Science 6/7 : Chemistry

1SCIENCE 6/7 : CHEMISTRY MATTEREverything in the world is made of matter – everything that is not energy is matter.Matter can be identified by its PROPERTIES Some are easy to identify and observe – wood, water, salt, glass, plants, animalsSome are less easy – oxygen, carbon dioxide, the air Are there differences and similarities between types of matter?PROPERTIES OF MATTERCharacteristics, describe an objectSpecific properties – describe how they are different Colour  Size Shape Odour  Texture Hardness Lustre Clarity 2Most can be observed by using the senses (QUALITATIVE OBSERVATION)General properties describe how all matter is the same: QUANTITATIVE OBSERVATION Mass Weight  Volume  Density MASS AND WEIGHTMASS The most important general property of matter The amount of matter in an object The mass of an object is constant – does not change unless matter is added or removed from the object Mass does not change with greater or lesser gravityMASS and INERTIAInertia is the resistance of an object in changes to its motion (Newton’s First Law of Motion)Objects that have mass resist changes in their motion If an object is at rest, a force is needed to make it move 3 If an object is in motion, a force must be used to slow it down or stop itThe more mass an object has, the greater its inertiaTherefore: the force that must be used to overcome the inertia also has to be greater than the resistance MEASUREMENT of MASSMass is measured in units called grams (g) and kilograms (kg)1 kilogram = 1000 grams Mass of small objects usually measured in grams or milligrams Mass of large objects usually measured in kilograms or TONNES (1000 kg)The amount of medicine in a pill can be about 100 – 250 milligramsA paper clip is about 1 gramA nickel is about 5 gramsA can of pop is about 350 gramsA jug of milk is about 4000 grams, or 4 kilogramsA full-grown person may be about 80 kilogramsAn elephant may be more than 3 600 kilograms (3.6 tonnes)WEIGHT Another general property of matter Weight is not constant – changes according to certain conditions 4WEIGHT and GRAVITYEarth’s force attracts the mass of an object depending on how close to the origin of the force, i.e. Earth’s core. The closer that an object gets to Earth’s core, the greater the pull of gravity on the mass of the object – the force weakens as the distance away from Earth’s core increases.Therefore: an object on top of a mountain would weigh less than the same object deep in a mine.All objects have a gravitational force, but it depends on the size of the object – the force increases with size. We weigh less on the moon because the moon is only a fraction of the size of Earth. In space, we are so far away from a large source of gravity that we become weightless, even though our mass is still the same.FORCE is the combination of the mass of an object times the speed in which it is moving. The amount of force increases as the mass and/or speed increase. This is Newton’s Second Law of Motion (Force equals mass times acceleration: F = ma)VOLUME AND DENSITYVOLUME is the amount of space that an object takes upVolume is measured by metric units called LITRES (L), Millilitres (mL), and CUBIC CENTIMETRES (cc).Litres are generally used to measure the volume of liquids, and cubic centimeters are generally used to measure the volume of solids1 litre = 1000 milliletres 51 millilitre = I cubic centimeter; therefore,1000 cubic centimeters = 1 litre Products such as milk are sold in 4 L containers, but also in 250 ml, 500 ml, and 1 L containersHypodermic needles inject liquids measured in cubic centimeters: 10 ccMATTER IS ANYTHING THAT HAS MASS AND VOLUMEDENSITYThe properties of mass and volume can be used to describe the DENSITY of an objectDensity is the MASS PER VOLUME of an objectFormula: Density = Mass/Volume Allows us to compare different types of matter Density of pure water is 1 g / mL (one gram per millilitre) This also tells us that, since 1000 mL = 1 Litre, then 1 Litre equals 1000 grams, or 1 kilogramIf we know the volume of a container of pure water, we can estimate the mass; this also works in reverse.Objects with lesser density than water will float. Wood has a lower ratio of mass to volume, or lesser density, than water, so it will not submerge into the water without the application of force. 6When water freezes, it floats because it expands during the freezing process, which lowers its density. Ice has a density of .89 grams per mL, or only 89% of the density of water.This also tells us that only the remaining 11% of the ice will stay above the water, while the rest is submerged. This is about the same percentage of the tip of an iceberg that sticks out of the water.Some liquids are less dense than pure water (oil, gasoline), and will rise and float on the surface of water when they are mixed together. This makes it less work to clean up oil spills on the ocean.MEASURING MASS and VOLUMEMASS of Solids - use direct measurement – place on a balance or scaleMASS of a quantity of water - measured with an empty, dry container – weigh the container, weigh the container and water, then subtract the mass of the container – indirect measurementVOLUME of a liquid – direct measurement in a graduated cylinder Measure at the bottom of the meniscusVOLUME of a solidRectangular solid – multiply length x width x height in ccIrregular Solid – measurement amount of displacement in a body of water: Vol. of solid = (Vol. of water + solid) – volume of waterSTATES of MATTER Whether a substance is a solid, liquid, or gasA substance may be found in all three states: 7Water (liquid) >>> ice (solid) >>> vapour (gas); depends on the temperature Melting and Boiling PointsMelting point - the temperature at which the solid form of the substance changes to a liquid: water = 0o CelsiusFreezing Point - the temperature at which the liquid form changes to a solid – water: 0o CelsiusBoiling Point – the temperature at which the liquid form of a substance changes to a gas: water = 100o CelsiusPlasma – gas that has electricity running through it Found in fluorescent lights, the Northern Lights, neon signs, and plasma TVs.MATTER IS MADE UP OF MOVING PARTICLESPARTICLE MODEL1. All matter is made up of tiny particles2. The particles are always moving3. The particles have spaces between them4. Adding heat to matter makes the particles move fasterCan be used to explain  the properties of solids, liquids, and gases 8 what happens in changes of stateSOLID Particles are held together strongly Spaces between particles are small Has a fixed shape and fixed volume Particles vibrate back and forth but stay in fixed positionSolid is heated >>> particles vibrate faster and faster >>> >>> break away from fixed positions >>> particles move about freely >>> solid is MELTING – changing from solid to liquidThe reverse process of melting is FREEZING, or SOLIDIFICATIONLIQUID Particles are separated by spaces that are large enough to allow the particles to slide past each other Takes the shape of the container because the particles can move around more freely Particles are still held closely together >>> fixed volume, like a solidLiquid absorbs heat energy, which is converted to kinetic energy >>> particles move about more quicklySome particles gain enough energy to break free of other particles >>>>>> becomes a GAS 9The change from liquid to gas is called EVAPORATIONThe reverse process of evaporation is CONDENSATION – as the gas cools, the particles in the gas lose energy and move about more slowly until the gas condenses to a liquidGAS Particles are separated by much larger spaces than in liquids or solids Gas is mostly empty space  Always fills whatever container it is in – spreads throughout the container, no matter what volume or shapeSUBLIMATIONSome solids can change directly into a gas without first becoming a liquid >>> individual particles gain enough energy to break free from other particles, forming a gas Examples: room deodorizer, dry ice (frozen carbon dioxide), ice evaporating inside your freezerALL STATES HAVE A FIXED MASSWhenever matter changes shape, it does not lose or gain mass. The mass of water vapour that is produced by melting the ice cube and then boiling the water is the same as the mass of the original cube. 10When a liquid is poured from one container to a different container, its shape changes, but the mass stays the sameIf the volume of gas is squeezed into a smaller container (e.g. oxygen tanks), the mass does not change – mass is FIXEDFIXED STATE FIXED MASS? VOLUME? FIXED SHAPE? Solid Liquid Gas BRAINSTORM EXAMPLES OF CHANGES IN STATE BY DESCRIBING THE MOVEMENT AND SPACING OF PARTICLESCOLLOIDSIn a liquid, the molecules move around a little. In a solid, the molecules stay in a fixed position. Some substances have the properties of both a liquid and a solid. In the oobleck (mixture of water and cornstarch), long chains of molecules (polymers) coil together like a pile of spaghetti. The molecules don`t flow easily under high pressure or force, and will act like a solid. If an object moves slowly through it, the polymers have time to move and get out of the way. The cornstarch isn`t dissolved into the water, it`s just mixed into a permanent suspension of solids in a liquid that will never settle if left to stand. Other examples of colloids are blood, fog, whipped cream, foams (including Styrofoam), Jell-O, and styling gel.PHYSICAL AND CHEMICAL CHANGES 11PHYSICAL CHANGESThe substance that is involved remains the same, even though the state may change e.g. when ice melts, it is still iceCHANGES OF STATE ARE PHYSICAL CHANGESParticles of a substance may move further or closer apart, or they may mix with particles of other substances but no new kinds of particles are producedREVERSIBLE CHANGES Dissolving is a physical change – even though water and sugar particles are mixed together, you can reverse the process by evaporating the water and collecting the sugar; ice can be changed back into water. The water in the oobleck will evaporate, and the cornstarch may be used again, if not heated.NON-REVERSIBLE CHANGES e.g. Sawing a log into pieces cannot be reversedCHEMICAL CHANGESThe original substance is changed into one or more different substances with DIFFERENT PROPERTIES 12 e.g. candle burns >>> some wax particles react with oxygen to produce water, heat, CO2 gas, and light – cannot be reversed e.g. fry an egg - liquid white part changes colour and becomes a solid – acquires properties that are different from the uncooked eggCHEMICAL CHANGES ALWAYS INVOLVE THE PRODUCTION OF NEW SUBSTANCES. MOST CHEMICAL CHANGES ARE DIFFICULT TO REVERSETHE IMPORTANCE OF CHEMICAL CHANGEChemical changes are essential to the production of food, converting energy into motion, exchange of gases within your body. e.g. FOOD WEB: a plant combines water with carbon dioxide, plus the light energy from the sun, to produce carbohydrates, which it uses for food (photosynthesis). We eat the plants, and the energy is converted to stored energy inside our bodies, which we use to produce body heat, motion, and other bodily functions like digestion. Our body takes in oxygen, which is a waste product of photosynthesis, and then releases carbon dioxide and other waste products back into the food web, where decomposers convert it into nutrients that plants may use to help them grow 13EVIDENCE OF CHEMICAL CHANGE  A new colour appears Heat, light, or sound is given off Bubbles of gas are formed; a new odour may be noticed A solid material (called a precipitate) forms in a liquid (cornstarch thickening due to the application of heat) The change is difficult or impossible to reverse e.g. making a cake; combining ingredients, then baking and cooling involve all of the aboveTYPES OF CHANGESPHYSICAL CHEMICAL CLUE CHANGE CHANGE Change difficult or impossible to reverse A new colour appears Bubbles of gas are formed Substance stays the same Heat, light, or sound given off Solid material forms in a liquid Change of state is usually 14 reversible No new kinds of particles are produced Any one of these clues could indicate that a chemical or physical changed is taking place. Consider several clues to determine which kind of change is taking place.Example: heat is given off To cook potatoes: chemical change To melt ice: physical changeChemical Changes in the Living EnvironmentChemical changes recycle matter into new forms to be used again. e.g. forest fires turn trees into smoke in the air and ash on the ground – breaks down matter into elements that nourish trees and plants e.g. animals and trees die and decay, and elements are returned to the soil to nourish trees and plants – the work of the digestive systems of decomposersAgain, think of the chemical changes that occur in photosynthesisFactors that influence the type and amount of chemical change in the natural environmentWater: Most chemical changes in the natural environment cannot occur without the presence of water. The more available water in an 15 ecosystem, the greater the chances for a large number and greater diversity (different kinds) of organisms that live in the ecosystem; however, the presence of water without sufficient heat will not create the best environment for natural growth (arctic desert)Heat: Most chemical and physical changes occur more quickly and easily with the greater presence of heat in the natural environment; however, heat without sufficient moisture will not produce a great number or diversity of life in an ecosystem (tropical desert).Water and Heat: the number and diversity of living things in an environment generally increase with the amount of water and heat. A warm, wet environment can quickly and efficiently break down organic matter into compounds and elements that are returned to the soil, which promotes the growth of plants, which feeds the animals and creates and sustains food webs (a temperate rainforest has greater number and diversity of life than a grasslands area, but a tropical rainforest has ten times the diversity of a temperate rainforest). Chemical Changes in the Non-Living EnvironmentMost common is what happens to metals that contain iron (Fe).Chemical change is called RUSTING. Iron reacts with water and oxygen to produce a new, soft, flaky substance called hydrated iron oxide, or RUST. You can sometimes observe rust in the form of liquid brown streaks running down rock faces.Silver and copper also combine with oxygen in the air to form new substances that are a different colour than the original. Silver reacts to 16 sulphur compounds in the air to become silver sulphide (dark blue and black), and copper reacts with oxygen to become a green substance commonly known as patina. You can observe patina on the roofs of the Parliament Buildings in Ottawa or the Statue of Liberty in New York Harbour.CLASSIFICATION OF MATTER: PURE SUBSTANCES AND MIXTURESAll matter is made up of particles.There are many different kinds of particles.Different substances have different properties because they have different kinds of particles.PURE SUBSTANCES Contains only one kind of particle Very few found in nature e.g. water, but water in nature usually contains dissolved minerals in nature, pure substances tend to mix with other substances few exceptions include diamonds all samples of a pure substance have the same properties, e.g. all samples of pure gold around the world have the same density, melting points, and boiling points 17Most pure substances are made pure through refining, including aluminum foil, sugar, waterMIXTURESAlmost all of the natural and manufactured substances in the world are mixtures of pure substances Contains two or more pure substances Can be any combination of solids, liquids, or gases. E.g.  Soft drinks are mixtures made from liquid water, solid sugar, and carbon dioxide. Breads are mixtures of yeast, flour, sugar, water, air, and other chemicals – differences in properties of bread result of different levels of the different types of particles.ELEMENTS AND COMPOUNDSELEMENTS Pure substances that cannot be broken down into any other pure substances 104 pure substances that are elements Composed of only one type of particle 18 e.g. aluminum foil made of the element aluminum, composed only of particles of aluminum Some elements are common in nature, but usually mixed with other elements. Some elements are extremely rare (e.g. krypton) Some are explosive or poisonous (sodium, chlorine)COMPOUNDS Elements combine with other elements to form new pure substances called compounds Pure substances that are made up of two or more elements Similar to letters of the alphabet used to make words Can be solids, liquids, or gases, e.g. WATER, made up of hydrogen (2 parts) and oxygen (1 part) – every particle of water is the same as the other; also known as H2OCompound Elements combined in compound water hydrogen and oxygen table salt (sodium chloride) sodium and chlorine carbon dioxide carbon and oxygen sugar (any type) carbon, hydrogen, and oxygen alcohol carbon, hydrogen, and oxygen chalk calcium, carbon, and oxygen baking soda sodium. Hydrogen, carbon, and oxygen Different combinations of elements in compounds give them different properties Properties can be very different from the elements which make them up e.g. sodium is a soft, silvery metal that is poisonous and reacts violently with water; chlorine is a greenish-yellow gas that 19 is extremely poisonous. Either on its own would be fatal to swallow or inhale, but the combination of these elements forms table salt (sodium chloride) that you use on your food.MIXTURES Most common substances are not pure substances Mixtures of two or more substancesClassifying MixturesMechanical mixture: two or more different parts can be seen with the unaided (without a microscope) eye, e.g., bird seed, granola, concreteSuspension: cloudy mixture in which clumps of a solid or droplets of liquid are scattered throughout a liquid or gas, e.g. smoke, whipped cream.Fresh milk – fat globules (cream) will float to the top (less dense than the water component); commercial milk (from the store) is homogenized – milk is sprayed though an ultra fine screen to break down the fat into droplets so tiny that they stay suspended - emulsionSolution: a mixture that appears to be only one substance; individual parts cannot be seen, even under a microscope. Particles of the substance that dissolves fills the spaces between the particles that it dissolves. e.g. apple juice, waterSEPARATING MIXTURES 20Picking apartPieces are distinguishable from each other - use observable properties (size, shape, colour, etc.) to separate the mixtureFilteringRemove solid pieces of matter by passing the mixture through a device that allows smaller particles to pass through, but holds back the larger particles: liquid is called the filtrate, and the solid matter is called the residue. Examples are tea bags, window screens, coffee filters, painters’ masks.DensityIf substances have different densities, one substance may rise to the surface and float for easy removal, while the other may settle to the bottom of a container of liquid. Example is separating wood chips from sand.MagnetismThis can be used to separate a mechanical mixture if one of the substances is attracted to a magnet. Example is retrieving metal pieces (e.g. screws) from sand.DissolvingIf one of the substances can be dissolved with a liquid, then the other substance can be separated from the mix. Example is adding water to a mixture of sand and salt, and then filtering out the water to separate the sand. 21EvaporatingEvaporate part of a solution to get a substance dissolved in it. Example is obtaining sea salt by evaporating the water, leaving solid crystals of salt.How would you separate these mixtures?Mixture Method marbles and foam balls sand and water oil and water salt and pepper wood chips and pieces of brick sand and pebbles sugar and water aluminum nails and iron nails MEASURING THE CONCENTRATION AND SOLUBILITY OF SOLUTIONSCONCENTRATIONA solid dissolves in a liquid Solid that dissolves – solute The liquid that does the dissolving – the solventExamples: orange-drink crystals into water, salt into water Concentration is the amount of solute that is dissolved in a given quantity of solvent or solution.Example: for every litre of sea water, there is 35 grams of dissolved salts (sodium chloride). The greater the concentration of salt, the lower the freezing point. 22 A solution with a low concentration of solute is called a dilute. A solution with a higher concentration is said to be more concentrated. If you add more solvent (water) to a solution without adding a related amount of solute (salt), then you are diluting the solution.SOLUBILITYIf a substance dissolves in water, then you may say that it is soluble in water. For example, salt and sugar are soluble in water, but oil and wax are not. An insoluble substance is one that does not dissolve.Oil-based paint is insoluble in water, but is soluble in chemical solvent.Saturated and Unsaturated SolutionsA solution is SATURATED with a solute when no more of the solute can be dissolved in it.A solution is UNSATURATED with a solute when more of the solute can be dissolved in it.You can dissolve more solute in warm water than in cold water.Solubility is different for each combination of solute and solvent.MEASURING THE ACIDITY OF SOLUTIONS 23ACIDS are compounds that form solutions with these properties: Have a sour taste React with metals (corrode) Can cause serious burns on skinMany acidic solutions are harmless, e.g. lemon juice, vinegar, give food a tangy flavourSome acidic solutions are dangerous, e.g. hydrochloric acid, used to etch concrete and would make holes in your skin and clothing.Common acids: lemon juice, vinegar, cola soft drinksBASES are compounds that form solutions with these properties: Have a bitter taste Feel slippery React with (break down) fats and oils Can cause serious burns on skinSome basic solutions are harmless, e.g. baking soda and water. Some basic solutions should be used with extreme care, e.g. drain cleaner.Common basic solutions: ammonia, dishwashing liquid, Drano, oven cleanerIDENTIFYING ACIDS AND BASES 24Acidity is measured on the pH scale A scale of numbers running from 0 to 14 Compounds that are neither acid nor base are neutral and has a pH of 7.0; pure water is neutral Acidic solutions have pH values below 7 Basic solutions have pH values above 7 The more acidic a solution, the lower its pH value. The more basic a solution, the higher its pH valueSolution pH battery acid 0.5 lemon juice 2 Vinegar 2.2 Apples 3 normal rain 5.6 Milk 6.6 pure water 7 human blood 7.4 baking soda 8.2 ocean water 8.3 Milk of Magnesia 10.5 Ammonia 11.1 drain cleaner 13.8

Science 6/7 : Chemistry

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