Salt is any substance in water that produces a different cation than H+ and an anion different from OH-.
Salts are formed from the reaction of an acid with a base, which is the neutralization reaction, forming also water. Examples:
HCl + NaOH → NaCl + H2O
acid base salt water
The main features are:
- Conduct electricity when in the liquid phase (fused) or in aqueous solution, because in these cases there are free electrons;
- are usually solid at room temperature and pressure (25 ° C and 1atm).
- Sodium chloride (NaCl) - is obtained from seawater and used as food for cooking salt and meat preservation. In industry, it is used for the production of caustic soda and chlorine gas.
- Sodium carbonate (Na2CO3) - also called soda or canister. Used for the manufacture of glass, soap, dyes and in pool water treatment.
- Calcium carbonate (CaCO3) - In nature, it is found in the form of marble, limestone and calcite. It forms the stalactites and stalagmites of caves. Used in the production of cement and virgin lime (Cao). Reduces soil acidity.
stalactite marble and stalagmite in caves
- Sodium hypochlorite (NaOCl) - used as an antiseptic and bleach (whitening clothes).
The name of the salt is formed from the name of the acid that originated it. Like this:
Origin acid anion name + eto / act / ito + cation name from the source base. Example:
|chlor acidhydric||sodium hydroxide||chloreto sodium||Water|
CaF2 - calcium fluoride
NaBr - Sodium Bromide
Li2(ONLY4) - lithium sulphate
KNO2 - potassium nitrite
At2CO3 - sodium carbonate
Base Acid and pH Indicators
Acid-base indicators are organic substances that when in contact with an acid become one color, and when in contact with a base they become another color. Thus, to know if a substance is acid or base, we can use an organic indicator to identify chemical function.
Examples of acid-base indicators are phenolphthalein, methyl orange, litmus paper, bromothymol blue. Some natural indicators can also be used, such as red cabbage and the hortensis and hibiscus flower.
Here's the color that key indicators can get when they come in contact with an acid or base:
For the other indicators:
- Red cabbage, in aqueous medium, turns red in contact with acid, green in contact with base and red when neutral.
- Methyl orange turns red in contact with acid, yellow-orange on base and when neutral;
- Bromothymol blue turns yellow in acid, and blue in base and when neutral;
- The hydrangea flower turns blue in acid medium and pink in base;
- The hibiscus or mime-venus, which is pink in color, turns orange-red in contact with acid and green in basic medium.
Some acid-base indicators are so efficient that they even indicate the degree of acidity or alkalinity (basicity) of substances. This degree is called the pH (hydrogen product) which measures the amount of cation H + in solutions.
There is a scale of acidity and alkalinity ranging from zero to fourteen. The largest number indicates basic (alkaline) solution and the smallest number indicates an acidic solution. If the pH value is seven, ie half, then the solution is neither acidic nor basic, it is neutral.
The closer the solution gets to zero, the more acidic it is. The closer the solution gets to fourteen, the more basic it is.
0 7 14
neutral acid base
In practice, pH can be measured with acid-base indicators and also by means of devices that measure the electrical conductivity of solutions.
The indicators change color at different pH values. For this color change, we call it turning and for the pH value we give the name of turning point. Here are some daily examples of pH values:
Caustic Soda Solution (NaOH)
NaHCO3 aqueous solution
Tap water, rainwater
Gastric Juice (HCl)
HCl aqueous solution
Modern acid and base theories
Generally speaking, we know that acid is every substance that produces an H + cation in water and that base is every substance that produces an OH- anion in water. This theory has long been used to explain the concept of acid and base. And the Arrhenius Theory.
But new theory of acid and base emerged over time. It's the calls Modern acid-base theories. Are they:
- Bronsted-Lowry Theory
- Lewis Theory
First, let's look at Arrhenius's Theory:
For this scientist, acids and bases are electrolytes, which in contact with water release ions. When an acid releases ions in aqueous solution, a ionization. Example:
HCl + H2O → H + + Cl-
It actually releases the hydronium ion (H3O +) like this:
HCl + H2O → H3O + + Cl-
When a base releases ions in aqueous solution, a dissociation.
NaOH + H2O → Na + + OH-
Arrhenius Acid - is every substance that produces an H + cation in water.
Arrhenius Base - is any substance that in water produces an OH- anion.
This theory is based on the studies of chemists Johannes Nicolaus Bronsted and Thomas Martin Lowry. Together they defined acid and base in the absence of water, which is not explained by Arrhenius's theory.
The theory is based on giving or receiving 1 proton.
Bronsted-Lowry Acid - is the whole chemical species that donates 1 proton.
Bronsted-Lowry Base - is every chemical species that gets 1 proton.
donate receive donate receive
HCl + NH3 ↔ NH4+ + Cl-
acid base acid base
In this case, HCl donates 1 proton to ammonia (NH3). In the reverse reaction, NH4 + donates 1 proton to the Cl- ion.
Bronsted-Lowry acids and bases form conjugate pairs. Always an acid and a base. The acid of the first reaction and the base it formed.
HCl and Cl- are conjugated pairs.
HCl is the conjugate acid of its conjugate base Cl-.
NH3 and NH4+ are conjugate pairs.
NH3 is the conjugate base of your NH conjugate acid4+.
US chemist Gilbert Newton Lewis has developed an acid-base theory related to electron pair.
Lewis acid - is the chemical species that receives the electron pair in a chemical reaction.
Lewis base - is the chemical species that donates the electron pair in a chemical reaction.
:NH3 + H + ↔ NH4+
Summary table of acid-base theories:
Release H + in aqueous solution
Releases OH- in aqueous solution
Donate 1 proton
Receive 1 proton
Receives pair of electrons
Donate electron pair