Base (chemistry)

A base is a substance that can accept a hydrogen ion (H+) from another substance. A chemical can accept a proton if it has a negative charge, or if the molecule has an electronegative atom like oxygen, nitrogen, or chlorine that is rich in electrons. Like acids, some bases are strong and others are weak. The weak bases are less likely to accept protons, while the strong bases quickly take protons in solution or from other molecules. An acid is a base's "chemical opposite". An acid is a substance that will donate a hydrogen atom to the base.

Bases have a pH greater than 7.0. Weak bases generally have a pH value of 7–9 while strong bases have a pH value of 9–14.

How bases work

Bases can be used to neutralize acids. When a base, often OH^–, accepts a proton from an acid, it forms a water molecule which is harmless. When all of the acids and bases react to form water molecules and other neutral salts, it is called neutralization. Acids can also be used to neutralize bases.

Every base has a conjugate acid formed by adding a hydrogen atom to the base. For example, NH₃ (ammonia) is a base and its conjugate acid is the ammonium ion, NH₄⁺. A weak base forms a strong conjugate acid and a strong base forms a weaker conjugate acid. Since ammonia is a moderately strong base, ammonium is a considerably weaker acid.

Characteristics

[change | change source]

Bases have these characteristics:

• Bitter taste (opposed to sour taste of acids)
• Slimy, or soapy feel on fingers (Slippery)
• Many bases react with acids and precipitate salts.
• Strong bases may react violently with acids. An acid spill can be safely neutralised by using a mild base.
• Bases turn red litmus paper blue
• Bases are substances that contain metal oxides or hydroxides
• Bases which are soluble in water form alkalis (soluble bases)

Some common household products are bases. For example, caustic soda and drain cleaner are made from sodium hydroxide, a strong base. Ammonia or an ammonia-based cleaner such as window and glass cleaner, is basic. These stronger bases may cause a skin irritation. Other bases, like cooking ingredients sodium bicarbonate (baking soda) or cream of tartar are basic, but these are not harmful and suitable for cooking.

Gloves should always be worn when handling bases. If skin irritation is encountered, the affected area should be rinsed thoroughly with cold water. If that does not stop the problem, contact medical help as soon as possible.

Strong bases

A strong base is a base that completely converts to hydroxide ions, OH−, in water. Most strong bases are hydroxide salts, which dissolve in water rather than reacting with it.

Sodium hydroxide is the most commonly used strong base, but all salts of alkali metals and alkaline earth metals and the hydroxide ion are strong bases:

• Lithium hydroxide - LiOH
• Sodium hydroxide - NaOH
• Potassium hydroxide - KOH
• Rubidium hydroxide - RbOH
• Cesium hydroxide - CsOH
• Calcium hydroxide - Ca(OH)2
• Strontium hydroxide - Sr(OH)2
• Barium hydroxide - Ba(OH)2

These are sometimes listed as the only strong bases, following the Arrhenius acid-base theory, but this is inaccurate in general. Because of the leveling effect, stronger bases than the hydroxide ion will react with water to produce hydroxide and their conjugate acid. For example, the strong base sodium methoxide reacts to make sodium hydroxide and methanol in water:

NaCH3O + H2O → NaOH + CH3OH

 

Acids and bases

 Acids and bases are common chemicals. Acids release H⁺ ions when in water, and bases release OH⁻ ions when in water. Acids can react with bases. The H⁺ ion is taken from the acid by the base. This makes water, H₂O. A salt is also made when an acid and a base react together. An example would be reacting hydrochloric acid (HCl) and sodium hydroxide (NaOH). Hydrochloric acid releases H⁺ and Cl^- ions in water. The base releases Na⁺ and OH^- ions. The H⁺ and the OH^- react to make water. There is a solution of sodium chloride (NaCl) left. Sodium chloride is a salt.

An acid is a substance that can donate a hydrogen ion (H⁺) (generally speaking, this will be a proton) to another substance. Acids have a pH less than 7.0. A chemical can donate a proton if the hydrogen atom is attached to an electronegative atom like oxygen, nitrogen, or chlorine. Some acids are strong and others are weak. The weak acids hold on to some of their protons, while the strong acids let go of all of them. All acids will release hydrogen ions into solutions. The amount of ions that get released per molecule will determine if the acid is weak or strong. Weak acids are acids that partially release the hydrogen atoms that are attached. These acids, then, may lower pH by dissociation of hydrogen ions, but not completely. Weak acids generally have a pH value of 4-6 while strong acids have a pH value of 1 to 3.

A base is an acid's "chemical opposite." A base is a substance that will accept the acid's hydrogen atom. Bases are molecules that can split apart in water and release hydroxide ions.

Acids can have different strengths, some are more reactive than others. More reactive acids are often more dangerous.

Acids can have a lot of different properties depending on their molecular structure. Most acids have the following properties:

• taste sour when they are eaten
• can sting the skin when they are touched
• can corrode (or eat away at) metals and skin
• can be used as a reactant during electrolysis due to the presence of mobile ions
• turn blue litmus paper red
• turn red or orange on universal indicator
• conduct electricity

Acids can burn the skin, the severity of the burn depending on the type and concentration of the acid. These chemical burns require immediate medical attention.

Because acids donate hydrogen ions, all acids must have hydrogen in them.

Acids can have different strengths, some are more reactive than others. More reactive acids are often more dangerous.

Acids can have a lot of different properties depending on their molecular structure. Most acids have the following properties:

• taste sour when they are eaten
• can sting the skin when they are touched
• can corrode (or eat away at) metals and skin
• can be used as a reactant during electrolysis due to the presence of mobile ions
• turn blue litmus paper red
• turn red or orange on universal indicator
• conduct electricity

Acids can burn the skin, the severity of the burn depending on the type and concentration of the acid. These chemical burns require immediate medical attention.

Because acids donate hydrogen ions, all acids must have hydrogen in them.