in order to understand the biochemistry which takes place within our own bodies the nature and health of aquatic systems in our lakes and oceans and the chemistry of our air to name only a few applications we need to understand the nature of chemical reactions involving the hydrogen ion and the hydroxide ion this is acidbase chemistry and can be described as proton transfer reactions this is the hydrogen atom has lost one electron and therefore can also be described as a lone proton thus the characterization as proton transfer these reactions involve the movement of a hydrogen ion or a proton from one species to another and are extremely important in understanding the natural world in this video we will examine the nature of proton transfer and how this this describes acidbase Behavior we'll also cover some of the theories defining acids and bases the Swedish chemist Sante arenus recognized the critical role that the hydrogen ion and the hydroxide ion played in aquatic systems and described acids and bases relative to the liberation of a hydrogen ion by an acid and a hydroxide ion by a base over time this definition limited the number of substances that could be identified as an acid or base and it became clear that substances that did not fit the arenus description influenced acidbase properties as a result Johannes brownstead and Martin Lowry developed the widely accepted view of acids and bases that can be viewed as proton transfer reactions the brownstead Larry theory states that acids are proton donors and bases are proton acceptors therefore acids and bases must come in pairs this proton transfer affects the concentrations of the hydrogen and hydroxide ions and the acid base characterization is altered let's take a look at a few more examples we'll start by looking at two common acids hydrochloric acid and acetic or ethanoic acid acidbase chemistry occurs in aquous environments so we'll Begin by examining how these two acids interact with water here hydrochloric acid is identified as the acid and is donating a proton to water so in this example water is considered the proton acceptor or the base note that the production of the hydronium ion h3o+ is is indicative of an acid the hydrogen ion Associates to a water molecule creating hydronium the production of this ion increases the acidity of the system in this next example acidic acid otherwise known as ethanoic acid is donating a proton to water and is therefore considered the acid while again water is accepting the proton and is considered the base it is important to note here that a bron stead Larry acid must have a base to which it can donate its proton next we will also introduce the idea of brownstead lowry conjugate acid base pairs the Bron stad Lowry acid forms a conjugate base after donating a proton in the reactions mentioned the Bron delari base forms a conjugate acid after accepting the proton therefore in the hydrochloric acid reaction the first acid base conjugate pair is HCl and the chloride ion as the chloride ion remains after the proton has been donated the second acidbase conjugate pair is the water molecule and the hydronium ion as the hydronium forms after water accepts a proton in the ethanoic acid reaction the first acidbase conjugate pair is ethanolic acid and the ethanolate ion and the second acidbase conjugate pair is again the water molecule and the hydronium ion it is very important to observe that the acidbase conjugate pairs differ only by one proton and the charge decreases by one when the proton is donated while the charge increases by one when the proton is accepted now let's examine a common Bron stad Lowry base reaction with ammonia NH H3 in this case the ammonia accepts a proton from water and is therefore considered the Bron said Lowry base while water is now donating a proton and is considered the bronstad Lowry acid if we track the acidbase pairings the first acidbase conjugate pair is ammonia and the ammonium ion and the second a based conjugate pair is water and the hydroxide ion note that using the Bron dead Larry Theory here ammonia increases the hydroxide concentration thereby decreasing the acidity of the system or increasing the basicity of the system as we have seen acidbase reactions are typically aquous and occur in water we have seen that water can act as a a base a proton acceptor which increases the concentration of hydronium ions and increases the acidity but it can also act as an acid a proton donor which increases the concentration of hydroxide ions and increases the basicity since water can act as an acid and a base it can also Auto ionize and this is the basis for understanding the pH scale which we will discuss in a separate video Let's consider what happens in a glass of water with many moles of water molecules most remain as molecular H2O but a small number of molecules can ionize according to this equation with one molecule acting as a brumstead lowy acid and another acting as a brumstead lowy base this is a reversible reaction and we can therefore write an expression for the equilibrium constant in this case the constant is given the special designation of KW the ionization product constant for water recall that pure liquids including water are removed from the equilibrium expression so the expression for KW is shown here the concentration of hydronium ions times the concentration of hydroxide ions the value of KW the ionization constant for water at 25° C has a value of 1 * 10-14 examining the balanced equation we showed earlier we can see that a transfer of one proton keeps all the stochiometric coefficients at one therefore in this equation the concentration of hydronium ions equals the concentration of hydroxide ions so it can be determined that at 25° celius the concentration of hydronium ions equals the concentration of hydroxide ions equal 1 * 10 the -7 moles per decim cubed again this will be relevant in a later video when we discuss P calculations from our previous study of equilibrium and rates we know that as temperature increases the rate of reaction also increases and therefore the value of the equilibrium constant changes this same concept is true of the auto ionization of water and the value of KW increases with increasing temperature the table below shows the different values of KW at temperatures other than 25° C since the equilibrium expression for the auto ionization of water does not change only the value of KW changes the table also shows how the calculated values of the concentration of hydronium ions and concentration of hydroxide ions will also change with changing temperatures these values are calculating using the KW value at the given temperature set equal to the KW expression also remembering that the concentration of hydroxide ions equals the concentration of hydronium ions in the auto ization of water just like the math shown earlier so that's it for this video on acid and base theories in this video we learned that under the bronzed Lowry acid base Theory bronzed Lowry acids like hydrochloric acid are proton donors on the other hand we learned that Bron dead Lowry bases such as ammonia are proton acceptors we also learned that conjugate acid base pairs different by only one proton for example ammonia and the ammonium ion we also learned that since water can act as a bronz delari acid or base it can Auto ionize the auto ionization constant for water is 1 * 10-4 and this number has implications for pH calculations which we will cover in a future video