The pH meter was invented because Florida orange growers needed a way to test the acidity of their fruit. The first meter was invented by Arnold Beckman, who went on to form Beckman Instruments.
The numerical value of K a or K b can be determined from an experiment. A solution of known concentration is prepared and its pH is measured with an instrument called a pH meter.
Figure 1. A pH meter is a laboratory device that provides quick, accurate measurements of the pH of solutions. Determine the K a for formic acid. Step 1: List the known values and plan the problem. All concentrations are then substituted into the K a expression and the K a value is calculated. We assume that the initial concentrations of each ion are zero, resulting in the following ICE table. Now substituting into the K a expression gives:. Step 3: Think about your result. The value of K a is consistent with that of a weak acid.
Two significant figures are appropriate for the answer, since there are two digits after the decimal point in the reported pH. Similar steps can be taken to determine the K b of a base. For example, a 0. The pOH is 14 — The ICE table is then set up as shown below. Substituting into the K b expression yields the K b for ethylamine. Read the material at the link below and answer the following questions:.
Skip to main content. Acids and Bases. Search for:. List some strong acids. Define a weak acid. List some weak acids. Write the expression for the acid ionization constant. Define strong and weak bases. Give examples of strong and weak bases.
Write the expression for the base ionization constant. Perform calculations of acid and base ionization constants. How do they etch glass? When an acid dissolves in water, the solution is said to be an acidic solution. Some acids, like nitric acid, ionize completely when they dissolve in water. This means that during the dissolving process, all HNO3 molecules dissociate into separate ions. We know that nitric acid ionizes when dissolved in a solution.
In chemical equations representing ionization, water is typically included as a reactant or written above the reaction arrow. However, in the answer choices, aq is used instead, which represents the solution containing water. The products in our ionization equation will be the dissolved ions.
One of these ions, ion A, will have a positive charge, and the other ion, ion B, will have a negative charge. So, what ions would HNO3 produce when dissolved in water? Chemical and spectroscopic studies have shown that concentrated solutions of both these acids do contain some unionised molecules. For our purpose, however, their ionisation is effectively complete. This is particularly true in dilute solutions.
I cannot understand the part that is in the bold. What are these unionised molecules? I know that these acids are considered strong acids which completely ionise in water solution. If that is the case, then why does the text indicate that there are some unionised molecules? You could view this as a dilution, in the sense that the resulting solution is less acidic than highly concentrated nitric acid would be, but the process of dilution of acid by mixing with water inevitably involves an acid-base reaction.
As to your second question, the unionized molecules are the neutral water and nitric acid on the reactant side, while the ions are the products resulting from the acid-base reaction. Nitric acid is relatively strong, meaning it tends to ionize almost completely in aqueous solution.
Additionally, the less acidic the solution already is prior to addition of the acid, the more extensively the added acid will dissociate into ions to understand this, please read up on acid-base equilibria and Le Chatelier's principle, as the topics are too lengthy and complex to cover adequately here.
This is why the author emphasizes that the dissociation is more complete in dilute solutions. Statistically, however, some proportion of the nitric acid molecules will inevitably not dissociate into ions.
The stronger an acid, the greater the extent of dissociation, but there is always some statistical chance that a proportion of the molecules will remain unreacted. For strong acids, however, the overwhelming preponderance of the molecules will dissociate, while only a tiny fraction remain unreacted. Hence, for many if not most purposes, it's reasonable when dealing with strong acids to proceed as if the dissociation is truly complete, since the unreacted portion is typically negligible in quantity.
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