Science Grade 8 Notes

Table of Contents - Unit 1: Measurement in Science (Pg 1-24) - Unit 2: Food and Nutrients (Pg 25-50) - Unit 3: Mixtures and Separation Techniques (Pg 51-82) - Unit 4: Forces and Pressure around us (Pg 83-120) - Unit 5: Digestive and Respiratory Systems (Pg 121 -160) - Unit 6: The Language of Chemistry (Pg 161-200) - Unit 7: Work, Energy and Power (Pg 201-240) - Unit 8: Acids, Bases and Salts (Pg 241-282) - Unit 9: Communicable & Non-communicable Diseases (Pg 283-306) ### Unit 1: Measurement in Science -

PortantoLearning Outcomes:- Express physical quantities in appropriate SI units. - Recall the use of different instruments to measure volume and mass of solid objects. - Calculate the volume of regularly and irregularly shaped solids. - Demonstrate a simple understanding of accuracy in measurements. - Demonstrate an understanding of density. - Define density as the mass per unit volume of a substance. - State the formula for density: $density = [ mass/volume ]$ - Recall and use the formula for density in calculations. - Discuss the experimental determination of the density of a solid through the measurement of mass and volume. - Compare the relative densities of solids, liquids and gases. - A physical quantity has a magnitude and a unit. - Length, time, mass, and temperature are physical quantities measured directly using a ruler, stopwatch, beam balance, and thermometer, respectively. - Volume is either measured directly or calculated using appropriate formulae. - Solids have regular or irregular shapes. - A regular object has a well-defined shape; its volume can be calculated using well-known formulae (e.g., cube, cuboid, cylinder, sphere). - An irregular object does not have a well-defined shape. - The SI unit of volume is the cubic metre, $m^3$. Another commonly used unit is the cubic centimetre, $cm^3$. - Most physical quantities can be measured. - SI units are used for scientific and technical work in many parts of the world. - The space occupied by a solid is its volume. - Volume of liquids is measured using graduated measuring cylinders and beakers. - $1 cm^3 = 1 mL$ - When water is poured into a measuring cylinder, the liquid forms a curved surface at the edge, known as the meniscus of the liquid. While reading volume, the eye must be at the same level as the lower meniscus. - A measurement needs to be accurate, meaning how close the measured value is to the true value. In order to improve accuracy, we need to avoid errors of measurement. - Two main errors are: Zero error and Parallax error. - An instrument has zero error if it gives a non-zero reading when the true reading is zero. - Parallax error is a common error made in the measurement of volume, for example, when using a measuring cylinder. It occurs when the eye is incorrectly positioned. - The curved surface of a liquid is its meniscus. It is important to avoid parallax error to increase accuracy of a measurement. - Since an irregular solid does not have a well-defined shape, its volume is measured by using the displacement method. - Mass is a measure of the amount of matter found in a body. - The SI unit of mass is the kilogram (kg). Another commonly used unit is the gram (g).- $1 kg = 1000 g$ - $1 g = 1000 mg$ - 1 mg = [rac{1}{1000} g - The density of a substance is defined as its mass per unit volume.- Density = [rac{mass}{volume} - The SI unit for density is $kg/m^3$. Another commonly used unit is $g/cm^3$.- $1 g/cm^3 = 1000 kg/m^3$ - Relative densities of solids, liquids and gases are significantly different. - In a solid, the particles are regularly and compactly arranged. There is very little free space between the particles. - In a liquid, the particles are arranged in small groups. There is some space between the groups. - In a gas, the particles are far apart. There are large spaces between them. - Generally, the density of solids > density of liquids > density of gases. - The [riangle formula” is useful in density problems.- D = [rac{M}{V} - $M = D [imes V$ - V = [rac{M}{D} - For a solid to float on a liquid, the density of the solid must be less than the density of the liquid. ### Unit 2: Food and Nutrients - PortantoLearning Outcomes:- Define nutrients as food substances or molecules that all organisms need for the proper functioning of their body. - Classify nutrients into carbohydrates, fats, proteins, vitamins and minerals. - Select and list examples of food sources rich in carbohydrates, fats, proteins, vitamins, minerals and dietary fibres. - State the main role of carbohydrates, proteins and vitamins (A and D) in our body. - State that carbohydrates are subdivided into simple and complex carbohydrates, giving examples such as glucose and starch respectively. - Demonstrate an understanding of starch as a complex carbohydrate made up of many simple sugar units. - Recognise different examples of food sources rich in glucose and starch. - State that proteins are large food molecules that are made up of smaller units called amino acids. - Carry out simple food tests. - Identify the components of various food samples using the different food tests. - Define the term ‘balanced diet’ as comprising carbohydrates, fats, proteins, vitamins, minerals, water and dietary fibres in the correct proportion. - Recognise that malnutrition may be the result of either a lack or an excess of a particular nutrient in the diet. - State the deficiency diseases of vitamin A, vitamin D, iron and calcium. - Show an awareness that excess of carbohydrates in the diet can lead to diabetes while excess of fats in diet can lead to obesity and heart diseases. - Food provides us with energy, allows us to grow and helps our body fight against diseases. - There are different nutrients present in our food, where each nutrient is responsible for its function(s) in our body. - Types of Nutrients and their Groups:- Carbohydrates and fats (lipids): Nutrients for energy - Proteins: Nutrients for growth/body building - Vitamins and minerals: Nutrients for health - Two other substances that are equally important to our body; they are water and dietary fibre or simply fibre. - Both carbohydrates and fats are the main energy-providing nutrients. They are made up of carbon, hydrogen and oxygen. - Fats release more energy when burnt as compared to the same amount of carbohydrate. - Fat is a good energy storage nutrient and is stored under the skin as adipose tissue. - Carbohydrates are classified into two groups namely simple and complex carbohydrates - A simple carbohydrate is made up of one sugar molecule; a complex carbohydrate is made up of many simple sugars forming long chains. - Glucose is a simple carbohydrate. Complex carbohydrates are examples include starch in plants and glycogen in animals. - The food manufactured from either simple carbohydrate or starch is termed as processed food. - Proteins are very large molecules made up of small building units known as amino acids. Proteins cannot be stored in the human body. - Food tests may be carried out to show the presence of simple carbohydrates, starch, proteins or fats in a food sample. - Food Tests:- Simple carbohydrates (glucose, fructose): Benedict’s test (Benedict’s solution) - Starch: Iodine test (Iodine solution) - Proteins: Biuret test (Sodium hydroxide, Copper (II) sulfate solution) - Fats: Emulsion test (Ethanol) - The Benedict’s test produces a green/yellow/orange/brick red precipitate when simple carbohydrate is present but it remains blue when a simple carbohydrate is absent. - Iodine test: A blue-black colour shows the presence of starch and a yellow/brown colour shows an absence of starch. - Biuret test: A purple or violet colour is formed in the presence of protein but when protein is absent the colour remains blue. - Emulsion test: A white emulsion is formed in the presence of fats. - Vitamins and minerals are needed in very small amount in our diet. Each has a particular function in our body. - Functions and Sources of Vitamins and Minerals:- Vitamin A:- Function(s): Essential for eyesight, especially night vision; Increases our body’s defence against infection - Sources: Egg yolk, oily fish (salmon, sardines), broccoli, yellow or orange vegetables such as carrot and pumpkin - Vitamin D:- Function(s): Helps in bone and teeth formation - Sources: Cod liver oil, tuna and milk; Produced in the skin on exposure to sunlight - Iron:- Function(s): Essential for the formation of red blood pigment called haemoglobin - Sources: Green leafy vegetables, red meat, cashew nuts, pulses and moringa leaves - Calcium:- Function(s): Builds and maintains healthy bones and teeth; Helps in blood clotting - Sources: Milk and dairy products such as yogurt and cheese; Almonds - Fibres or dietary fibres form the indigestible compounds of plants. They are mainly carbohydrates and one example of a fibre is cellulose. - Fibres provide bulk to the undigested food, helping it to move along the large intestine by peristalsis and help in the elimination of faeces. - The human body consists of about 70% of water. Water is important for cells to function properly. - Balanced diet is the daily intake of food comprising carbohydrates, fats, proteins, vitamins, minerals, water and dietary fibres in the correct proportion. - Factors affecting a balanced diet:- Biological factors such as age, gender, health conditions and genetic make-up of the individual. - Climatic factors: Individuals living in very cold regions need a diet rich in fat catering for the larger need in energy. - Occupation: Someone who does heavy work will need more energy each day than a person doing light work. - An unbalanced diet may lead to malnutrition which can be either undernutrition or overnutrition. - Deficiency diseases occur as a result of inadequate intake of nutrients such as vitamins and minerals:- Vitamin A: Night blindness - Vitamin D: Rickets - Iron: Anaemia - Calcium: Rickets - Over nutrition: Overnutrition often implies an excess of carbohydrate or fat intake that the body cannot use. Excess of carbohydrate can lead to diabetes. Excess fats get stored in our body (under the skin or around organs) and lead to obesity. - Nutrition information is presented on food containers or packaging. ### Unit 3: Mixtures and Separation Techniques -
PortantoLearning Outcomes:- Recall mixtures and their properties - Identify solutions and suspensions and give examples of both - Distinguish between the properties of solutions and suspensions - Explain that differences in properties allow the separation of the components of a mixture - Investigate how mixtures can be separated into their respective components by the following techniques: magnetic attraction, filtration, decantation and evaporation - Draw labelled diagrams to illustrate the steps involved in separation techniques - Explain the principles involved in magnetic attraction, filtration, decantation and evaporation as separation techniques - Explain what alloys are and identify alloys as mixtures - Identify bronze, brass, steel and stainless steel as alloys and state their respective components and composition - Show understanding of the uses of these alloys and relate their uses to their properties - A mixture consists of two or more components which are physically combined together: salads, air and sea water are examples of mixtures. - Properties of a mixture:- The composition of the different components in a mixture can vary; thus a mixture has variable composition. - The components of a mixture can be separated by simple methods. - Blood is a mixture consisting of several components including water, sugar, and different types of blood cells. - A solution consists of two components: a solute and a solvent.- A solute is the dissolved component in a solution. - A solvent is the liquid in which the solute is dissolved. - Examples of solutions include sugar solution, salt solution, caustic soda solution and food colouring dissolved in water. - A suspension consists of a mixture of a liquid with undissolved solid particles.- Examples of suspensions include muddy water, corn starch and water, water and powdered chalk. - Solution vs Suspension:- A solution is clear; we can see through it. A suspension is usually cloudy; we cannot see through it. - The solid particles are completely dissolved in the solution. The solid particles are not dissolved in a suspension. - The solid particles do not settle to the bottom if a solution is left to stand. The solid particles settle at the bottom if a suspension is left to stand. - A colloid is a mixture in which the dispersed undissolved solid particles are smaller in size than the undissolved solid particles in a suspension. An example of a colloid is mayonnaise. - The components of a mixture are separated for example in the filtration of muddy water, in the making of filter coffee and in obtaining salt from seawater. - Different materials have different properties which allows the separation of components of a mixture. For example, iron has a magnetic property whereas glass, paper, wood, plastic and some metals like magnesium do not. - Magnetic materials such as iron can be separated from non-magnetic materials using a bar magnet. - Decantation is a method of separating a heavy insoluble solid from a liquid- Decantation is the process of carefully pouring out the liquid from the mixture, leaving the heavy insoluble solid behind in the container. - For an insoluble solid to be separated from a liquid by decantation, the solid must not float, but must settle down. - Decantation can be used to separate mixtures such as rice and water, sand and water, and baby corn and water. - Filtration is another separating technique that is used to separate finely divided insoluble solids from a liquid using a filter.- Filtration is possible when the size of the insoluble solid particles is larger than the pores of the filter used. - The liquid which passes through the filter paper during filtration is called a filtrate. - The solid which remains on the filter paper during filtration is called residue. - In laboratories, filtration is usually used to separate a mixture of a liquid and an insoluble solid. - Hairs in our nostrils trap the dust particles that we breathe in and allow only clean air to pass through the trachea to our lungs. - Filtration of blood occurs in the kidneys. The wastes are then excreted via urine. - Evaporation is a method used to separate a solute from a solution.- The solution is placed in an evaporating basin and is heated over a water bath. - The solvent evaporates from the solution and the solid is left behind. - Alloys are materials composed of one metal and one or more metal or non-metal element. - Alloys are usually made to improve the properties of the constituent metals, such as increased strength or resistance to corrosion. ### Unit 4: Forces and Pressure around us - PortantoLearning Outcomes:- Recognise and investigate different examples of forces around us - Demonstrate a simple understanding of the force of gravity, frictional force and magnetic force. - Define force as a push or a pull and state its unit of measurement - Investigate the effects of forces