Acid–base reaction - Wikipedia
Understanding the relationship between properties and structures/bonding is also a hot pursuit. Chemistry is traditionally divided into organic and inorganic . However, there are exceptions such as NH3, which is a base. An organic base is an organic compound which acts as a base. Organic bases are usually, but not always, proton acceptors. They usually contain nitrogen. Examples of compounds are water, carbon dioxide, sucrose and sodium chloride (and other salts) and inorganic acids and bases such as HCl and NaOH. 3. molecule - a substance that . The relationship between activity and concentration is.
Ka is dependent on the rate of the forward and reverse reactions and at equilibrium these two rates are equal. When water is added, the concentrations of all species in solution are decreased. In the forward direction, the rate of reaction is proportional to the product of [HA][H2O]. The concentration of water itself, before and after dilution, does not change nearly as much as the concentration of the other species.
Therefore dilution decreases the rate of the reverse reaction much more than the rate of the forward reaction and the system is no longer at equilibrium. This is because the product of two smaller numbers will be considerably less than the product of one smaller and a number that does not change substantially, the [H2O].
The forward reaction now proceeds more rapidly than the reverse reaction until equilibrium is again achieved. Besides changing the concentration of species, dilution also changes the activity of ionic species and this in turn affects the pH. The effect of changes in activity are detectable when the extent of dilution is relatively small, in general less than fold. When dilution is greater than fold, the dilution of species outweighs changes in activity. The effect of dilution on the activity of ions will be discussed further in class.
Also recall that temperature changes equilibrium concentrations, and this results in a change in Keq and therefore a change in pKa and pKb. The above discussion emphasizes that while Ka and Kb and pKa and pKb are constants at a particular temperature, the degree of ionization percent ionization of a weak acid or base is not a constant but varies depending on the conditions. A second solution of HA was prepared by mixing 25 mL of 0. A third solution of HA was prepared by mixing 25 mL of 0.
A second solution was prepared from 50 mL of 0. Researchers often want to know what proportion of such biological compounds are in the conjugate acid and conjugate base forms at a particular pH. The Henderson-Hasselbalch equation relates these values. The derivation of this equation is described.
Names and Formulas of Inorganic Compounds - Chemistry LibreTexts
The equation that describes the dissociation reaction of any weak acid at equilibrium is: This equation describes the ionization of a weak acid in pure water at equilibrium.
Commonly the above expression is rearranged into a more useful form as follows: Take logarithms, multiply by -1, and rearrange the log term This is the Henderson-Hasselbalch equation. An analogous expression can be derived for weak bases that are amines. Rearrange, take logarithms, multiply by -1, and rearrange log term. What is the pH of a solution prepared by adding 0.Biomolecules (Updated)
Titration curves were originally made to determine the best color indicator to use to determine the equivalence end-point of a titration.
The titration curve of 20 mL of a 0. In this case the pH is 2. Consequently, the milliequivalents of A- in solution are basically equal to the milliequivalents of strong base added. However, a small portion of HA is always ionized; but with each addition of NaOH, less is ionized because the concentration of A- has increased and A- suppresses HA ionization.
This results in an increase in pH. Note that initally, the rate of increase in pH per constant amount of NaOH added continually decreases. This continues to occur until 0. At this point, the rate of increase in pH per constant amount of NaOH added begins to increase until the rate of increase is maximal at 1 milliequivalent of strong base added.
Stated in another way, there is an inflection point a change in the direction of the curve at the point where 0. There is no portion of the curve that is a straight line, that is, the curve is continually changing in one direction or another. Finally, note that the pH changes least, that is, resistance to change in pH is greatest, at the first inflection point.
What is the concentration of the two species when different amounts of NaOH is added? When no NaOH has been added, the ratio is It is extremely important to understand what this ratio means and how to use it to calculate the concentration of the two species in any particular solution i.
In the above example, the sum of the concentrations of the two species is 0. The ratio states the relative concentration of each species in that particular solution. In this example, the sum of the two relative concentrations is 1.
The actual concentration of each species can be calculated from knowing the relative concentration of each species, the sum of the two relative concentrations, and the sum of actual concentration of the two species. The sum of the actual concentration of the two species is 0. The actual concentrations of the A- and HA are: In the above example, it was 0. An alternative method for calculating the concentrations of the individual species in the above example is to adjust the two numbers of the ratio so that the sum of the numbers is equal to 1.
In the above example, the ratio obtained was 0. The ratio values can be adjusted so their sum is 1. In the above example, 3. The actual concentrations of each are: Although any concentration term could be used, let concentrations be expressed as molarity moles L In the above example Since A- and HA are in the same volume, 20 mL, the volume term can be cancelled.
Now the ratio states the amount of each of the two species in the solution.
Formulas of Inorganic and Organic Compounds - Chemistry LibreTexts
The [ ] have been removed and the 20 mL terms cancelled because concentration is no longer being expressed but we must always remember these amounts are in a known volume which in this example is 20 mL.
The ratio now tells the relative number of moles or molecules of A- and HA in the 20 mL. If the ratio is expressed on the basis of 1 the sum of A- and HA is set equal to 1 then the numbers of the ratio when multiplied by state the percent of the total moles or molecules of A- plus HA in 20 mL that is A- and the percent of the total that is HA. Construct a titration curve for the titration of 10 mL of 0.
Place pH on the ordinate. Assume the titration curve is mathematically expressed by the Henderson-Hasselbalch equation. The expression, describes the concentration of the three species at any point on the titration curve as long as the system has come to equilibrium. The equation is a mathematical description of the titration curve. Since the Henderson-Hasselbalch equation was derived from this equation, the Henderson-Hasselbalch equation is also a mathematical description of the titration curve.
The titration of a weak base by a strong acid yields analogous information except the titration curve begins in the basic region of the pH scale and the expression involving pKb is used. A buffer consists of a solution of a weak acid and the corresponding conjugate base.
One can also state it consists of a solution of a weak base and its conjugate acid. These two statements say the same thing. A buffer may be prepared from either a weak acid or a weak base. For example, a 0. It is prepared from acetic acid by converting some of the acetic acid to acetate ion with strong base. The word "acetate" in acetate buffer refers to both the conjugate acid in this example, acetic acid and the conjugate base acetate ion.
These two species together make up the acetate buffer. Each species is present in the buffer at a specific concentration and the concentration given for the acetate buffer is the sum of the concentrations of these two species, in this example 0.
The ratio of the concentrations of the two species in the buffer is obtained from the Henderson-Hasselbalch equation.
How do we know what weak acid or base to select for the preparation of a buffer? First, the pH of the buffer to be prepared must be decided.
This is dictated by what pH is needed in the experiment being performed. Recall from the discussion of titration curves that the pH of a solution of a weak acid changes least at the pKa of the acid. Finally the weak acid and conjugate base should not interfere in any way in the experiment, such as by altering the activity of an enzyme, or by reacting chemically with any of the substances present in the experimental solution. As an example, assume the activity of an enzyme is to be tested at pH 5.
What buffer should be used? A weak acid whose pKa is about 5. Acetic acid has a pKa of 4. How is a buffer prepared? Find the empirical formula for C8H16O2. Structural Formula A structural formula displays the atoms of the molecule in the order they are bonded. It also depicts how the atoms are bonded to one another, for example single, double, and triple covalent bond. Covalent bonds are shown using lines. The number of dashes indicate whether the bond is a single, double, or triple covalent bond.
Structural formulas are helpful because they explain the properties and structure of the compound which empirical and molecular formulas cannot always represent.
Structural Formula for Ethanol: Condensed Structural Formula Condensed structural formulas show the order of atoms like a structural formula but are written in a single line to save space and make it more convenient and faster to write out. Condensed structural formulas are also helpful when showing that a group of atoms is connected to a single atom in a compound. When this happens, parenthesis are used around the group of atoms to show they are together.
3.6: Names and Formulas of Inorganic Compounds
Condensed Structural Formula for Ethanol: Line-Angle Formula Because organic compounds can be complex at times, line-angle formulas are used to write carbon and hydrogen atoms more efficiently by replacing the letters with lines.
A carbon atom is present wherever a line intersects another line. Hydrogen atoms are then assumed to complete each of carbon's four bonds.
All other atoms that are connected to carbon atoms are written out. Line angle formulas help show structure and order of the atoms in a compound making the advantages and disadvantages similar to structural formulas. Line-Angle Formula for Ethanol: Formulas of Inorganic Compounds Inorganic compounds are typically not of biological origin.
Formulas of Inorganic and Organic Compounds
Inorganic compounds are made up of atoms connected using ionic bonds. These inorganic compounds can be binary compounds, binary acids, or polyatomic ions. Binary compounds Binary compounds are formed between two elements, either a metal paired with a nonmetal or two nonmetals paired together.
When a metal is paired with a nonmetal, they form ionic compounds in which one is a negatively charged ion and the other is positvely charged. The net charge of the compound must then become neutral. Transition metals have different charges; therefore, it is important to specify what type of ion it is during the naming of the compound. When two nonmetals are paired together, the compound is a molecular compound. When writing out the formula, the element with a positive oxidation state is placed first.
BaBr2 Barium Bromide Ex.
N2O4 Dinitrogen Tetroxide Binary acids Binary acids are binary compounds in which hydrogen bonds with a nonmetal forming an acid. However, there are exceptions such as NH3, which is a base. Because hydrogen is positively charged, it is placed first when writing out these binary acids.
HBr Hydrobromic Acid Polyatomic ions Polyatomic ions is formed when two or more atoms are connected with covalent bonds. Cations are ions that have are postively charged, while anions are negatively charged ions. The most common polyatomic ions that exists are those of anions. The two main polyatomic cations are Ammonium and Mercury I.
Many polyatomic ions are typically paired with metals using ionic bonds to form chemical compounds. When one of those three elements is oxygen, the acid is known as a oxoacid. In other words, oxacids are compounds that contain hydrogen, oxgygen, and one other element. A common example is hydrates: When this happens, a dot is shown between H2O and the other part of the compound. Because the H2O molecules are embedded within the compound, the compound is not necessarily "wet".
When hydrates are heated, the water in the compound evaporates and the compound becomes anhydrous. These compounds can be used to attract water such as CoCl2. Most organic compounds are seen in biological origin, as they are found in nature.
Hydrocarbons Hydrocarbons are compounds that consist of only carbon and hydrogen atoms.