functions associated with living organisms in particular students will describe molecular polarity and ionization as an influence on molecular interactions and fundamental organization in solutions and cells and students will model and relate molecular ionization related to acids bases and ph to understand the significance of water we need to go back 4.4 billion years researchers oscillate between water originating on earth with the hydrogen inside our planet playing a role in the formation of the oceans and the idea that water was delivered to earth by impacts from icy objects from space our earth was formed 4.54 billion years ago and the origin of water is murky at best what is clear is that water became a prominent component of the biosphere shortly after the birth of our earth and that there was an almost instantaneous emergence of life the hydrothermal vents in the deepest depths of the ocean is where the story of life begins these deep sea vents harbored the conditions conducive to the emergence of primordial life forms that gave rise to all life on earth it's no wonder we have an entire chapter dedicated to water water not only makes life possible on earth it created life on earth as oceans were the birthplace of life water's properties are quite suitable to the continuation and support of living organisms water exists in three phases on earth solid liquid and gas in fact water is the only common substance to exist in the natural environment in all three of these physical states of matter here is a phase diagram of water along the y-axis is pressure and along the x-axis is temperature we see the freezing point at one atmosphere which is where we are at we see the freezing point at one atmosphere of pressure highlighted at zero degrees celsius and the boiling point is shown at 100 degrees celsius water's unique emergent properties arise from the structure of the water molecule which determines how it interacts with other molecules in the last lecture we learned about the various types of bonds polar covalent nonpolar covalent hydrogen and van der waals forces check out my video if you need a refresher when introducing the polar covalent bond we discussed water as a great example within the water molecule the electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen this is due to the unique electronegativities of these atoms electronegativity is an atom's affinity for electrons the larger the electronegativity number the more that atom will hog the electrons being shared within the bond oxygen is highly electronegative while hydrogen has a low electronegativity this large difference in electronegativity causes electrons to gather around the oxygen creating partial charges denoted by the lower case greek letter delta remember electrons have a negative charge while protons have a positive charge the electronegative oxygen carries a partial negative charge due to the accumulation of electrons while the hydrogen carries a partial positive charge because the two o h bonds are polar covalent in nature the water molecule is a polar molecule in which the overall charge is unevenly distributed with the electrons favoring the oxygen atom this polarity of the water molecule results in a new type of bond called a hydrogen bond hydrogen bonds are a weak type of intermolecular bond in which the partially charged hydrogen atom of one polar molecule is attracted to the partially negative atom usually oxygen or nitrogen of another molecule water is special because of this polarity and the resulting hydrogen bonds the hydrogen bonds are like an intermolecular glue that attracts the water molecules and holds them together this property of water leads to the occurrence of four special emergent properties which contribute to earth's suitability for life they are cohesive behavior the ability to moderate temperature expansion upon freezing and versatility as a solvent the first emergent property is cohesion and adhesion of water molecules we just learned about those hydrogen bonds that act like a glue between the water molecules collectively this results in a phenomenon called cohesion you may have witnessed cohesion when you over pour a glass of water and liquid seems to dome above the surface of the glass this is due to something called surface tension which is the measure of how difficult it is to break the surface of a liquid water has an unusually high surface tension due to hydrogen bonding between the molecules at the air water surface and to the water below again this is all due to those hydrogen bonds surface tension is also the reason why small insects may walk on water cohesion also helps to transport water molecules against gravity in plants have you ever wondered how water taken in at a tree's roots gets all the way up to the top of a tall tree in this example we see the water being taken up by the root via a process called osmosis we'll learn more about this in a later chapter the water molecules within the tree's xylem are in contact with each other and thus are forming hydrogen bonds at the top of the tree the leaves are losing water due to high temperatures through evaporation this is called transpiration which is actually good for the tree because it helps it to cool down the loss of water molecules at the top creates a difference in hydrostatic pressure and the water molecules will want to move up the tree to replace the ones that were just lost this creates another negative hydrostatic pressure down at the roots which allows for more water to be absorbed the hydrogen bonds between all the water molecules act as a chain holding them together so that when water molecules at the top want to rise they will pull up at the molecule below them however this process also involves something called adhesion adhesion is an attraction between different substances for example between water and plant cell walls in this case the adhesion is occurring between the water molecules and the bark of the tree's inner xylem so note that cohesion is between two water molecules while adhesion is between two different substances so it could be a water molecule and something else emergent property number two is the moderation of temperature for this one we need to revisit our oceans did you know that oceans absorb 90 percent of all heat that humans are adding into the atmosphere in fact 2019 was the hottest year recorded for our world's oceans john abram an engineering professor specializing in thermal sciences at the university of st thomas stated it's about five hiroshima bombs of heat every second day and night 365 days a year environmental scientists warn of the dangers of the warming oceans as this accelerates the melting of ice shelves affecting marine mammal migration patterns fishery stocks and coral reefs and contributes to more intense storm systems sea water has high density and can hold four times more heat than air for example one degree celsius change in the ocean's temperature would be equivalent to a 000 degrees celsius change in our atmosphere because of this ocean warming is a more accurate way to measure how hot the world is getting than air temperature air temperature might be hot one year and cooler than next but water is denser than air and takes longer to heat and cool now you might be wondering how the oceans absorb all of that heat without evaporating well of course there is a cycle of evaporation and rainfall however water can absorb or release a large amount of heat with only a slight change in its own temperature and can you guess what gives water this unique quality of course the answer is hydrogen bonds the hydrogen bonds formed between the water molecules are able to absorb some of that heat because of this water absorbs heat from warmer air and releases stored heat to cooler air you may have witnessed this on a cool morning off a lake the lake absorbs the heat beating down from the sun all day then in the morning when the temperature has dropped heat is released back into the air and you can see it coming off the lake this is the moderation of temperature but what even is temperature what do we mean when we say heat we need to cover the second major type of energy to answer this question energy occurs in many forms including chemical energy thermal energy electromagnetic radiation gravitational energy electric energy elastic energy nuclear energy and rest energy these can be categorized into two main classes potential and kinetic energy in the last chapter we covered potential energy which is the energy due to location or structure kinetic energy is the energy of motion as an example this archer has fully drawn the bow back and is holding it at this position which has a high potential energy now the archer may release the arrow which will convert that potential energy into kinetic energy as the tension from the bow launches the arrow through the air when talking about chemistry the kinetic energy associated with random motion of atoms or molecules has its own name called thermal energy probably heard of this word before it simply describes molecules and atoms in motion we use the word temperature to describe this thermal energy temperature represents the average kinetic energy of the molecules in a body of matter when thermal energy is transferred from one body of matter to another we define it as heat nearly 66 percent of the chemical energy that we ingest from food is actually lost as heat which is why you can feel warmth emanating from yourself and other living organisms and speaking of chemical energy and heat what is a calorie we use calories as our measure of energy in the food we eat but do you know what it actually means a calorie which is lower case cal is the amount of heat required to raise the temperature of one gram of water by one degrees celsius so let's get a visual for this this black spoon is filled with one gram of water remember gram is a measure of mass one gram of water is equivalent to the volume one centimeter cube or we say one cubic centimeter which is also equivalent to one milliliter of water cubic centimeter and milliliter are both ways to express a volume so grams is a mass while the other two are a volume so one calorie is the amount of energy required to raise this gram of water by one degree celsius it's also the amount of heat released when one gram of water cools by one degree celsius now that was calories with the lowercase c the capital c calories that we see on food packages are actually kilocalories which is kcal looking at our table of units we see that kilo is 1000 times greater than the base unit so a kilocalorie is 1000 lowercase c calories the joule represented by a capital j is another unit of energy one joule equals 0.239 lowercase c calories or one calorie equals 4.184 joules you'll see joules used more in chemistry and physics class related to calories is the property of specific heat the specific heat of a substance is the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by one degree celsius this sounds a lot like the definition of a calorie right furthermore the specific heat of water is one calorie so why is the specific heat of water the definition of one calorie you have to remember that all of these units in science that we use to measure things are man-made they're created as a means to help scientists quantify scientific phenomena scientists need to identify a standard which we can use to quantify everything else and water is often that standard this is also why one gram of water equals one cubic centimeter and one milliliter this is not true of all substances let's look at the specific heat of another substance ethanol ethanol is alcohol that you would find in beer or wine ethanol specific heat is 0.59 calories this is much lower of a specific heat than water this means it takes less energy or calories to heat ethanol if you've ever used wine or beer in a cooking recipe you've seen this in real life the alcohol cooks off and evaporates much faster than water water resists changing its temperature because of its high specific heat and water's high specific heat can be traced to hydrogen bonding and this is because of the ability for hydrogen bonds to absorb and release energy heat is absorbed when hydrogen bonds break and heat is released when hydrogen bonds form another way to say this is to break bonds we need to add heat to them all of the water molecules in the ocean are held together by a net of hydrogen bonds which absorb the heat radiating down from the sun they will only break when they've absorbed enough heat at which point that water molecule will evaporate away having absorbed enough thermal energy to transform from liquid to gas in this way the high specific heat of water minimizes temperature fluctuations to within limits that permit life and this is related to evaporation evaporation or also referred to as vaporization is transformation of a substance from liquid to gas now of course there are thousands of different liquids that exist and each will require a different amount of heat to turn it into a gas we call this the heat of vaporization specifically heat of vaporization is the heat a liquid must absorb for one gram to be converted to gas just like with specific heat and calories we are using one gram as our mass measure as i mentioned scientists like to standardize measuring units our bodies utilize the heat of vaporization of water for a process called evaporative cooling we all know sweating is the primary means of thermoregulation for humans a mechanism we've adapted to cool us down but how does it work well that sweat sits atop of your skin where it begins to absorb heat from your body this heat is converted to thermal energy eventually those water molecules gain enough energy and reach their heat of vaporization at which time they will convert from a liquid to a gas as that liquid evaporates taking away the heat and energy from your body the surface that it leaves will cool down this process is called evaporative cooling in this way evaporative cooling of water helps stabilize temperatures in organisms and bodies of water we perspire and if you recall trees have their own version of this called transpiration the third emergent property of water is the floating of ice on liquid water a quick trip back to elementary school science and you might remember that buoyancy or floating has to do with density let's shine a light on density the density of a substance is the mass per unit of volume in other words d equals m over v let's use these two sponges as an example both sponges have the same mass of 100 grams however the bottom sponge has been squeezed to create a smaller volume the top has a volume of 100 cubic centimeters while the bottom has a volume one-tenth of that to just 10 cubic centimeters now we can calculate the densities and they are one gram per centimeter cubed and 10 grams per centimeter cubed the top sponge has a lower density than the bottom sponge because that mass is spread out over a greater volume ice floats in liquid water because hydrogen bonds in ice are more ordered which forces them to spread out making ice less dense than liquid water in this image you can see the ice molecules have formed a crystal lattice structure and they are highly organized and have no motion so there's no kinetic energy here in comparison the image on the right shows liquid water whose molecules contain thermal energy so they are in motion molecules are also much closer together than the ice molecules the crystal lattice structure in ice is able to form because there is a lack of thermal energy no heat so no motion so these bonds are more stable the liquid water bonds on the other hand have more thermal energy and motion so these molecules are continuously forming and breaking those hydrogen bonds ice floats because freezing causes expansion and an increased volume and this lowers the density when we heat ice and it melts the volume decreases which increases the density and let's just think about this for a minute what would happen if ice didn't float what would happen if it sank well if ice continuously sank leaving liquid water at the top of a water source there would be a cycle of freezing and sinking until the entire body of water was frozen this would kill all life because ice floats an entire ecosystem of wildlife is able to flourish under the frozen lakes and oceans like this krill here and not just that have you ever seen the thermohaline circulation system imagine if this global conveyor belt of water which drives our temperatures and weather patterns was blocked by a chunk of frozen waters due to ice sinking if ice sank all bodies of water would eventually freeze solid making life impossible on earth the fourth and final emergent property of water is water's ability to act as a solvent of life let's shine the light on a few important terms before we continue when we talk about mixtures we mean a thing that contains two or more substances in any given ratio the mixtures are then classified by their homogeneity and we can have completely mixed partially mixed or not mixed at all we have either homogeneous or homogeneous mixtures or heterogeneous mixtures a completely homogeneous mixture is called a solution and this means that their components cannot be distinguished by the naked eye heterogeneous mixtures on the other hand can be distinguished and their mixtures include colloids and suspensions among other things in a mixture the solvent is the dissolving agent of a solution the solute is the substance that is being dissolved so just remember the solvent dissolves the solute an aqueous solution is a special type of solution in which water is the solvent if you've ever been told to gargle salt water after losing a tooth in adding salt to water you've created an aqueous solution water is the solvent and salt is the solute remember water is a polar molecule due to the polar covalent bonds and this makes water very versatile as a solvent here's another term for you like dissolves like essentially water being a polar solvent will easily dissolve any polar atoms or molecules this includes anything with a charge when an ionic compound like the sodium chloride shown here is dissolved in water each ion is surrounded by a sphere of water molecules called a hydration shell notice how the partially positive hydrogen of the water molecule is interacting with the negatively charged chlorine ion while the partially negatively charged oxygen of the water molecule is interacting with the positively charged sodium ion in this image we see that water can also dissolve compounds made of non-ionic polar molecules the purple entity is a protein which is made of amino acids we'll get to amino acids in a later chapter but for now just note that they can carry a negative or positive charge on them this allows them to be dissolved by water in a solution and this makes sense right what is the majority of your intracellular fluid and blood made of water we are 71 water our proteins need to be able to dissolve in our body remember like dissolves like even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions this brings us to a very important concept in cellular physiology which is hydrophilic and hydrophobic substances it's very simple a hydrophilic substance is one that has an affinity for water a hydrophobic substance is one that does not have an affinity for water and let's break down those words hydro comes from the greek hydra meaning water and filos meaning loving it literally means water loving hydrophobic also comes from the greek word hydro for water and the greek phobos meaning fearing so hydrophobic means water fearing hydrophilic molecules the water loving substances are anything that is polar or charged on the other hand hydrophobic molecules tend to be nonpolar such as oil molecules which have relatively non-polar bonds we'll learn more about this in chapter 5 when we discuss the macromolecules let's do a quick recap water is the molecule that supports all life there are four emergent properties of water which lend to its benefits one adhesion and cohesion are an attraction between water and another substance or water in itself cohesion also results in surface tension which allows insects to walk on water two moderation of temperature water can absorb a large amount of heat with only slight changes in temperature this is due to water's high specific heat which is the number of calories needed to raise one gram of a substance by one degree celsius water has a specific heat of one the specific heat of a substance also leads to its heat of vaporization the heat a liquid must absorb for one gram to be converted to a gas our bodies use this in sweat and evaporative cooling three floating of ice on liquid water which is due to the lower density of ice if ice sank all bodies of water would eventually freeze and four water is the solvent of life it is highly soluble due to its polarity light dissolves like so water will dissolve hydrophilic substances substances with polar or ionic regions water will not dissolve hydrophobic substances the chemical characteristic of water that lends to these four emergent properties is the polarity of water which is a result of the polar covalent bonds and leads to special bonds called hydrogen bonds now would be a good time for a quick break the remainder of this lecture is going to focus on calculating different types of solute concentrations and acid-base chemistry alright so this is a biology lecture but we do still need to cover some chemistry biology is chemistry brought to life and we would be nothing without the trillions of chemical reactions taking place as part of our metabolism as i mentioned we are mostly water so most of our chemical reactions involve solutes dissolved in water which makes us one giant aqueous solution there are three ways that we can calculate solute concentrations but before we do let's shine the light on a few terms we are going to use mass to calculate the number of solute molecules in an aqueous solution remember molecules are tiny there's no way that we could actually count the individual molecules of a solution if we were working in a lab but by using something called the molecular mass we can quantify the solute and accomplish this molecular mass is the sum of all masses of all the atoms in a molecule makes sense right molecular mass we learned about daltons in the last chapter as the unit to represent mass of an atom because a gram is just too large well there's a little bit more to this numbers of molecules are actually usually measured in moles where one mole which is mol equals 6.02 times 10 to the 23rd molecules this is called avogadro's number and is a huge number think of a mole the way you think of a dozen a dozen is always 12 and a mole is always 6.02 times 10 to the 23rd i can have a mole of sodium atoms i can have a mole of glucose molecules i can have a mole of students and this does relate back to daltons avogadro's number and the unit dalton were defined such that 6.02 times 10 to the 23rd daltons equals one gram in other words one mole of daltons equals one gram the mole was defined in such a way that the molar mass of a compound in grams per mole is numerically equal for all practical purposes to the average mass of one molecule in daltons thus for example the average molecular mass of water is about 18.0153 daltons and the molar mass of water is about 18.0153 grams per mole i know this can get a little confusing when you look at the periodic table the number you see represents both the atomic mass in daltons and the molar mass in grams per mole so to calculate the molecular mass of a molecule let's use salt nacl as an example looking at the periodic table i see that the atomic mass of sodium na is 23 and chlorine is 35 cl nacl the compound contains one sodium and one chlorine so i add these two molar masses together to calculate the molecular mass of 58 grams per mole so if i have one mole 6.02 times 10 to the 23rd molecules of salt i would have a mass of 58 grams let's do one more glucose glucose is c6h12o6 looking at the periodic table i see the molar mass of carbon is 12.01 the molar mass of hydrogen is 1.01 and the molar mass of oxygen is 16. this is a larger molecule there are 6 carbons 12 hydrogens and 6 oxygens so we need to multiply the molar mass by the number of atoms for each element so you can see in this table six carbons times 12 grams per mole because each carbon has a mass of 12 grams per mole 6 times 12 equals 72 grams per mole 12 hydrogens times one gram per mole equals 12 grams per mole and six oxygens times 16 grams per mole is 96 grams per mole sum these numbers to reach a total molecular mass of 180 grams per mole for glucose so one mole of glucose that's 6.02 times 10 to the 23rd molecules of glucose has a mass of 180 grams we need to understand how to calculate the molecular mass in order to understand the first method of calculating solute concentration which is molarity molarity which is represented by that capital m is the number of moles of solute per liter of solution to illustrate molarity let's walk through a problem if you dissolve 174 grams of nacl in one liter of water what will be the concentration of that salt solution in molarity with word problems always begin with writing down what you know and calling out what you need to know what we know is that the solute is salt nacl and we have 174 grams of it for our solution volume we have one liter of water the problem is asking for the concentration of this salt solution in molarity capital m so i also want to write out the formula for molarity capital m equals moles over liter i'll also write the molar mass equals grams per mole okay so we need to figure out capital m molarity this means we need to figure out how many moles of salt we have and how many liters of solution well we actually already know this one we have one liter of water so i will fill this in we don't have to do any other calculating for this but we do have to convert that 174 grams of salt into moles so how can we accomplish this luckily we also wrote down that the molar mass is in grams per mole we have grams total grams but how many moles of salt is this for this we have to visit the periodic table and fetch the molar masses for sodium and chlorine n a sodium's mass is 23 grams per mole while cl chlorine's mass is 35 grams per mole we already calculated the molecular mass for sodium chloride before it's 23 plus 35 which gives us a total of 58 grams per mole so one mole of sodium chloride has a molecular mass of 58 grams how many moles does 174 grams equate to for this just set up a quick stoichiometry problem remember with these that the units always have to cross out so we have 174 grams we're going to multiply this by a fraction we're going to use the molar mass grams per mole but because those grams have to cross out we're going to do one mole over 58 grams and see now grams can be crossed out 174 divided by 58 equals three and the unit we have left over is mole we have three moles of sodium chloride so plug this into the molarity equation 3 moles divided by 1 liter is a 3 molar solution try to figure out this on your own how many grams of salt do you need to use to make 2 liters of a 1.5 molar salt solution i'll put the answer at the end of the video there are two other ways to measure solution concentration we have the percent solution and the mass to volume ratio in a percent solution it is always in grams of solute per milliliters of solvent times 100 so for example what is the percent solution if you have three grams of salt in a 150 milliliter amount of water three grams of salt divided by 150 mils times 100 equals two so this is a two percent salt solution and finally in the mass to volume ratio this uses any mass of solute and divided by any volume of solvent for example if you have a solution of three thousand milligrams in one thousand milliliters of water three thousand milligrams divided by one thousand milliliters will give you a mass to volume ratio of three migs per ml or three milligrams per milliliter and always remember your units here are a few more practice problems for percent solutions and mass to volume ratio pause the video and give them a try all of what we've learned so far in this chapter leads us to acid-base chemistry we all have experiences with acids and bases in our daily lives for example we use them daily for cooking and cleaning our bodies also strategically use acids and bases for metabolism and homeostasis acidic and basic conditions are a crucial aspect of an organism's biochemistry and environment so let's define them as a heads up there are actually a number of ways to define an acid and a base we are going to use the bronsted-lowry definition there are also the lewis system and arrhenius theory a bronsted-lowry acid is a substance that increases the h plus concentration of a solution while a bronsted-lowry base is a substance that reduces the h plus concentration of a solution let's revisit hydrogen for a moment recall that hydrogen is a proton in the nucleus with one orbiting electron again an acid is a substance that increases the h plus concentration of a solution an h plus is a positively charged hydrogen which means a proton without the electron for this reason acids are also called proton donors and conversely if a base is a substance that reduces the h plus concentration of a solution bases are proton acceptors so do you think water is an acid or a base this is a bit of a trick question a hydrogen atom in a hydrogen bond between two molecules of water can shift from one to the other when this happens the hydrogen atom leaves its electron behind and is transferred as a proton or hydrogen ion h plus the molecule that lost the proton is now a hydroxide ion which is o h minus it has a negative charge because it has one more electron than protons now the molecule with the extra proton is now a hydronium ion h3o plus though it is often represented as that h plus ion so when we say h plus we're actually referring to h3o plus so is water an acid or a base it's actually both it is both a proton donor and proton acceptor water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed for this reason concentrations of h plus and o h minus are equal in pure water when talking about acids and bases we can have strong acids or weak acids this just means how easily they dissociate or break apart and release that proton strong acids dissociate completely in water weak acids reversibly release and accept back hydrogen ions but can still shift the balance of h plus and oh minus away from neutrality another way of defining acid-base chemistry is with the arrhenius system an arrhenius acid is a substance that dissociates in water to form hydrogen ions or protons while an arrhenius base is a substance that dissociates in water to form hydroxide ions o h minus adding certain acids and bases to a solution modifies the concentration of h plus and o h minus more h plus corresponds to higher acidity while more o h minus corresponds to lower acidity and higher basicity we use the ph scale to describe whether a solution is acidic or basic so let's crunch some numbers if we have any aqueous solution at 25 degrees celsius which by the way that's room temperature the product of h plus and o h minus is constant and can be written as the concentration of h plus times the concentration of o h minus equals 10 to the negative 14. for this annotation brackets in chemistry and biochemistry mean concentration so we'd say the concentration of h plus times the concentration of o h minus and you would immediately say 10 to the 14 what there are no units here well these concentrations are a molarity capital m so it would it should say 10 to the negative 14 molar so let's just say my solution contains solely water nothing else if the concentration of h plus and the concentration of o h minus are equal in water as we said before what are the respective concentrations in pure water h plus equals ten to the negative seven and o h minus equals ten to the negative seven when we multiply exponents we add those exponent numbers so seven plus seven equals fourteen now that was for pure water all other solutions will have other h plus and o h concentrations though they will still all have a constant product when you multiply them of 10 to the negative 14 molar so that is the concentration of ions in solutions how do we translate this in an easy to read ph scale we use this formula the ph of a solution is defined by the negative logarithm of the concentration of hydrogen ions written as ph equals negative log concentration of h plus so for a neutral aqueous solution of pure water we've already determined that the h plus concentration is 10 to the negative 7 molar so the ph equals the opposite of the log of 10 to the negative seven which equals seven so the ph of water is seven you do need a calculator that is capable of performing logarithms for these things but there is a trick and we'll get to that in a second the ph scale runs from 0 to 14. acidic solutions have ph values less than seven while basic solutions have ph values greater than seven most biological fluids have ph values in the range of six to eight human blood for example falls around a ph of 7.4 we see right in the middle at ph 7 is our neutral friend water and notice how the concentration of hydrogen ions is equal to the concentration of hydroxide ions o h minus now you'll also notice here that the concentration of h plus is greater than the concentration of o h minus for acidic solutions and for bases it's reversed the concentration of h plus ions is lower than the concentration of o h minus ions remember this formula concentration of hydrogen ions times the concentration of hydroxide ions equals 10 to the negative 14. here we see a representation of hydrogen ions in comparison to hydroxide ions in a solution notice at neutral ph 7 the concentrations are the same at the low ph ranges to the left we see higher concentrations of h plus and gradually lower concentrations of oh minus the opposite is true if we move to the right the hydrogen ion concentration drops it plummets while the o h minus rises we can see that the h plus concentrations along the top and the o-h concentrations along the bottom 10 to the 0 is actually 1. so the top left shows the highest concentration of h plus for acids at 1 molar if you need a quick refresher on exponents every time we see 10 with an exponent in front of it there is actually a 1 so it is 1 times and then your exponent 10 to the negative 1 1 times 10 to the negative 13. when you see a negative number this is telling you to move the decimal to the left and if you see a positive number after that exponent it's telling you to move it to the right so for 10 to the negative 1 which is 1 times 10 to the negative 1 we move the decimal to the left 1 space which gives us 0.1 for 10 to the negative 10 which is 1 times 10 to the negative 10 we move the decimal to the left 10 times so don't let the large number next to the 10 fool you the larger the negative exponent the smaller that number becomes so back to our formula the concentration of hydrogen ions times the concentration of hydroxide ions equals 10 to the negative 14. we can see this is true using the table that i drew up here the rows we have are ph concentration of hydrogen ions concentration of hydroxide ions and poh if ph equals negative log of the concentration of hydrogen ions poh equals the negative log of the concentration of hydroxide ions but it's really quite simple look at ph 11 for the full column filled in if a solution has a ph of 11 the concentration of hydrogen ions is 10 to the negative 11. you just take that ph and you set that as the negative exponent we want the exponents to add up to 14 right 10 to the negative 14 divided by 10 to the negative 11 you would do 14 minus 11 which is 3. so the concentration of hydroxide ions is 10 to the negative 3. if the concentration of hydroxide ions is 10 to the negative 3 then the poh is 3 and look at ph plus poh that equals 14 always make a chart like this and fill them in it's really good practice and it's an easy way to understand acids and bases without having to understand logarithms and all the math that goes on beneath it and one final thing this ph scale is called a logarithmic scale specifically it's using a logarithm to the base of 10 this means between the each ph value so if we take a ph of 0 and a ph of 1 there's actually a difference of 10 fold or 10 times the concentration the difference between ph 0 and ph 2 is 10 times 10. so this is actually a 100 fold difference or 100 times difference in concentration with the ph of 0 having a 100 times greater concentration of hydrogen ions than the ph of 2. for a little bit of practice what is the ph of a solution containing 1 times 10 to the negative 5th molar of hydrogen ion what is the ph of a solution containing 1 times 10 to the negative 8 molar hydroxyl ion and what is the fold difference in hydrogen ion concentration between solution a which is has a ph of 4 and solution b which has a ph of 9. the last thing we need to discuss is buffers the internal ph of most living cells is close to seven and it's vital that they remain that way buffers are just substances that have the ability to minimize change in concentrations of h plus and oh minus in a solution most buffer solutions contain a weak acid and its corresponding base which combine reversibly with hydrogen ions in the example we see here carbonic acid which is h2co3 is a type of weak acid formed from the dissolving of carbon dioxide in water bicarbonate which is hco3 is the deprotonated form of carbonic acid bicarbonate serves a crucial biochemical role in our ph buffering system by helping to maintain a healthy physiological ph it works by either accepting a proton to become carbonic acid or donating a proton to become carbonate so that's it for our water chapter we covered a lot we covered the emergent properties of water we talked about solutions and we even got into a little bit of acid-base chemistry in the next chapter we will be diving into carbon and the crucial role that it plays in building biological molecules for us