Senior Science Notes
1. LIFESTYLE CHEMISTRY 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 Detergents -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 Lubricants 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 Pesticides -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 results from corrosion chemical reaction of the metal substances in the air -some metal cleaners contain phosphoric acid and hiourea which dissolve the metal oxide, exposing fresh shiny metal underneath -other metal cleaners contain abrasives which remove the tarnished layer using small particles of grit and so aren’t suitable for use on plated items such as silverware which contain only a thin layer of silver on a base metal -metal cleaners also contain detergents and corrosion inhibitors to slow further tarnishing Body hygiene chemicals and cosmetics -term covers a large range of products such as skin-care products, fragrances and toothpastes -colloid mixtures are the most common but can also be solutions or suspensions -these products clean oil and dirt from the body and therefore contain surfactants Pharmaceuticals -chemical substances which alter the biochemical processes in our bodies in ways which lead to an improvement in health -their chemical properties influence the wide variety of methods used to administer them Safe use and handling of chemicals most chemicals used in products around the house are safe as long as the product is used correctly -some chemicals involved, such as solvents or propellants, may be dangerous if misused while others such as enzymes may cause skin or eye irritation -manufacturers’ instructions may include warnings about the safe use of the product around flames, that the product shouldn’t make contact with the skin or eyes, that the product should be used in a well-ventilated area and not inhaled, or any special instructions regarding disposal -many cleaning agents are toxic to people and the environment -majority of household poisonings are due to the inhalation of cleaning products -most problems could be avoided if instructions and warning labels were read before use Poisons -toxic substances that have an effect on the body, either by impairing normal sense or by inuring body organs -many household chemicals are poisons and children under four are at most risk from accidental poisoning -poisons can nclude perfumes and aftershaves, insecticides and weedkillers, plants, etc -different types of poisons have different effects on the body and so the treatment required in each case can vary which makes it difficult to give general advice on treatment so first course of action should always be to call for advice from a doctor or the Poisons Information Centre -poisons may be inhaled, injected or absorbed through the skin -most commonly, poisoning in the home is caused by a toxic substance being swallowed -symptoms of poisoning include vomiting, convulsions, drowsiness, unconsciousness or stomach pains -patients should not be made to vomit as they can often choke on the vomit -if poison was acidic or alkaline, patient should swallow small amount of water to dilute the poison -vomiting acids and alkalis can cause severe chemical burns and too much water can induce vomiting -if poison was an organic solvent like petrol then vomiting can cause the poison to enter the lungs -milk can settle the stomach and help keep the poison down if it is a shampoo or detergent Emulsifiers -many consumer products are mixtures of chemicals and appear in the form of solutions, colloids and suspensions -products containing these types of mixtures may have emulsifiers added to them-substances which help one substance mix with another -emulsifiers improve the consistency, uniformity and stability of many consumer products Solutions solutions contain at least one substance dissolved in another (solute— dissolved substance, solvent— substance it is dissolved in) -a solution is homogenous (uniform throughout)- can’t see individual substances contained in it -e. g. perfumes, food colourings, petrol Colloids -also contain particles but remain suspended for long periods of time -colloids contain properties that are halfway between solutions and suspensions -colloids have larger particles than a solution but smaller than suspensions -not completely homogenous but isn’t as heterogeneous as a suspension -many types of colloids classified on the type of particle which is dispersed in the medium -medium and particles may be solid, liquids or gas -e. g. aerosols, cements foams advantage of a mixture being in colloid form is that it can be delivered to a specific area of the body such as sunscreen on skin -another advantage is that it’s in a stable form ready to use- doesn’t need to be shaken or stirred -makes product look uniform and attractive in appearance Suspensions -contain large particles which are NOT dissolved in a solvent but mix uniformly together if the product is shaken -over time, suspensions settle out or form layers -suspensions are mixtures that are heterogeneous (non-uniform) and particles are large enough to see -the force of attraction between the solvent particles and the large particles isn’t strong enough and over time they are pulled downwards by gravity -advantage of mixtures being in this form is that suspensions form a stable mixture that lasts well -e. g. salad dressings, cough mixtures TYNDALL EFFECT-bigger particles scatter more light Surface tension in any liquid there are forces of attraction between molecules which act over short distances and are very weak and so are continually breaking and reforming -it is these forces that ‘hold’ the molecules in their liquid state -forces of attraction act equally in all directions on the molecules of the liquid -at the surface of the liquid the forces don’t act equally on the molecules -molecules in the surface layer are very strongly attracted by the molecules in the layer underneath, but not by the molecules in the air above creating surface tension -unbalanced attractive forces result in molecules being pulled inwards -water has a high degree of surface tension allowing some insects to push back on the water without breaking the surface allowing them to move forward -meniscus shape is the result of two forces acting-cohesion and adhesion: attractive forces between the glass and the water (adhesion) are stronger than forces between the water molecules (cohesion) which results in water being pulled up the sides of the glass columns at the edges Surfactants water alone is not a very effective cleaning agent as dirt tends to be trapped in oil -oil and water don’t mix as oils are non-polar substances while water is a polar solvent -cleaning products rely on surfactants (surface-active agents) to make oil dissolve in water -makes the oil/ dirt and water mixture into a liquid-in-liquid colloid- an emulsion and so this process is called emulsification -molecules of surface-active agents have both polar and non-polar parts -surfactant molecules tend to pack together and lie across the oil water interface -the non-polar (hydrophobic) end of the surfactant molecule dissolves easily in the oil while the polar (hydrophilic) end dissolves easily in the water surfactants lower the surface tension of the water and make it ‘spread out’ and make more contact with the dirt particles (‘wetter’) -tails of the surfactants make contact with the greasy dirt particles, while the heads of the surfactant molecules form a layer around the dirt and draw water onto the fabric fibres and the dirt particles -small clump of surfactant molecules (micelle) forms, trapping the grease and dirt -dirt can then be separated from the surface with help of agitation and heat -new surfactant particles then attach themselves to the surface of the cloth -slight electrical repulsion occurs between the heads of the surfactants and prevents dirt from redepositing onto the fabric -the solution containing the dirt/ surfactant complex is then washed away -household cleaners make up the largest user of surfactants in Australia but surfactants are also used in other industries, e. g. in wool industry to remove dirt and grease from raw wool Surfactant and colloid cleaning products -emulsion: a liquid-in-liquid colloid containing two substances that normally don’t dissolve in each other -many cleaning and cosmetic products are in the form of emulsions because this allows an oily material and water to be applied to the surface at the same time Properties of emulsions -two liquids that don’t ordinarily mix are called phases to make the two phases mix together an emulsifier must be added to reduce the difference in surface tension -particles in an emulsion must also be small; if too heavy will settle into layers -emulsifier has strong affinity for either oil or liquid phase -emulsifiers given a number from 1 to 20 on scale called HLB (hydrophilic-lipophilic balance) -name of emulsion gives tells you phase the emulsifier had greater affinity for so an oil-in-water emulsion contains an emulsifier with an affinity for water 1-3: antifoaming agents-reduces surface tension thus preventing formation of foam 3-6:water-in-oil emulsions 7-9:wetting agents- make products such as agricultural sprays adhere to hydrophobic waxy leaves 7-14:oil-in-water emulsions 13-16: detergents 5-20:solubilisers- used to dissolve small amounts of oil (usually fragrances) in water-based products such as skin toners -most of the pigments, perfumes and active ingredients in cosmetic preparations must be used in small amounts for best effect but often need to be spread over a large area of skin -perfect moisturizer should moisten skin by adding water but also coat skin with thin layer of oil to prevent further water evaporating, thus most face creams have both an oil and water component -balance of oil and water varies depending on the use of the cream -cream designed to cover blemishes and even skin tone such as foundation should remain on the surface of the skin while an artificial tanning lotion should be completely absorbed -water evaporates from oil-in-water emulsions leaving a film of the oily substance behind which is useful when applying products such as oils and waxes -oil-in-water emulsion creates cooling effect -water-in-oil emulsions are useful because they allow direct contact between the surface and oil phase -in case of sunscreen this allows direct contact between skin and active ingredients -evaporation of water from surface is much slower and gives warming effect 2. MEDICAL TECHNOLOGY 3. INFORMATION SYSTEMS
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