CHEMICALS: ACIDS, BASES & SALTS

Chemicals are materials used in chemical reactions. Chemicals can be elements e.g. Magnesium or they can be compounds e.g. sulphuric acid. Many different chemicals are used at home. For instance we use different types of products to wash clothes, bathe and paint our house. Some examples of these products are disinfectants, soap, detergent and insecticides.

Water is the most common chemical found in the household and it is used in many household products because it is n excellent solvent. Most household products have labels which show safety information and the names of the chemicals present. It is very important to read these labels carefully when choosing household products.

COMMON HOUSEHOLD CHEMICALS

PRODUCTS CHEMICAL NAME CHEMICAL FORMULA

Baking Soda Sodium Hydrogen Carbonate NaHCO3

Toothpaste Fluorides F

Washing soda Sodium Carbonate Na2CO3

Salt Sodium Chloride NaCl

Hair relaxer Sodium Hydroxide NaOH

Fruit Juices Citric Acid C6H8O7

Soda Water / club soda Carbonic Acid H2CO3

Water Hydrogen oxide H2O

Milk of Magnesia Magnesium Oxide MgO

Vinegar Acetic / ethanoic Acid CH3COOH

Bleach Sodium Hypochlorite NaClO

Epsom salts Magnesium Sulphate MgSO4

Plaster of paris Calcium Sulphate CaSO4

Chalk Calcium Carbonate CaCO3

Chemicals can be classified according to whether they are acidic, basic or neutral.

ACIDS:

An acid is a substance that produces hydrogen ions when dissolved in water. An acid is also a substance that contains hydrogen that can be replaced directly or indirectly by a metal to form a salt. An acid is a proton donor - it can give protons to other substances.

Properties of acids:

• They have a sour taste • They are corrosive • They turn blue lithmus paper red • They have a pH less than 7 • They conduct electricity

Some common household acids are:

Product Name Chemical Substance Use

Battery Acid Sulphuric Acid The electrolyte in car batteries

Club Soda Carbonic Acid A soft drink

Vinegar Ethanoic Acid In dilute solution used in food preservation

Fruit Juices Citric Acid Food

BASES or ALKALIS:

A base is a substance that reacts with an acid to form a salt and water. It contains hydroxyl ions (OH) and it is a proton acceptor. Al metal oxides and hydroxides are bases. Bases that dissolve in water to give hydroxide ions are also known as alkalis.

Properties of bases:

• They have a bitter taste • They are corrosive • They are soapy to touch • They turn red lithums paper blue • They conduct electricity

Some common household bases are:

Product Name Chemical Substance Use

Milk of Magnesia Magnesium Oxide Medicine to neutralize stomach acid

Rouge Ferric Oxide Makeup

Oven Cleaner Sodium Hydroxide Cleaning ovens Ammonia Ammonia Cleaning agent

SALTS:

Salts are solid compounds derived from reacting acids with substances such as bases and some metals. Salts get the second part of their name from the acids from which they are produced. The first part of the name comes from the metal or base.

The table below gives the name of some common acids, the salts they form and their uses.

REACTIONS OF ACIDS and BASES (ALKALIS):

1. Acids react with bases to form a salt and water only.

Acid + Base Salt + Water

Mg(OH)2(s) + 2HCl(aq) MgCl2(aq) + 2H2O(l)

The reaction between an acids and a base to form a salt and water is called a neutralization reaction. (Neutralization is trying to make a solution less acidic or basic).

For example most anti-acid tablets contain sodium hydrogen carbonate. When mixed with stomach acid (Hydrochloric acid) the acid is neutralized. The reaction could be considered to be a neutralization reaction.

2. Acids react with carbonates or hydrogen carbonates to form a salt, water and carbon dioxide.

Acid + Carbonate or Hydrogen Carbonate Salt + Water + Carbon Dioxide

CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

3. Acids (except nitric acid) react with the reactive metals (iron and above in the reactivity series) to form a salt and hydrogen.

Reactive Metal + Acid Salt + Hydrogen

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

4. Alkalis react with ammonium salts to form a salt, water and ammonia.

Alkali + Ammonium Salt Salt + Water + Ammonia

NaOH(aq) + NH4Cl(aq) NaCl(aq) + H2O(l) + NH3(g)

5. Alkalis react with solution containing metal ion (except potassium and sodium) to form insoluble precipitates.

IDENTIFICATION OF ACIDS AND BASES:

It is good to know whether chemicals are acidic, basic or neutral so that they can be handled safely. We can make use of indicators to test the acidity or alkalinity of a substance.

1. Indicators:

An indicator is a substance which has one colour when mixed with and acidic solution and a different colour when mixed with an alkaline solution.

2. Lithmus Paper:

Blue and red lithmus paper are common indicators used in the lab. An acid turns damp blue lithmus paper red and a base turns damp red lithmus paper blue. Neutral componuds will not cause any colour change with red or blue lithmus paper.

3. Universal Indicator:

In the lab pH can be measured using universal indicator paper or solution. A universal indicator comes with a colour chart with colours ranging from red through orange, yellow, green, blue and deep purple. Each colour on the chart is associated with a specific pH.

When the indicator paper is dipped into an acidic or alkaline solution being tested, the colour of the paper will change. The new colour is matched against the colours on the colour chart. The corresponding number on the colour chart gives the pH of the solution being tested.

4. The pH Scale:

Scientists have devised a scale called the pH scale which gives a measure of the strength of an acid or alkali. It consists of numbers ranging from 0 to 14. Substances with pH less than 7 are acids and those with pH greater than 7 are alkaline. A pH of 7 indicates a neutral substance.

SOME USEFUL NEUTRALIZATION REACTIONS

1. Reducing tooth decay:

Toothpaste is alkaline with a pH greater than 7. The bacteria present in our mouths convert food we eat to acids with pH less than 7. This acid, if allowed to build up in our moths, will destroy the teeth and cause cavities. Toothpaste helps to neutralize the acid and reduce the likelihood of cavities being formed.

2. Reducing indigestion:

Sometimes the food we eat lead to acid build up in the stomach, which can be quite uncomfortable. The discomfort can be relieved by drinking an antacid such as milk of magnesia or baking soda (sodium hydrogencarbonate) solution. These antacids are alkaline and they neutralize the acid build up in the stomach.

3. Metal cleaning:

Copper ornaments often get tarnished by a thin coat of copper oxide when exposed to air. This causes the metal to lose its sheen and become darker in appearance. Copper objects can be cleaned by rubbing with lemon juice. The acidic lemon juice will neutralise the basic copper oxide.

4. Stain removal:

Some stains can be removed using the reactions of acids and bases.