acids and bases have different strengths for example stomach acid is a strong acid while ammonia is a weak base here we will learn what this means we will also learn how acids and bases react with each other and how to graph the changing pH of an acidbase reaction during a process called titration weak acids such as ethanoic acid I i i in water only partially forming an equilibrium with their ions the equilibrium lies to the left meaning that in solution it is primarily the unionized form that exists the conjugate base of a weak acid in this case the ethanolate ion readily accepts a proton from the hydronium ion to reform the acid and so weak acids are poor proton donors however some acids such as hydrobromic acid are strong acids meaning they ionize fully or completely into their ions in solution the equilibrium lies so far to the right that the reverse reaction is considered negligible the conjugate base of a strong acid in this case the bromide ion does not readily accept a proton from the hydronium ion to reform the acid and so strong acids are good prot on donus we can similarly describe bases bases that dissociate fully into ions in solution are strong bases for example sodium hydroxide and bases which dissociate or ionize partially are called weak bases ammonia is an example of a weak base in aquous medium it ionizes to only a small extent forming a low concentration of ions there are some common examples of strong and weak acids and bases it will be helpful for you to know these examples notice that the acid halides except hydrochloric acid are strong acids Nitric and sulfuric acid are strong but nitrous and sulfurous acid are weak Carbonic and phosphoric acid are weak acids the group one hydroxides are strong base as well as the more soluble group 2 hydroxides ammonia is a weak base as well as methyl amine in fact most organic compounds are either weak acids or weak bases we must not get confused and assume that a strong acid or base is concentrated and a weak acid or base is dilute concentration is a measure of the amount of solute in moles or or mass usually per unit quantity of solution usually volume or mass chemists tend to use marity which is moles of solute per decim cubed of solution the term concentrated means a high proportion of solute relative to a given volume of solution and dilute refers to a small amount of solute in a given volume of solution any acid or base can be concentrated if a large quantity of it is placed in a small quantity of solvent and any acid or base can be dilute if a small quantity of it is placed in lots of solvent however if the same number of moles of a strong acid and a weak acid are placed in the same solution volumes in other words the acids have the same concentration the strong acid will have a higher concentration of dissolved ions the same is true for bases since a strong acid has a higher concentration of dissolved ions relative to a weak acid assuming the same number of moles of both acids are placed in the same solution volumes their properties will differ the more mobile ions there are in solution the higher is the electrical conduct it so strong acids have higher electrical conductivity than weak acids the more hydrogen ions released from acids during ionization the faster is an acidbase reaction as particles will collide more frequently and the more hydrogen ions there are in solution the lower is the pH the same is true for bases except reaction rate depends on the concentration of hydroxide ions in solution in the case of alkaly and the pH is higher for a stronger base and lower for a weaker base when an acid and a base react an acid base reaction also called a neutralization reaction occurs forming a salt and water as products these reactions are exothermic the base can be a metal hydroxide the hydroxide ion from the base combines with the hydrogen ion from the acid to form water and the anion from the acid combines with a cation from the base to form a salt for example when hydrochloric acid and potassium hydroxide react the products are the salt potassium chloride and water since the salt is made from components of both the acid and the base we call hydrochloric acid the parent acid and potassium hydroxide the parent base of the salt potassium chloride here is another example of neutralization where the organic acid ethanolic acid reacts with sodium hydroxide to produce the salt sodium ethanolate the base in a neutralization reaction can also be a metal oxide for example when copper oxide reacts with sulfuric acid a salt and water are still formed here is another example where the metal oxide is sodium oxide and the acid is hydrochloric acid note that the reason why we call metal oxides bases is that many of them react with water to form alkaline Solutions these Solutions have a high pH and so these metal oxides must be basic as a side note remember that ammonia is a weak base in water it forms an alkaline solution of ammonium hydroxide when an acid reacts with a metal carbonate or a metal hydrogen carbonate the products are a salt water and carbon dioxide gas for example when hydrochloric acid is added to pellets of calcium carbonate if a vesence occurs these bubbles are carbon dioxide gas bubbles being released if you've ever done the volcano experiment you would have taken powdered sodium hydrogen carbonate also called sodium bicarbonate and added vinegar to this the main component of vinegar is ethanoic acid and this acid reacts with the metal hydrogen carbonate rapid evolution of carbon dioxide gas is what makes this volcano erupt often the salt formed in a neutralization reaction is soluble in water and the salt can be recovered by first filtering the salt solution to ensure that there are no insoluble impurities then evaporating off most of the water solvent first with heat and then evaporating to dry minus at room temperature this process is called crystallization the amount or concentration of acid or base in a product such as fruit juice or Cosmetics or in waste water during treatment and during pharmaceutical manufacturer can be determined using a process called titration titration involves a neutralization reaction we will only investigate it titration between a strong acid and a strong base an accurately measured volume of the analyte that is the solution whose acid or base concentration is being determined is peted into a conical flask with a few drops of indicator let's assume the analyte is the strong acid hydrochloric acid we can record the acid volume its initial pH can be measured using a probe from a pH meter and the pH value is plotted on the Y AIS of a pH curve for a strong acid analy such as hydrochloric acid the initial pH is low since the analy is an acid in this example then the buet is filled with a base in this case sodium hydroxide of accurately known concentration the solution in the buet is is called the titrant we record the titrant concentration and we record the initial buet reading let's assume it is at 0.0 Mill or cm cubed but it could be at any other value the tap or stopcock on the buet is opened and titrant is then slowly added to the analyte whil swirling the chicle flask to ensure proper mixing and a neutri neutralization reaction occurs in this example this is the neutralization reaction the pH of the solution in the conical flask is measured and plotted as more and more titrant is added the pH in this titration will increase as the volume of Base added to the flask increases but there is still excess acid present and so the pH is still in the acidic range notice the pH curve is not linear but gradually increases equivalence point or stochiometric Point occurs when just the right amount of titrant has been added to exactly neutralize the anite in other words equivalence point occurs when neither the acid nor the base in the flask is in excess but only salt and water exist for hydrochloric acid and and sodium hydroxide this occurs when the moles of acid to base in the flask is 1 as to one according to the mole ratio from the balanced equation when just one or two drops of titrant have been added after equivalence point has been reached the indicator changes color and this is called end point but for practical purposes end point is often referred to as equivalence point at this stage the buet tap is closed and the final meniscus reading is recorded and the volume of titrant added to achieve complete neutralization called the titer can be determined the pH at equivalence point will be seven or neutral for the reaction of a strong acid with a strong base notice on the curve there is a sudden increase in gradient as equival vence point is reached then if excess base titrant is added and the pH is recorded the curve would extend like this this is the typical shape of a pH curve for the titration of a strong acid analyte with a strong base titrant incidentally if the analyte was a strong base and the titrant a strong acid the curve would look like this starting with a high pH a neutral equivalence point and an acidic pH if excess acid is added it is always a good idea to repeat the titration in full several times and record the data tighter results that are close in value in other words are concordant are used in calculations as they are more reliable and are considered to have less random error since these results are are repeatable usually we use the average of the concordant results for the tighter value after the titration we can use this data to work out the concentration of the analyte first we take the volume of the titrant added and its concentration to calculate the number of moles added at equivalence point then using the mole ratio from the balanced equation we can determine the moles of acid which were initially added to the flask which in this case is the same as the moles of Base at equivalence point finally from the moles of acid and the volume of acid per peted the concentration of the acid can be calculated let's summarize the key points the strength of an acid or base refers to the degree of ionization or dissociation in solution strong acids and bases ionize completely while weak ones ionize partially concentrated does not mean strong concentrated means a large number of moles of dissolved solute dilute does not mean weak dilute means a small number of moles of dissolved solute the more dissolved ions there are in solution the higher is the electrical conductivity and the faster the reaction rate a neutralization reaction occurs between an acid and a base and the products are a salt and water the base can be a metal hydroxide or a metal oxide acids also react with metal carbonates and metal hydrogen carbonates to produce salt water and carbon dioxide gas during a titration of a strong acid with a strong base the pH of the analyte in the flask changes as more titrant is added and at equivalence point the pH is seven or neutral