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Properties of Acids and Bases

Now that you are aware of the acid-base theories, you can learn about the physical and chemical properties of acids and bases. Acids and bases have very different properties, allowing them to be distinguished by observation.


Bromothymol blue is an indicator that turns blue in a base, or yellow in acid.

Made with special chemical compounds that react slightly with an acid or base, indicators will change color in the presence of an acid or base. A common indicator is litmus paper. Litmus paper turns red in acidic conditions and blue in basic conditions. Phenolphthalein purple is colorless in acidic and neutral solutions, but it turns purple once the solution becomes basic. It is useful when attempting to neutralize an acidic solution; once the indicator turns purple, enough base has been added.


A less informative method is to test for conductivity. Acids and bases in aqueous solutions will conduct electricity because they contain dissolved ions. Therefore, acids and bases are electrolytes. Strong acids and bases will be strong electrolytes. Weak acids and bases will be weak electrolytes. This affects the amount of conductivity.

However, acids will react with metal, so testing conductivity may not be plausible.

Physical properties

The physical properties of acids and bases are opposites.












These properties are very general; they may not be true for every single acid or base.

Another warning: if an acid or base is spilled, it must be cleaned up immediately and properly (according to the procedures of the lab you are working in). If, for example, sodium hydroxide is spilled, the water will begin to evaporate. Sodium hydroxide does not evaporate, so the concentration of the base steadily increases until it becomes damaging to its surrounding surfaces.

Chemical Reactions


Acids will react with bases to form a salt and water. This is a neutralization reaction. The products of a neutralization reaction are much less acidic or basic than the reactants were. For example, sodium hydroxide (a base) is added to hydrochloric acid.

{\displaystyle {\hbox{NaOH}}_{(aq)}+{\hbox{HCl}}_{(aq)}\to {\hbox{NaCl}}_{(aq)}+{\hbox{H}}_{2}{\hbox{O}}_{(l)}}This is a double replacement reaction.


{\displaystyle 2{\hbox{HCl}}_{(aq)}+{\hbox{Zn}}_{(s)}\to {\hbox{ZnCl}}_{2(aq)}+{\hbox{H}}_{2(g)}}

Acids react with metal to produce a metal salt and hydrogen gas bubbles.

{\displaystyle {\hbox{H}}_{2}{\hbox{SO}}_{4(aq)}+{\hbox{CaCO}}_{3(s)}\to {\hbox{CaSO}}_{4(s)}+{\hbox{H}}_{2}{\hbox{O}}_{(l)}+{\hbox{CO}}_{2(g)}}

Acids react with metal carbonates to produce water, CO2 gas bubbles, and a salt.

{\displaystyle 2{\hbox{HNO}}_{3(aq)}+{\hbox{Na}}_{2}{\hbox{O}}_{(s)}\to 2{\hbox{NaNO}}_{3(aq)}+{\hbox{H}}_{2}{\hbox{O}}}

Acids react with metal oxides to produce water and a salt.


Bases are typically less reactive and violent than acids. They do still undergo many chemical reactions, especially with organic compounds. A common reactions is saponificiation: the reaction of a base with fat or oil to create soap.

Earth Chemistry
The chemical term earths was historically applied to certain chemical substances, once thought to be elements, and this name was borrowed from one of the four classical elements of Plato. "Earths" later turned out to be chemical compounds, albeit difficult to concentrate, such as rare earths and alkaline earths.

Earths are metallic oxides, and the corresponding metals were classified into the corresponding groups: rare earth metals and alkaline earth metals

Let’s take a moment for a closer look at the Earth’s chemistry; in particular, the chemical elements interspersed in the Earth’s major depths.

With an atmosphere containing 78% nitrogen and 21% oxygen, the Earth is the only planet in the solar system capable of initiating and sustaining life-forms; the various chemical elements that make up the Earth, from the crust, down to the mantle and core, have a little something to do with that.

Defining the Earth’s Boundaries and Elements

As scientists are not able to visit the Earth’s deep interior or place instruments within it, they explore in subtle ways. One approach is to study the Earth with non-material probes, such as seismic waves emitted by earthquakes.  As seismic waves pass through the Earth, they undergo sudden changes in direction and velocity at certain depths. These depths mark the major boundaries, also called discontinuities, that divide the Earth into crust, mantle and core.

The Crust.  The Earth’s crust is the thin outermost layer of the Earth, with an average depth of 24 km (15 mi).  The crust accounts for 1.05% of the Earth’s volume and 0.5% of its mass.  The chemical elements oxygen, silicon and aluminum dominate the crustal composition. The major mineral type – the feldspars – are alumino-silicates of the alkali and alkaline-earth metals. Silicon dioxide is the second most common group.

The Mantle.  The mantle extends from the base of the crust to the core and is about 2865 km (1780 mi) thick, occupying about 82.5% of the Earth’s volume. The upper mantle is rich in olivine and pyroxenes. The major mineral type in the lower mantle appears to be pyroxenes, especially magnesium silicate.  Scientists think that the lowest layer of the mantle called “D layer” is richer in aluminum and calcium than the higher layers of the mantle.

The Core.  The core extends from the base of the mantle to the Earth’s center, and is 6964 kn (4327 mi) in diameter – accounting for only 16.3% of the Earth’s volume, but 33.5% of its mass. The core is made up of two distinct parts – a liquid outer core, which is 2260 km (1404 mi) thick, and a solid inner core, which has a radius of 1222 km (759 mi).  The core is chemically distinct from the mantle and contains about 89% iron and 6% nickel.  The remaining 5% is made of lighter elements, possibly sulfur – but we cannot rule out the presence of oxygen and silicon, in light of a 2013 study published in Nature, which calls them “prime candidates” for the lighter elements in the Earth’s core.

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