Any acid or base is technically a conjugate acid or conjugate base also; these terms are simply used to identify species in solution i. How does one define acids and bases? In chemistry, acids and bases have been defined differently by three sets of theories.
Also, the Lewis theory of acids and bases states that acids are electron pair acceptors while bases are electron pair donors. Acids and bases can be defined by their physical and chemical observations. This scale is shown by the following formula:. The pH scale is often measured on a 1 to 14 range, but this is incorrect see pH for more details. Something with a pH less than 7 indicates acidic properties and greater than 7 indicates basic properties.
A pH at exactly 7 is neutral. The Lewis theory of acids and bases states that acids act as electron pair acceptors and bases act as electron pair doners. This definition doesn't mention anything about the hydrogen atom at all, unlike the other definitions. It only talks about the transfer of electron pairs. To demonstrate this theory, consider the following example.
This is a reaction between ammonia NH 3 and boron trifluoride BF 3. Since there is no transfer of hydrogen atoms here, it is clear that this is a Lewis acid-base reaction. In this reaction, NH 3 has a lone pair of electrons and BF 3 has an incomplete octet, since boron doesn't have enough electrons around it to form an octet. Because boron only has 6 electrons around it, it can hold 2 more.
BF 3 can act as a Lewis acid and accept the pair of electrons from the nitrogen in NH 3 , which will then form a bond between the nitrogen and the boron. This is considered an acid-base reaction where NH 3 base is donating the pair of electrons to BF 3. A special property of acids and bases is their ability to neutralize the other's properties. Another product of a neutralization reaction is an ionic compound called a salt.
Therefore, the general form of an acid-base reaction is:. Titrations are performed with acids and bases to determine their concentrations. At the equivalence point, the number of moles of the acid will equal the number of moles of the base. This indicates that the reaction has been neutralized.
For instance, 30 mL of 1. The concentration of HCl needs to be determined. At the eqivalence point:. The pH inside cells 6. However, the environment in the stomach is highly acidic, with a pH of 1 to 2. So how do the cells of the stomach survive in such an acidic environment? How do they homeostatically maintain the near neutral pH inside them?
The answer is that they cannot do it and are constantly dying. New stomach cells are constantly produced to replace dead ones, which are digested by the stomach acids. It is estimated that the lining of the human stomach is completely replaced every seven to ten days. Acids have a pH below 7; bases have a pH above. Strong acids have the lowest pH levels and strong bases have the highest pH levels Neutral solutions have a pH of 7 and they are neither acidic nor basic.
Litmus is a natural acid-base indicator extracted from a type of lichen. If you have red and blue litmus paper, you can test different solutions for whether they are acids or bases. Blue litmus paper turns red when a solution is acidic; red litmus paper turns blue in basic solutions. Try testing window cleaner, toilet bowl cleaner, orange juice, and apple juice—pour a little of each into separate test tubes or small glasses or jars.
Use the litmus paper to determine which are acids and which are bases. Here are the pH levels of some other substances that you might test: lemon juice 2 , vinegar 3 , milk 6 , egg whites 8 , baking soda 9 , and ammonia Human blood has an ideal pH of 7. You can also make your own pH indicator —use a blender to mix one part chopped red cabbage with two parts boiling water and use the juice to test different solutions.
Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green. Water may seem plain and boring sometimes, but it does have some interesting physical properties!
The chemical composition of water is H 2 O —two hydrogen atoms and one oxygen. The two H atoms form weak hydrogen bonds with the oxygen; they attach to the top of the molecule rather like Mickey Mouse ears. This molecular structure gives the water molecule polarity , or a lopsided electrical charge that attracts other atoms. The end of the molecule with the two H atoms is positively charged. The other end, with the oxygen, is negatively charged. Just like in a magnet, where north poles are attracted to south poles opposites attract , the positive end of the water molecule will connect with the negative end of other molecules.
Water is the only natural substance that can exist in all three states of matter —solid, liquid, and gas—at the temperatures normally found on Earth. Let's start with a typical metal hydroxide: sodium hydroxide. As a result, the electrons in the Na O bond are not shared equally these electrons are drawn toward the more electronegative oxygen atom.
We get a very different pattern when we apply the same procedure to hypochlorous acid, HOCl, a typical nonmetal hydroxide. As a result, the electrons in the Cl O bond are shared more or less equally by the two atoms. There is no abrupt change from metal to nonmetal across a row or down a column of the periodic table. We should therefore expect to find compounds that lie between the extremes of metal and nonmetal oxides, or metal and nonmetal hydroxides.
These compounds, such as Al 2 O 3 and Al OH 3 , are called amphoteric literally, "either or both" because they can act as either acids or bases. Al OH 3 , for example, acts as an acid when it reacts with a base. The Br nsted Definition of Acids and Bases. Even the Brnsted model is naive. The reaction between HCl and water provides the basis for understanding the definitions of a Brnsted acid and a Brnsted base.
Some chemists call it a hydrogen ion; others call it a proton. As a result, Brnsted acids are known as either hydrogen-ion donors or proton donors. Brnsted bases are hydrogen-ion acceptors or proton acceptors.
Acids can be neutral molecules. The Brnsted theory therefore expands the number of potential acids. It also allows us to decide which compounds are acids from their chemical formulas. Brnsted bases can be identified from their Lewis structures.
0コメント