Acids and Bases
The Natural Sources of Acids and Bases
The Natural Source of Salts in Daily Life
Investigate the natural source of salts in daily life
A
salt is a substance formed when some or all of the hydrogen atoms of an
acid are replaced by a metal or ammonium ion. A salt, therefore, may be
defined as a compound in which the replaceable hydrogen of an acid has been wholly or partially replaced by a metal.
salt is a substance formed when some or all of the hydrogen atoms of an
acid are replaced by a metal or ammonium ion. A salt, therefore, may be
defined as a compound in which the replaceable hydrogen of an acid has been wholly or partially replaced by a metal.
In
sodium chloride (NaCl), for example, the hydrogen atom of hydrochloric
acid (HCl) has been wholly replaced by an atom of sodium. In magnesium
sulphate (MgSO4) and sodium sulphate (Na2SO4), both hydrogen atoms of sulphuric acid (H2SO4) have been replaced by one atom of magnesium and two atoms of sodium respectively. In sodium hydrogen sulphate (NaHSO4),
only one out of two hydrogen atoms has been replaced by an atom of
sodium. This type of a salt is called an acid salt, because it still
contains a replaceable hydrogen atom.
sodium chloride (NaCl), for example, the hydrogen atom of hydrochloric
acid (HCl) has been wholly replaced by an atom of sodium. In magnesium
sulphate (MgSO4) and sodium sulphate (Na2SO4), both hydrogen atoms of sulphuric acid (H2SO4) have been replaced by one atom of magnesium and two atoms of sodium respectively. In sodium hydrogen sulphate (NaHSO4),
only one out of two hydrogen atoms has been replaced by an atom of
sodium. This type of a salt is called an acid salt, because it still
contains a replaceable hydrogen atom.
Many
chemical compounds may be classified as salts. The salt most familiar
to every body is table salt (sodium chloride). Baking soda is the salt,
sodium bicarbonate (NaHCO3). Magnesium sulphate (also called Epsom salt) is often found in the home.
chemical compounds may be classified as salts. The salt most familiar
to every body is table salt (sodium chloride). Baking soda is the salt,
sodium bicarbonate (NaHCO3). Magnesium sulphate (also called Epsom salt) is often found in the home.
In
general, salts are ionic impounds that are composed of metal and non
metal ions. For example, sodium chloride is is composed of metallic
sodium ions (Na+) and non-metallic chloride ions (Cl–). Some salts are made of metallic and non-metallic radicals e.g ammonium nitrate (NH4NO3) is composed of ammonium radical (NH4+) and nitrate radical (NO3–).
general, salts are ionic impounds that are composed of metal and non
metal ions. For example, sodium chloride is is composed of metallic
sodium ions (Na+) and non-metallic chloride ions (Cl–). Some salts are made of metallic and non-metallic radicals e.g ammonium nitrate (NH4NO3) is composed of ammonium radical (NH4+) and nitrate radical (NO3–).
There
is a wide range of types and natural sources of salts. Common salt is
mined from underground deposits. The salt obtained from such a source
contains sodium chloride mixed with rock impurities.
is a wide range of types and natural sources of salts. Common salt is
mined from underground deposits. The salt obtained from such a source
contains sodium chloride mixed with rock impurities.
The
other source of sodium chloride is seawater. The salty taste of
seawater is due to the presence of salts such as sodium chloride and
magnesium bromide. However, there are many different types of salts
present in seawater, though in small proportions, as shown in the table
below (table 3.5)
other source of sodium chloride is seawater. The salty taste of
seawater is due to the presence of salts such as sodium chloride and
magnesium bromide. However, there are many different types of salts
present in seawater, though in small proportions, as shown in the table
below (table 3.5)
| Salt | Formula | Percentage composition |
| Sodium chloride | NaCl | 2.72 |
| Magnesium chloride | MgCl2 | 0.38 |
| Magnesium sulphate | MgSO4 | 0.17 |
| Calcium sulphate | CaSO4 | 0.13 |
| Potassium chloride | KCl | 0.09 |
| Calcium chloride | CaCO3 | 0.01 |
| Magnesium bromide | MgBr2 | 0.01 |
Sodium nitrate (Chile saltpetre), NaNO3 and calcium carbonate, CaCO3
are found in underground deposits. Calcium carbonate occurs naturally
as marble, limestone or chalk in the ground from which it can be mined
mechanically. What other natural sources of salts do you know?
are found in underground deposits. Calcium carbonate occurs naturally
as marble, limestone or chalk in the ground from which it can be mined
mechanically. What other natural sources of salts do you know?
Types of Salts
Salts
may be classified according to their mode of formation. The following
are types of salts grouped according to their mode of formation:
may be classified according to their mode of formation. The following
are types of salts grouped according to their mode of formation:
Normal salt:-
This is a salt formed when all of the replaceable hydrogen atoms of an
acid have been replaced by a metal atom e.g. sodium chloride is a normal
salt because all hydrogen atoms are replaced from an acid during its
formation.
This is a salt formed when all of the replaceable hydrogen atoms of an
acid have been replaced by a metal atom e.g. sodium chloride is a normal
salt because all hydrogen atoms are replaced from an acid during its
formation.
2Na(s) + 2HCl(aq)→ 2NaCl(aq) + H2(g)
Other normal salts include magnesium chloride (MgCl2), potassium chloride (KCl), copper (II) sulphate (CuSO4), sodium sulphate (Na2SO4), sodium carbonate (Na2CO3), trisodium phosphate (Na3PO4), etc.
Acid salt:-
An acid salt is a salt formed when part of the replaceable hydrogen
atoms of an acid are displaced by a metal e.g., sodium bisulphate (NaHSO4) is an acid salt.
An acid salt is a salt formed when part of the replaceable hydrogen
atoms of an acid are displaced by a metal e.g., sodium bisulphate (NaHSO4) is an acid salt.
H2SO4(aq) + NaOH(aq)→ NaHSO4(aq) + H2O(l)
Other examples of acid salts include sodium hydrogensulphate, (NaHSO4), sodium hydrogensulphide, (NaHS) and sodium hydrogencarbonate (NaHCO3). Since acid salts contain hydrogen ions, they exhibit some acidic properties. Hence, they behave like acids, for example:
they react with bases to form salts and water only. NaHSO4(aq) + NaOH(aq)→ Na2SO4(aq) + H2O(l)
they react with carbonates to yield carbon dioxide.2NaHSO4(aq) + Na2CO3(aq)→ 2Na2SO4(aq) + H2O(l) + CO2(g)
Basic salt:-
A basic salt is formed by the action of an acid with higher proportions
of the base, than is necessary for the formation of a normal salt.
A basic salt is formed by the action of an acid with higher proportions
of the base, than is necessary for the formation of a normal salt.
Examples of basic salts are:
Basic copper carbonate, CuCO3.Cu(OH)2
Basic lead carbonate (white lead), PbCO3.Pb(OH)2
Basic magnesium chloride, MgCl2.Mg(OH)2
Basic zinc chloride, ZnCl2.Zn(OH)2
A
basic salt may also be formed by the partial replacement of the
hydroxyl groups of a diacidic or triacidic base by an acid radical.
basic salt may also be formed by the partial replacement of the
hydroxyl groups of a diacidic or triacidic base by an acid radical.
Pb(OH)2(s) [lead hydroxide] + HNO3(aq) [nitric acid] → Pb(OH)NO3(s) [basic lead nitrate]+ H2O(l) [water]
Basic
salts are usually insoluble in water. Such salts are formed by the
close association of two simple salts, when crystallized from a solution
of a mixture of the two.
salts are usually insoluble in water. Such salts are formed by the
close association of two simple salts, when crystallized from a solution
of a mixture of the two.
The Solubility of Different Salts in the Laboratory
Analyse the solubility of different salts in the laboratory
Some
salts are more soluble in water than others are. However, other salts
are insoluble in water. The knowledge of solubility of different salts
in water is very important because it can help us prepare different
salts in the laboratory by such methods as precipitation, direct
combination (synthesis), crystallization and so forth.
salts are more soluble in water than others are. However, other salts
are insoluble in water. The knowledge of solubility of different salts
in water is very important because it can help us prepare different
salts in the laboratory by such methods as precipitation, direct
combination (synthesis), crystallization and so forth.
As
regards to solubilities, salts can be classified into two groups: salts
which are soluble in water (soluble salts) and salts which do not
dissolve in water (insoluble salts). Table 3.6 summarizes the solubility
of different salts in water.
regards to solubilities, salts can be classified into two groups: salts
which are soluble in water (soluble salts) and salts which do not
dissolve in water (insoluble salts). Table 3.6 summarizes the solubility
of different salts in water.
The patterns of solubility for various types of salts
| Soluble salts | Insoluble salts |
| 1. All sodium, potassium and ammonium salts. | silver, mercury(I) and lead chlorides barium, lead (II) and calcium sulphates but other common carbonates are insoluble.but other common hydroxides are insoluble. |
| 2. All nitrates of metals | |
| 3. All chlorides except .………………….. | |
| 4. All sulphates except………………….. | |
| 5. Sodium, potassium, and ammonium carbonates…………………………… hydroxides………………………….…… | |
| 6. Sodium, potassium and ammonium |
Salts in the Laboratory
Prepare salts in the laboratory
Several
methods are available for the preparation of salts. The solubilities of
the prepared salts determine their methods of preparation. Hence, in
the choice of a method of preparation of a particular salt, one has to
be acquainted with its solubility properties.
methods are available for the preparation of salts. The solubilities of
the prepared salts determine their methods of preparation. Hence, in
the choice of a method of preparation of a particular salt, one has to
be acquainted with its solubility properties.
Soluble salts are usually prepared by methods which involve crystallization. In this method, as the name suggests, resultant salts are in the form of crystals.
Insoluble salts are usually prepared by methods which involve precipitation.
These methods are sometimes referred to as double decomposition. To
precipitate an insoluble salt, you must mix a solution that contains its
positive ions with the one that contains its negative ions.
These methods are sometimes referred to as double decomposition. To
precipitate an insoluble salt, you must mix a solution that contains its
positive ions with the one that contains its negative ions.
Salts may also be prepared by direct combination (or synthesis). For example, magnesium chloride may be prepared in the laboratory by heating magnesium in a stream of chlorine.
Mg(s) + Cl2(g) → MgCl2(s)
Preparation of soluble salts
Soluble salts may be prepared by any of the following methods:
Reaction between an acid and an alkali:In
this method, a dilute acid is added to an alkali in the appropriate
volume ratio. The reaction between an acid and an alkali is termed as
neutralization. For example, sodium chloride may be prepared by the
following neutralization reaction:NaOH(aq) + HCl(aq)→ NaCl(aq) + H2O(l). Both
reactants are soluble, and no gas is given off during the reaction. So,
it is difficult to know when the reaction is over. In this case, you
have to use an indicator. A universal indicator or litmus could be used,
but even better is phenolphthalein. This is pink in alkaline solution,
but colourless in neutral or acidic solutions.
Reaction of a metal with an acid:This
is another general method for preparing salts. For example, zinc
sulphate can be made by reacting dilute sulphuric acid with zinc:Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g).
However, this method is not suitable for all metals or all acids. It is
good for preparing salts of fairly reactive metals such as magnesium,
aluminium, zinc and iron. However, the reactions of highly reactive
metals like sodium, potassium and calcium with acids are very violent
and dangerous. The reaction with lead is too slow. Copper, silver and
gold do not react at all.
Reaction of a metal oxide with an acid.Metal
oxides, as you studied early, react with dilute acids to produce salts.
Copper oxide is an insoluble base. Although copper will not react with
dilute sulphuric acid, copper (II) oxide will. The salt that forms is
copper (II) sulphate.CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
Reaction of a metal carbonate with an acid.The
reaction between metal carbonates and dilute acids are accompanied with
evolution of carbon dioxide gas. The evolution of a gas can be used to
indicate when the reaction is over. An example of such reactions is the
reaction between calcium carbonate and dilute hydrochloric acid. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
General methods of preparing soluble salts
The
above methods for preparing soluble salts are specific for each method
mentioned. Generally, soluble salts may be prepared by two broad
methods.
above methods for preparing soluble salts are specific for each method
mentioned. Generally, soluble salts may be prepared by two broad
methods.
Method 1:This
route is essentially the same whether starting with a solid metal, a
solid base (oxide) or a solid carbonate. The route can be divided into
four stages:
route is essentially the same whether starting with a solid metal, a
solid base (oxide) or a solid carbonate. The route can be divided into
four stages:
Stage 1:An
excess (more than enough) of the solid is added to the acid and allowed
to react. Using an excess of the solid makes sure that all the acid
used up. If it is not used up at this stage, the acid would become more
concentrated when the water is evaporated later (stage 3).
Stage 2:The excess solid is filtered out after the reaction is completed.
Stage 3: The
filtrate is gently evaporated to concentrate the solution. This can be
done on a heated water bath. Do not heat so strongly or “spitting” might
take place.
Stage 4:The concentrated solution is
cooled down to let the crystals form. Filter off the crystals. Wash them
with a little distilled water. Dry the crystals carefully between the
filter papers.
Method 2:This
method (titration method) involves the neutralization of an acid with
an alkali (for example sodium hydroxide) or a soluble carbonate (for
example sodium carbonate). Since both the reactants and the products are
colourless, an indicator is used to find the neutralization point or end point (when all the acid has just
been neutralized). Once the end point is reached, the resulting salt
solution is evaporated and cooled to form crystals as described in
method 1.
method (titration method) involves the neutralization of an acid with
an alkali (for example sodium hydroxide) or a soluble carbonate (for
example sodium carbonate). Since both the reactants and the products are
colourless, an indicator is used to find the neutralization point or end point (when all the acid has just
been neutralized). Once the end point is reached, the resulting salt
solution is evaporated and cooled to form crystals as described in
method 1.
General methods for preparing insoluble salts
Some
salts are insoluble in water (for example silver chloride and barium
sulphate – see table 3.6). Such salts are generally prepared by ionic
precipitation.Precipitation is the sudden formation of a solid either:
when two solutions are mixed; or when a gas is bubbled into a solution.
salts are insoluble in water (for example silver chloride and barium
sulphate – see table 3.6). Such salts are generally prepared by ionic
precipitation.Precipitation is the sudden formation of a solid either:
when two solutions are mixed; or when a gas is bubbled into a solution.
For
example, barium sulphate can be prepared by adding a solution of a
soluble sulphate (for example sodium sulphate) to a solution of a
soluble barium salt (for example barium chloride). The insoluble barium
sulphate is formed immediately. This solid falls to the bottom of the
container as a precipitate (figure 3.2). The precipitate can be filtered
off. It is then washed with distilled water and dried in a warm oven.
The equation for the reaction is:
example, barium sulphate can be prepared by adding a solution of a
soluble sulphate (for example sodium sulphate) to a solution of a
soluble barium salt (for example barium chloride). The insoluble barium
sulphate is formed immediately. This solid falls to the bottom of the
container as a precipitate (figure 3.2). The precipitate can be filtered
off. It is then washed with distilled water and dried in a warm oven.
The equation for the reaction is:
BaCl2(aq) + Na2SO4(aq)→ BaSO4(s) + 2NaCl(aq)
This
shows how important the state symbols can be – it is only through state
symbols that we can tell this equation shows a precipitation.
shows how important the state symbols can be – it is only through state
symbols that we can tell this equation shows a precipitation.
Barium
sulphate could also be made from barium nitrate and sodium sulphate,
for example, since these salts are both soluble. As long as barium and
sulphate ions are present, barium sulphate will be precipitated.
sulphate could also be made from barium nitrate and sodium sulphate,
for example, since these salts are both soluble. As long as barium and
sulphate ions are present, barium sulphate will be precipitated.
Ba2+(aq) + SO42-(aq) →BaSO4(s)
Precipitation reactions are often used in a qualitative analysis to identify salts such as chlorides, iodides and sulphates.
Preparation of salts by direct combination (synthesis)
Some
soluble and insoluble salts can be made directly by reacting two
elements together. This is called combination (or synthesis). This type
of reaction is mainly possible for metal chlorides, bromides and
iodides. For instance, if a piece of burning sodium is lowered into a
gas jar of chlorine, the two react violently to produce a white powder
of sodium chloride:
soluble and insoluble salts can be made directly by reacting two
elements together. This is called combination (or synthesis). This type
of reaction is mainly possible for metal chlorides, bromides and
iodides. For instance, if a piece of burning sodium is lowered into a
gas jar of chlorine, the two react violently to produce a white powder
of sodium chloride:
2Na(s) + Cl2(g) → 2NaCl(s)
Other
chlorides can also be prepared by combination, for example, iron (III)
chloride and aluminium chloride can be made by heating iron and
aluminium metals in stream of chlorine:
chlorides can also be prepared by combination, for example, iron (III)
chloride and aluminium chloride can be made by heating iron and
aluminium metals in stream of chlorine:
2Fe(s) + 3Cl2(g) → 2FeCl3(s)
2Al(s) + 3Cl2(g) → 2AlCl3(s)
The reaction between ammonia gas and hydrogen chloride gas to produce ammonium chloride is also a synthesis reaction.
NH3(g) + HCl(g) → NH4Cl(s)
Direct combination reactions do not produce crystals of the salt, but only a powder.
The Effects of Heat on Salts
Examine the effects of heat on salts
When
different salts are heated, they behave in different manners. The
crystals of some salts contain water of crystallization. When these
hydrated salts are heated, their water of crystallization is driven off
as steam. The crystals then lose their shape and become a powder. The
following are few examples of hydrated salts:
different salts are heated, they behave in different manners. The
crystals of some salts contain water of crystallization. When these
hydrated salts are heated, their water of crystallization is driven off
as steam. The crystals then lose their shape and become a powder. The
following are few examples of hydrated salts:
| Salt formula | Chemical name |
| CuSO4.5H2O | Copper (II) sulphate five water |
| Na2CO3.I0H2O | Sodium carbonate ten water |
| MgCl2.6H2O | Magnesium chloride six water |
| FeCl3.6H2O | Iron (III) chloride six water |
| FeSO4.7H2O | Iron (II) sulphate seven water |
| CoCl2.6H2O | Cobalt (II) chloride six water |
| MgSO4.7H2O | Magnesium sulphate seven water |
| CaSO4.2H2O | Calcium sulphate two water |
Sulphates
Sulphates
of potassium, sodium, calcium, lithium and magnesium are stable to heat
and do not decompose when heated. Other sulphates decompose to give the
oxide and sulphur trioxide gas except iron (III) sulphate which
decomposes to give sulphur dioxide and sulphur trioxide.
of potassium, sodium, calcium, lithium and magnesium are stable to heat
and do not decompose when heated. Other sulphates decompose to give the
oxide and sulphur trioxide gas except iron (III) sulphate which
decomposes to give sulphur dioxide and sulphur trioxide.
Copper (II) sulphate five water crystals are blue in colour, but when heated, they are dehydrated to form a white powder:
CuSO4.5H2O(s)hydrated (blue)→ CuSO4(s)anhydrous (white) + 5H2O(g)
Crystals
that have lost their water of crystallization are called anhydrous. If
water is added back to the anhydrous copper (II) sulphate powder, the
powder turns into blue crystals again and heat is evolved. This can be
used as a qualitative test for water.If the white, anhydrous powder is
further heated strongly, it decomposes to black copper (II) oxide:
that have lost their water of crystallization are called anhydrous. If
water is added back to the anhydrous copper (II) sulphate powder, the
powder turns into blue crystals again and heat is evolved. This can be
used as a qualitative test for water.If the white, anhydrous powder is
further heated strongly, it decomposes to black copper (II) oxide:
CuSO4(s)white→ CuO(s)black+ SO3(g)
Hydrated
iron (II) sulphate is green in colour. When heated, it loses all its
water of crystallization and changes colour from green to white:
iron (II) sulphate is green in colour. When heated, it loses all its
water of crystallization and changes colour from green to white:
FeSO4.7H2O(s)green→ FeSO4(s)white + 7H2O(g)
When heated even more strongly, the white powder decomposes to form a black oxide:
2FeSO4(s)white→ Fe2O3(s)black+ SO2(g) + SO3(g)
Iron (III) sulphate decomposes on heating to form slightly different products:
Fe2(SO4)3(s) → Fe2O3 + 3SO3(g)
Chlorides
The
chlorides of most metals are hydrated except those of potassium, lead,
mercury and silver. Hydrated chlorides do not usually give the anhydrous
salt when heated. Instead, a chemical change termed as hydrolysis
normally occurs. The reaction is accompanied by the evolution of steam
and hydrogen chloride gas, and the formation of the basic chloride or
oxide. When, for example, hydrated magnesium chloride is heated, its
basic chloride is formed:
chlorides of most metals are hydrated except those of potassium, lead,
mercury and silver. Hydrated chlorides do not usually give the anhydrous
salt when heated. Instead, a chemical change termed as hydrolysis
normally occurs. The reaction is accompanied by the evolution of steam
and hydrogen chloride gas, and the formation of the basic chloride or
oxide. When, for example, hydrated magnesium chloride is heated, its
basic chloride is formed:
MgCl2.6H2O(s) → Mg (OH)Cl(s) + HCl(g) + 5H2O(g)
The
same case applies when hydrated calcium chloride is heated. However,
when hydrated aluminum chloride is heated, it does not produce the
anhydrous salt. Instead, the oxide is formed thus:
same case applies when hydrated calcium chloride is heated. However,
when hydrated aluminum chloride is heated, it does not produce the
anhydrous salt. Instead, the oxide is formed thus:
2AlCl3.6H2O(s) → Al2O3(s) + 6HCl(g) + 3H2O(g)
Ammonium
chloride sublimes when heated. The reaction is reversible and the
products may recombine on cooling to form the salt back.
chloride sublimes when heated. The reaction is reversible and the
products may recombine on cooling to form the salt back.
NH4Cl=⇔NH3(g) + HCl(g)
Carbonates and hydrogencarbonates
The
carbonates of potassium and sodium are very stable to heat. They do not
decompose even when heated to very high temperatures. All other
carbonates decompose when heated to give the oxide and carbon dioxide:
carbonates of potassium and sodium are very stable to heat. They do not
decompose even when heated to very high temperatures. All other
carbonates decompose when heated to give the oxide and carbon dioxide:
CaCO3(s) ⇔CaO(s) + CO2(g)
CuCO3(s) → CuO(s) + CO2(g)
However,
there are very few and exceptional carbonates that do not behave like
this. Ammonium carbonate, for example, decomposes readily when heated to
give ammonia gas, water vapour and carbon dioxide gas:
there are very few and exceptional carbonates that do not behave like
this. Ammonium carbonate, for example, decomposes readily when heated to
give ammonia gas, water vapour and carbon dioxide gas:
(NH4)2CO3(s) → 2NH3(g) + H2O(g) + CO2(g)
All hydrogencarbonates decompose on heating to give the carbonates, water vapour and carbon dioxide:
2NaHCO3(s) → Na2CO3(s) + H2O(g) CO2(g)
Nitrates
When heated, potassium and sodium nitrates decompose to give the nitrite and oxygen:
2KNO3(s) → 2KNO2(s) + O2(g)
2NaNO3(s) → 2NaNO2(s) + O2(g)
The
nitrates of common heavy metals (such as Pb, Al, Ca, Mg, Zn and Cu)
decompose on heating to give the oxide, nitrogen dioxide and oxygen:
nitrates of common heavy metals (such as Pb, Al, Ca, Mg, Zn and Cu)
decompose on heating to give the oxide, nitrogen dioxide and oxygen:
2Pb(NO3)2(s) → 2PbO(s) + 4NO2 (g) + O2 (g)
2Ca(NO3)2(s) → 2CaO(s) + 4NO2 (g) + O2 (g)
The nitrates of silver and mercury are completely decomposed to the metal, nitrogen dioxide and oxygen:
2AgNO3(s) → 2Ag (g) + 2NO2 (g) + O2 (g)
Hg(NO3)2(s) → Hg(l) + 2NO2(g) + O2(g)
Ammonium nitrate is decomposed by heat into dinitrogen oxide and water:
NH4NO3(s) → N2O (g) + 2H2O (l)
Hydroxides
Potassium
and sodium hydroxides are very stable to heat. They do not decompose
even when heated strongly. All other hydroxides decompose to give the
oxide and water vapour, e.g.:
and sodium hydroxides are very stable to heat. They do not decompose
even when heated strongly. All other hydroxides decompose to give the
oxide and water vapour, e.g.:
Ca(OH)2(s) → CaO(s) + H2O(g)
DELIQUESCENCE, EFFLORESCENCE AND HYGROSCOPY
Deliquescence
Deliquescence is the absorbing of moisture from the atmosphere by a solid to form a solution.If calcium chloride (CaCl2)
is exposed to air, it absorbs water vapour from the atmosphere and
eventually dissolves. Its tendency to absorb water vapour explains why
it is used as a drying agent for gases (not ammonia, because it combines
with the gas).
is exposed to air, it absorbs water vapour from the atmosphere and
eventually dissolves. Its tendency to absorb water vapour explains why
it is used as a drying agent for gases (not ammonia, because it combines
with the gas).
Solid
sodium hydroxide is also deliquescent. On exposure to air, pellets of
sodium hydroxide quickly become shiny and then sticky as they absorb
water vapour from the atmosphere. Eventually the sodium hydroxide
pellets absorb moisture from the atmosphere so much that they dissolve
to form a solution of sodium hydroxide.
sodium hydroxide is also deliquescent. On exposure to air, pellets of
sodium hydroxide quickly become shiny and then sticky as they absorb
water vapour from the atmosphere. Eventually the sodium hydroxide
pellets absorb moisture from the atmosphere so much that they dissolve
to form a solution of sodium hydroxide.
Copper
(II) nitrate and zinc chloride are the other deliquescent salts. Pure
table salt (NaCl) is not deliquescent. However, if the salt is directly
obtained from the sea, it is deliquescent. The salt from the sea
contains magnesium chloride as one as the impurities. It is this
magnesium chloride salt that deliquesces and not sodium chloride.
(II) nitrate and zinc chloride are the other deliquescent salts. Pure
table salt (NaCl) is not deliquescent. However, if the salt is directly
obtained from the sea, it is deliquescent. The salt from the sea
contains magnesium chloride as one as the impurities. It is this
magnesium chloride salt that deliquesces and not sodium chloride.
Hygroscopy
Some
substances tend to absorb water vapour from the air but do not change
their physical states. Copper (II) oxide and calcium oxide are both
hygroscopic solids because they can absorb moisture from the atmosphere
and yet retain their solid states. Because of this behaviour, calcium
oxide is used as a drying agent, which absorbs moisture from gases
prepared in the laboratory.
substances tend to absorb water vapour from the air but do not change
their physical states. Copper (II) oxide and calcium oxide are both
hygroscopic solids because they can absorb moisture from the atmosphere
and yet retain their solid states. Because of this behaviour, calcium
oxide is used as a drying agent, which absorbs moisture from gases
prepared in the laboratory.
Concentrated
sulphuric acid is a hygroscopic liquid. When exposed to air, the acid
absorbs water vapour from the atmosphere diluting itself to absorb 3
times its original volume.
sulphuric acid is a hygroscopic liquid. When exposed to air, the acid
absorbs water vapour from the atmosphere diluting itself to absorb 3
times its original volume.
Therefore, hygroscopy
may be defined as the tendency of a substance to absorb water vapour
from the atmosphere without changing its physical states.The word
hygroscopy is a general term applied to all substances that absorb water
vapour from the air. Any substance that can take up moisture from the
atmosphere is said to be hygroscopic in nature.
may be defined as the tendency of a substance to absorb water vapour
from the atmosphere without changing its physical states.The word
hygroscopy is a general term applied to all substances that absorb water
vapour from the air. Any substance that can take up moisture from the
atmosphere is said to be hygroscopic in nature.
Efflorescence
Efflorescence
is the tendency of a hydrated substance to lose the water of
crystallization to the atmosphere. Some salt crystals give out some or
all of their water of crystallization to the atmosphere when exposed to
air. Such substances are said to be efflorescent and the process of water loss is known as efflorescence.
Sodium carbonate ten water (washing soda) is a good example of an
efflorescent substance. If washing soda crystals are exposed to open air
at room temperature, they lose some of the water of crystallization.
The solid loses nine of its ten molecules of water of crystallization to
the air. One molecule of water, which remains fixed, can be removed
only by strong heating.
is the tendency of a hydrated substance to lose the water of
crystallization to the atmosphere. Some salt crystals give out some or
all of their water of crystallization to the atmosphere when exposed to
air. Such substances are said to be efflorescent and the process of water loss is known as efflorescence.
Sodium carbonate ten water (washing soda) is a good example of an
efflorescent substance. If washing soda crystals are exposed to open air
at room temperature, they lose some of the water of crystallization.
The solid loses nine of its ten molecules of water of crystallization to
the air. One molecule of water, which remains fixed, can be removed
only by strong heating.
Na2CO3.10H2O(s)crystals → Na2CO3.H2O(s)powder + 9H2O(g)
The
crystal lattice is broken down as the salt loses its after of
crystallization. Thus, transparent crystals of hydrated sodium
carbonates become white and powdery on the surface.
crystal lattice is broken down as the salt loses its after of
crystallization. Thus, transparent crystals of hydrated sodium
carbonates become white and powdery on the surface.
Another efflorescent compound is Glauber’s salt, sodium sulphate ten water (Na2SO4.10H2O). On exposure to air, it loses the whole of its water of crystallization to the air.
Na2SO4.10H2O(s) → Na2SO4(s) + 10H2O(g)
Iron (II) sulphate seven water (FeSO4.7H2O) is also efflorescent.
The Uses of Different Types of Salts in Everyday Life
Explain the uses of different types of salts in everyday life
There
is a wide range of salts. A great number of them play an important role
in our everyday life. The following are the uses of some salts:
is a wide range of salts. A great number of them play an important role
in our everyday life. The following are the uses of some salts:
Sodium chloride (common salt)
Sodium
chloride often called common salt or table salt, is essential for life
and is an important raw material for industries. At home, it is used for
cooking, that is, flavouring different foods.Biologically, it has a
number of functions: it is involved in muscle contraction; it enables
the conduction of nerve impulses in the nervous system; it regulates
osmosis (the passage of solvent molecules through membranes); and it is
converted into the hydrochloric acid that aids digestions in the
stomach.
chloride often called common salt or table salt, is essential for life
and is an important raw material for industries. At home, it is used for
cooking, that is, flavouring different foods.Biologically, it has a
number of functions: it is involved in muscle contraction; it enables
the conduction of nerve impulses in the nervous system; it regulates
osmosis (the passage of solvent molecules through membranes); and it is
converted into the hydrochloric acid that aids digestions in the
stomach.
Some
industrial uses of sodium chloride include curing bacon, flavouring
foods, and in the manufacture of margarine, butter and cheese. It is
also used to tan leather in the leather industry. Rock salt is used as a
fertilizer for sugar beet, and is spread on roads to melt the ice
during winter. The salt is the starting point for many important
chemicals, for example, the electrolysis of brine (concentrated solution
of sodium chloride) gives sodium hydroxide, chlorine and hydrogen. What
other uses of sodium chloride do you know? Mention them.
industrial uses of sodium chloride include curing bacon, flavouring
foods, and in the manufacture of margarine, butter and cheese. It is
also used to tan leather in the leather industry. Rock salt is used as a
fertilizer for sugar beet, and is spread on roads to melt the ice
during winter. The salt is the starting point for many important
chemicals, for example, the electrolysis of brine (concentrated solution
of sodium chloride) gives sodium hydroxide, chlorine and hydrogen. What
other uses of sodium chloride do you know? Mention them.
Calcium carbonate (marble, limestone, chalk)
Calcium carbonate finds a wide range of uses:
An
important use of calcium carbonate is in the building industry. It is
widely used in making cement, lime, mortar and making steel from iron.
Powdered
limestone is used as a liming material to neutralize soil acidity. When
used in this way, it is termed as agricultural lime. When added in the
soil, agricultural lime acts as a calcium source for plants as well as
increasing the pH and water retaining capacity of acidic soils.
It is also used in making paint, plastic, rubber, ceramic and glass; and in oil refining, and iron ore purification.
Calcium carbonate is the most preferred mineral in the paper industry. It helps in the production of the best quality papers.
Since calcium is essential for healthy bones and teeth, it is used as a dietary calcium supplement.
Limestone can also be well shaped, painted, and then used as decorative stones.
Ammonium salts
Most ammonium salts such as (NH4)3PO4, NH4Cl, NH4NO3, (NH4)2SO4,
CAN, urea, etc are used as nitrogenous fertilizers which are applied to
the soil to improve soil fertility and hence enhance plant growth and
production. Millions of tonnes of fertilizers are produced every year.
Without these chemicals, world food production would probably be halved.
CAN, urea, etc are used as nitrogenous fertilizers which are applied to
the soil to improve soil fertility and hence enhance plant growth and
production. Millions of tonnes of fertilizers are produced every year.
Without these chemicals, world food production would probably be halved.
Calcium sulphate (anhydride, CaSO4; gypsum, CaSO4.H2O)
Gypsum
is chiefly used for the manufacture of Plaster of Paris (P.O.P). The
Plaster of Paris is used for making casts for statuary ( the expansion
during setting ensures a fine impression), in surgery to maintain joints
in a fixed position and in cement and wall plasters.
is chiefly used for the manufacture of Plaster of Paris (P.O.P). The
Plaster of Paris is used for making casts for statuary ( the expansion
during setting ensures a fine impression), in surgery to maintain joints
in a fixed position and in cement and wall plasters.
Among
the many other uses of calcium sulphate are as a pigment in white
paints, as a soil conditioner, in Portland cement, as a sizer, filler,
and coating agent in papers, in the manufacture of sulphuric acid and
sulphur, in the metallurgy of zinc ores and as a drying agent in many
laboratory and commercial processes.
the many other uses of calcium sulphate are as a pigment in white
paints, as a soil conditioner, in Portland cement, as a sizer, filler,
and coating agent in papers, in the manufacture of sulphuric acid and
sulphur, in the metallurgy of zinc ores and as a drying agent in many
laboratory and commercial processes.
Sodium carbonate (washing soda)
Sodium
carbonate is widely used as one of the raw materials for making glass.
Glass is made by heating a mixture of limestone, sand, sodium carbonate,
and recycled glass in a furnace.The cosmetic industry uses it for
manufacturing soap. The chemical industry uses it as a precursor to
numerous sodium-containing reagents
carbonate is widely used as one of the raw materials for making glass.
Glass is made by heating a mixture of limestone, sand, sodium carbonate,
and recycled glass in a furnace.The cosmetic industry uses it for
manufacturing soap. The chemical industry uses it as a precursor to
numerous sodium-containing reagents
It
is also important in photography and in the textile industry. In
addition to these industrial applications, sodium carbonate is used in
medicine as an anti-acid
is also important in photography and in the textile industry. In
addition to these industrial applications, sodium carbonate is used in
medicine as an anti-acid
Sodium
carbonate has various environmental applications. Large quantities of
the carbonate are used in sewage treatment; in water softening as
washing soda crystals, Na2CO3.10H2O, and in desulphurisation of flue gas.
carbonate has various environmental applications. Large quantities of
the carbonate are used in sewage treatment; in water softening as
washing soda crystals, Na2CO3.10H2O, and in desulphurisation of flue gas.
Magnesium sulphate (Epsom salt)
Magnesium
sulphate is mainly employed for making health salts (laxative, mild
purgative). The health salt is used as a medicine (laxative) which aids
to empty the bowels following constipation or other health problems.
sulphate is mainly employed for making health salts (laxative, mild
purgative). The health salt is used as a medicine (laxative) which aids
to empty the bowels following constipation or other health problems.
Copper (II) sulphate
Copper
(II) sulphate is used in fungicides, which are sprayed on crops,
especially vines and potatoes, to kill moulds which would injure plants
and hence curtail crop yield. It is also used in the manufacture of
certain green pigments which are used for painting.
(II) sulphate is used in fungicides, which are sprayed on crops,
especially vines and potatoes, to kill moulds which would injure plants
and hence curtail crop yield. It is also used in the manufacture of
certain green pigments which are used for painting.
Calcium phosphate
It
is largely used in making phosphoric acid and fertilizers. Calcium
phosphate is used in baking. It is also used in cheese products.
