SALTS.
71. Acids and Bases are usually Opposite in Character.--When two
forces act in opposition they tend to neutralize each other. We
may see an analogy to this in the union of the two opposite
classes of compounds, acids and bases, to form salts.
72. Neutralization.
Experiment 44.--Put into an evaporating-dish 5 cc. of NaOH
solution. Add HCl to this from a t.t., a few drops at a time,
stirring the mixture with a glass rod (Fig. 20), and testing it
with litmus paper, until the liquid is neutral, i.e. will not
turn the test paper from blue to red, or red to blue. Test with
both colors. If it turns blue to red, too much acid has been
added; if red to blue, too much base. When it is very nearly
neutral, add the reagent, HCl or NaOH, a drop at a time with the
stirring-rod. It must be absolutely neutral to both colors.
Evaporate the water by heating the dish over asbestus paper, wire
gauze, or sand, in an iron plate (Fig. 21) till the residue
becomes dry and white. Cool the residue, taste, and name it. The
equation is: HCl + NaOH = NaCl + HOH or H2O. Note which elements,
positive or negative, change places. Why was the liquid boiled?
The residue is a type of a large class of compounds, called
salts.
(Fig. 20) (Fig. 21)
Experiment 45. -- Experiment in the same way with KOH solution
and H2SO4, applying the same tests. H2SO4 + 2 KOH = K2SO4 + 2
HOH. What is the solid product?
Experiment 46.--Neutralize NH4OH with HNO3, evaporate, apply the
tests, and write the equation. Write equations for the
combination of NaOH and H2SO4; NaOH and HNO3; KOH and HCl; KOH
and HNO3; NH4OH and HCl; NH4OH and H2SO4. Describe the experiment
represented by each equation, and be sure you can perform it if
asked to do so. What is the usual action of a salt on litmus? How
is a salt made? What else is formed at the same time? Have all
salts a saline taste? Does every salt contain a positive element
or radical? A negative?
73. A Salt is the product of the union of a positive and a
negative element or radical; it may be made by mixing a base and
an acid.
The salt KI represents what acid? What base, or hydrate? Write
the equation for making KI from its acid and base. Describe the
experiment in full. Classify, as to acids, bases, or salts: KBr,
Fe(OH)2, HI, NaBr, HNO2, Al2(OH)6, KClO3, HClO3, H2S, K2S, H2S03,
K2SO4, Ca(OH)2, CaCO3, NaBr03, CaSO4, H2CO3, K2CO3, Cu(OH)2,
Cu(NO3)2, PbSO4, H3P04, Na2P04. In the SALTS above, draw a light
vertical line, separating the positive from the negative part of
the symbol. Now state what acid each represents. What base. Write
the reaction in the preparation of each salt above from its acid
and base; then state the experiment for producing it.
74. Naming Salts.--(NO3) is the nitrate radical; KNO3 is
potassium nitrate. From what acid? (NO2) is the nitrite radical;
KN02 is potassium nitrite. From what acid? Note that the endings
of the acids are OUS and IC; also that the names of their salts
end in ITE and ATE. From which acid--IC or OUS--is the salt
ending in ATE derived? That ending in ITE?
Name these salts, the acids from which they are derived, and the
endings of both acids and salts: NaNO3, NaNO2, K2SO4, K2SO3,
CaSO4, CaSO3, KClO3, KClO2, KClO, KClO4 (use prefixes HYPO and
PER, as with acids), Ca3(PO4)2, Ca3(P03)2, CuSO4, CuSO3, AgNO3,
Cu(NO3)2. FeS, FeS2, are respectively FERROUS SULPHIDE and FERRIC
SULPHIDE. Name: HgCl, HgCl2, FeCl2, Fe2Cl6, FeSO4, Fe2(SO4)3.75.
Acid Salts.--Write symbols for nitric, sulphuric, phosphoric
acids. How many H atoms in each? Replace all the H in the symbol
of each with Na, and name the products. Again, in sulphuric acid
replace one atom of H with Na; then in phosphoric replace first
one, then two, and finally three H atoms with Na. HNaSO4 is
hydrogen sodium sulphate; HNa2P04 is hydrogen di-sodium
phosphate. Name the other salts symbolized. Name HNaNH4P04.
Though these products are all salts, some contain replaceable H,
and are called acid salts. Those which have all the H replaced by
a metal are normal salts. Name and classify, as to normal or acid
salts: Na2CO3, HNaCO3, K2SO4, HKSO4, (NH4)2SO4, HNH4SO4, Na3P04,
HNa2P04, H2NaP04.
The BASICITY of an acid is determined by the number of
replaceable H atoms in its molecule. It is called MONOBASIC if it
has one; DIBASIC if two; TRI- if three, etc. Note the basicity of
each acid named above. How many possible salts of H2SO4 with Na?
Of H3P04 with Na? Which are normal and which acid? What is the
basicity of H4Si04?
Some normal, as well as acid, salts change litmus. Na2CO3,
representing a strong base and a weak acid, turns it blue. There
are other modes of obtaining salts, but this is the only one
which we sball consider.
76. Salts Occur Abundantly in Nature, such as NaCl, MgSO4, CaCO3.
Acids and bases are found in small quantities only. Why is this?
Why are there not springs of H2SO4 and NH4OH? We have seen that
acids and bases are extremely active, have opposite characters,
and combine to form relatively inactive salts. If they existed in
the free state, they would soon combine by reason of their strong
affinities. This is what in all ages of the world has taken
place, and this is why salts are common, acids and bases rare.
Active agents rarely exist in the free state in large quantities.
Oxygen seems to be an exception, but this is because there is a
superabundance of it. While vast quantities are locked up in
compounds in rocks, water, and salts of the earth, much remains
with which there is nothing to combine.