TWO TYPES OF CHANGES Physical Changes Chemical Changes A change that alters a physical property of a substance (eg shape, state, temperature) but doesn’t make a new substance. A change that forms one or more new substances Usually reversible – can get the original substances back easily Usually irreversible – cannot get the original substances back. Examples – cutting paper, freezing water to form ice, dissolving sugar in water Examples – cooking an egg, burning paper, baking a cake

CHEMICAL REACTIONS Chemical reaction: a process where one or more chemical substances undergo a chemical change to form a new substance Signs of a chemical reaction A new substance is formed A gas a released (bubbles formed) A solid forms (also called a precipitate) A rise or drop in temperature Colour is permanently changed

CHEMICAL REACTIONS Reactant: a chemical substance that is present at the start of a chemical reaction (what we start with) Product: a chemical substance that is formed as a result of a chemical reaction (what we end up with)

CHEMICAL REACTIONS We can describe what is happening using a chemical equation. Chemical equations are always written in the form: reactants → products We can write chemical equations using: Words (eg hydrogen + oxygen → water) Chemical formula (eg H2 + O2 → H2O)

WRITING WORD EQUATIONS Sodium reacts with iron (III) chloride to form sodium chloride and iron. When propanol is burnt in oxygen gas, carbon dioxide and water are formed. Hydrogen peroxide splits to form water and oxygen gas. A piece of aluminium was dropped into hydrochloric acid. The aluminium dissolved and reacted to form aluminium chloride. As it did so, hydrogen gas bubbled to the surface.

QUICK QUIZ Write the definition of a chemical reaction. Write the definition of reactant and product. Which of the following signs shows that a chemical change has occurred during a reaction? The reaction is reversible There has been a change in state (eg solid, liquid or gas). There is a permanent colour change. There has been a change in shape

DUE: Tomorrow (Friday Lesson 6) PRACTICAL REPORT For this practical report, you need to include: Title Introduction (include aim, hypothesis and state independent, dependent and control variables) Materials Method (written in numbered steps, include a diagram) Results Discussion (include your observations here) Conclusion For more information about what to include in these sections, refer to the “Writing a Scientific Report” sheet DUE: Tomorrow (Friday Lesson 6)

What results were we expecting from the practical? Law of Conservation of Mass: mass is neither created nor destroyed during a chemical reaction (in other words, you have to finish with the same number and type of atoms that you started with … the mass at the beginning should be the same as the mass at the end) CaCO3 + HCl → CaCl2 + H2O + CO2 In the beaker, where did the CO2 go? What should have happened to the weight? In the flask, where did the CO2 go? What should have happened to the weight?

PRACTICAL REPORT CHECKLIST Title Introduction – aim, hypothesis, independent variable, dependent variable, control variables, word and formula equation of the reaction. Materials – a list of all equipment and chemicals you used. Method – numbered steps of what you did during the practical, diagram of the prac set up. Results – could be written neatly or in a table. DO NOT need a graph for this prac. Discussion – what observations did you have during the practical, describe your results in sentence form, did your results support your hypothesis, were the results you obtained what you were expecting to get, could there be any sources of error in the practical (human or equipment), what could you do next time to improve the practical. Conclusion – Short! A quick summary – was your hypothesis supported or rejected, what did you find out during the practical?

ACIDS Acid: a substance that releases hydrogen ions (H+) into a solution. Properties of acids Contain hydrogen atoms Turn blue litmus paper red Taste sour Corrosive

BASES Base: a substance that releases hydroxide ions (OH-) into a solution. Properties of bases Bases are commonly found in cleaning products. Turn red litmus paper blue Taste bitter Feel slippery

pH SCALE AND INDICATORS pH scale: a scale from 0-14 that shows how acidic or basic a substance is. Acid: pH < 7 Neutral: pH = 7 Base: pH > 7 To test to pH of a substance we can use an indicator. An indicator is a substance that changes colour when an acid or base is present.

(Alkaline = basic)

REACTIONS WITH ACIDS All acids react in predictable ways: Acid + Metal → Salt + Hydrogen gas Acid + Carbonate → Salt + Water + Carbon Dioxide Open textbook to Page 149-150

QUICK QUIZ Use the pH scale to match the pH measurements with the solutions below: pH 4 Neutral solution pH 7 Moderately acidic solution pH 1 Moderately basic solution pH 8 Very acidic solution pH 10 Slightly basic solution

IMPORTANCE OF pH

PHOTOSYNTHESIS Plants use the energy in sunlight to produce food in the form of a simple sugar called glucose. Photosynthesis can be summarized by the equation: Carbon dioxide + Water Glucose + Oxygen Sunlight and chlorophyll are written over the arrow to show that they are necessary for the reaction to occur, but are not used up in the reaction. Sunlight Chlorophyll

PHOTOSYNTHESIS Plant cells contain structures called chloroplasts. These contain chlorophyll, which gives plants their green colour. Chlorophyll absorbs energy from the sun to start the process of photosynthesis.

PHOTOSYNTHESIS For photosynthesis to occur, a plant needs sunlight, chlorophyll, carbon dioxide and water. Sunlight comes from the sun Carbon dioxide is absorbed from the atmosphere through tiny openings in the leaves called stomata. Water is carried from the plant’s roots into the leaves. Chlorophyll is found in the chloroplasts.

Quick Quiz What is the definition of an acid? What is the definition of a base? If you mix an acid and a base together, what do you think would be produced? Hint: think about what acids and bases release into a solution.

NEUTRALISATION REACTIONS Neutralisation Reaction: a reaction where an acid and a base cancel each other out to form a salt and a water. Acid + Base  Salt + Water The H+ ions from the acid combine with the OH- ions from the base to form water. The ions left over combine to form a salt.

HOW TO WRITE YOUR PRACTICAL REPORT Your report MUST have the following headings: introduction, aim, hypothesis, variables, safety, materials, method, results, discussion, conclusion.

HOW TO WRITE YOUR PRACTICAL REPORT Aim: explains the purpose of the practical – it is not a question. Variables: are factors in an experiment that could vary. Independent variable – the variable that you change on purpose. Dependent variable – the variable that you measure Control variables – the variables that must be kept the same during the entire experiment.

HOW TO WRITE YOUR PRACTICAL REPORT Hypothesis: a prediction about what you think will happen. A hypothesis should always be written as a if/then statement: If …(change independent variable)… , then .. (what happens to dependent variable)…

HOW TO WRITE YOUR PRACTICAL REPORT Materials: a list of everything that you used – all equipment and chemicals. Be specific about the concentration and amount of chemicals that you used and the sizes of the equipment you used. Method: a step-by-step description of what you did. Must be in past tense. Instead of “we put the acid in the flask and then dropped in a few drops of methyl orange indicator”, say “A flask was filled with 50 mL of hydrochloric acid and 3-4 drops of methyl orange indicator were added.” Include a diagram of your practical set-up

HOW TO WRITE YOUR PRACTICAL REPORT Results: this is where you record/display the data that was collected during the practical. Include any observations that you recorded during the practical Display your data in a table Can your data be displayed in a graph format?

PRACTICAL REPORT Aim: purpose of the practical – this is not a question. Hypothesis: If …(change independent variable), then .. (what happens to dependent variable) Title Introduction – aim, hypothesis, independent variable, dependent variable, control variables, word and formula equation of the reaction. Materials – a list of all equipment and chemicals you used. Method – numbered steps of what you did during the practical, diagram of the prac set up. Results – could be written neatly or in a table. DO NOT need a graph for this prac. Discussion – what observations did you have during the practical, describe your results in sentence form, did your results support your hypothesis, were the results you obtained what you were expecting to get, could there be any sources of error in the practical (human or equipment), what could you do next time to improve the practical. Conclusion – Short! A quick summary – was your hypothesis supported or rejected, what did you find out during the practical?