Lifelong Learning Programme

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Chemistry is all around us
Copyright 2015
This project has been funded with
support from the European Commission

Educational Packages

Chemistry at Home

Cleaning products at home


Cleaning products
In every house there are several cleaning products which we use for our personal hygiene (toothpastes, shampoos, soaps etc) or for cleaning our house (cleaning products for floors, windows etc) or in order to clean several objects we have at home (cleaning products for dishes, silvery, furniture etc). These commercial cleaning products can be found in every grocery store or drug store and provide easy cleaning. Commercial cleaning products contain many chemical substances, unknown to the general public, which can be dangerous. There are ways to do cleaning without using commercial cleaning products, which can be expensive, they may contain harmful toxic substances and cause environmental problems as well (water pollution, fish poisoning etc). In this way, we can use as cleaning products, everyday materials that can be found in every house. These materials can have the same or better cleaning result with the commercial products and they are certainly safer for human health and much cheaper to get.

Toothpaste’s history
Toothpaste has come a long way since Egyptians (3000 – 5000 BC) first made a dental cream by mixing powdered ashes of oxen hooves with myrrh, burned egg shells, pumice, and water. Hippocrates also suggested cleaning teeth with powdered marble. Over the years people have used as toothpastes, toothpowders which were made up of materials like powdered charcoal, powdered bark and some flavoring agents, or toothpastes containing soap and chalk.

Toothpaste’s action
On the surface of the teeth dental plaque is created from food residues that accumulate in the mouth. Many types of microorganisms are growing in the plaque. Microorganisms in our mouth are fed by leftover food to create acid and volatile sulfur compounds. Acid harms the tooth enamel to produce cavities while volatile sulfur compounds give breath a bad odor. In the early stages, dental plaque is soft and can be removed by brushing. Gradually it grows, becomes harder, and tartar is formed. Tooth tartar can only be removed by a dentist. Toothpaste works in tandem with tooth brushing in order to clean teeth and remove plaque bacteria.

Toothpaste should be abrasive enough to remove plaque and stains, but not hard enough to damage tooth enamel. Hardness is measured according to a scale called Mohs’ Scale. Tooth enamel is quite hard (5.5-7.0 degree Mohs) but it can be worn away by a harder abrasive. We can check toothpaste to see if it scratches against glass (which rates 5.5). Toothpaste should be below 5.5 and thus not scratch glass.

Toothpaste’s composition
Toothpaste has a solid phase (an abrasive agent or blend of agents) suspended in an aqueous phase. A small percentage of detergent is added to form foam.

Nowadays commercial toothpastes contain a lot of ingredients. The toothpaste companies produce toothpastes via recipes which are kept secret. So we don’t know the exact composition of any toothpaste, but we do know that toothpastes’ ingredients can be divided into nine categories:
  1. Abrasives: Abrasives give toothpaste its cleaning power. They have granular texture and with the use of toothbrush they remove stains and plaque through abrasion. Baking soda is a mild abrasive which also helps retain a slightly basic environment in the mouth. Table salt has abrasive action as well.
  2. Detergents: Detergents create the foaming action we associate with toothpastes. Foam keeps the toothpaste in our mouths as we brush.
  3. Humectants (like glycerin): Humectants give toothpaste its texture and consistency as well as retain moisture so that your toothpaste does not dry out.
  4. Fluoride (like sodium fluoride): Perhaps the most important toothpaste ingredient is fluoride. Fluoride incorporates itself into tooth enamel making your teeth more resistant to acids produced by plaque bacteria, as well as acids found in fruit juices and certain foods.
  5. Preservatives: Preservatives prevent the growth of microorganisms in toothpaste. Baking soda has anti-bacterial properties and acts as a preservative.
  6. Flavoring Agents: Flavoring αgents are added to improve the taste of toothpaste and cover up the horrid taste of most detergents.
  7. Sweeteners: Sweeteners improve the taste of toothpaste.
  8. Coloring Agents: Coloring agents provide toothpaste with pleasing colors.
  9. Bleaching agent: Toothpaste typically has components to grind off stains formed by coloured substances that have adsorbed onto the teeth from food. Hydrogen peroxide acts like a bleaching agent when used in tooth pastes, teeth whitening solutions, disinfectants, and mouth washes.

Cleaning tarnished silverware
When silver and silver-plated objects tarnish, silver combines with sulphur and sulphur compounds to form silver sulphide (Ag2S). Silver sulphide is black. When a thin coating of silver sulphide forms on the surface of silver, it darkens the silver. Contact with materials that contain sulphur compounds, such as hard-boiled eggs, mayonnaise, mustard, and rubber bands can cause tarnish. In atmospheric air, a silver object can tarnish due to the reaction of silver with hydrogen sulphide (H2S). This is a gas found in the air as a result of some industrial processes and the decomposition of dead plants and animals. The silver can be returned to its former lustre by removing the silver sulphide coating from the surface.

There are two ways to remove the coating of silver sulphide. One way is to mechanically remove the silver sulphide from the object’s surface (polishing). Polishes that contain an abrasive, make the silver shine by rubbing off the silver sulphide and some of the silver along with it. Another kind of commercial tarnish remover dissolves the silver sulphide in a liquid. These polishes are used with two ways: a) by dipping the silver into the liquid, or b) by rubbing the liquid on the silver object with a cloth and then washing it off. These polishes also remove some of the silver. The other way is to reverse the chemical reaction and transform silver sulphide back into silver. In the first method, some silver is removed in the process of polishing. In the second, the silver remains in place.

The tarnish-removal method used in the proposed activity is based on the second way of cleaning tarnished objects. The chemical reaction which occurs is called silver’s reduction and converts the silver sulphide back into silver. With this method the silver remains in place and it’s not removed from the object. Many metals in addition to silver form compounds with sulphur. Some of them have a greater affinity for sulphur than silver does. Aluminium is such a metal. In this tarnish-removal method, the silver sulphide reacts with aluminium. In the reaction, the silver sulphide breaks down because sulphur prefers to join aluminium, which is a more drastic metal than silver, forming a new chemical compound known as sulphide aluminium. As a result silver, is liberated and the silver object is clean again (no sulphur compounds on it).

The reaction between silver sulphide and aluminium takes place when the two substances are in contact while they are immersed in a baking soda solution. The reaction is faster when the solution is warm. The solution carries the sulphur from the silver to the aluminium. The aluminium sulphide may adhere to the aluminium foil, or it may form tiny, pale yellow flakes in the bottom of the solution. The silver and aluminium must be in contact with each other, because a small electric current flows between them during the reaction. This type of reaction, which involves an electric current, is called an electrochemical reaction. Reactions of this type are used in batteries to produce electricity.