Grade 8 Science Midterm Review PDF

Chemistry Basics Atom Smallest particle that all matter is made of Comprised of a nucleus (in centre) and electron shells (orbit the nucleus) Atoms contain 3 subatomic particles- protons, neutrons, electrons Protons (positively charged) and Neutrons (neutral) are located in the nucleus Ele...

Chemistry Basics Atom Smallest particle that all matter is made of Comprised of a nucleus (in centre) and electron shells (orbit the nucleus) Atoms contain 3 subatomic particles- protons, neutrons, electrons Protons (positively charged) and Neutrons (neutral) are located in the nucleus Electrons (negatively charged) orbit the nucleus in electron shells Electron shell maximum electron capacity 1st shell = 2 2nd shell = 8 3rd shell = 18 (stable at 8) 4th shell = 32 Element Consist of the same type of atom Elements are the building blocks from which all substances are made They are listed in the Periodic Table in order according to the number of protons in the nucleus. This is known as the atomic number. Each has its own symbol. Examples: Hydrogen H, Carbon C, Nitrogen N, silver Ag, Lead PB, Mercury Hg. Molecule More than one atom joined together by a chemical bond If they are the same type of atom= molecule of element (eg.O2), different atoms= molecule of compound (eg. CO2) Compound When 2 or more different types of atoms are bonded together Common examples: water H2O, carbon dioxide CO2, methane CH4, glucose C6H12O6 The formula tells us how many atoms from each element are present. Eg. CO2 = 1 carbon atom and 2 oxygen atoms Mixture Can be comprised of atoms, elements and compounds in varying quantities No formula can be written  Mixtures can be separated by physical means using separation techniques Examples: salt water, air, soft drink, perfume Periodic Table Is a list of all of the known elements Listed in order of atomic number The rows are called periods and columns are called groups Metals are found on the left and non-metals to the right. The group that divides them are the metalloids. The information provided for each element includes: Atomic number, symbol, name and atomic mass. Atomic Number = The number of protons in an atom = The number of electrons in an atom Atomic Mass = How heavy the nucleus is. This is equal to the number of protons + the number of neutrons. Easy Steps for Balancing Chemical Equations Follow four easy steps to balance a chemical equation: 1. Write the unbalanced equation to show the reactants and products. 2. Write down how many atoms of each element there are on each side of the reaction arrow. 3. Add coefficients (the numbers in front of the formulas) so the number of atoms of each element is the same on both sides of the equation. It's easiest to balance the hydrogen and oxygen atoms last. 4. Indicate the state of matter of the reactants and products and check your work. Write the Unbalanced Chemical Equation The first step is to write down the unbalanced chemical equation. If you're lucky, this will be given to you. If you're told to balance a chemical equation and only given the names of the products and reactants, you'll need to either look them up or apply rules of naming compounds to determine their formulas. Let's practice using a reaction from real life, the rusting of iron in the air. To write the reaction, you need to identify the reactants (iron and oxygen) and the products (rust). Next, write the unbalanced chemical equation: Fe + O2 → Fe2O3 Note the reactants always go on the left side of the arrow. A "plus" sign separates them. Next, there is an arrow indicating the direction of the reaction (reactants become products). The products are always on the right side of the arrow. The order in which you write the reactants and products is not important. Write Down Number of Atoms The next step for balancing chemical equations is to determine how many atoms of each element are present on each side of the arrow: Fe + O2 → Fe2O3 To do this, keep in mind a subscript indicates the number of atoms. For example, O2 has 2 atoms of oxygen. There are 2 atoms of iron and 3 atoms of oxygen in Fe2O3. There is 1 atom in Fe. When there is no subscript, it means there is 1 atom. On the reactant side: 1 Fe 2O On the product side: 2 Fe 3O How do you know the equation isn't already balanced? Because the number of atoms on each side isn't the same! Conservation of Mass states mass isn't created or destroyed in a chemical reaction, so you need to add coefficients in front of the chemical formulas to adjust the number of atoms so they will be the same on both sides. Add Coefficients To Balance Mass in a Chemical Equation When balancing chemical equations, you never change subscripts. You add coefficients. Coefficients are whole number multipliers. If, for example, you write 2 H2O, that means you have 2 times the number of atoms in each water molecule, which would be 4 hydrogen atoms and 2 oxygen atoms. As with subscripts, you don't write the coefficient of "1", so if you don't see a coefficient, it means there is one molecule. There is a strategy that will help you balance equations more quickly. It is called balancing by inspection. Basically, you look at how many atoms you have on each side of the equation and add coefficients to the molecules to balance out the number of atoms. Balance atoms present in a single molecule of reactant and product first. Balance any oxygen or hydrogen atoms last. In the example: Fe + O2 → Fe2O3 Iron is present in one reactant and one product, so balance its atoms first. There is one atom of iron on the left and two on the right, so you might think putting 2 Fe on the left would work. While that would balance iron, you already know you're going to have to adjust oxygen, too, because it isn't balanced. By inspection (i.e., looking at it), you know you have to discard a coefficient of 2 for some higher number. 3 Fe doesn't work on the left because you can't put a coefficient in front of Fe2O3 that would balance it. 4 Fe works, if you then add a coefficient of 2 in front of the rust (iron oxide) molecule, making it 2 Fe2O3. This gives you: 4 Fe + O2 → 2 Fe2O3 Iron is balanced, with 4 atoms of iron on each side of the equation. Next you need to balance oxygen. Balance Oxygen and Hydrogen Atoms Last This is the equation balanced for iron: 4 Fe + O2 → 2 Fe2O3 When balancing chemical equations, the last step is to add coefficients to oxygen and hydrogen atoms. The reason is that they usually appear in multiple reactants and products, so if you tackle them first you're usually making extra work for yourself. Now, look at the equation (use inspection) to see which coefficient will work to balance oxygen. If you put a 2 in front of O2, that will give you 4 atoms of oxygen, but you have 6 atoms of oxygen in the product (coefficient of 2 multiplied by the subscript of 3). So, 2 does not work. If you try 3 O2, then you have 6 oxygen atoms on the reactant side and also 6 oxygen atoms on the product side. This works! The balanced chemical equation is: 4 Fe + 3 O2 → 2 Fe2O3 Note: You could have written a balanced equation using multiples of the coefficients. For example, if you double all of the coefficients, you still have a balanced equation: 8 Fe + 6 O2 → 4 Fe2O3 However, chemists always write the simplest equation, so check your work to make sure you can't reduce your coefficients. This is how you balance a simple chemical equation for mass. You may also need to balance equations for both mass and charge. Also, you may need to indicate the state of matter (solid, liquid, aqueous, gas) of reactants and products. Balancing Equations Practice Name ____________________________ Part A: Identify the following parts of each chemical formula by circling the subscripts and drawing a square around the coefficients. H2 2 HCl 4 O2 CH4 3 CO3 2 NaOH Part B: List the symbols for the atoms in each formula and give the number of each. C2H6 2MgO 4P4O10 NH3 3 Al(OH)3 2 H2O2 Part C: Balance each of the following equations following the procedure described in class. Be sure to show your work. P + O2 → P4O10 Mg + O2 → MgO P = P = Mg = Mg = O = O = O = O = HgO → Hg + O2 Al2O3 → Al + O2 Hg = Hg = Al = Al = O = O = O = O = BaCl2 + H2SO4 → BaSO4 + HCl Ba = Ba = Cl = Cl = H=H= S=S= O=O= T. Trimpe 2006 http://sciencespot.net/ Part D: Practice Problems – Balance each equation using the process from Part C. Cl2 + NaBr → NaCl + Br2 H2 + N2 → NH3 Na + Br2 → NaBr CuCl2 + H2S → CuS + HCl HgO + Cl2 → HgCl + O2 C + H2 → CH4 Challenge Problem: Give it your best shot! C2H6 + O2 → CO2 + H2O  T. Trimpe 2006 http://sciencespot.net/ Balancing Equations Practice ANSWER KEY Part A: Identify the following parts of each chemical formula by circling the subscripts and drawing a square around the coefficients. H2 2 HCl 4 O2 CH4 3 CO3 2 NaOH Part B: List the symbols for the atoms in each formula and give the number of each. C2H6 2MgO 4P4O10 C = 2 Mg = 2 P = 16 H = 6 O = 2 O = 40 NH3 3 Al(OH)3 2 H2O2 N = 1 Al = 3 H = 4 H=3O=9O=4 H=9 Part C: Balance each of the following equations following the procedure described in class. Be sure to show your work. 4P + 5O2 → P4O10 2Mg + O2 → 2MgO P = P = Mg = Mg = O = O = O = O = 2HgO → 2Hg + O2 2Al2O3 → 4Al + 3O2 Hg = Hg = Al = Al = O = O = O = O = BaCl2 + H2SO4 → BaSO4 + 2HCl Ba = Ba = Cl = Cl = H=H= S=S= O=O= T. Trimpe 2006 http://sciencespot.net/ Part D: Practice Problems – Balance each equation using the process from Part C. Cl2 + 2NaBr → 2NaCl + Br2 3H2 + N2 → 2NH3 2Na + Br2 → 2NaBr CuCl2 + H2S → CuS + 2HCl 2HgO + Cl2 → 2HgCl + O2 C + 2H2 → CH4  Challenge Problem: 2C2H6 + 7O2 → 4CO2 + 6H2O T. Trimpe 2006 http://sciencespot.net/ What is ecology? The study of how organisms interact with each other and with their environment. Environment = all the factors, both living and non-living, in an organism’s surroundings that affect it, e.g temperature, rainfall, the presence of other organisms. Habitat = the place where an organism lives. Ecosystems An ecosystem is a system formed by a group of living things, interacting with each other and their non-living surroundings. The three main components of an ecosystem are: 1. Physical surroundings such as rocks, soil and water 2. Living organisms (the community) 3. Living and non-living factors that make up the environment, Eg. competition  for food and amount of rainfall Factors influencing organisms Organisms in an ecosystem are affected by: Abiotic factors: non living things and Biotic factors: living things and interactions involving living things Factors influencing organisms Abiotic Biotic  Temperature Population numbers Light Intensity Competitors Texture and pH of soil Collaborators Availability of water Predators Concentration of gases in Disease causing organisms water or air and parasites Availability of mates Interactions between living things Competition: occurs when organisms both try to obtain the same resource. Resources include, food, shelter and available mates Competition can be: Intraspecific: between members of the same species Interspecific: between members of different species Task: Give one example for both intraspecific and interspecific competition. Collaboration When living things interact in a way that provides benefit Examples: Dolphins hunting in packs Meerkats living in groups for protection against predators Mutualism When two organisms live closely together and both benefit. Example: The oxpecker bird eats the parasites (fleas and ticks) on the antelope  Commensalism Where one organism benefits and the other is unaffected. Example: A possum living in a tree hollow The possum gains shelter, the tree is unaffected Parasitism Where one organism lives on or in another organism (the host) and feeds off it. The host is usually harmed but not always killed. Example: A parasitic wasp lays its eggs on a caterpillar which will hatch and eat the caterpillar.. Summary  9.2 Sustainability Sustainability Most natural ecosystems are sustainable. This means they are capable of maintaining living conditions for the community.  - A supply of matter - Energy - A large range of species Food chains: Producers Organisms such as green plants which are able to produce their own food (nutrition) through photosynthesis. Photosynthesis is the process whereby plants take in carbon dioxide through their leaves and water through their roots and using energy from sunlight, convert the CO2  and H2O into sugars (glucose) Photosynthesis equation Consumers Organisms such as animals that are unable to produce their own food. They must consume (eat) other organisms such as plants or animals to obtain their nutrition. Types of consumers Herbivores: only eat plants Omnivores: eat both plants and animals Carnivores: only eat other animals Food chains Food chains ○ Start with a producer ○ End with a consumer ○ Show the levels of consumers Decomposers  Decomposers are organisms such as fungi and bacteria which break down dead materials and waste and recycle matter and nutrients back into the soil for producers to reuse. Energy flow in ecosystems  The arrows on a food chain show the flow of energy in an ecosystem Uses of energy Living things use energy: To build new cells needed for growth and repair To provide energy for movement and internal processes Living things also lose energy as heat.  Because living things use the energy they gain from food, only approx. 10% of all the energy found at each level in a food chain is passed onto the next level. Energy flow The progressive loss of energy along food chains explains why the chains are short. Rarely will they have more than four steps. There is little energy available to organisms by the time it reaches the end of the chain. This limits the number of organisms found at each level. Pyramid of Biomass Show the total mass of organisms at each stage of a food chain. These pyramids can be used to show the productivity of an area – how well the area supports life. Natural and Human Impacts Natural and Human Impacts  How could this ecosystem be affected by drought? Abiotic factors: Biotic factors: Natural and Human Impacts How could this ecosystem be affected by introduced species?  Abiotic factors: Biotic factors: Natural and Human Impacts How could this ecosystem be affected by chemical pesticides? Abiotic factors: Biotic factors: Natural and Human Impacts How could this ecosystem be affected by over fishing? Abiotic factors: Biotic factors: Earth’s Spheres