China 九年级（初三） Chemistry
Chapters: 12
1. Introduction
What chemistry studies
- Chemistry and Society – Chemistry studies how atoms join and rearrange. By choosing which atoms to join and how, chemists make new materials, medicines, fertilisers and fuels. Atoms are never lost in a reaction, so every product has a cost and a waste that we must plan for.
2. U1 Into the world of chemistry
Physical and chemical changes and properties · Experiments and inquiry; lab safety and basic skills
- Physical and Chemical Changes – In a physical change, a substance changes its shape, size or state, but no new substance forms; the particles stay the same. In a chemical change, the atoms rearrange to make one or more new substances with new properties. Signs include gas, colour change, heat or light, a precipitate and a new smell. In both kinds, the total mass stays the same.
- Lab Safety and Safe Experiments – Dress for safety (goggles, coat, closed shoes, hair tied). Read labels and hazard pictograms. Heat gently with the mouth of the tube pointing away. Add acid to water, waft smells, never taste. Report every accident at once. Plan experiments step by step, assess the risks first and dispose of waste correctly.
3. U2 Air and oxygen
Air around us · Oxygen · Preparing oxygen; catalysts · Lab activity 1: preparing and testing O₂ · Interdisciplinary 1: micro air-quality station
- Composition of Air – Air is a mixture of gases. By volume, dry air is about 78% nitrogen, 21% oxygen, 0.93% argon and 0.04% carbon dioxide, with tiny amounts of other noble gases. Water vapour changes from 0 to about 4%. We can show air is a mixture and measure its oxygen by letting iron rust (or phosphorus burn) in a closed tube: water rises about one fifth. Pollutants such as smoke, sulfur dioxide, nitrogen oxides and carbon monoxide make air harmful, and we can reduce them.
- Oxygen – Oxygen (O, atomic number 8) is a colourless, odourless gas that makes up about 21% of air by volume. It exists as O₂ molecules. In the lab it is made by breaking down hydrogen peroxide with a manganese dioxide catalyst (2H₂O₂ → 2H₂O + O₂) or by heating potassium manganate(VII); in industry it comes from fractional distillation of liquid air. It relights a glowing splint. Oxygen supports burning and respiration and reacts with most elements to form oxides: metal oxides are basic, non-metal oxides are mostly acidic. Its other form, ozone (O₃), shields Earth from UV rays.
- Catalysts: Speeding Up Reactions Without Being Used Up – A catalyst is a substance that makes a chemical reaction faster but is not used up; its mass and chemical nature are the same at the end. It works by giving the reaction a different route with a lower activation energy. Manganese dioxide speeds up the breakdown of hydrogen peroxide into water and oxygen. Enzymes are catalysts in living things.
- Lab Activity: Preparing and Testing Oxygen – In the lab, oxygen is made by breaking down hydrogen peroxide with manganese dioxide (a catalyst) at room temperature, or by heating potassium permanganate. The gas goes through a delivery tube and is collected in a gas jar, either over water or by upward displacement of air. Oxygen is tested with a glowing splint: it bursts into flame again. Key safety rules: check the set-up is airtight, wait for steady bubbles, and take the tube out of the water before stopping the heat.
- Interdisciplinary Project: A Micro Air-Quality Station – A micro air-quality station is a small box that measures the air. A dust sensor counts tiny particles (PM2.5) by watching how they scatter a light beam. Gas and temperature sensors measure other things. A small computer (microcontroller) reads each sensor, turns the signal into numbers, shows them on a screen with a colour band and sounds an alarm when a threshold is crossed. Good stations are placed carefully, calibrated and averaged over time.
4. U3 Composition of matter
Molecules and atoms · Atomic structure; ions · Elements; periodic table intro · Interdisciplinary 2: models of atomic discovery
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
- Structure of the Atom – An atom has a tiny, heavy, positive nucleus made of protons and neutrons. Electrons move around it in fixed shells K, L, M, N. The number of protons (Z) tells the element; protons + neutrons give the mass number (A). Outer electrons decide valency. Isotopes share Z; isobars share A.
5. U4 Water in nature
Water resources and purification · Composition of water · Chemical formulae and valence; relative formula mass · Lab activity 2: composition of water · Interdisciplinary 3: water testing and home-made filter
- Water Purification: From Dirty Water to Safe Drinking Water – Potable water is water that is safe to drink. It is not pure: it still has some dissolved salts, but only small amounts and no harmful germs. To make it, we choose a good source, let solids settle, filter it, and kill germs with chlorine, ozone or UV light. Where fresh water is short, sea water is desalinated by distillation or reverse osmosis. Waste water from homes and farms is treated before it goes back to rivers. Hard water has dissolved calcium and magnesium salts; it can be softened by boiling or ion exchange.
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
6. U5 Quantitative relations in reactions
Conservation of mass · Chemical equations and simple calculations · Interdisciplinary 4: simple oxygen supplier
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
- Chemical Reactions and Balancing Equations – In a chemical reaction atoms are not made or destroyed; they only change partners. So a chemical equation must have the same number of each kind of atom on both sides. We balance it by changing the numbers in front of formulas, never the formulas themselves.
- Design a Simple Oxygen Supplier – A simple oxygen supplier uses 2H₂O₂ → 2H₂O + O₂ with MnO₂ as catalyst. It needs no heating. The gas passes through a water bottle, which cools it and lets you count bubbles, then leaves by an outlet tube. A glowing splint that relights proves it is oxygen. This is a science model, not medical equipment.
7. U6 Carbon and its oxides
Forms of carbon · Oxides of carbon · Preparing CO₂ in the lab · Lab activity 3: CO₂ preparation and properties · Interdisciplinary 5: low-carbon action plan
- Allotropes of Carbon: Diamond, Graphite, Graphene and Fullerenes – Allotropes are different forms of the same element in the same state. Carbon has several. In diamond each atom makes 4 strong covalent bonds in a giant 3D network, so it is very hard, has a very high melting point and does not conduct electricity. In graphite each atom bonds to 3 others in flat layers of hexagons; the layers slide (soft, slippery) and one spare electron per atom is free to move, so graphite conducts. Graphene is a single graphite layer: strong, light and an excellent conductor. Fullerenes such as C₆₀ are hollow cages; nanotubes are rolled-up tubes. All of them burn in oxygen to make carbon dioxide.
- Oxides of Carbon: Carbon Dioxide and Carbon Monoxide – Carbon makes two common oxides. CO₂ is heavy, does not burn, dissolves a little in water, and traps heat in the air. CO is a poisonous gas from incomplete burning; it sticks to haemoglobin and, as a reducing agent, takes oxygen from metal oxides.
- Preparing Carbon Dioxide in the Lab – In the lab, CO₂ is made by pouring dilute hydrochloric acid on marble chips (CaCO₃): CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The gas is heavier than air, so it is collected by upward delivery in a jar. A burning splint goes out in it and limewater turns milky.
- Preparing and Testing Carbon Dioxide in the Lab – Marble (calcium carbonate) reacts with dilute hydrochloric acid to give carbon dioxide, calcium chloride and water: CaCO3 + 2HCl -> CaCl2 + H2O + CO2. CO2 is colourless, odourless and heavier than air, so it is collected by upward delivery. It turns limewater milky, puts out a burning splint and turns moist blue litmus red.
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
8. U7 Using and developing energy
Combustion of fuels; fire safety · Fossil fuels and their wise use · Lab activity 4: conditions for burning · Interdisciplinary 6: household fuels
- Combustion – Combustion (burning) is a chemical change in which a fuel reacts fast with oxygen and gives out heat and light. It needs three things: fuel, oxygen and heat (to reach the ignition temperature). Remove any one and the fire goes out. With plenty of air, fuels that contain carbon and hydrogen burn completely to carbon dioxide and water (blue flame). With too little air, burning is incomplete and gives soot and poisonous carbon monoxide (yellow, smoky flame). Carbon dioxide turns limewater milky. The energy released by burning 1 g of a fuel is its calorific value.
- Household Fuels: Change Over Time and Safe Use – Homes moved from dung cakes and wood to coal, kerosene, LPG, piped natural gas and electric or solar cooking. Cleaner fuels make less smoke and put more heat into the pot. Every fuel needs safe use: good ventilation, leak checks for gas, and never burning fuel in a closed room because poisonous carbon monoxide builds up.
9. U8 Metals and metal materials
Metal materials and alloys · Chemical properties of metals; reactivity series · Using and protecting metal resources; rusting · Lab activity 5: properties of common metals · Interdisciplinary 7: waste sorting and recycling
- Corrosion, Its Prevention and Alloys – Corrosion is the slow eating away of a metal by air, moisture or chemicals around it. Iron rusts only when both air (oxygen) and water are present, forming hydrated iron oxide. It can be prevented by painting, oiling, galvanising, chrome plating, anodising or making alloys. An alloy is a uniform mixture of a metal with other metals or a non-metal; alloys are usually harder, stronger and more corrosion-resistant than the pure metal.
- Occurrence and Extraction of Metals – Metals are found in the earth's crust, mostly as compounds called minerals; a mineral from which a metal can be taken out profitably is an ore. Extraction has three stages: enrichment (removing gangue), getting the crude metal (roasting or calcination, then reduction or electrolysis, chosen by the metal's place in the reactivity series), and refining (usually electrolytic).
- Ionic Compounds: How Metals and Non-metals React – A metal atom gives its outer electrons to a non-metal atom so that both get a full outer shell (octet). The metal becomes a positive ion (cation), the non-metal a negative ion (anion), and the strong pull between them is an ionic (electrovalent) bond. Ionic compounds are hard crystalline solids with high melting points, dissolve in water, and conduct electricity only when molten or dissolved.
- Metals and Non-metals: Properties and the Reactivity Series – Metals are usually shiny, hard, malleable, ductile and good conductors; non-metals are usually dull, brittle and poor conductors. Metals form basic oxides, react with water and dilute acids (giving hydrogen) and a more reactive metal pushes a less reactive one out of its salt solution. Listing metals from most to least reactive gives the reactivity series.
- Ozone Layer Depletion and Waste Management – High above us, ozone (O₃) blocks harmful UV rays, but CFCs thin it; on the ground, biodegradable waste breaks down naturally while non-biodegradable waste stays for years, so we must reduce, reuse, recycle and segregate.
10. U9 Solutions
Solutions and uses · Solubility · Mass fraction of solute · Lab activity 6: preparing NaCl solution · Lab activity 7: removing insoluble impurities from salt · Interdisciplinary 8: marine resources and salt making
- Mixtures and Their Separation – A mixture has two or more substances mixed without any fixed ratio, and each keeps its own properties. Homogeneous mixtures (solutions) look the same everywhere; heterogeneous ones do not. By particle size we get solutions (< 1 nm), colloids (1–1000 nm) and suspensions (> 1000 nm). Colloids scatter light (Tyndall effect). Concentration tells how much solute is in a solution. We separate mixtures by using a difference in their parts: evaporation, crystallisation, distillation, chromatography, sublimation, centrifugation and coagulation.
- Solutions: How Things Dissolve and How Much Can Dissolve – A solution is a uniform mixture of a solute dissolved in a solvent. In water (an aqueous solution) the solute breaks into particles too small to see, so it never settles and passes through filter paper. Concentration tells how much solute is present (mass % = solute ÷ solution × 100). Solubility is the most that can dissolve in 100 g of solvent at a given temperature; beyond it the solution is saturated. Evaporation, crystallisation and distillation separate solutions.
- Lab: Preparing a Salt (NaCl) Solution of a Given Mass Percent – To make a solution with a chosen mass percent, first calculate: salt = total mass x percent / 100, and water = total mass - salt. Weigh the salt on a balance, measure the water in a measuring cylinder (1 g of water is 1 mL), pour both into a beaker and stir until every grain has dissolved.
- Salt from Sea Water and the Ocean's Resources – Sea water holds about 3.5% dissolved salt. In salt pans, sun and wind evaporate only the water. The brine gets stronger until the salt cannot stay dissolved and crystallises. Raw salt is purified by dissolving, filtering and evaporating. The sea also gives food, minerals, energy and fresh water, which must be used with care.
11. U10 Common acids, bases and salts
Acidity/alkalinity; pH; indicators · Common acids and bases; neutralisation · Common salts; double decomposition; fertilisers · Lab activity 8: acids and bases · Interdisciplinary 9: soil acidity and plants
- The pH Scale: How Strong Is an Acid or a Base? – pH is a number from 0 to 14 that tells how acidic or basic a solution is. 7 is neutral, below 7 is acidic and above 7 is basic. Each step down means ten times more H⁺ ions.
- Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.
- Salts and Important Chemicals from Common Salt – A salt is made when an acid and a base neutralise each other. Salts can be neutral, acidic or basic. From common salt we make sodium hydroxide, bleaching powder, baking soda and washing soda, and some salts hold water inside their crystals.
- Soil Acidity and Plant Growth: A Project – Soil pH tells us if the soil is acidic (below 7), neutral (about 7) or alkaline (above 7). Plants take food from the soil water, and pH changes which nutrients dissolve. Most crops grow best between pH 6 and 7.5, tea likes acid soil near pH 5, and in very acidic or very alkaline soil many plants grow badly. To measure pH we mix soil with distilled water, let it settle and test the clear water with indicator paper or solution or a pH meter. Acidic soil is treated with lime (a base) and alkaline soil with sulfur, compost or acidic fertiliser. In the project we test, compare plants with a fair test, and decide how to treat the soil.
12. U11 Chemistry and society
Chemistry and human health (nutrients, elements) · Chemistry and sustainable development (materials, green chemistry) · Interdisciplinary 10: new materials and energy in aerospace
- Nutrition – Nutrition is how we get and use the substances in food. The body needs six groups of nutrients: carbohydrates and fats (mainly energy), proteins (growth and repair), vitamins and minerals (small amounts to keep the body working), and water, plus fibre for healthy digestion. Carbohydrate and protein give about 17 kJ per gram, fat about 37 kJ per gram. A balanced diet gives all nutrients in the right amounts, and energy in should roughly equal energy out.
- Green Chemistry – Green chemistry means designing chemical products and processes that make less waste, use safer substances, save energy and use raw materials that can be renewed. Key tools are high atom economy, catalysts, safer solvents such as water, renewable feedstocks, and products that break down safely. A life cycle assessment checks the impact of a product from raw material to disposal.
- New Materials and Energy in Space Technology – A rocket must survive great heat, be very light yet strong, carry energy-rich fuel and, for satellites, make power from sunlight. So engineers choose materials with a high melting point for heat shields (titanium alloys, ceramics), low density and high strength for the body (aluminium alloys, carbon-fibre composites), and fuels with high energy per kilogram, such as liquid hydrogen (about 120 MJ/kg) with liquid oxygen, which burns to give only steam. Satellites use solar panels, whose power is about sunlight strength × area × efficiency × cos of the tilt angle. In this project you research one material or energy source, compare facts in a table, judge them against a clear need, and present your findings with sources.