Cleaning products and using them safely

1Why this matters

Walk through a market or a small shop and you will find shelves of bar soap, washing powder, scouring powder and bottles of bleach, often sold as Javel. Each one is made for a particular kind of dirt. Used well, they save time and kill germs. Used badly, they damage surfaces, burn skin, or even give off poisonous gas.

This lesson sorts cleaning products into groups, shows you how to dilute bleach correctly, and sets out the safety rules you must follow every time.

2Water, the first cleaning agent

A cleaning agent is any substance used to remove dirt from a surface. The first and cheapest is clean water: it dissolves sugar, salt and many fresh spills, and it rinses away the dirt loosened by other products.

3Soaps and detergents

Water cannot remove grease on its own. Soaps (made from fats or oils and an alkali) and detergents (made in factories, mostly from petroleum) contain molecules called surfactants. One end of a surfactant molecule is attracted to water, and the other end is attracted to grease. The grease-loving ends bury themselves in the grease, the water-loving ends face outwards, and when you rub and rinse, the grease is carried away in tiny droplets. Detergents also work in hard water, where soap forms a grey scum.

4Groups of cleaning products

Household bleach has a pH of about 12 and ammonia about 11, which makes both strongly alkaline. An abrasive cleans by rubbing: its hard, tiny particles scrape the dirt off.

5Low-cost and local products

• Sand or wood ash with water scours burnt food and soot from cooking pots. Wood ash is also alkaline, so it helps to cut grease. Wear gloves: it dries and irritates the skin.
• Lemon juice or vinegar dissolves scale and lightens rust marks.
• Bar soap is cheap and does most everyday jobs.
• Sunlight dries and freshens cloths and mats and helps to kill some germs.

Worked example: diluting bleach

Bleach is sold concentrated and must be diluted with water before use. A 0.1% chlorine solution is a common strength for wiping surfaces, and a 0.5% solution for cleaning up spills of vomit, blood or faeces. The label tells you the strength of the bottle.

Problem. Ishimwe's bottle says 5% bleach. How much bleach and how much water does he need to make 1 litre (1000 mL) of 0.1% solution?

Step 1: find the dilution. 5% ÷ 0.1% = 50, so the bleach must be diluted 50 times. The final 1000 mL must contain 1000 ÷ 50 = 20 mL of bleach.

Step 2: find the water. 1000 mL − 20 mL = 980 mL of water.

Check. 20 mL of 5% bleach contains 20 × 0.05 = 1 mL of active chlorine product, and 1 mL in 1000 mL is 0.1%. Correct.

Rule. Volume of bleach = final volume × (strength wanted ÷ strength of the bottle).

Mix it in cold water, in a container labelled clearly, for example "0.1% bleach, do not drink". A diluted bleach solution weakens over time, so make a fresh one each day.

6Safety rules for cleaning products

1. Read the label first, including the hazard symbols and the words "Danger" or "Warning".
2. Never mix bleach with an acid such as vinegar or a toilet cleaner: the mixture releases chlorine gas, which damages the lungs. Never mix bleach with ammonia: that releases other poisonous gases called chloramines.
3. Use the right amount. More product does not clean better; it only wastes money and leaves residue.
4. Protect yourself. Wear gloves, open windows, and keep products away from your eyes and mouth.
5. Store products safely in their original labelled containers, closed, high up and away from food and children. Never pour a cleaning product into a drinking bottle.

First aid. If a product splashes into the eyes, rinse them with clean running water for at least 15 minutes and get medical help. If a child swallows a product, do not make them vomit; take them to the nearest health centre at once, with the container so the nurse can read the label.

Practice

Solution. (a) An acid such as vinegar, because scale is a mineral that dissolves in acid. (b) An abrasive such as sand, ash or scouring powder, because the burnt layer must be scraped off. (c) A disinfectant, diluted bleach, because the aim is to kill germs.

Solution. Dilution = 4 ÷ 0.1 = 40 times. Bleach = 2000 mL ÷ 40 = 50 mL, topped up with 1950 mL of water.

Solution. Most toilet cleaners are acidic. An acid mixed with bleach releases chlorine gas, which irritates the eyes and throat and can seriously damage the lungs in a small, closed room. He should use one product, rinse, and never combine them.

Solution. It is abrasive. It scratches the plastic, and dirt and germs then collect in the scratches, making the basin harder to clean next time.