Science notes for eoy.pdf

Hwa Chong Institution Secondary One Lower Secondary Science (LSS) Term 4 EOY Notes Lower Secondary Science Chapter 6.2: Human Digestive System Complex Molecules (Starch, Proteins, Fats)- too large to diffuse through selectively permeable membrane of cells of the small intestine→cannot be absorbed...

Hwa Chong Institution Secondary One Lower Secondary Science (LSS) Term 4 EOY Notes Lower Secondary Science Chapter 6.2: Human Digestive System Complex Molecules (Starch, Proteins, Fats)- too large to diffuse through selectively permeable membrane of cells of the small intestine→cannot be absorbed into the bloodstream Digestion- breaks down large food molecules into smaller and soluble ones so that they can be absorbed and used by our body cells Physical Digestion - breaking up of food into smaller pieces without chemical change - E.g. Chewing of food in mouth, churning action of stomach, action of bile salts in the small intestine - Increase the surface area of food particles so that chemical digestion by enzymes can take place faster Chemical Digestion - breaking down of large food molecules into smaller molecules due to the chemical action of enzymes - allows smaller molecules to be absorbed (by diffusion and active transport) into the walls of the villi, into the bloodstream and be transported into other cells in the body Enzymes - special type of protein that speeds up chemical reactions in the body but remains unchanged at the end of the reaction - specialised; work on specific substrates (a molecule upon which an enzyme acts on) - made in the cytoplasm under instructions from genes on the chromosomes in the nucleus - works best at an optimum temperature and pH, will be denatured by excess heat and pH Effects of temperature on enzyme action - work within a temperature range - has an optimum temperature where it is most effective (40-45 d.C) - Below the optimum temperature→ inactivated - Above the optimum temperature→ denatured - *rate of reaction doubles with an increase in temperature of 10 degrees* Celsius until the optimum temperature is reached - increase in temperature increases molecular motion→molecules of substrate and enzyme gain more kinetic energy and move more quickly→increases frequency of effective collisions between substrate molecules and enzyme’s active site - rate of enzyme-substrate complex formation increases→greater probability of a reaction occurring - rate of reaction increases until optimum temperature reached - enzyme’s optimum temperature produces highest rate of contact between substrate molecules and enzyme’s active site. Rate of enzyme-substrate complex formation is at highest - above optimum temperature, rate of reaction drops rapidly despite increasing frequency of effective collisions→because at high temperatures the specific 3 dimensional conformation of the enzyme active site is altered and no longer complementary to the shape of the substrate→no enzyme-substrate complex is formed and enzyme is denatured - if temperature is much lower than optimum temperature for enzyme, enzyme-substrate complexes are formed slowly, and rate of reaction is slow→enzymes are inactivated if the temperature is reduced to near or below freezing point; regain their catalytic influence when higher temperatures are restored Effect of pH on enzyme action - work best at their optimum pH→maximum rate of reaction occurs - when pH is altered above or below optimum pH, rate of enzyme activity diminishes - extremes of pH will denature the enzyme - effectiveness of enzyme depends on the pH of its surrounding medium - optimum pH of each enzyme depends on where it is found in the body 5 Enzymes that involved in digestion process 1. Amylase catalyses the breakdown of starch into maltose 2. Maltose is further catalysed to break down into glucose by the enzyme maltase 3. The enzyme pepsin catalyses the breakdown of proteins into polypeptides 4. Polypeptides are catalysed to break down into amino acids by other types of proteases(e.g. peptidases) 5. The enzyme lipase catalyses the breakdown of fats into fatty acids and glycerol The Digestive System Alimentary canal- a continuous tube in the body starting from the mouth and ending at the anus Digestive System- a broader term that includes other structures like the accessory organs of digestion (Salivary glands, liver, gallbladder, pancreas) 1. Mouth Digestion begins in the mouth  Teeth help to break up large food pieces into smaller pieces(physical digestion), increasing the surface area exposed to digestive enzymes Food is mixed with saliva produced by salivary glands. Saliva contains the enzyme salivary amylase, which catalyses the breakdown of starch into maltose (chemical digestion) Tongue mixes the food with saliva and rolls the partially digested food into a small ball (bolus), and swallowed down the oesophagus 2. Oesophagus Long and narrow tube joining the mouth to the stomach No enzymes are secreted by oesophageal cells→only digestion of starch into maltose occurs as the boli are swallowed Strong muscles in walls are circular and longitudinal which contract and relax, producing a wave-like movement that pushes the food into the stomach. Involuntary wave-like pattern of muscular contractions- peristalsis Peristalsis- helps push food along the alimentary canal; begins in the oesophagus once a food bolus is formed and ends in the anus 3. Stomach Stores food; has elastic walls and can expand to fit in a large meal Produces gastric juice- mixture of hydrochloric acid and enzyme pepsin Hydrochloric acid- provides acidic conditions in the stomach for pepsin to work and kills bacteria which may have been swallowed Acidic condition stops the action of salivary amylase in the stomach Peristalsis in the stomach wall churns and breaks up the food (physical digestion); mixes food well with gastric juice Pepsin in stomach catalyses the breakdown of proteins into shorter chains of polypeptides (chemical digestion) Food remains in the stomach for about 3-4 hours. Partially digested food becomes liquefied, forming chyme 4. Small intestine Stomach slowly releases chyme into small intestine  Long and narrow tube joining stomach and large intestine, where most of the chemical digestion and absorption of food takes place Chyme mixed with secretions from the liver, pancreas and small intestine as it enters the small intestine from the stomach Pancreas produces pancreatic juice, contains amylase, proteases and lipase, while small intestine produces intestinal juice, contains maltase, peptidases and lipase Starch is catalysed to break down into maltose by amylase Maltose is catalysed to break down into glucose by maltase Protein is catalysed to break down into polypeptides by proteases. Polypeptides are catalysed to break down amino acids by proteases Fat is emulsified into tiny fat droplets by bile and then catalysed to break down into fatty acids and glycerol by lipase 5. Liver Largest organ in the body; many functions ○ Regulation of blood glucose concentration by storing glucose reserves (glycogen) or breaking them down ○ Produces bile, stored in gall bladder and released into small intestine through bile duct. Bile emulsifies fats by breaking them up into small droplets(physical digestion), increasing the total surface area of fat droplets to speed up digestion by lipase (chemical digestion) The main end products of digestion are glucose, amino acids, fatty acids and glycerol. They are absorbed in the small intestine. The absorbed nutrients pass through the small intestine into the bloodstream. Villi- Finger-like projections along the inner walls of the small intestine Microvilli- Under the microscope, the epithelial cells of villi have numerous microvilli. Adaptation of Small Intestine for Absorption 1. The small intestine is long. This allows sufficient time and presents a large total surface area for absorption of digested food.  2. Presence of numerous folds with finger-like projections called villi. This increases the total surface area for diffusion and/or active transport/absorption of digested food to occur more efficiently. 3. The epithelial cells of the villus have microvilli. This further increases the surface area to volume ratio of each epithelial cell for absorption of digested food to occur more efficiently. 4. The villus has a one-cell thick epithelium. There will only be a short distance to allow faster and more efficient absorption of digested food. 5. There is a dense network of blood capillaries, and a lacteal/lymphatic capillary is found in each villus. This ensures that absorbed nutrients can be transported away quickly to maintain a steep concentration gradient of nutrients for efficient absorption by diffusion. The blood capillaries transport sugars and amino acids from the intestine while the lacteals transport fats. 6. Large Intestine The undigested food moves from the small intestine into the large intestine by peristalsis. Water, fibres and mineral salts pass into the large intestine Absorb water and dissolved mineral salts. 7. Rectum Any undigested and unabsorbed matter is stored temporarily in the rectum before it is discharged as faeces through the anus. The removal of undigested matter from the body is known as egestion or defaecation. Summary Starch is catalysed to break down into maltose by amylase (mouth, pancreas) Maltose is catalysed to break down into glucose by maltase (secreted by the small intestine)  Protein is catalysed to break down into polypeptides by pepsin in gastric juice and proteases in pancreatic and intestinal juice. Polypeptides are catalysed to break down by peptidases into amino acids. Fat is emulsified into tiny fat droplets by bile (secreted by the liver and stored in the gall bladder) and then catalysed to break down into fatty acids and glycerol by lipase (small intestine). Chapter 7: Human Respiratory System Respiration- The chemical energy stored in food molecules is eventually released to living organisms through cellular respiration. Cellular Respiration - takes place in all the living cells of organisms - when glucose is broken down during cellular respiration, some energy released is used to form another molecule called adenosine triphosphate (ATP) - ATP molecules: small packets of energy, store energy temporarily and provide energy for all reactions taking place in the cell Types of cellular respiration: 1. Aerobic respiration 2. Anaerobic respiration Aerobic Respiration - occurs all the time in plant and animal cells - glucose is broken down in the presence of oxygen - release a large amount of energy in living cells - carbon dioxide and water are released as waste products - respiration is different from breathing(ventilation) - aerobic respiration is a multi-step reaction that is catalysed by enzymes in the mitochondria **Glucose + Oxygen —> carbon dioxide + water + large amounts of energy Importance of aerobic respiration- aerobic respiration is used for…: Active Transport Cell division  Growth (building up of proteins) Muscular contractions (e.g. heartbeats) Digestion and absorption of food substances Transmission of nerve impulses Human Respiratory System At the nose: - Air enters 2 external nostrils - Nostrils lead into 2 nasal passages, lined with a moist mucous membrane - Passing the air through the nasal cavity has advantages: Hairs in nostrils and mucus on the mucous membrane trap dust and foreign particles Air is moistened and warmed before it enters the lungs From the nose to the trachea: - Air in nasal passages enters the pharynx - Air passes into larynx then into the trachea from the pharynx The trachea and the bronchi: - Trachea lies in front of the oesophagus; extends downwards from the larynx into the chest cavity - supported by C shaped cartilages, ensuring that the trachea is always kept open - lower end of trachea divides into two tubes called bronchi - each bronchus connects to each lung - each bronchus divides continually and ends in bronchioles - each bronchiole ends in a cluster of air sacs or alveoli (singular: alveolus) - walls of trachea and bronchi are lined with cilia and gland cells that secrete mucus - mucus traps dust particles and bacteria while cilia help to sweep these particles up the bronchi and trachea into the pharynx - the particles are then swallowed or spat out Gaseous exchange in the alveoli - millions of alveoli within the lungs providing a large total surface area for gaseous exchange - alveoli are well-supplied with blood capillaries for gaseous exchange Adaptations of an alveolus that increase the efficiency of gaseous exchange 1. Well supplied with blood capillaries with a continuous flow of blood Maintains a steep concentration gradient for carbon dioxide to diffuse out of the blood capillary into the alveolus and oxygen to diffuse into the blood capillary from the alveolus 2. One-cell thick wall of the alveolus Shortens the diffusion distance for oxygen to diffuse from the alveoli to the blood capillaries and carbon dioxide to diffuse from the blood capillaries to the alveoli 3. Inner surface of the alveoli is coated with a film of moisture Allows oxygen to dissolve in it, facilitating diffusion Breathing - The physical process by which respiratory gases are exchanged with the surroundings - Inhalation/Inspiration- taking in air from the surroundings - Exhalation/Expiration- giving out air to the surroundings - Air breathed in is called inhaled air, air breathe out is called exhaled air Inhaled air 21% Oxygen 0.03% Carbon Dioxide Contains less water vapour than exhaled air Exhaled air 16% Oxygen About 4% Carbon Dioxide Contains more water vapour than inhaled air Stimulus for breathing- high concentration of carbon dioxide in the blood or the alveolar air, not a lack of oxygen. No breathing movements occur when there is too little carbon dioxide in the lungs. Anaerobic respiration in humans - The breakdown of glucose in the absence of oxygen. - Anaerobic respiration releases less energy in the form of ATP than aerobic respiration. Lactic acid is produced. - Glucose —-> Lactic acid + ATP - Lactic acid accumulation in muscles causes fatigue and muscular pain. When anaerobic respiration occurs in humans 1. During vigorous muscular contractions, muscle cells respire aerobically. Carbon dioxide is removed quickly, and oxygen is replenished via panting. Heart beats faster to bring oxygen at a faster rate to your muscles as well. 2. There is a limit to the rate of breathing and heartbeat. 3. After a while, muscles become deprived of oxygen, and anaerobic respiration takes place to release extra energy. The small amount of energy released in anaerobic respiration, together with that produced in aerobic respiration, is sufficient to keep the muscles contracting. 4. The lactic acid formed will cause fatigue and muscular pain in the muscles. 5. After resting, the lactic acid will be removed from the muscles and transported to the liver. Some of the lactic acids are broken down in the liver to release energy. This energy converts the remaining lactic acid into glucose, which is transported back to the muscle. Anaerobic respiration in plants and yeast/microorganisms - Used during brewing and bread-making: - Glucose → ethanol + carbon dioxide Glucose is only partially broken down in anaerobic respiration. The ethanol produced still contains much energy. This explains why only a small amount of energy is set free in anaerobic respiration. Ethanol is the alcohol found in alcoholic drinks like beer and wine. In bread-making, carbon dioxide gas expands the dough and helps the bread rise. Effects of smoking on the Respiratory System Chronic Bronchitis Prolonged exposure to irritant particles that are found in tobacco smoke may cause chronic bronchitis. In chronic bronchitis: The epithelium lining of the air passages, e.g., bronchi, becomes inflamed.  Excessive mucus is secreted by the epithelial cells. The cilia on the epithelium are paralysed, and mucus and dust particles cannot be removed. The air passages, e.g., bronchi, become blocked, making breathing difficult. A common symptom of bronchitis is shortness of breath. The patient will frequently cough to remove the irritating material from the respiratory system. Pneumonia Pneumonia can be caused by bacteria, viruses, fungi, or chemical and physical injury. In pneumonia: The alveoli are filled with mucus and phlegm that block the alveoli. This increases the diffusion distance for oxygen to diffuse from the alveoli to the blood capillaries and reduces the volume of oxygen to be absorbed by the lungs. When the lungs become congested with fluids, breathing becomes difficult. A common symptom of pneumonia is shortness of breath. The patient will frequently cough to remove the irritating material from the respiratory system. Thick, sticky mucus blocks up the airway Emphysema Incurable disease that is frequently caused by smoking, exposure to noxious gas, or repeated lung infections. The alveolar walls in a lung affected by emphysema break down to form larger air sacs. The larger air sacs have a reduced surface area for gaseous exchange, and the large amount of scar tissue also affects their functions. Patients with advanced emphysema always exhibit shortness of breath and constantly gasp for air, even while resting or trying to sleep.  Treatment of emphysema involves drugs that open the lungs to their maximum volume and antibiotics to treat infection at the earliest possible stage. Lung cancer - Tar in cigarette smoke increases the risk of getting lung cancer. - Cancer refers to the uncontrolled division of cells. This causes the lungs to lose their function when the abnormal cells overwhelm the normal cells. Other respiratory diseases Asthma - An allergy that affects the bronchial tubes. Breathing is obstructed by muscle spasms in the walls of the bronchial tubes, swelling of the lining of the tubes, and excessive production of thick, sticky mucus. - During an asthma attack it becomes very difficult to breathe. An asthma attack may be gradual or sudden and may be mild or severe enough to require hospitalisation. - A doctor may prescribe drugs to relax the bronchial tube muscles and reduce the production of mucus. Mechanism of Breathing (Advanced) The chest wall is supported by ribs. Two sets of muscles are found between the ribs. They are external and internal intercostal muscles. They are antagonistic muscles, meaning when the external intercostal muscle contracts, the internal intercostal muscle relaxes and vice versa. When you inhale, When you exhale, Your diaphragm muscles contract, Your diaphragm muscles relax, and the diaphragm flattens. and the diaphragm arches The external intercostal muscles upwards. contract, and the internal intercostal The external intercostal muscles muscles relax. (RICE) relax, and internal intercostal  This causes the ribcage to move muscles contract. (ERIC) upwards and outwards. This causes the ribcage to move The volume of your lungs is downwards and inwards. increased. Air pressure in the The volume of your lungs is lungs is reduced below decreased. atmospheric pressure. Air pressure within the lungs is Atmospheric pressure is now now higher than atmospheric higher than the pressure within your pressure. The air is forced out of lungs. This causes air to rush into your lungs to the exterior. your lungs. Chapter 8: Classification of Matter Matter - anything that has mass and occupies space - exist in 3 physical states: solid, liquid and gas, depending on the temperature and pressure of their surroundings - 2 other states (no need to know) - Bose Einstein Condensate and Plasma States of Matter Solid Liquid Gas Shape Fixed Not fixed Not fixed (Assumes the (Assumes the shape of the shape of the container) container) Volume Fixed Fixed Not fixed (Assumes the shape of the container) Ability to flow Does not flow Flows easily Flows easily easily Compressibility Not Not easily Highly  compressible compressible compressible Density Much higher Higher than Low than gases and gases most liquids ***Kinetic Particle Model of matter- states that matter is made of a large number of tiny particles (atoms or molecules), which are in continuous and random motion Brownian Motion - the continuous and random motion of small solid particles in fluids (liquids and gases). - provided the evidence of molecular motion and proved the existence of particles that cannot be observed with a standard microscope Diffusion - particles move randomly from a region of high concentration to a lower concentration - the spreading of molecules independently without any external aid - e.g. perfume molecules/smell perfume from the other corner of the room Diffusion in Gas - Bromine vapour shows diffusion of gases; reddish-brown liquid at r.t.p., but evaporates easily to form a reddish-brown vapour - reddish-brown vapour spreads quickly through the space when bromine vapour is released into a similar gas jar full of air (harmful vapour) Diffusion in Liquid - slower rate than diffusion in gas - tiny crystal of potassium manganate (VII) placed in water→dissolves to form purple solution - purple colour spreads throughout the water as the purple particles have diffused throughout the liquid The rate of diffusion of gases depends on: 1. The temperature of the gases Higher temperature, faster rate of diffusion 2. The molecular mass of the gases  Greater molecular mass of molecules, slower rate of diffusion Molecular Model of 3 States of Matter Particles in a Solid Diagram: Arrangement: - Very closely packed together in a regular arrangement - High densities Movement: - cannot move freely but vibrate about fixed positions - held in position by very strong, attractive forces - have fixed volumes and shapes Particles in a Liquid Diagram: Arrangement: - randomly arranged with particles slightly further apart as compared to that of solids - not arranged in a regular arrangement - relatively high densities Movement: - Rotate and slide past one another - Free to move about but confined within the vessel containing it - Have intermolecular forces between particles - Have fixed volumes but take the shape of vessels containing them Particles in a Gas Diagram: Arrangement: - Very far apart - Randomly arranged - Occupy any available space - Relatively very low densities Movement: - Weak intermolecular forces  - Move about randomly at a very high speed - No fixed volume and shape - Highly compressible Change of State (Kinetic Particle model) - The internal energy of a body is the combination of the total kinetic energy and potential energy of the molecules in a body. - Kinetic energy is due to the vibration of molecules- directly related to temperature - Potential energy is due to the “stretching” and “compressing” of the intermolecular forces as the molecules vibrate Melting (Solid to Liquid) Before reaching melting point: When a solid is heated, the particles absorb heat. The particles gain kinetic energy, start to vibrate faster, and move further apart. At melting point: At the melting point, the particles have enough potential energy to overcome the strong intermolecular forces. The particles start to break away from one another, and the solid becomes a liquid. After melting point: At the liquid state, the particles rotate and slide past one another. Boiling (Liquid to Gas) Before reaching boiling point: When a liquid is heated, the particles absorb heat. The particles gain kinetic energy and slide over each other more rapidly. At boiling point: At the boiling point, the particles have enough potential energy to overcome the strong intermolecular forces. The particles start to move further away from one another, and the liquid becomes a gas. After boiling point:  At the gaseous state, the particles move far apart rapidly in all directions. Freezing (Liquid to Solid) Before reaching freezing point: When a liquid is cooled down, the particles lose heat. The particles lose kinetic energy and vibrate slower. At freezing point: At the freezing point, the particles no longer have enough potential energy to overcome the strong intermolecular forces. The particles start to come together in a regular arrangement, and the liquid becomes a solid. After freezing point: At the solid state, the particles will vibrate at fixed positions. Evaporation vs Boiling During evaporation, the particles on the surface of the liquid absorb heat from the surroundings. The surface particles gain sufficient kinetic energy and slide over each other more rapidly. The surface particles possess enough kinetic energy to overcome the strong intermolecular forces. These particles start to move further away from each other, and the liquid particles on the surface escape and become a gas. Note: No potential energy is involved as the state change during evaporation did not occur at a fixed temperature. Chapter 9: Elements, Compounds and Mixtures Element - a substance that cannot be broken down into simpler substances by any known chemical methods - 118 elements, 94 naturally occurring - water is made up of 2 elements - hydrogen and oxygen, glucose is made up of 3 elements - carbon, oxygen and hydrogen - human body: 10 main elements- calcium in bones and iron in blood Classifying Elements Periodic Table - groups and periods Group - vertical column of elements - elements in same group have same number of valence electrons - elements with same number of valence electrons have similar chemical properties - no. of valence electrons = element’s group number - unique symbol represents each element - each element has its unique proton number, the number of protons MEMORISE: first 20 elements of periodic table and common metals From left to right of the periodic table, gradual change in properties from metallic to non-metallic. Elements- metals or non-metals, depending on their physical properties Physical properties Metals Non-metals Electrical conductivity Good conductors of Usually do not electricity conduct electricity (except carbon in form of graphite) Heat conductivity Good conductors of Usually poor  heat conductors of heat Appearance Shiny (lustrous) Dull (non-lustrous) Melting & Boiling High (except Group 1 Low (except carbon points metals and mercury) and silicon) Ductility and Ductile (can be Brittle if solid malleability drawn into wires) Malleable (can be hammered into different shapes without breaking) Sonority Sonorous (make a Not sonorous ringing sound when struck) Atoms - smallest particle of any element; tiny particles in matter - very small, diameter of about 0.1 nanometre - cannot be seen with naked eye; can be seen with electron microscope - each elements consists of an atom; each element’s atoms differ from those of any other element - made up of subatomic particles called protons, neutrons and electrons - all atoms of same element have same number of protons (atomic number) and electrons - isotopes are atoms of same element with same number of protons and electrons but different number of neutrons Molecules - group of two or more atoms held together by chemical bonds - may consist of atoms of a single element, or of different elements Physical and Chemical Changes Physical change- no new substance is formed (changes easily reversed) E.g. Dissolving of salt in water, Boiling of water Chemical change (Chemical Reaction)  - New substance is formed (changes are NOT easily reversed) - New substance has different properties such as different melting points and different chemical reactions - E.g. Rusting of iron, burning of a candle Compounds - a pure substance containing two or more chemically combined elements in a fixed composition - has very different properties from its elements - E.g. magnesium oxide- made up of 2 elements magnesium and oxygen: produced by burning magnesium in the air Water- made up of 2 elements hydrogen and oxygen: applying a lighted splint to a mixture of hydrogen and oxygen - Contains the same elements: always present in a fixed proportion - when elements chemically combine to form a compound, it cannot be separated again into its elements by physical means; chemical bonds firmly join the particles - atoms of different elements in a compound can only be broken apart in chemical reactions, which require some energy - so, compounds can be separated but only by chemical means or electrolysis Mixture - In a mixture of elements, atoms of the elements are not chemically combined - Percentage of each element in a mixture is not always the same - Does not have a fixed composition - Each element in a mixture retains its properties - Easily be separated by physical means such as filtration, crystallisation or distillation - Consist of different compounds - A single compound has a fixed melting point and a fixed boiling point - A mixture boils/melts over a range of temperatures Compound vs Mixture Chapter 10: Solutions and Suspensions Solutions Solvent: The substance that the solute or solutes dissolve in and it forms the bulk of the solution Solute: The substance that dissolves in the solvent - Cannot see dissolved solute particles like salt particles - Liquid solvents - salt dissolved in water (solid solute dissolved in a liquid solvent), ethanol dissolved in water (liquid solute dissolved in a liquid solvent), oxygen dissolved in water (gaseous solute dissolved in a liquid solvent) - Solid in another solid (brass alloy = zinc solute + copper solvent) - Gas in another gas (air = oxygen solute and nitrogen solvent) - Water is the main solvent → aqueous solution/oil, ethanol, hexane - Solutions are mixtures  - No fixed composition (different concentrations) - Many solutions are formed without any chemical changes taking place - Homogeneous mixture - Colour, density, appearance and other physical and chemical properties are the same in every part of the solution - Solute particles spread evenly in the solvent are too small to reflect any light passing through the solution, therefore light will pass through the solution - If a solution is filtered, no residue left as solute particles are too small. Solubility - The maximum mass of that substance which can dissolve in 100g of the solvent at a given temperature (g/100g of solvent) - The volume of solvent does not affect the solubility of the solute - Copper (II) sulfate has a solubility of 32g/100g of water→ maximum of 32g of copper(II) sulfate crystals can dissolve in 100g of water Describing Solutions A dilute solution contains a small amount of solute in a large volume of solvent. A concentrated solution contains a large amount of solute dissolved in its solvent. A saturated solution contains a large amount of solute dissolved in its solvent so that no further solute can dissolve. Factors affecting solubility: 1. Temperature of solvent 2. Nature of solvent 3. Nature of solute Solubility graphs- solubility usually increases as the temperature increases Rate of Dissolving - How fast a solute dissolves in a solvent, from the time the solute is added to the solvent, until the solute is completely dissolved - An increase in the rate of dissolving would dissolve the solute faster. - ***The rate of dissolving is NOT solubility, which is related to how much of a solute can dissolve. Factors affecting the rate of dissolving: 1. Temperature of solvent 2. Rate of stirring 3. Particle size of solute Increasing the temperature of the solvent results in an increased rate of dissolving. Increasing the rate of stirring results in an increased rate of dissolving.  Decreasing the particle size of the solute results in an increased rate of dissolving (for example, 10g of salt in powder form has more surface area and dissolves faster than 10g of salt in one large cube). (increase surface area to volume ratio) Suspensions - Formed when the substance does not dissolve in the solvent or when the amount of substance present is over its solubility limit - E.g. The solubility of potassium nitrate increases with increases with increasing temperature from 0 to 100 d.C. Given a saturated aqueous solution of potassium nitrate at 40 d.C, a suspension is formed by: - Adding more potassium nitrate to the saturated solution - Decreasing the temperature, which decreases solubility of potassium nitrate, resulting in the amount of potassium nitrate present being over the solubility limit - A suspension is usually non-homogeneous or heterogeneous. - The different substances in a suspension will not remain uniformly distributed if they are not actively being mixed or stirred. - When a suspension is left to stand for some time, insoluble solid particles settle to the bottom due to gravity. - The insoluble solid particles in a suspension are large enough to prevent light from passing through the suspension and also large enough such that they cannot pass through filter paper. Chapter 11: Methods of Separation Pure Substances Single substance not mixed with anything else - E.g. white sugar, copper (II) sulfate crystals Have fixed boiling point unlike mixtures - impure (melt or boil over a range of temperatures) - Greater the percentage of impurity, the lower the melting point - Purity of substance can be checked by: 1. Melting point - Impurities cause an impure solid to have a lower melting point than a pure solid 2. Boiling point - When distilled, if all of the substance distils at the same temperature, it is pure - The temperature is called the boiling point - Boiling range for an impure substance depends on the actual impurities present and their percentage Compound/Element Mixtures are impure and they can be easily separated into pure substances - Purification - Can be done using physical methods and does not require any chemical reactions 3. Chromatography - Impure if the dye separates into multiple spots on chromatogram - Intense spot is pure dye, faint spots are impurities - One spot on chromatogram, - dye is pure Separating solids from solids Magnetic Attraction - Separates ferromagnetic solids from solids that are not ferromagnetic  - Mixture cannot contain solutions or liquids, which will not completely separate from the solids - Examples: Electromagnets remove scrap steel and iron at junkyards and magnets used to remove iron splinters from a patient’s eyes in hospitals - Ferromagnetic metals: iron, nickel, cobalt/alloys of these metals - Nonferromagnetic metals: gold, silver, copper, platinum, aluminium Sublimation - Separates mixture of solids - ONLY one solid must be able to sublime (e.g. carbon dioxide in the form of dry ice, naphthalene, iodine), changing state from solid to gas upon heating - Gas of sublimed solid then cooled to deposit pure crystals, changing state from gas back to solid - Non-subliming solid in the mixture should have high melting point and should not decompose upon heating Separating insoluble solid from solid-liquid mixture Decanting - Separates an insoluble solid from liquid by pouring off the liquid from the container Filtration  -Usual Method of separating solid from a liquid -Mixture is poured through filter paper -Solid collected in filter paper is called residue -Liquid passing through the filter and being collected in the beaker is called the filtrate - The filtrate is often a solution (e.g. salt dissolved in water), can be separated by crystallisation - Filtrate is often a solid dissolved in water Separating soluble solid from solution (solid-liquid mixture) Crystallisation - Solution is heated to allow most of the solvent to be evaporated off - Solution then is cooled, to form a saturated solution - Solution then cools, reducing solubility of the solute - Mass of solute that can dissolve in the solution is decreased - Solution cannot hold any more solute and thus dissolved solute appears as pure crystals - Cold solution is removed by filtration - Residue of pure crystals is rinsed with cold distilled water - Crystals are then dried by pressing them between pieces of filter paper Evaporation to dryness - Similar to crystallisation except for evaporation step - Except all solvent will be evaporated during evaporation to dryness Problems with evaporation to dryness - Cannot separate a pure substance from its impure form as soluble impurities will be deposited along with the required solid - Using this method, some solids will also decompose upon heating (sugar, copper (II) sulfate)  - Hence, evaporation to dryness can only be used when the solids are thermally stable and do not decompose upon heating Separating two immiscible (not able to be mixed) liquids Separating funnel - Separate such mixtures that contain liquids which are immiscible - Less dense liquid forms a separate layer on top of the denser liquid - Tap is opened so that the lower water layer runs out first into a beaker to collect it - Tap is closed as the last drop of water leaves - Tap is then opened again to run the other liquid into another beaker Separating two miscible (able to be mixed) liquids Simple Distillation - Obtain a solvent (liquid) from a solution - Liquid is changed into a pure gas by boiling - Other impurities are left behind - Gas then condenses to form pure liquid called distillate - Also be used to obtain a pure solvent from a solution of a solute - Liebig condenser provides a temperature gradient to cool and condense the vapour. The water inlet is at the bottom of the condenser, while the water outlet is at the top - Water enters from the bottom of the Liebig condenser and exits from the top - To ensure that the water jacket (surrounding tube) of the condenser is fully filled with water for effective cooling of the hot vapour - Allows for a smaller temperature difference between the vapour and the glass walls of the condenser or the glass connections may crack due to differences in expansion - Thermometer shows temperature of the vapour that has been boiled Fractional Distillation - Used to separate a mixture of 2 or more miscible liquids with different boiling points - Similar to simple distillation - Involves fractionating column, many glass beads/plates to provide  a large surface area for condensation - As the vapour mixture moves up the fractionating column, it repeatedly condenses and boils inside the column, causing the vapours of the lower boiling fraction to reach the top of the column first, followed by vapours of the higher boiling fraction. Hence, the liquid with the lowest boiling point is distilled first. - When vapour reaches top of the condensation column, it is pure - Thermometer shows temperature of the vapour that has been boiled - Complete separation is not affected - Effectiveness is increased as fractionating column is utilised Application of Fractional Distillation - Fractional Distillation of Air - Obtain pure oxygen and pure nitrogen from the air - Air first cooled to about -200 dC, a liquid - Liquid air then distilled by allowing liquid to warm up - Nitrogen has a lower boiling point than oxygen so it distils first. - Then, the oxygen distils, producing oxygen and nitrogen separately - Fractional Distillation of Petroleum - Petroleum: mixture of liquids called hydrocarbons - Used to separate the hydrocarbons into, for example, lower boiling point petrol and higher boiling point kerosene - Large amounts of liquid chemicals are manufactured in the petroleum industry, and fractional distillation is commonly used to separate the chemicals into pure liquids To separate small quantities of solids dissolved in a solvent Chromatography  Method of separating and identifying mixtures Paper chromatography is most commonly used Small drop of dye is placed on the start line on a piece of chromatography paper Place the paper in a boiling bath with a suitable solvent. The solvent will travel up the paper. When the solvent reaches the top of the paper, take the paper out of the beaker and dry Dyes on the pencil line dissolve in the solvent and travel up the paper at different speeds and are separated in the end Result is called a chromatogram Can also be used to separate colourless dyes - Sprayed with a locating agent to show where the substances are on the paper - Chemical that reacts with the substances to produce a coloured product Start line must be drawn by a pencil - Made up of graphite and is not soluble in the solvent used - While pen ink consists of resins, pigments and other colouring dyes - May affect the end chromatography result Can be used to identify very tiny amounts of substances - Can detect less than 0.000 000 000 001 gram or 10^-12 g of the substance -END-