Acidity is caused by the presence of hydrogen ions in the solution. If ANY acid has a high concentration then this will consequently increase the hydrogen ion concentration making the acid 'stronger'. When chemists refer to strong and weak acids they are referring to the degree with which the acid molecules break apart to give ions in aqueous solution dissociation.
Strong and weak acids are defined by the ease with which they lose or donate hydrogen ions protons. A weak acid will, however, only partially dissociate into ions, leaving a high percentage of unreacted molecules in the solution. This means that, given an equal number of moles of acid, they will be neutralized by the same amount of strong base, but their solutions will have different pH values. Students should consider hydrochloric acid, nitric acid and sulfuric acid as examples of strong acids and carboxylic acids and carbonic acid aqueous carbon dioxide as weak acids.
Students should consider all group 1 hydroxides and barium hydroxide as strong bases - ammonia and amines as weak bases. Weak acids only partially dissociate into ions. This does not mean that they do not react fully with bases. Le Chatelier's principle tells us that if we remove one of the components from one side of an equilibrium, the equilibrium responds by making more.
The sodium hydroxide reacts with the available hydrogen ions removing them from the right hand side of the equilibrium below. The equilibrium then responds by dissociating some ethanoic acid molecules to make more hydrogen ions. These then react with the sodium hydroxide and get removed from the equilibrium.
The equilibrium makes more by dissociating even more ethanoic acid, and so on until all the ethanoic acid has been neutralised by the sodium hydroxide. The net result is that all the ethanoic acid reacts with the sodium hydroxide if there is enough sodium hydroxide. However, group two metal hydroxides, like barium hydroxide and calcium hydroxide, produce two moles of hydroxide ions for each mole of base. Ionic metal oxides, like sodium oxide and calcium oxide, are also strong bases.
Their oxide ion reacts with water and produces hydroxide ions. The concentration of hydroxide ions can be used to calculate a pOH and pH of the solution. For example, a five times ten to the negative five molar potassium hydroxide solution has an equal amount of hydroxide ions as strong base and therefore has a pOH of 4. Like pH, a pOH of the solution can also be used to determine hydroxide ion concentration by solving the equation: pOH equals the negative log of the hydroxide ion concentration.
A strong acid is a compound that dissociates completely in an aqueous solution and produces a concentration of hydronium ions equal to the initial concentration of acid. On the other hand, a strong base is a compound that dissociates completely in an aqueous solution and produces hydroxide ions.
Group 2 metal hydroxides, like barium hydroxide [Ba OH 2 ] and strontium hydroxide [Sr OH 2 ], are also strong bases and possess two hydroxide ions. As strong acids and bases dissociate completely, molar ratios can be used to determine their hydronium and hydroxide concentrations, which in turn can be used to calculate the pH or pOH of a solution.
For example, a 0. Therefore the pH of this solution will be. Similarly, the concentration of hydroxide ions produced by strong bases can be used to determine the pOH of a solution using the equation.
The above equation can also be used to determine the hydroxide ion concentration when pOH is known. For example, if the pOH of a solution is 3. Thus, the hydronium ion concentration of the solution with pOH 3 is 1.
A similar method can be used to determine the hydronium ion concentration of a solution if its pH is known. To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired. Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team.
When an ionic compound dissolves, it separates into its constituent ions:. This page was constructed from content via the following contributor s and edited topically or extensively by the LibreTexts development team to meet platform style, presentation, and quality:. Learning Objectives Define a strong and a weak acid and base. Strong acids protonate the carbonyl, which makes the oxygen positively charged so that it can easily receive the double-bond electrons when the alcohol attacks the carbonyl carbon; this enables ester synthesis and hydrolysis.
Weak acids have very small values for K a and therefore higher values for pK a compared to strong acids, which have very large K a values and slightly negative pK a values.
The majority of acids are weak. On average, only about 1 percent of a weak acid solution dissociates in water in a 0. Vinegars : All vinegars contain acetic acid, a common weak acid. Weak acids ionize in a water solution only to a very moderate extent. The generalized dissociation reaction is given by:. The strength of a weak acid is represented as either an equilibrium constant or a percent dissociation.
The equilibrium concentrations of reactants and products are related by the acid dissociation constant expression, K a :. The K a of weak acids varies between 1. Acids with a K a less than 1. If acids are polyprotic, each proton will have a unique K a. For example, H 2 CO 3 has two K a values because it has two acidic protons. The first K a refers to the first dissociation step:. This K a value is 4.
The second K a is 4.
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