Senior Science Notes

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-many consumer products have been developed because of increased understanding of chemical substances, chemical reactions & the biochemistry of human body surfaces -some products are used as cleaning agents while others have been developed to act as barriers against environmental factors like wind and heat -some products are mixtures, used for medicinal purposes, & require a different understanding of body chemistry & chemical interaction -production of these substances on a commercial scale resulted from developments in chemical technology and an understanding of the different properties of chemicals and of chemical interactions -these products include a range of different types of substances, mixtures & polymer molecules. -many products are applied to the hair and skin, to keep them clean or offer some protection from the elements -these products are designed to take into account the properties of water and alcohol, as solvents, and numerous aspects of body chemistry -the different types of chemical substances and how they are combined to make mixtures depend upon their specific physical and chemical properties -types of products used & the ways in which they are used have changed over time and are continuing to change as people become more aware of the environmental and health impacts of some of the synthetic substances produced

2.1 Physical and chemical properties of substances

-chemicals are used daily to make cleaning jobs easier, to beautify our surroundings, to control dangerous pests and to maintain our homes -although there a millions of chemical compounds, they can be broadly grouped according to their use and some of these groups include: surfactant cleaners, degreasers, lubricants, pesticides, solvents, metal cleaners, body hygiene chemicals and cosmetics

-surfactants are the main ingredients in detergents
-surfactants are synthetic chemicals which help water to wet a dirty surface and lift dirt off it -other ingredients soften water, break up fatty substances, prevent the redeposition of dirt and add fragrance -common products made with detergents include: washing powder, washing up detergents, shampoos, shower gels & surface-cleaning products

-reduce friction and wear between moving surfaces
-usually oil-based and are used in engines and other machines where moving parts rub together -may be in liquid form as oil or solid form as grease

-materials that are able to selectively kill an animal considered to be a nuisance -use a variety of complex chemicals and are classified by the type of animal killed, the way they act or the chemical group to which they belong (e.g. Rodenticides kill rats and mice -many pesticides are accumulated in the food chain & thus cause environmental concern -some become less effective over time as many species develop greater resistance to them Solvents

-liquids in which we can dissolve another substance (dissolved substance is the solute) resulting mixture is a solution -the solvent molecules are able to surround the solute molecules & prevent them from rejoining -ordinarily, when we say a substance is soluble we are referring to its ability to dissolve in water -water is often referred to as the universal solvent because so many substances dissolve in it -many other solvents turps to dissolve paints, dry-cleaning spirit and pre-wash stain removers to remove oil and grease stains from clothing -general rules that chemists use to predict solubility is that like dissolves like: -ionic substances (where a positive ion is bonded with a negative ion) and polar substances dissolve in polar solvents like water and alcohol -non-polar substances dissolve in non-polar solvents such as petrol

Metal cleaners
-used to remove tarnish from metals such as stainless steel, copper, brass and silver -tarnish dulls the surface of metals and makes them less attractive -tarnish...
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