Junior Secondary Science Revision Notes PDF

1 Introducing science 1.1 Learning about science (Book 1A, p. 2–15) 1 Science is the study of phenomena and events in Nature. 2 We often apply scientific knowledge to deal with daily life problems. 3 Science is based on evidence. Scientists usually do experiment...

1 Introducing science 1.1 Learning about science (Book 1A, p. 2–15) 1 Science is the study of phenomena and events in Nature. 2 We often apply scientific knowledge to deal with daily life problems. 3 Science is based on evidence. Scientists usually do experiments to collect evidence. 4 Scientific knowledge is subject to change when new evidence is found. 5 Scientific knowledge has limitations. It cannot solve all problems. There are still many questions about Nature that cannot be answered using present scientific knowledge. 6 Scientific discoveries have increased our understanding of the natural world. Example: The discovery of microorganisms helped people understand that some microorganisms cause diseases. 7 Scientific discoveries have also led to many inventions that have improved our quality of life. Example: The discovery of microorganisms led to invention of drugs to treat diseases caused by them. 8 Using scientific knowledge, we can manage natural resources more effectively. Example: Ways to use other energy sources to generate electricity are developed to reduce the use of fossil fuels. 9 Scientific knowledge is applied in the development of technology. Example: The discovery of microwaves speeded up the development of wireless communication technology. Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 1  1 Introducing science 10 When solving daily life problems, we often need to integrate and apply knowledge and skills of science, technology and mathematics. Example: When finding ways to fight a disease caused by a new virus, we need to apply the following knowledge and skills. Knowledge and skills Examples of solving daily life problems To understand the cause of the disease and develop Science treatments for the disease To develop machines for rapid detection of the disease Technology and production of masks Use statistics to trace infections and find the Mathematics effectiveness of new drugs 11 The applications of science bring benefits to us. However, they can be harmful if we misuse them. 1.2 Practice of science (Book 1A, p. 16–27) 1 Basic steps of scientific investigations: Making Asking Proposing Doing Drawing observations a question a hypothesis experiments a conclusion 2 In a fair test, we should only change the variable under study and keep all other variables the same in different set-ups. 3 There are three types of variables in a fair test: Independent variable: the variable that we change Dependent variable: the variable we measure Controlled variables: the variables that are kept the same 4 There are many types of scientific investigations. Fair testing, pattern seeking and classifying are examples. Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 2  1 Introducing science 1.3 Safety in the laboratory (Book 1A, p. 28–39) 1 A laboratory is a suitable place for doing experiments. 2 Laboratory equipment: water tap and sink gas tap electric socket safety spectacles gloves laboratory coat fire extinguisher sand bucket fire blanket first aid box eye wash bottle fume cupboard Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 3  1 Introducing science 3 We must follow laboratory safety rules to prevent accidents in the laboratory. Below are some general safety rules: DOs DON’Ts ✓ Strictly follow your teacher’s ✗ Do not enter the laboratory or do instructions. experiments without your teacher’s ✓ Keep all exits and passages clear. permission. ✓ Keep the laboratory clean and tidy. ✗ Do not eat, drink, run or play in the ✓ Wear safety spectacles when heating or laboratory. mixing substances. ✗ Do not leave experimental set-ups ✓ Tie up long hair and fasten school ties unattended. when doing experiments to prevent ✗ Do not point a test tube towards anyone them from catching fire or dipping into when heating it. chemicals. ✗ Do not touch hot objects with bare ✓ Wash hands thoroughly after doing hands. experiments. ✗ Do not touch electric plugs with wet ✓ Report all accidents to your teacher hands. at once. ✗ Do not smell or taste any chemicals unless instructed by your teacher. 4 When we handle chemicals in the laboratory, we must read the hazard warning symbols on their containers and take safety precautions. Hazard warning symbol Safety precaution Keep away from flames and sparks. Keep flammable and oxidizing chemicals away from one another. Wear safety spectacles and protective gloves. Keep the room well-ventilated. Wear safety spectacles and protective gloves. Keep the room well-ventilated. Carry out experiment in a fume cupboard if chemicals give out toxic or irritating gases. Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 4  1 Introducing science 5 When there is an accident in the laboratory, we must keep calm, report it to the teacher at once and take emergency actions. Below are some common laboratory accidents and the emergency actions needed: Laboratory accident Emergency action Cuts Clean and dress the cut Heat burns Splash of chemicals on skin Wash the affected area with slow running water. Splash of chemicals into eyes Wash the eyes with distilled water from an eye wash bottle. 6 The three necessary conditions for a fire to occur are a fuel, a high temperature and oxygen. They form the fire triangle. 7 We can put out a fire by removing any one or more of the conditions in the fire triangle. fuel Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 5  1 Introducing science 1.4 Laboratory apparatus and basic practical skills (Book 1A, p. 40–71) 1 Common laboratory apparatus: d e c a b Apparatus Function a test tube To hold liquids or solids b boiling tube To hold a larger amount of liquids or solids c beaker To hold liquids or solids d conical flask To hold liquids or solids e reagent bottle To store liquids h f i g Apparatus Function f Bunsen burner To heat substances g insulating mat To protect the bench from overheating h wire gauze To support apparatus when heating i tripod To support the wire gauze Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 6  1 Introducing science j k l Apparatus Function j test tube rack To hold test tubes k test tube holder To hold a test tube when heating l test tube brush To clean test tubes m q n o p Apparatus Function m glass rod To stir liquids n dropper To transfer a few drops of liquids o spatula To transfer a small amount of solids To hold filter paper and allow liquids to flow p filter funnel down during filtration q stand and clamp To fix the position of apparatus Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 7  1 Introducing science 2 We draw sectional diagrams to show experimental set-ups. test tube beaker conical flask dropper glass rod wire gauze clamp filter tripod paper filter Bunsen burner funnel stand insulating mat 3 Skills of drawing experimental set-ups: Draw straight lines using a ruler. Do not shade the diagrams. Keep all parts in proportion. Label each apparatus. filter paper filter funnel muddy water conical flask filtered water Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 8  1 Introducing science 4 Skills of transferring solution from reagent bottle to test tube: reagent bottle test tube stopper (placed upside down) reagent bottle a Take out the stopper from the reagent bottle and put it upside down. b Hold a test tube at an angle. Slowly pour the solution from the reagent bottle into the test tube until the test tube is about one-third full. c Close the reagent bottle with the stopper immediately after use. Then put the test tube into a test tube rack. 5 Skills of transferring solution using dropper: a Squeeze the rubber bulb of a dropper and do not release it. Lower the tip of the dropper into the solution. b Release the rubber bulb slowly to suck some solution into the dropper. c Let the tip of the dropper touch the inner wall of the test tube to remove any droplets from the tip of the dropper. d Take the dropper to an empty test tube. Gently squeeze the rubber bulb to add a few drops of solution into the test tube. e After the practical, wash the dropper with water in another beaker by squeezing and releasing the rubber bulb several times. Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 9  1 Introducing science 6 Skills of mixing solution: Method 1 Method 2 Gently shake the test tube. Gently tap the test tube with the index finger. 7 Some measurements and their units: Measurement Unit Symbol kilometre km metre m length centimetre cm millimetre mm cubic metre m3 cubic centimetre cm3 volume litre L millilitre mL kilogram kg mass gram g milligram mg temperature degree Celsius °C second s time minute min hour h Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 10  1 Introducing science 8 Apparatus and instruments used to make measurements: We usually use a plastic ruler, a half-metre rule, a meter rule or a measuring tape to measure length. meter rule half-meter rule measuring tape plastic ruler We usually use a measuring cylinder to measure the volume of liquids, and measure the mass of an object using a top pan balance or an electronic balance. measuring cylinder top pan balance electronic balance We usually use an alcohol thermometer or a mercury thermometer to measure temperature, and use a stopwatch to measure a period of time. mercury thermometer alcohol thermometer stopwatch Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 11  1 Introducing science 9 Reading the scale: Your eyes should be vertically above the scale of the ruler, or at the same level as the bottom of the meniscus. The interval between two marks on a scale is the limitation of reading. 10 Error in measurement: Error of measurement can be taken as half of the limitation of reading. Example: The end of the sticky note falls between two marks on a scale. We take the nearest sticky note reading, i.e. 7.6 cm, accurate up to 0.1 cm. Limitation of reading = 0.1 cm Reading error = ±0.05 cm Errors are not mistakes. They cannot be avoided even if we read the scale correctly. 11 ‘Zero’ function of electronic balance: When we put an object on the balance and then press the zero button, the balance of the reading is set to zero. This function is useful when we measure the mass of an object that needs to be put in a container (e.g. a liquid or solid power). Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 12  1 Introducing science 12 Different types of errors: Type of error Source of error Loading time The instrument is not completely started up when taking measurement Reading error The actual value is less than half of the limitation of reading (i.e. interval between two marks on the scale) Parallax error Looking at the scale on the instrument at an incorrect angle Zero error The reading on the measurement instrument is not reset to zero before each measurement 13 Accuracy and precision in measurement: Errors affect the accuracy and precision of measurements. Being accurate means that a reading is close to the true value (i.e. correct). Being precise means that repeated measurements of the same item are close to each other (i.e. consistent). reading of measurement true value not accurate not accurate accurate but accurate and not precise but precise not precise precise Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 13  1 Introducing science 14 Structure of a Bunsen burner: chimney air hole collar rubber tubing base 15 Differences between the Bunsen flames when the air hole is closed and opened: Air hole closed Air hole opened Type of flame luminous non-luminous Shape of flame irregular regular Colour of flame yellow blue Noise of burner quiet noisy 16 We usually use a non-luminous flame for heating. 17 When heating liquids or solids in a boiling tube over a Bunsen flame, we should hold the boiling tube at an angle using a test tube holder. Move the tube around in circles over the flame. test tube holder boiling tube water Junior Secondary Science Mastering Concepts and Skills © Oxford University Press 2023 14