Created by Natalia Cliff
about 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 |
Image:
Q=Mc T (image/png)
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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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