Chemical Changes (Part II) Student Slides PDF

Chem Chemical Changes (Part II)  Overview Part I 1. How do we identify a chemical change? 2a. What are the different types of chemical changes? Part II 2b. What reactions can acids undergo? 3. How do chemical changes occur? 4. How does the knowledge of chemical reactions...

Chem Chemical Changes (Part II)  Overview Part I 1. How do we identify a chemical change? 2a. What are the different types of chemical changes? Part II 2b. What reactions can acids undergo? 3. How do chemical changes occur? 4. How does the knowledge of chemical reactions help us in our daily lives? 2  Success Criteria I can: describe the chemical reactions between: – acids and alkalis; – acids and metals (optional for G2); and – acids and carbonates (optional for G2). describe the effect of acidic, alkaline and neutral solutions on indicators (include litmus paper, Universal Indicator and natural indicators obtained from plants). 3  Success Criteria I can: describe the chemical changes that matter (i.e., element, compound or mixture) undergoes upon: mixing (e.g. neutralisation); heating (e.g. thermal decomposition); exposure to light (e.g. photosynthesis); interacting with oxygen (e.g. rusting and cellular respiration); and using an electric current (e.g. electroplating) (optional for G2). 4  Success Criteria I can: state how chemical reactions can benefit our lives (e.g. cooking, respiration) and cause harm to our health and environment (e.g. rusting, decay, burning). 5 Recall that: neutralisation occurs when an acid and an alkali are mixed. Example: & Acid on our teeth Toothpaste contains an alkali So what are the properties of acids & alkalis? 6  Some Common Acids Organic Acids Mineral Acids Acetic acid Hydrochloric acid Citric acid Nitric acid Sulfuric acid Lactic acid 7  Some Common Alkalis Soap (contains sodium Detergent Baking soda hydroxide) (contains ammonia) Can you derive some of their properties? 8  Properties Of Acids & Alkalis Acids Alkalis Have a _______ taste Have a _______ taste Have a ________ feel ___________ / Burn the skin pH level _________ 7 pH level _______ 7 Turn _____ litmus Turn ____ litmus paper ____ paper ____ Can react with Can react with _______, ________, _________ and _____________  Uses Of Common Acids Acid Uses Hydrochloric Removes rust from iron / steel objects acid, HCl Sulfuric acid, Used in car batteries H2SO4 Nitric acid, Making explosives / fertilisers HNO3 Ascorbic acid Found in Vitamin C tablets  Uses Of Common Alkalis Alkali Uses Sodium hydroxide, Making soaps and detergents NaOH Calcium Reducing soil acidity in agriculture Hydroxide, Ca(OH)2 Aqueous ammonia, Making fertilisers NH3  2. What Reactions Can Acids Undergo? Neutralisation: A chemical reaction between an acid and an alkali. General word equation: acid + alkali  ______ + _______ A “salt” refers to a compound containing a metal element and non-metal element(s). More details will be covered in Upper Sec Chemistry.  Reactions Of Acids: Neutralisation acid + alkali  salt + water Example: hydrochloric acid (acid) reacts with sodium hydroxide (alkali) to form sodium chloride (salt) and water. Word Equation: hydrochloric acid + sodium hydroxide  sodium chloride + water Chemical Equation: HCl + NaOH  NaCl + H2O 13  Reactions Of Acids: Neutralisation acid + alkali  salt + water Example: sulfuric acid (acid) reacts with potassium hydroxide (alkali) to form potassium sulfate (salt) and water. Word Equation: sulfuric acid + potassium hydroxide  potassium sulfate + water Chemical Equation: H2SO4 + 2 KOH  K2SO4 + 2 H2O 14  Reactions of Acids with Metals Optional for G2 Acids react with metals to form salt and hydrogen gas. General word equation: acid + metal  ______ + __________ Note: Metals such as copper, silver and gold do NOT react with acids as they are unreactive.  Reactions of Acids with Metals Optional acid + metal  salt + hydrogen for G2 Example: hydrochloric acid (acid) reacts with magnesium (metal) to form magnesium chloride (salt) and hydrogen. Word Equation: magnesium + hydrochloric acid  magnesium chloride + hydrogen Chemical Equation: Mg + 2 HCl  MgCl2 + H2 16  Test For Hydrogen Gas Optional for G2 https://www.youtube.com/watch?v=bRu2nwFK9O8  Test For Hydrogen Gas Optional for G2 Place a lighted splint at the mouth of the test tube. The lighted splint will be _____________ with a __________________. 18 Reactions of Acids with Carbonates Optional for G2 Acids react with carbonates to form salt, carbon dioxide gas and water. General word equation: acid + carbonate  _____ + __________________ + ______ Note: Carbonates will be covered in Upper Sec Chemistry  Reactions Of Acids With Carbonates Optional for G2 acid + carbonate  salt + carbon dioxide + water Example: hydrochloric acid (acid) reacts with magnesium carbonate (carbonate) to form magnesium chloride (salt), carbon dioxide and water. Word Equation: magnesium carbonate + hydrochloric acid  magnesium chloride + carbon dioxide + water Chemical Equation: MgCO3 + 2HCl  MgCl2 + CO2 + H2O 20  Test For Carbon Dioxide Gas Optional for G2 https://www.youtube.com/watch?v=0J4HpjwKwsg&t=12s (stop at 1.05)  Test For Carbon Dioxide Gas Optional for G2 delivery tube hydrochloric acid calcium carbonate limewater ___________ bubble the gas the gas through ___________ limewater and a _______________________ white precipitate will be formed. X lime water will turn chalky 22  Summary Neutralisation acid + alkali  salt + water *Optional *acid + metal  salt + hydrogen for G2 extinguish with a pop sound (presence of hydrogen) *acid + carbonate  salt + carbon dioxide + water bubble the gas in limewater ; a white precipitate is formed  Summary Optional for G2 Gas Hydrogen Carbon Dioxide Test Lighted splint Pass through limewater Observation Extinguished with a White precipitate pop sound formed  Checkpoint Optional for G2 Which statement is correct ? A: Hydrogen is produced when acids react with carbonates. B: Carbon dioxide is produced when acids react with metals. C: Hydrogen forms a white precipitate when passed through limewater. D: Salt and water are produced when neutralisation takes place.  Acidity & Alkalinity Of A Solution Why are these acids corrosive ? but these acids are not ? 26  The pH Scale The pH scale is a set of numbers used to indicate whether a solution is _______, ________ or Acidic Neutral __________. Alkali neutral Increasingly acidic Increasingly alkaline Acids: pH less than 7 Alkalis: pH greater than 7 Neutral (neither acidic nor alkaline) solutions: pH of exactly 7. 27  pH Of Common Chemicals Sulfuric acid, Pure water Sodium nitric acid, hydroxide Aqueous hydrochloric ammonia acid Ethanoic acid (vinegar) 28 pH Of Common Substances 29  Checkpoint A liquid has a pH of 7. What does this mean? A) It is weakly acidic. B) It is weakly alkaline. C) It is water. D) It is neutral.  Determining pH Of A Solution 1) Using ________ Indicators 2) Using a pH probe attached to a data logger 31 https://www.youtube.com/watch?v=xYQlvTblgCY  Litmus Indicator Litmus paper can be used to determine whether a solution is acidic or alkaline. Acidic Alkaline solution: solution: turn blue turn red litmus red litmus blue 33  Universal Indicator Universal Indicator contains a mixture of dyes. It is green when neutral and gives different colours in solutions of different pH. Acidic Alkaline solution: solution: green turns green turns _________ _________ Neutral solution: remains green 34  Summary (Including Other Common Indicators) Indicator Colour in Neutral Colour in acid colour of alkali indicator Red Litmus Red Red Blue Blue Litmus Red Blue Blue Universal Red / Green Purple / Indicator orange blue Methyl Orange Red Orange Yellow Bromothymol Yellow Green Blue Blue 35  Checkpoint A student would like to identify an unknown solution X. She dipped red and blue litmus papers into Solution X. The results obtained are shown below. Which could be Solution X? A distilled water B lime juice red litmus blue litmus paper turns paper C detergent blue remains blue D vinegar Solution X 36  Checkpoint The table below shows information about three indicators. Indicator Colour change from pH at which colour low to high pH change takes place Phenolphthalein Colourless to pink 9.0 Bromothymol Blue Yellow to blue 6.5 Methyl Orange Red to yellow 4.0 If equal volumes of these three indicators were mixed, which colour would be observed if the mixture was added to a solution of pH 5.5? A) Orange B) Green C) Yellow D) Violet 37 Importance Of pH In Daily Life https://www.youtube.com/watch?v=x-nI3Ws7nxQ 38  Optimal pH For Plant Growth It is important to control the pH of soil because this affects the growth of plants. Most plants grow best when the soil is _________ neutral or _________ slightly acidic __________ (around pH 6 or 7). acidic soil alkaline soil 39  Use Of Antacids To Relieve Stomach Discomfort Antacids (alkaline compounds) are common medications used to neutralise excess acid produced in the stomach hence helping to relieve discomfort. 40  Teeth Brushing Bacteria present on our teeth produce acids which causes tooth decay. Toothpaste is weakly alkaline and it helps to neutralise any acid present in our mouth when we brush our teeth daily. 41 3. How Do Chemical Changes Occur? 42 43  Mixing When two or more reactants are mixed together, they may combine irreversibly to form new products. Example: mixing lemon juice and baking powder during baking or an acid and an alkali during neutralisation. 44 45  Heating Some reactions do not begin spontaneously even when the reactants are mixed. Thermal energy is needed to start a chemical reaction. Example: butane gas (in kitchen stove) must be heated up with a spark from a lighter before it undergoes combustion. 46 47  Exposure To Light Some reactants need to absorb enough light energy before a chemical reaction begins. Example: green plants photosynthesize to produce glucose and water by absorbing light energy from the sun. 48 49  Interaction With Oxygen Interaction with oxygen in the atmosphere may cause chemical changes to occur. Example: rusting of iron takes place when iron is exposed to oxygen and water vapour in the atmosphere. 50  Optional for G2 Copper Electroplating Experiment - Faraday's Law of Electrolysis (Chemistry) - YouTube 51  Using An Electric Current Optional for G2 An electric current may cause chemical changes (e.g. Electroplating) to take place. Note: will be covered in Upper Sec Chemistry 52  Theory Activity 11.3.1: Identifying Powder X heating 4. How Does The Knowledge Of Chemical Reactions Help Us In Our Daily Lives? 54  Cooking heating and ,mixing Cooking causes chemical reactions in food. This makes food softer, more flavorful, and easier for the body to digest and absorb. However, some of the nutrients may be destroyed in the process. 55  Respiration Respiration takes place in the cytoplasm and mitochondria of both plant and animal cells. decomposition Glucose is broken down in the presence of oxygen to produce water and carbon dioxide. releases energy The chemical potential energy in the glucose molecules is converted to other forms of energy to enable the cells to do work. 56  Decomposition/Decay Organic matter, such as fresh food products, will be broken down into simpler substances. Nutrients can then be returned to the environment. To slow down decomposition, we could vacuum pack food to reduce the amount of oxygen gas available for bacteria to decompose the food. 57  Rusting To prevent rusting, bare metal surfaces are coated with a substance to reduce their exposure to oxygen and water. Examples of coating: - paint - oil - varnish - galvanic coating 58  Combustion Burning of fuels helps us convert chemical potential energy into other forms of energy to do work. negative effects: combustion starts wildfires causes greenhouse gases Examples: from combustion of fossil - combustion of natural gas to generate electricity - combustion of petrol or diesel fuel in engines of motor vehicles 59 Combustion of fuels releases pollutant gases like carbon monoxide, sulfur dioxide and oxides of nitrogen. Deforestation increases the amount of carbon dioxide in the atmosphere, which could lead to global warming and acidification of oceans. 60 https://www.youtube.com/watch?v=gZGj0BbDT38 61  Ocean Acidification Large amount of carbon dioxide dissolve in seawater, causing it to become more acidic. Marine organisms cannot form new shells as their shells (calcium carbonate) will react with the acidic seawater. Death of plants/fishes as they cannot survive in conditions of low pH. 62  Practice Practice Questions