Chemistry Kenya
Acids, Bases and Salts
Acids, Bases and Salts
Acids, Bases and Salts
Acids and Bases
In everyday life, we deal with many substances that chemists classify as acids. For example, orange juice and grapefruit juice contain citric acid. These juices, and others of the like, contain ascorbic acid, a substance more commonly known as vitamin C. Examples of natural sources of acids and the type of acids they contain are shown in table below.
| Source | Type of acid present |
| Mineral acids (HCl, H2SO4, HNO3, etc.) | Minerals |
| Tobacco | Salicylic acid |
| Tea | Tannic acid |
| Coffee | Chlorogenic acid |
| Sugar beet | Glutaric and adipic acids |
| Blackberry | Isocitric acid |
| Spinach, tomato | Oxalic acid |
| Sour (fermented milk) | Lactic acid |
| Bee, ant and nettle stings | Methanoic acid (formic acid) |
| Grapes, bananas, tamarinds | Tartaric acid |
| Citrus fruits | Citric acid ( lemons and limes have particularly high concentrations of citric acid; it can constitute as much as 8% of the dry weight of these fruits) |
Acids have a sour taste. Vinegar, lemon juice, grapefruit juice and spoilt or fermented milk are all sour tasting because of the presence of acids. The acids present in animal and plant materials are known as organic acids.
Salads are often flavoured with vinegar, which contains dilute acetic acid. Boric acid is a substance that is sometimes used to wash the eyes.
In any chemistry laboratory, we find acids such as hydrochloric acid (HCl), sulphuric acid (H2SO4), and nitric acid (HNO3). These acids are called mineral acids because they can be prepared from naturally occurring compounds called minerals. Mineral acids are generally stronger and should be handled with great care, especially the concentrated acids, for they are very corrosive. They can eat away metals, skin and clothing. Nevertheless, some acids are not corrosive even when they are concentrated. They are called weak acids. Ethanoic acid is one example. It is found in vinegar. In general, organic acids are weaker than natural acids.
You can tell if a substance is acid or not by its effect on litmus. Litmus is a purple dye. It can be used as a solution, or on paper, called litmus paper.Litmus solution is purple. Litmus paper for testing acids is blue while that for testing bases is red in colour. Acids will turn litmus solution red. They will also turn blue litmus paper red.
Bases do not usually occur naturally. So they are not normally obtained from natural sources. However, they are prepared in the laboratory or in industry. Bases can be classified into oxides, hydroxides or carbonates. Therefore, bases can be defined as the oxides, hydroxides or carbonates of metals. Bases taste bitter. A bitter taste is a characteristic of all bases.
Most bases are insoluble in water. The bases which dissolve in water are known as alkalis. The most common alkalis are potassium hydroxide (KOH), sodium hydroxide (NaOH), calcium hydroxide, Ca(OH)2, and ammonium hydroxide (NH4OH), also known as ammonia solution.
Alkalis turn litmus solution blue and red litmus paper blue.A substance, such as litmus, which changes from one colour to another when mixed with an acid or base, is called an indicator. Table 3.2 shows how acids and bases (alkalis) affect the colours of different indicators. We can use this clue of colour changes to tell whether an unknown substance is an acid or base (alkali).
| Indicator | Colour in acid | Colour in alkali (base) |
| Methyl orange | orange | yellow |
| Phenolphthalein | colourless | Pink |
| Litmus | red | blue |
| Bromothymol blue | yellow | blue |
Acids react with different substances to produce different products. These reactions are best carried out by using dilute acid solutions. The following are some reactions of dilute acids with various substances.
Reaction with metals
Acids react with quite reactive metals (not very reactive ones) to produce salt and liberate a hydrogen gas.
metal + acid → salt + hydrogen
It is unsafe to try this reaction with very reactive metals such as sodium or calcium. The reaction with such metals is so violent. Metals less reactive than lead, such as silver and gold have no reaction with dilute acids. Even with lead, it is difficult to see any reaction in a short time.
The salt produced when a dilute acid reacts with a metal depends on the acid and a metal used:
- Mg(s) + 2HNO3(aq) → Mg(NO3)2(aq) + H2(g)
- Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
Reaction with carbonates
Acids react with carbonates to give salt, water and carbon dioxide. In general, all carbonates give off carbon dioxide when they react with acids.
acid + metal carbonate → salt + water + carbon dioxide
The normal methods of preparing carbon dioxide in the laboratory are based on this reaction. Dilute hydrochloric acid is reacted with marble chips (calcium carbonates):
2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g)
Reaction with oxides and hydroxides (alkalis)
Hydroxides: acids react with alkalis, forming salt and water:
NaOH(aq) + HNO3(aq) → CaCl(aq) + H2O(l)
Oxides: They also react with metals oxides, forming salt and water:
ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l)
The bases (oxides, hydroxides) all react in the same way with acids, and in the process, salts are formed. This type of reaction is known as neutralization reaction. It can be summarized up in a general equation:
acid + base → salt + water
Reaction with hydrogencarbonates (bicarbonates)
Acids react with hydrogencarbonates, forming salt, water and liberating carbon dioxide gas:
NaHCO3(aq) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)
Alkalis react with acids to produce salt and water. All alkalis, except ammonia solution, will react with ammonium compounds liberating ammonia gas. Aqueous solutions of alkalis will precipitate the insoluble hydroxides of other metals from the solutions of metal salts. Caustic alkalis attack aluminium, zinc and lead to form salts. They react with carbon dioxide to form carbonates.
Characteristic reactions of bases
Dissolution in water
Most bases are insoluble in water. Some are soluble in water. Soluble bases are known as alkalis. The commonest alkalis are sodium hydroxide, (NaOH), calcium hydroxide, Ca(OH)2, potassium hydroxide, (KOH), and ammonium hydroxide or ammonia solution, (NH4OH). All alkaline solutions contain hydroxyl ions, OH-. In sodium hydroxide solution, the ions are produced like this:
NaOH(aq)→ Na+(aq)+ OH-(aq)
Like acids, alkalis can also be classified as strong or weak. Ammonia solution is a weak base because it ionizes just partially:
The rest of the bases are strong bases because they ionize fully into ions in solution.
Reaction with acids
Bases react with acids to produce salt and water. Refer to the reactions of acids with oxides and hydroxides discussed early.
Reaction with ammonium compounds
Alkalis turn litmus solution blue and red litmus paper blue.A substance, such as litmus, which changes from one colour to another when mixed with an acid or base, is called an indicator. Table 3.2 shows how acids and bases (alkalis) affect the colours of different indicators. We can use this clue of colour changes to tell whether an unknown substance is an acid or base (alkali).
Reaction with aqueous salts of metals
Aqueous solutions of alkalis will precipitate the insoluble hydroxides of other metals from the solutions of metal salts. Only NH4OH, KOH and NaOH are soluble enough in water.
All other hydroxides are insoluble and can be precipitated from aqueous solution by these three alkalis.
- When sodium hydroxide solution is added to copper (II) sulphate solution, a pale blue precipitate of copper (II) hydroxide is formed. CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2 SO4(aq)
- Another example is the reaction between potassium hydroxide and iron (II) chloride, which precipitates iron (II) hydroxide. FeCl3(aq) + 3KOH(aq) → Fe(OH)3(s) + 3KCl(aq)
Reaction with metals
Caustic alkalis attack very few metals. The metals known to be attacked by the alkalis are aluminum, zinc and lead, where the aluminate, zincate and plumbate (II) are formed respectively. The aluminum will react thus:2Al(s) + 6NaOH(aq) + 6H2O(l) → 2Na3Al(OH)6(aq) + 3H2(g)(sodium aluminate)
Reaction with carbon dioxide
When carbon dioxide gas is bubbled through aqueous solutions of the caustic alkalis, the carbonates are formed.
2NaOH(aq) +CO2(g) → Na2CO3(aq) + H2O(l). With excess of the gas, the hydrogencarbonates are formed.Na2CO3(aq) + H2O(l) + CO2(g) → 2NaHCO3(aq)
Reaction with chlorine
Chlorine reacts with excess of cold dilute caustic alkalis to form the hypochlorite, (NaClO or KClO). 2NaOH(aq) + Cl2(g) → NaCl(aq) + NaClO(aq) + H2O(l).2KOH(aq) + Cl2(g) → KCl(aq) + KClO(aq) + H2O(l)
If excess chlorine is bubbled through hot concentrated solutions of caustic alkalis, the chlorates are formed, (NaClO3 or KClO3).
6NaOH(aq) + 3Cl2(g) → 5NaCl(aq) + NaClO3(aq) + 3H2O(l).6KOH(aq) + 3Cl2(g) → 5KCl(aq) + KClO3(aq) + 3H2O(l)
Acid-base neutralization has many applications in everyday life. The following are some of these applications:
Indigestion and pain relief
The dilute hydrochloric acid produced in your stomach is used for digestion and killing bacteria that might have been swallowed together with food or taken with water. However, excess acid causes indigestion, which can be painful. To ease the pain, we take an anti-acid treatment. Anti-acids are a broad group of compounds with no toxic effects on the body. They are used to neutralize the effects of acid indigestion.
Some of these anti-acids such as milk of magnesia [insoluble magnesium hydroxide, Mg(OH)2] help to neutralize and hence counteract the excess acid in the stomach. This treatment, therefore, prevents indigestion and pains. The neutralization reaction equation is:
Mg(OH)2(aq) + 2HCl(aq)→ MgCl2(aq) + 2H2O(l)
Other anti-acids such as “Alka-Seltzer” contain soluble materials, including sodium hydrogencarbonate. These tablets also contain some citric acid (a solid acid). On adding water, the acid and some of the sodium hydrogencarbonate react, producing carbon dioxide gas. This helps to spread and dissolve the other less soluble material. When taken, more sodium hydrogencarbonate neutralizes the excess hydrochloric acid in the stomach, thus easing digestion.
Some anti-acid tablets also contain painkiller to relieve pain. “Soluble aspirin” tablets dissolve and work in a similar way to “Alker-Seltzer” tablets. Vitamin C (ascorbic acid) can be added to the tablets. Note that it is important to add water to start the action of the acid.
Descaling kettles
The limescale (CaCO3) is formed inside boilers, kettles and water heaters when hard water is boiled. The limescale can be removed by treatment with an acid that is strong enough to react with CaCO3, but not strong enough to damage the metal. Vinegar can be used to discale kettles. Commercial “discalers” use other acid solutions such as methanoic acid
Prevention of tooth decay
Food remnants sticking onto teeth (plaque), after eating especially sugary food is acted upon by bacteria in your mouth. The pH of a sugar solution is 7. However, bacteria in your mouth break down the sugar in plaque to form acids, for example lactic acid. These acids lower the pH. Tooth decay begins when the pH falls below 5.8. The acid attacks the tooth enamel.
To help prevent tooth decay many types of toothpaste contain basic substances to neutralize the acids produced by these bacteria in your mouth. The pH of these basic substances is alkaline (higher than 7). The pH of saliva is slightly alkaline (pH 7.4), so it can also help to counteract the acid, particularly after a meal. After eating a sweet, for example, it takes about 15 minutes for saliva to raise the pH above 5.8, and stop further decay.
Soil treatment
Most plants grow best when pH of the soil is close to 7. They prefer the pH of between 6.5 and 7.0. If the soil pH is below 6.0, the soil is too acidic. Above the pH of 8.0, the soil is too alkaline. If the soil is too acidic or too alkaline, the plants grow poorly or not at all.
Chemicals can be added to the soil to adjust its pH. Most often, if the soil is too acidic, it is usually treated by liming. In this context, liming means addition of quicklime (calcium oxide), slaked lime (calcium hydroxide) or powdered chalk or limestone (calcium carbonate) to an acidic soil. These compounds (bases) have the effect of neutralizing the acidity of the soil.
If the soil is too alkaline, acids such as sulphuric acid, nitric acid or hydrochloric acid may be added to the soil to neutralize excessive alkalinity. However, these compounds are very expensive and hence uneconomical to apply on large-scale basis.
Insect stings treatment
When a bee stings someone, it injects an acid liquid into the skin. The bee sting, which is acidic in nature, can be neutralized by rubbing on calamine solution, which contains zinc carbonate or baking soda, which is sodium hydrogencarbonate. These compounds are basic in nature and so have the effect of neutralizing the acid in the sting.
Wasp stings are alkaline in nature, and can be neutralized with vinegar, which contains ethanoic acid. Ant and nettle stings contain methanoic acid. These may be neutralized by rubbing an extract squeezed from crushed onion leaves (which contain basic compounds) on the affected skin. The acid in the sting can also be neutralized by applying weak alkalis such as ammonia solution, ash extract, baking powder, etc.
Factory wastes treatment
Liquid wastes from factories often contain acid. If it reaches a river, lake or ocean, the acid will kill fish and other aquatic life. This can be prevented by adding slaked lime (calcium hydroxide) to the waste, to neutralize the acid before being dumped into water bodies.
Characteristics of Amphoteric oxides and hydroxides
Effect of solvent
Salts
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.
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.
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.
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-).
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.
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)
| 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?
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:
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.
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
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.
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.
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.
Complex ions
Water hardness
As water flows over the land, it dissolves many mineral substances. The dissolved minerals are deposited together with water in rivers, lakes and oceans. Water is said to be hard if it contains some specific type of dissolved minerals. It is important to note that not all dissolved salts make water hard.
As you learned early, water is treated in water purification plants before being piped to your home. The treatment removes only the insoluble particles and kills bacteria. So the water still is not pure. It contains natural compounds dissolved from rocks and soil. It may also contain traces of chemicals dumped from homes, farms and factories.
Water obtained from an area where the rocks contains chalk, limestone, dolomite or gypsum, contains dissolved calcium and magnesium sulphates and hydrogen carbonates. These salts make the water hard.
One can distinguish between hard and soft water when washing with soap. Hard water does not form lather easily. Instead, it forms a precipitate or scum. It requires much soap to react with all the dissolved minerals before enough lather is formed. Therefore, hard water wastes soap during washing.
When soap is used with hard water a “scum” forms on the surface. This is a result of a precipitation reaction between calcium and/or magnesium ions and soap. Soaps are the sodium or potassium salts of long-chain organic acids. Soaps are made from animal fats by treatment with alkali (NaOH or KOH). Ordinary washing soap is a compound of stearic acid, C17H35COOH. The nature of such soaps is the salt, sodium stearate, C17H35COONa+. Sodium stearate is soluble in water but calcium stearate is not.
When soap is mixed with hard water, the calcium or magnesium salts in the hard water react with soap and precipitates as scum. The nature of scum is either calcium stearate or magnesium stearate:
Soap will not form any lather with water until all the calcium and magnesium ions have been precipitated. Hard water, therefore, wastes soap. This means that more soap may be used for an efficient washing. The amount of soap needed to just produce froth can be used to estimate the hardness of water.
The problem of scum formation only occurs with soaps. Soapless detergents do not produce scum. The trade names for some soapy detergents sold in Tanzania include Komoa, Kuku, Taifa, Mbuni, Mshindi, Changu, Jamaa and several other bar soaps. The trade names for some soapless detergents include Omo, Foma, Tesa, Toss, Dynamo, Swan, etc.
The hard water in some areas can be softened simply by boiling the water, but this is not true in all cases. This means that the hardness in water can be divided into two types – temporary and permanent hardness.
Temporary hardness
Temporary hardness in water is caused by dissolved calcium or magnesium hydrogencarbonates. The most important characteristic of temporarily hard water is that it can be softened by simply boiling. When the water is boiled, the soluble sodium hydrogencarbonate is decomposed to form the insoluble calcium carbonate.
The decomposition causes the “furring” of kettles, hot water pipes and shower heads. This means that the inside of kettles, pipes and shower heads become coated with a layer of calcium carbonate (limescale) caused by the decomposition of the hydrogen carbonate according to the equation above.
In many supermarkets, it is possible to buy a limescale remover. This is often a solution of methanoic acid (formic acid). This weak acid is strong enough to react with limescale but not with the metal. The insoluble limescale (carbonate) is probably dissolved to a soluble compound, calcium methanoate that can be flushed away with water.
2COOH(aq) + CaCO3(s)(insoluble)→ Ca(HCOO)2(aq) + H2O(l) + CO2(g)calcium methanoate (soluble)
Permanent hardness
Permanent hardness in water is caused by soluble sulphates and chlorides of calcium and magnesium (CaSO4, MgSO4, CaCl2 and MgCl2). This type of hardness cannot be removed by boiling the water. This is because boiling does not decompose the chlorides of calcium or magnesium. Such water may only be softened by chemical treatment or ion exchange methods
Because of the problem it causes, hard water is often softened for use in factories, industries and homes. That means removing the dissolved calcium and magnesium ions. Described below are the methods of treating and purifying hard water.
Boiling
Boiling removes temporary hardness in water, as you saw early. Boiling causes calcium carbonate to precipitate. The hydrogencarbonate in water are decomposed to carbonates, which are insoluble in water
In this way, the calcium is removed, since the calcium carbonates being insoluble, takes no further part in the reaction. An insoluble calcium salt cannot cause hardness. However, this method uses a lot of fuel, which makes it expensive to do on a large scale.
Distillation
Distillation removes all impurities from water. This gets rid of both temporary and permanent hardness. In distillation, the water is boiled and the steam collected, cooled and condensed. Distilled water is pure and softest water. All the dissolved substances have been removed. Like boiling, it is an expensive option in terms of fuel used. But it is essential for some purposes, for example for laboratory experiments and for making drugs.
Addition of calcium hydroxide
Addition of calculated amounts of calcium hydroxide can remove temporary hardness. The quantity to be added should be properly calculated because excess would cause hardness on its own account. The amount of calcium hydroxide to be added is calculated based on knowledge of the hardness of water and the capacity of the reservoir (Clark’s method). The calcium hydroxide reacts with the hydrogencarbonates dissolved in water and precipitates as the insoluble calcium carbonates.
Ca(OH)2(s) slightly soluble + Ca(HCO3)2(aq) → 2CaCO3(s) + 2H2O(l)insoluble
Addition of sodium carbonate (washing soda)
Washing soda removes both temporary and permanent hardness by precipitating calcium carbonate. It reacts with calcium hydrogencarbonate (which causes temporary hardness) to form sodium hydrogencarbonate like this:
Na2CO3(aq)+ Ca(HCO3)2(aq)→ 2NaHCO3(aq))+ CaCO3(s)
It also reacts with calcium sulphate (which causes permanent hardness) to form sodium sulphate thus:Na2CO3(aq)+ CaSO4(aq)→ CaCO3(s)+ Na2SO4(aq)
These sodium salts are soluble, but do not cause the water to be hard. The calcium and magnesium ions are precipitated as insoluble calcium and magnesium carbonates. Ionically, the situation is like this:
Ca2+(aq)+ CO32-(aq)→ CaCO3(s)
Mg2+(aq)+ CO32-(aq)→ MgCO3(s)
Ion Exchange
Another method that removes both temporary and permanent hardness in water is the use of ion exchange resin. A typical ion exchanger is a container full of small beads. These beads are made of special plastic called ion exchange resin. The resin beads are porous and contain sodium ions. When hard water flows through the resin, the calcium and magnesium ions in the water are exchanged for the sodium ions and attach themselves to the resin. This process, therefore, removes calcium and magnesium ions from the water. They are replaced by sodium ions, which do not make the water hard.
When all sodium ions have been removed from the resin, it is regenerated by pouring a concentrated solution of sodium chloride through it. The sodium ions remove the calcium and/or magnesium ions off the resin and the ion exchanger is ready for the use again. Other ions could also be used instead of sodium for the resin. But sodium chloride is normally used to supply the sodium ions because salt is cheap.
Use of softeners
Many modern washing powders now have softeners added to them. The softeners are often phosphates. The phosphates ions react with calcium ions to form calcium phosphate and remove the hardness. 3Ca2+(aq)+ 2PO43-(aq)→ Ca3(PO4)2(s)
The significance of water in daily life is well known to everyone. The water we obtain from natural sources is never pure. It contains dissolved minerals which render the water unfit for direct uses. The water from some sources contains calcium and magnesium compounds dissolved in it. These compounds are responsible for water hardness. To make the water fit for various uses, it is imperative to remove the hardness. The following points state why it is important to treat and purify hard water:
Hard water wastes soap. To get enough lather with hard water, it requires more soap than it does with soft water. So it is important to soften the water in order to save the soap and hence reduce the cost of washing. Laundry uses less soap and can be done at lower temperatures.
Treating and purifying hard water eliminates the possibility of forming limescale deposits in water boilers, kettles, washing machines, water heaters, shower heads and dish washers. The scale formed around the heating elements can cause the element to overheat and fail
Treated and purified water leaves no scum on clothes during washing. Scum spoils the finishing of some fabrics. It forms nasty deposits (marks) on clothing that has been washed.
Softened water has the advantage of not blocking the water pipes. In industry, deposits of scales can block the pipes in boilers. This is a safety hazard as it could cause pressure to build up until there is an explosion. A similar coating can occur in hot water pipes at home and in central heating systems.
Hard water is not always disadvantageous. The following points explain the importance of hard water:
- The dissolved calcium and magnesium salts improve the taste of water. Distilled water is tasteless and quite unpleasant to drink. This is why water-processing plants add some salts in the distilled water to make it tasteful.
- Calcium dissolved in hard water is an essential mineral for growth of bones and teeth. It makes our teeth and bones hard, strong and resistant to shear and pressure.
- In some places, old lead pipes are used for water supply. Lead is very poisonous, and a little of it can dissolve in soft water. But the carbonate (CO32-) or sulphate (SO42-) ions present in hard water reacts with lead to form a coating of lead carbonate or lead sulphate that prevents lead from dissolving. This prevents lead poisoning.
- A coating of calcium carbonate inside pipes, boilers and radiators helps to prevent corrosion.
- In recent years, it has been suggested that drinking hard water helps to prevent heart diseases. 6. It has also been found that hard water is good for brewing beer.
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