AQA Chemistry Unit 3

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Taken from the specification, so should be all you need o know for AQA Chemistry GCSE unit 3. Good luck =)
Natalia  Cliff
Flashcards by Natalia Cliff, updated more than 1 year ago
Natalia  Cliff
Created by Natalia Cliff almost 7 years ago
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Question Answer
What is the periodic table? -An arrangement of elements according to proton number, electrons in outer shells (groups) and number of electron shells (periods) -Called a periodic table because similar properties occurred at regular intervals
Newlands Periodic Table -Arranged elements according to their atomic weights -Came up with his law of octaves that every 8th element was similar to the one before it -However, it had issues as the pattern soon broke down -If strict order of atomic was followed, some lements were put in the wrong group
Mendeleev's Periodic table -Overcame some of the problems that NEwlands faced by leaving gaps for what he thought were undiscovered elements -Very accurate
Modern periodic table WHen protons and neutrons were discovered in the early 20th century, elements were arranged according to atomic numbers and so placed in appropriate groups
Properties of Group one -Alkali Metals -Metals with low density (first 3 are less dense than water) -React with non-metals to form ionic compounds where the metal ion has a 1+ charge. The compounds are white and dissolve to make a colourless solution -React with water, releasing hydrogen -Form hydroxides that dissolve in water to give alkaline solutions -The further down the group you go the more reactive the element and the lower it's melting point -React vigourusly with oxygen and water
Properties of transition metals -Have higher melting points than group one -Higher densities -Stronger and harder -Much less reactive so don't react as vigorously with oxygen and water -Have ions with different charges -Form coloured compounds -Are useful catalysts
Properties of group 7 -Halogens -React with metals to form ionic compounds where the halide ion has a -1 charge -A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt -The further down the group the less reactive it is and the higher it's melting and boiling point -This is because there are more shielding electron shells between the positive nucleus and the lectron it's trying to attract
Interaction of water with soap -Soft water readily forms a lather -Hard water reacts with soap to form scum, so more soap is needed for a lather -Soapless detergents do not form scum
What are the two types of hard water? -Temporary hard water becomes soft when boiled -Permanent hard water remains hard when boiled
How can you soften temporary hard water? -Temporary hard water contains Hydrocarbonate ions (HCO3-) -These ions thermally decompose when heated to produce carbonate ions -React with Calcium and Magnesium ions to form calcium carbonate and/or magnesium carbonate as a precipitate called scale
What are the negative aspects of using hard water? -Can increase costs because more soap is needed -When temporary hard water is heated it produces scale which reduces the efficiency of heating systems or kettles
What are the benefits of hard water? -Good for your bones and teeth -Helps reduce the risk of heart disease
How can hard water be softened? -Adding sodium carbonate, which reacts with Mg and Ca ions to form the precipitates calcium carbonate and/or magnesium carbonate -Using commercial softeners like ion exchange columns containing hydrogen or sodium ions which replace the magnesium and/or calcium ions when the water passes through the column
Why is water quality important? -Water quality is essential for life -For humans, drinking water should have sufficiently low levels of dissolved salts and microbes
How do we ensure water quality? -Choose an appropriate source -Filter the water to remove any solids -Steralise it with chlorine to remove microbes
What do water filters contain? -Carbon -Silver -Ion exchange resins -Can remove some dissolved substances from tap water to improve taste and quality
What chemicals are added to drinking water? Why? -Chlorine may be added to reduce microbes -Fluorine may be added to improve dental health, however some people object saying it causes tooth mottling and takes away personal choice
How can pure water be produced? -By distillation -However, this requires a lot of energy and is so expensive
What is calorimetry? -The relative amounts of energy released when substances burn can be measured by simple calorimetry -E.g. heating water in a glass or metal container -To improve method, insulate the container and add a lid -Can be used to compare the amount of energy released by food and fuel
Equation for calculating amount of energy released from a fuel
How can you measure the amount of energy released or absorbed in a chemical reaction? -Can be calculated from the measured temperature change of the solution where the reagents are mixed in an insulated container -Can be used for reactions of solids with water or neutralistation reactions
What can simple energy level diagrams be used for? To show relative energies of reactants and products, the activation energy and the overall energy change of a reaction
Labelled energy level diagram
Energy supply and release in chemical reactions -Energy needs to be supplied to break bonds -Energy is released when bonds are formed -In an exothermic reaction, energy released form new bonds is greater than energy needed to break bonds -In an endothermic reaction, energy needed to break bonds is gretaer than energy released when bonds are formed
How do catalysts work? Provide an alternate pathway for a chemical reaction with a lower activation energy
Using hydrogen in car engines -Hydrogen can be burned as a fuel in a combustion engine -Hydrogen + Oxygen -> Water -Hydrogen can also be used in fuel cells that provide electricity to power vehicles -Hydrogen combustion is less expensive but still produces some nitrate oxideS (Air is only 20% oxygen) -Fuel cells are much more efficient but also cost a lot more
Flame test colours Lithium - crimson Sodium - yellow Potassium - lilac Calcium - red Barium - green
Sodium hydroxide solution test -Aluminium, calcium and magnesium ions form white precipitates -Only aluminium hydroxide precipitate dissolves in excess sodium hydroxide -Copper(II) forms a blue precipitate -Iron(II) forms a green precipitate -Iron(III) forms a brown precipitate
Testing for carbonates -Carbonates react with any dilute acid to form carbon dioxide -Carbon dioxide forms a white precipitate with limewater which turns limewater cloudy
Testing for Halide Ions -Halide ions in a solution react with silver nitrate and dilute nitric acid to form a precipitate -Silver chloride is white -Silver bromide is cream -Silver iodide is yellow
Testing for Sulfate Ions -Sulfate ions in a solution produce a white precipitate with barium chloride and dilute hydrochloric acid
Titrations of acids and alkalis -Volumes of acids and alkali that react with each other can be tested in a titration with a suitable indicator -If the concentration of one reactant is known, the results of the titration can be used to find the concentration of the other reactant -Concentrations are in moles per dm3 -Masses are in grams per dm3
What are the raw materials for the Haber process and where are they obtained from? -Nitrogen from the air -Hydrogen from natural gas or other sources
The Haber process -Purified gases passed over an iron catalyst -Temperature of 450 C -Pressure of 200 atmospheres -Some of the hydrogen and nitrogen react to make ammonia -Reaction is reversible so ammonia breaks down into hydrogen and nitrogen as well -On cooling ammonia is liquefied and removed (lower boiling point) -Hydrogen and nitrogen are recycled
Equilibrium in a reversible reaction -Equilibrium is reached in a reversible reaction when reactions occur at exactly the same rate in each direction -The relative amounts of reacting substances at equilibrium depends on the conditions
Effect of temperature on equilibrium -If the temperature is raised, yield from the endothermic reaction increases as the equilibrium shifts -Converse for exothermic reaction
Effect of pressure on Equilibrium In Gaseous reactions, increase in pressure will favour the reaction that has the least number of molecules, so that yield decreases
Deciding conditions of the Haber process -The point of equilibrium is important, but reaction rate and economics must also be taken into consideration, it's a compromise -Low temperature good for ammonia, but rate of reaction too slow so 450 C compromise -High pressure good for ammonia but over 200 atmosphere's becomes too expensive
Alcohols -Have a functional group of -OH -Methanol, Ethanol and Propanol are the first 3 of a homologous series of alcohols
Structure of Alcohols CH3CH2OH
Methanol, Ethanol and Propanol properties -Dissolve in water to form a neutral solution -React with sodium to produce hydrogen -Burn in air -Are used as fuels and solvents -Ethanol is the main alcohol in alcoholic drinks
How to make ethanoic acid -Ethanol can be oxidised to ethanoic acid, either through a chemical oxidising agent or microbial action -Vinegar is an aqueous solution where the main acid is ethanoic acid
Carboxylic Acids -Have the functional group -COOH -First 3 are methanoic acid, ethanoic acid and propanoic acid
Carboxylic acid structure CH3COOH
Carboxylic Acids Properties -Dissolve in water to produce acidic solutions -React with carbonates to produce carbon dioxide -React with alcohols in the presence of an acid catalyst to produce esters -Do not ionise completely when dissolved in water and so are weak acids -Aqueous solutions of weak acids have a higher PH value than aqueous solutions of strong acids with the same concentration
Esters -Ethyl Ethanoate is the ester produced from ethanol and ethanoic acid -Have the functional group -COO- -Are volatile compounds with distinctive smells -Are used as flavourings and perfumes
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