Y10 Chemistry PDF

1.1 Solids, liquids and gases There are four states of matter: 1. Solid 2. Liquid 3. Gas 4. Plasma Solids liquids and gases can be distinguished by their shapes and how easily they spread out. General properties of solids, liquids and gases 1. Solids Arrangement: Fixed pattern...

1.1 Solids, liquids and gases There are four states of matter: 1. Solid 2. Liquid 3. Gas 4. Plasma Solids liquids and gases can be distinguished by their shapes and how easily they spread out. General properties of solids, liquids and gases 1. Solids Arrangement: Fixed pattern Motion: Only vibrate Separation: Close together 2. Liquids Arrangement: Random, no fixed pattern Motion: Slip and slide against each other Separation: Close together 3. Gases Arrangement: Random Motion: Move every where rapidly Separation: Far apart There are three types of particles that make up most matter 1. Atoms An atom is the smallest particle that cannot be broken down by chemical means Some atom examples include; Carbon, nitrogen and oxygen 2. Molecules A molecule is an uncharged particle made of two or more atoms together Some molecules are; O3 (ozone), H2O (water) 1  All compounds are molecules, but not all molecules are compounds 3. Ions An ion is an atom or group of atoms that carries a positive or negative electrical charge Some ion examples are; Na+, Cl– 1.2 Using the kinetic particle theory The kinetic particle theory states that all matter is made up of particles and are constantly in motion Changes of state: 1. Melting - The forces of attraction between particles are weakened and solid melts 2. Boiling / evaporation - As bubbling liquid turns into gas we say that the liquid boils 3. Condensing - Cooling a gas makes it condense into a liquid 4. Freezing - Further cooling a liquid results in freezing (solidifying) 5. Sublimation - Conversion of a substance from solid to a gaseous state without its becoming liquid. Eg. dry ice Gases and the Kinetic particle theory Pressure increases when temperature increases Volume decreases when pressure increases 2  Volume increases when temperature increases (when volume is not fixed) 1.3 Heating and cooling curves In a heating curve, energy is absorbed (endothermic) When a solid is heated, the particles gain energy and vibrate more. The temperature rises as heat is added. At the melting point, energy goes into breaking bonds between particles, turning the solid to liquid. The temperature stays the same during melting, giving a flat line on the graph. The same happens when a liquid is heated to boiling point. Energy is used to break the bonds completely, forming a gas. The temperature stays steady during boiling, giving another flat line. 3  In a cooling curve, energy is released (exothermic) When a gas is cooled, particles slow down and lose energy ( temperature drops) At the condensation point, particles come together and bond turning the gas into a liquid. The energy released stops the temperature dropping further. The temperature stays the same during condensation giving a flat line on the graph. The same happens when liquid is cooled to freezing point. Particles arrange into solid structure, releasing heat energy. This stops temperature dropping as liquid becomes solid, giving another flat line. 1.4 Solutions solutes and solvents Aqueous solution - When a solute dissolves in water Anhydrous - Without water Saturated solution - Contains maximum concentration of solute in the solvent Solubility - The maximum number of grams (g) of solute that 3 can be dissolved to make 1𝑑𝑚 Dissolving - The process of a solute mixing with a solvent Concentration is the amount of particles in a given volume 4  𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 (𝑔) Concentration = 3 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 ( 𝑑𝑚 ) 3 1000 cm = 1𝑑𝑚 Testing for water 1. When we add water to white anhydrous copper (II) sulfate it turns blue 2. When we add water to anhydrous cobalt (II) chloride, the cobalt chloride changes from blue to pink Water of crystallisation is water that is chemically bonded into a crystal structure. These crystals are hydrated crystals. Eg. CuSO4. 5H2O 1.5 Diffusion Diffusion - Gradual spreading out and mixing up of different particles by random movement (from an area of higher concentration to an area of lower concentration) Diffusion only occurs in liquids and gases A gas with a higher molecular mass will diffuse slower than a gas with lower molecular mass 2.1 Apparatus for measuring Volumes are are generally measured in cubic centimetres 3 3 𝑐𝑚 or decimetres cubed 𝑑𝑚 A burette is used to get more accurate measurements 5  We can measure the volume of gases using a gas syringe or an upturned measuring cylinder 2.2 Paper Chromatography The method of separating pigments using filter paper is called paper chromatography. The colours separate if: The pigments have different solubilities in the solvent The pigments have different degrees of attraction for the filter paper Solvent front - Line at the top of chromatography paper Baseline - Line at the bottom of chromatography paper Chromatography can also be used to identify colourless substances. The chromatography paper is is dried and sprayed with a chemical called the locating agent Retention Factor (R𝑓) can be defined as the ratio of the distance travelled by solute to the distance travelled by solvent 6 2.3 Is that chemical pure? If a chemical is impure: The melting point decreases The boiling point increases A pure substance melts and boils at sharp (definite) temperatures Ways of separating an undissolved substance from a liquid or solution Filtration Decanting Centrifugation 2.4 Separation and purification Filtration The solution which passes through the filter paper is the filtrate The solid that stays on the filter paper called the residue 7  Decanting and centrifugation Decanting is pouring off a liquid from an undissolved solid A centrifuge is a machine that spins test tubes around at very high speeds, which forces the solid to the bottom of the tube Crystallisation Crystallisation is used to obtain a crystalline solid from a solution The solvent, usually water is evaporated until it reaches the crystallisation point Solvent extraction Solvent extraction can be used to separate two solutes dissolved in a solvent. This is especially useful if one of the solutes is volatile 8  A second solvent is used to extract one of the solids from the first solvent. The second solvent must not mix with the first (immiscible) Two immiscible liquids will settle into two distinct layers Volatile - Evaporates readily Simple distillation Simple distillation is used to separate a solvent from a solution When a solution of salt water is heated, the water boils and escapes as steam leaving the salt behind as a solid The water has a much lower boiling point than salt and readily changes to the gaseous state. The steam turns back into water in the condenser. 9  Fractional distillation Fractional distillation is used to separate a mixture of liquids with different boiling points. Liquids which are miscible are separated by this method To separate liquids using fractional distillation, the solution is put into a distillation flask on top of a heat source The solution is then vaporised into a tall column (fractionating distillation) in which continuous evaporation and condensation of the liquid occurs There is a range of temperatures in the column, the temperature is lower at the bottom and higher at the top. The more volatile compounds in the liquid move further up the column than the less volatile compounds The most volatile compound reaches the condenser, where it changes to liquid (the distillate).They condense one at a time as fractions in order of increasing boiling points. 10  3.1 Inside the atom An atom is the smallest uncharged particle that can take part in a chemical change Atoms are made up of smaller particles called subatomic particles, which are; Protons, Electrons and Neutrons At the centre of an atom is a nucleus. It’s made up of protons and neutrons (nucleons) A proton has a positive charge, electron has a negative charge, neutron has no charge 1 An electron is approximately 2000 the mass of a proton The proton number (atomic number) is the number of protons in the nucleus of an atom 11  Atoms are arranged in order of increasing proton numbers on the periodic table 3.2 Isotopes Mass number or nucleon number is the number of protons and neutrons in an atom Isotopes are atoms of the same element which have the same proton number but different number of neutrons.Therefore they have the same atomic number but a different mass number. For example, there are three isotopes of hydrogen: The chemical properties of isotopes are the same because they have the same electronic configuration (the electrons are arranged in the same way). However, the physical properties of isotopes such as density may be slightly different Accurate relative atomic mass Relative atomic mass is the average mass of the isotopes of an element compared to 1/12th the mass of an atom compared to carbon-12 Some elements, like chlorine, have a mix of isotopes. Chlorine has two main isotopes: one with a mass of 35 (about 75.5% of 12  chlorine atoms) and one with a mass of 37 (about 24.5% of chlorine atoms). The percentage of each isotope in chlorine is called percentage abundance Isotope Chlorine-35 Chlorine-37 Number of electrons 18 20 Percentage abundance 75.5% 24.5% The relative atomic mass can be calculated using this formula To calculate the relative atomic mass of chlorine: ( 35 × 75.5% ) + ( 37 × 24.5% ) 100 = 35.5 (3s.f) Therefore the relative atomic mass of chlorine is 35.5 3.3 Electronic structure and the periodic table The arrangement of electrons in shells is called an electronic configuration Atoms of elements in the same group in the periodic table have the same number of outer shell electrons The noble gases are unreactive because they have a full outer shell 13  3.4 Elements, compounds and mixtures An element is a substance made up of one atom and cannot be broken down into simpler substances A compound is a substance containing two or more different types of atoms bonded together A mixture is a combination of two or more substances but are not chemically bonded. Differences between compounds and mixtures Compounds have fixed ratios but mixtures do not Compounds can only be separated by chemical means A mixture can be separated by physical means 3.5 Metals and non-metals Physical properties of metals and non-metals Physical property metal non-metal Good conductor of Conducts Poor conductor electricity (exceptions: graphite) Conductor of thermal Conducts Poor conductor 14 energy (exceptions: graphite and diamond) Malleable - can be Malleable Not malleable. beaten into different Non-metals are brittle: shapes with a hammer they break easily when hit Ductile - can be drawn Ductile Not ductile. Non-metals out into wires are brittle: they break easily when a pulling force is applied Lustrous - has a shiny Lustrous Dull surface (exceptions: surface when polished graphite and iodine have shiny surfaces0 Sonorous - makes a Sonorous Not sonorous. ringing sound when hit Non-metals make a dull with a hard object sound when hit with a hard Chemical properties of metals and non metals Some of the chemical properties to tell the difference between metals and non-metals during chemical reactions and energy changes are: Many metal oxides are basic Many non-metals are acidic Many metals react with acids Many non-metals do not react with acids When they react, metals form positive ions by losing electrons When they react with metals, non-metals form negative ions by gaining electrons. 15