Materials Used in Daily Life

The things we use every day contain different chemicals. Many of them are acids, bases (alkalis) or salts: in fruits and vegetables, soap and shampoo, hair conditioner, sanitizer and cleaning liquids.

What an acid is

The sour substances around us are acids. Acids dissolve in water, and when they dissolve they give hydrogen ions (H⁺). So an acid is a substance that gives hydrogen ions when it is dissolved in water.

Not every acid can be eaten. By their source, acids are of two types:

• Organic acids are found naturally in plants and animals: citric acid in lemons, lactic acid in curd, acetic acid in vinegar. They are compounds of carbon, and many are safe to eat in small amounts.
• Inorganic acids (or mineral acids) are made from minerals, usually in factories and laboratories: hydrochloric acid, sulphuric acid, nitric acid. Most contain no carbon (carbonic acid, H₂CO₃, is one that does), and the strong ones are dangerous to touch or eat.

By how many hydrogen ions they give in water, acids are again of two types:

• Strong acids give many hydrogen ions: almost every molecule splits up. Hydrochloric, sulphuric and nitric acids are strong.
• Weak acids give few hydrogen ions: only a small share of the molecules split up. Citric, acetic, lactic and carbonic acids are weak.

So, mostly, inorganic acids are strong and organic acids are weak. That is why you can squeeze lemon on your food but must never let a drop of sulphuric acid touch your skin.

Physical properties of acids

An indicator is a substance that shows, by its color, whether something is an acid or a base. Litmus, methyl orange and phenolphthalein are the indicators used in school laboratories.

The physical properties of acids:

• a.Acids taste sour.
• b.Acids are soluble in water.
• c.Acids turn blue litmus red; they don’t change red litmus.
• d.Acids turn methyl orange red.
• e.Phenolphthalein stays colorless in acids.

Chemical properties of acids

a. Acids give hydrogen ions in water

When an acid dissolves in water, its molecules split into ions. This splitting is called ionization. Every acid gives hydrogen ions:

Hydrochloric acid → hydrogen ion + chloride ion
HCl → H⁺ + Cl⁻

The hydrogen ions are what make all acids behave alike: the sour taste, the red litmus and the reactions below.

b. Acids react with metals

Acids react with many metals to form a salt of the metal and hydrogen gas:

Magnesium + hydrochloric acid → magnesium chloride + hydrogen
Mg + 2HCl → MgCl₂ + H₂

c. Acids react with metal carbonates

Acids react with metal carbonates to form a salt, water and carbon dioxide gas:

Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

d. Acids react with bases

An acid and a base react to form a salt and water. This is called neutralization, because each cancels the other’s properties:

Hydrochloric acid + sodium hydroxide → sodium chloride + water
HCl + NaOH → NaCl + H₂O

Uses of acids

Acid	Uses
Organic acids
citric acid	to preserve food for a long time; to make food sour
ascorbic acid (vitamin C)	in medicines and tablets, as a source of vitamin C
acetic acid (in vinegar)	to make pickles and to preserve food
tartaric acid	to make baking powder
Inorganic acids
hydrochloric acid	made in the stomach to help digest food; to clean toilets and bathrooms; to make PVC plastic
nitric acid	to make nitrogen fertilizers and explosives
sulphuric acid	in car and inverter batteries; to make fertilizers, dyes, detergents and artificial silk (rayon); to make hydrochloric acid

Metal oxides and metal hydroxides are called bases. Sodium oxide, sodium hydroxide, potassium oxide, potassium hydroxide and magnesium oxide are bases.

Some bases dissolve in water and some don’t. A base that dissolves in water is called an alkali. Sodium hydroxide and potassium hydroxide are alkalis. Copper oxide and iron oxide are bases that don’t dissolve, so they are not alkalis. Every alkali is a base, but not every base is an alkali.

When an alkali dissolves in water, it gives hydroxide ions (OH⁻). By how many hydroxide ions they give, bases are also strong or weak:

• Strong bases give many hydroxide ions: sodium hydroxide (caustic soda) and potassium hydroxide.
• Weak bases give few hydroxide ions: ammonium hydroxide (ammonia dissolved in water, a base with no metal in it).

The physical properties of bases:

• a.Bases turn red litmus blue; they don’t change blue litmus.
• b.Most bases taste bitter.
• c.Most bases feel slippery, like soapy water.
• d.Bases turn methyl orange yellow.
• e.Bases turn phenolphthalein pink.

Indicator	In an acid	In a base	In a neutral liquid
blue litmus	turns red	stays blue	stays blue
red litmus	stays red	turns blue	stays red
methyl orange	red	yellow	yellow (methyl orange can’t tell a neutral liquid from a base)
phenolphthalein	colorless	pink	colorless

Chemical properties of bases

a. Bases give hydroxide ions in water

Sodium hydroxide → sodium ion + hydroxide ion
NaOH → Na⁺ + OH⁻

b. Bases react with ammonium salts

A base reacts with an ammonium salt to give ammonia gas, a salt and water:

Ammonium sulphate + sodium hydroxide → sodium sulphate + ammonia + water
(NH₄)₂SO₄ + 2NaOH → Na₂SO₄ + 2NH₃ + 2H₂O

c. Bases react with acids

A base reacts with an acid to give a salt and water: the acid–base reaction, or neutralization.

Sulphuric acid + potassium hydroxide → potassium sulphate + water
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Uses of bases

Base	Uses
calcium hydroxide (slaked lime)	to make bleaching powder; to whitewash walls before painting a house; to reduce the acidity of soil
magnesium hydroxide (milk of magnesia)	as an antacid, to neutralize too much acid in the stomach (hyperacidity, or “gastric”)
sodium hydroxide (caustic soda)	to make soap, textiles and paper; in processing petroleum products
ammonium hydroxide	as a laboratory reagent; to make chemical fertilizers, rayon cloth, plastics and dyes

When an acid reacts with a base, the products are a salt and water. A salt is the compound formed when the hydrogen of an acid is replaced by a metal (or by ammonium), as happens in a reaction between an acid and a base. Common salt, sodium chloride, is just one of many salts: copper sulphate, washing soda and baking soda are salts too.

Depending on the acid and the base that make it, a salt can be neutral, acidic or basic. There are three types:

• a.Neutral salts are formed by a strong acid and a strong base (or a weak acid and a weak base). Sodium chloride (NaCl), from hydrochloric acid and sodium hydroxide, is neutral.
• b.Acidic salts are formed by a strong acid and a weak base. Ammonium chloride (NH₄Cl), from hydrochloric acid and ammonium hydroxide, is acidic.
• c.Basic salts are formed by a strong base and a weak acid. Sodium carbonate (Na₂CO₃, washing soda), from sodium hydroxide and carbonic acid, is basic.

The physical properties of salts:

• Table salt is salty, but most salts don’t taste salty: many have no taste and some are bitter. (Many salts are poisonous, so never taste them.)
• Most salts dissolve in water (though not all: chalk and marble, calcium carbonate, don’t).
• Most are white or colorless, but some are colored: copper sulphate is blue, iron sulphate green, potassium permanganate purple.
• Neutral salts don’t change the color of indicators.
• Salts have high melting and boiling points. Common salt melts at about 800 °C.

Chemical properties of salts

a. Salts split into ions in water

When a salt dissolves in water, it splits into positive ions of the metal and negative ions of the non-metal part:

Sodium chloride → sodium ion + chloride ion
NaCl → Na⁺ + Cl⁻

b. Salts react with acids

Some salts react with acids to form a new salt and a new acid:

Sulphuric acid + sodium chloride → sodium sulphate + hydrochloric acid
H₂SO₄ + 2NaCl → Na₂SO₄ + 2HCl

c. Salts react with bases

Some salts react with bases to form a new salt and a new base (here the new base, ammonia, escapes as a gas):

Ammonium chloride + calcium hydroxide → calcium chloride + ammonia + water
2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2NH₃ + 2H₂O

d. Displacement reactions

A more reactive metal displaces (pushes out) a less reactive metal from its salt, and forms a new salt:

Iron + copper sulphate → ferrous sulphate (iron sulphate) + copper
Fe + CuSO₄ → FeSO₄ + Cu

Uses of salts

Salt	Uses
table salt (sodium chloride)	to flavor food; to preserve food (achar, dried fish, butter); to make sodium hydroxide, washing soda, baking soda and soap
washing soda (sodium carbonate)	for washing and cleaning; to remove the permanent hardness of water; to make glass, paper and soap
baking soda (sodium bicarbonate)	to make baking powder; to make antacids; in some fire extinguishers

Rain is never perfectly pure water. As it falls, it dissolves a little carbon dioxide from the air, forming weak carbonic acid. So ordinary rain is slightly acidic, with a pH of about 5.6. (The pH scale runs from 0 to 14: 7 is neutral, below 7 is acidic, above 7 is basic.) This slight acidity does no harm.

Acid rain is rain made much more acidic, with a pH below 5.6 and often around 4 to 4.5, by strong acids formed in the air. These acids form in two ways:

• a.Natural causes. Volcanoes give out sulphur dioxide; lightning, and the decay of dead plants and animals, produce oxides of nitrogen and sulphur. In the air these react with water to form sulphuric acid and nitric acid, which fall with the rain.
• b.Human causes. Most acid rain is caused by people. Burning fossil fuels (coal, petrol, diesel) in power stations, brick kilns, factories and vehicles puts oxides of sulphur and nitrogen into the air. They react with water to form sulphuric acid and nitric acid (and carbonic acid from carbon dioxide), which come down with the rain.

Effects of acid rain on the environment

Rainwater is a major part of the environment: it refills rivers, lakes and the water under the ground, and every living thing needs it. When it is acidic, the harm spreads:

1. It makes rivers, lakes and ponds acidic, which harms fish and other water life. Fish eggs and young fish die first.
2. It damages the leaves of plants and lowers the quality of the soil by washing away its nutrients.
3. If it goes on for a long time, whole forests are destroyed.
4. It eats away temples, monuments and statues, especially those of marble and limestone (calcium carbonate, which reacts with acid just as in Activity 10.5), and corrodes metal.

Ways to prevent acid rain

1. Use less fossil fuel: walk, cycle or take public transport, and keep vehicles well maintained.
2. Reduce air pollution by using renewable energy, such as hydroelectricity and solar energy, instead of coal and oil. Nepal’s electric buses and cooking on electric stoves help.
3. Build industries and factories away from where people live, and make them clean their smoke (filters can remove sulphur dioxide) before it leaves the chimney.

1. Choose the correct answer

2. Differentiate between

3. Give reasons

4. Answer these questions

Water that lathers easily with soap is called soft water. Water that gives little lather is called hard water. Usually, surface water (rain, and most rivers and lakes) is soft, and groundwater (from wells, tube wells and springs) is hard. So, by how it lathers with soap, water is of two types: soft water and hard water.

Soft water

Soft water has little or no dissolved salts of calcium and magnesium. Soap lathers easily in it, so less soap is needed to wash clothes. Rainwater, distilled water and most surface water are soft. Boiled water is soft too, if its hardness was the temporary kind (below).

Hard water

Hard water has dissolved salts of calcium and magnesium: their sulphates, chlorides and bicarbonates. These salts react with soap to form a sticky, white, insoluble scum instead of lather, so a lot of soap is wasted. Clothes washed in hard water slowly turn dull and grayish, and a whitish crust builds up inside pipes, kettles and boilers. Groundwater is usually hard: as rainwater soaks down through the ground, it dissolves calcium and magnesium from rocks such as limestone.

The hardness of water is of two types: temporary hardness and permanent hardness.

Temporary hardness

Temporary hardness is caused by the dissolved bicarbonates of calcium and magnesium: calcium bicarbonate, Ca(HCO₃)₂, and magnesium bicarbonate, Mg(HCO₃)₂. It can be removed by boiling or by adding lime (calcium hydroxide).

Ways to remove temporary hardness

a. Boiling. When the water is boiled, the dissolved bicarbonates break down into insoluble carbonates, which settle out as a white solid. The water above is soft.

Calcium bicarbonate → calcium carbonate + water + carbon dioxide
Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂

b. Clark’s method. Adding just the right amount of calcium hydroxide (lime) to the water turns the dissolved bicarbonates of calcium and magnesium into insoluble carbonates. They settle at the bottom as a solid (a precipitate) and are removed by filtering. Removing temporary hardness with calcium hydroxide is called Clark’s method.

Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O

Permanent hardness

Permanent hardness is caused by the dissolved sulphates and chlorides of calcium and magnesium, such as calcium sulphate and magnesium chloride. Boiling can’t remove it. It is removed with washing soda or with zeolite (sodium aluminium silicate, a crystalline solid).

Ways to remove permanent hardness

a. Washing soda. Washing soda (sodium carbonate) turns the dissolved sulphates and chlorides of calcium and magnesium into insoluble carbonates, which are removed by filtering.

Calcium sulphate + sodium carbonate → calcium carbonate + sodium sulphate
CaSO₄ + Na₂CO₃ → CaCO₃ + Na₂SO₄

b. The permutit method. Removing permanent hardness with zeolite is called the permutit method. A tank is filled with layers of gravel, coarse sand and sodium zeolite. As the hard water trickles down through the zeolite, the calcium and magnesium ions in the water swap places with the sodium ions in the zeolite. The calcium and magnesium stay stuck in the zeolite; the sodium goes into the water, where it doesn’t cause hardness. Soft water comes out at the bottom. When the zeolite is full of calcium, it is washed with strong salt (sodium chloride) solution, which puts the sodium back, and it can be used again and again.

Soft water	Hard water
little or no dissolved calcium or magnesium salts	has dissolved calcium and magnesium salts
lathers easily with soap	gives little lather and a white scum
less soap is needed	more soap is wasted
e.g. rainwater, distilled water	e.g. water from many wells and tube wells

A material made by mixing a metal evenly with other metals or with a non-metal (melted together, then cooled) is called an alloy. An alloy is a homogeneous mixture: it is the same all the way through. In daily life we use alloys far more than pure metals, because mixing improves the metal’s properties and makes it more useful.

For example, aluminium is light, which makes it good for airplane bodies, but pure aluminium is soft and weak. Mixed with a little copper, manganese and magnesium, it becomes duralumin, which is nearly as strong as steel but still light.

Properties of alloys

1. Alloys are harder and stronger than the metals they are made of, and less easily drawn into wires or beaten into sheets (less ductile and malleable).
2. Many alloys don’t rust or corrode easily.
3. An alloy’s melting point is different from those of its metals: usually lower (solder melts more easily than tin or lead alone), sometimes higher.
4. An alloy can have a different color from its metals. Reddish copper and silvery-gray zinc make yellow brass; gold mixed with copper makes pinkish “rose gold”; and silver and zinc, both white metals, can even make a pink alloy.
5. On the whole, the properties of an alloy are better for its job than those of the pure metals.

a. Steel

Steel is iron mixed evenly with a small amount of carbon (usually less than 2%). Pure iron is soft and bends easily, so it is hard to use for building. A little carbon makes it hard and strong. Steel is used for buildings (the rods in concrete), bridges, railings, vehicles and tools.

Ordinary steel still rusts. Stainless steel is iron mixed with chromium and nickel (and a little carbon). The chromium forms an invisible, very thin layer on the surface that stops air and water from reaching the iron, so stainless steel doesn’t rust easily. It is used for kitchen utensils and for surgical instruments in hospitals.

b. Brass

Brass (pital) is an alloy of copper and zinc. It is golden yellow, doesn’t rust, and is easy to cast and shape. It is used for puja items, gagri (water pots), lota, idols and statues, and for nuts, bolts, taps, plumbing fittings and machine parts.

c. Bronze

Bronze (kansa) is an alloy of copper and tin. It is used for dinner plates, bowls and tumblers, and for medals, coins, bells, ship parts and statues. Many of the beautiful metal statues made by the craftsmen of Patan are cast in bronze or copper alloys by the lost-wax method: a wax model is covered in clay, the wax is melted out, and molten metal is poured into the hollow it leaves.

Alloy	Made of	Uses
steel	iron + a little carbon	buildings, bridges, railings, tools
stainless steel	iron + chromium + nickel (+ a little carbon)	kitchen utensils, surgical instruments
brass	copper + zinc	puja items, gagri, idols, taps, nuts and bolts
bronze	copper + tin	plates, bowls, tumblers, medals, bells, statues
duralumin	aluminium + copper, manganese, magnesium	airplane bodies
22-carat gold	gold + a little copper and silver	jewelry

1. Choose the correct answer

2. Differentiate between

3. Give reasons

4. Answer these questions