[Music] two important theories have been developed to explain the properties of acids bases and salts these are the arenius theory and the bronze dead Lowry Theory here we'll look at the bronze dead Lowry Theory this theory of acids was proposed independently in 1923 by two people Johan Nicholas brownstead a Danish chemist and Thomas Martin Lowry an English chemist we'll introduce the main point of this Theory before we do that just a quick word here about a hydrogen atom its atomic number is one so it has one proton a neutral hydrogen atom also has one electron it is known that over 99.98% of the hydrogen atoms on earth contain no neutrons so we'll State here that a hydrogen atom has no neutrons which is nearly always the case if one electron is removed from a hydrogen atom it forms an H+ ion here's the equation showing that a neutral H atom has one proton and one electron so removing an electron will leave a charge of positive one one proton and zero electrons so an H+ ion contains no electrons no neutrons and one proton therefore an H+ ion is the same thing as one proton or we can say say that H+ equals 1 proton we use the terms H+ ion and proton interchangeably in chemistry 12 according to the bronze dead Lowry Theory an acid is any species that donates a proton or H+ ion to another species let's look at an example of this let's start with a molecule of hydrogen chloride HCL and a molecule of water H2O here are the leis structures for these molecules HCL is a polar molecule there is a partial negative charge on the chlorine atom and a partial positive charge on the hydrogen atom shown by the Delta minus and Delta plus the water molecule is also polar the oxygen atom has a partial negative charge and each hydrogen atom has a partial positive charge the negative charge on the oxygen pulls the partially positive hydrogen atom away from the chlorine the hydrogen leaves it shared electron with the chlorine atom the chlorine atom has gained an electron so it acquires a negative charge and becomes a CL minus ion the hydrogen atom lost an electron so it acquires a positive charge forming an H+ ion which is also called a proton the proton moves to the water molecule and attaches to one of the lone pairs instead of staying with the hydrogen atom the positive charge is considered as the charge of the whole ion so we'll move it over here there are now three h atoms attached to one o so the formula is h3o instead of H2O we'll draw square brackets around the h3o because it's an ion and write the positive charge here in the formula chemists call the h3o+ ion the hydronium ion so we can summarize the whole process here we started with a molecule of HCL and we added a molecule of water which gave us an h3o+ or hydronium ion plus a c minus or chloride we can now write an equation to show this process we write HCL gas plus H2O liquid forms h3o plus aquous plus CL minus aquous we can also represent the process like this this shows an H+ ion or proton is being transferred from the HCL molecule to the water molecule so this is called a proton transfer H2O has gained one proton so it forms an h3o plus ion HCL has lost one proton or H+ ion so it forms a CL minus ion because the HCL is losing or donating a proton according to the Bron dead Lowry Theory it is called an acid to indicate this we often call it a bronze dead Lowry acid or Bron dead acid for short according to the bronze dead Lowry Theory a base is defined as any species that gains or accepts a proton or H+ ion from another species because the H2O is gaining or accepting a proton it can be defined as a bronze dead Lowry base or bronze dead base for short so in this reaction HCL is an acid and water is a base because the reactants HCL and H2O are not ions but the products h3o+ and cl minus are ions we call this process the ionization of HCL here's a question we're asked to write the equations for the ionization of the following acids when they're added to water and to identify the acids and bases on the reactant side we'll start the first reaction by adding liquid water as the other reactant the formula for this compound starts with an H so we assume it acts as an acid and we'll label it as an acid so the other reactant water must act as a base in this case now an acid is a proton donor and a base is a proton acceptor so that means a proton or H+ ion will be transferred from the acid hno3 to the base H2O so this means that water will gain an H+ which is one H and one positive charge adding an h and one positive charge to water gives us h3o+ the hydronium ion the acid hno3 has lost one H+ which means it has lost one H and one positive charge we remove the H Atom from H3 giving us NO3 and taking away one positive charge is the same as adding one negative charge so we have NO3 minus the nitrate ion both of the new ions formed are aquous so this is the equation for the ionization of hno3 hno3 is the acid on the left side and water is the base on the left side now we'll see what we get if we add hcn to water because hcn starts with H we'll treat it as an acid and H2O is a base so there will be a proton transfer from hcn to H2O the H2O will gain a proton or H+ and form h3o Plus or hydronium and the hcn will lose a proton or H+ and form CN minus so this is the equation for the ionization of hcn hcn is the acid on the left and water is the base a double arrow was used here because the ionization of hcn does not go to completion in a solution of hcn only a few molecules are ionized you'll be showing how you can tell whether to use a single or double arrow later in the course now let's consider this reaction again the Double Arrow here just tells us that this reaction action does not go to completion instead an equilibrium exists here we see that the NH3 has been converted to nh4+ in doing so it gains one H and one positive charge therefore it gains 1 H+ or one proton because it gains a proton in this case the NH3 is classified as a base looking at Water we see it has been converted to oh minus o minus has one less H and one less positive than H2O therefore it has one less H+ than H2O therefore when H2O converts to O minus it loses an H+ or proton for that reason we identify H2O as an acid in this case now we'll look at a previous reaction we had in which hno3 reacts with water in this reaction water acted as a base so we can now see that depending on what it's reacting with water can play the role of an acid or the role of a base such a species is said to be aprotic an aprotic species is one that can act either as an acid or as a base depending on what it's reacting with water is one aprotic substance there are many more as we shall see later in this unit monoprotic diprotic triprotic and polyprotic acids consider these two acids HCL and hno3 both of these are able to lose one proton only an acid that has one proton available to donate is called a monoprotic acid so both HCL and hno3 are monoprotic acids now consider this acid h2so4 it's called sulfuric acid notice it has two H atoms at the beginning of the formula acids that have two protons they can donate are said to be diprotic so h2so4 is a diprotic acid however when diprotic acids like h2so4 are added to water they do not lose both of their protons at once they do it in steps losing one proton at a time in the first step of the reaction of h2so4 and water the h2so4 loses one proton to water so the water is converted to h3o Plus or hydronium because the h2so4 is losing H+ it means it's losing one H atom and one positive charge this gives us hso4 with a minus charge hso4 minus is called the hydrogen sulfate or bisulfate ion notice that hso4 minus has one hydrogen it can lose so in the second step of the ionization of sulfuric acid the hso4 minus will react with water and donate its proton to water which would produce another hydronium ion the hso4 minus loses a proton so it loses one hydrogen and one positive charge so it will be left as s so4 and losing one positive charge will cause its charge to go down one from Nega 1 to -2 or 2 minus the product s so4 2us or sulfate ion does not have any hydrogens to donate so this is the last step in the ionization of sulfuric acid the Double Arrow here implies that there's an equilibrium this reaction does not go to completion whereas in the first step of the ionization of sulfuric acid there is a single Arrow which means this step goes to completion 100% of the sulfuric acid is converted to hydronium and hydrogen sulfate ions now we'll look at phosphoric acid we see that it has three H's at the front of its formula which means it has three protons it can lose for that reason phosphoric acid is called a triprotic acid when it's combined with water it doesn't lose all three protons at once just one at a time in the first step one proton is transferred to a water molecule so it produces one hydronium ion because it loses one H and one positive charge the other product would have two h's and a charge of ne1 H2 po4 minus is called the dihy hydrogen phosphate ion we see it still has two protons it can donate in the Second Step the H2 P4 minus ion loses one of its protons to water so it produces another hydronium ion and since this loses one H and one positive charge the other product would be hpo42 minus this product is called the monohydrogen phosphate ion we can see that it has one proton available to donate so in the last step the hpo42 minus donates a single proton to water producing another hydronium iion and because it loses one H and one positive charge the final ion that it forms is just p43 minus this is simply called the phosphate ion polyprotic acid is just a general term for any acid that can donate more than one proton examples could be Carbonic a acid which is diprotic phosphoric acid which is triprotic and pyrro phosphoric acid which has four protons it can donate [Music]