C3 | Flashcards

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How did Newlands and Mendelev arrange the elements in the periodic table	Newlands, and then Mendeleev, attempted to classify the elements by arranging them in order of their atomic weights.
How did Mendeleev overcome some of the problems with the early periodic table ?	The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed. Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered.
How is the modern periodic table arranged in ?	When electrons, protons and neutrons were discovered early in the 20th century, the periodic table was arranged in order of atomic (proton) numbers. When this was done, all elements were placed in appropriate groups.
How is the modern periodic table arranged in terms of electronic structure?	The modern periodic table can be seen as an arrangement of the elements in terms of their electronic structures. Elements in the same group have the same number of electrons in their highest occupied energy level (outer shell).
Evaluate the work of Newlands and Mendeleev in terms of their contributions to the development of the modern periodic table	Image: Rt (image/png)
explain why scientists regarded a periodic table of the elements first as a curiosity, then as a useful tool and finally as an important summary of the structure of atoms.	The Newland created the law of Octaves so he put all the elements in order of their atomic mass and then realised that generally every eigth element had similar properties. However this grouped together some elements that had really different properties. But then Mendeleev changed this slightly and left gaps in the periodic table for elements that hadn't been discovered yet and even predicted the properties of those elements.
Describe the elements in Group 1 of the periodic table (known as the alkali metals):	■ are metals with low density (the first three elements in the group are less dense than water) ■ react with non-metals to form ionic compounds in which the metal ion carries a charge of +1. The compounds are white solids that dissolve in water to form colourless solutions ■ react with water, releasing hydrogen ■ form hydroxides that dissolve in water to give alkaline solutions.
Describe what happens in Group 1, the further down the group an element is	■ the more reactive the element ■ the lower its melting point and boiling point.
Compare group 1 with the transition metals	group1 ■ have higher melting points (except for mercury) and higher densities ■ are stronger and harder ■ are much less reactive and so do not react as vigorously with water or oxygen.
Describe the transition metals	Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts.
Describe the elements in Group 7 of the periodic table (known as the halogens)	The elements in Group 7 of the periodic table (known as the halogens) react with metals to form ionic compounds in which the halide ion carries a charge of –1.
Describe what happens in Group 7, the further down the group an element is	In Group 7, the further down the group an element is: ■ the less reactive the element ■ the higher its melting point and boiling point.
Describe a displacement reaction in group 7	A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
Explain the trends in reactivity seen in group 1 and 7	The trends in reactivity within groups in the periodic table can be explained because the higher the energy level of the outer electrons: ■ the more easily electrons are lost ■ the less easily electrons are gained.
State the difference between soft and hard water	Soft water readily forms lather with soap. Hard water reacts with soap to form scum and so more soap is needed to form lather. Soapless detergents do not form scum.
What does hard water contain and where does this come from	Hard water contains dissolvedcompounds, usually of calcium or magnesium. The compounds are dissolved when water comes into contact with rocks.
Describe the difference between hard and soft water	There are two types of hard water. Permanent hard water remains hard when it is boiled. Temporary hard water is softened by boiling.
Explain how temporary hard water is softened by boiling.	Temporary hard water contains hydrogencarbonate ions (HCO3 –) that decompose on heating to produce carbonate ions which react with calcium and magnesium ions to form precipitates.
State the problems associated with both hard water and temporary hard water	Using hard water can increase costs because more soap is needed. When temporary hard water is heated it can produce scale that reduces the efficiency of heating systems and kettles.
Describe the benefits of hard water	Hard water has some benefits because calcium compounds are good for the development and maintenance of bones and teeth and also help to reduce heart disease.
Hard water can be made soft by removing the dissolved calcium and magnesium ions. This can be done by:	■ adding sodium carbonate, which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate ■ using commercial water softeners such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column.
Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. How is this achieved ?	Water of the correct quality is produced by: ■ choosing an appropriate source ■ passing the water through filter beds to remove any solids ■ sterilising with chlorine.
Explain the principle by which ion exchange resins work	The resin beads have sodium ions attached to them. As the hard water passes through the column, the calcium and magnesium ions swap places with the sodium ions. The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions. The hard water is softened because it no longer contains calcium or magnesium ions. Some ion exchange resins use hydrogen ions instead of sodium ions.
Some chemicals may be added to drinking water , what are these and why are they added ?	Chlorine may be added to drinking water to reduce microbes and fluoride may be added to improve dental health.
Why do some people argue against using fluoridation of water	Some people argue that extra fluoride should not be added to water, even if it does improve dental health. They claim that fluoridation: has been linked to tooth mottling (staining), bone disease and pain forces people to consume fluoride when they drink tap water - taking away their personal choice (making it unethical)
Pure water can be produced by distillation. Why is this expensive ?	the large amount of energy needed for distillation and, as a consequence, of the high costs involved.
How can the relative amounts of energy released from substances be measured ?	The relative amounts of energy released when substances burn can be measured by simple calorimetry, eg by heating water in a glass or metal container. This method can be used to compare the amount of energy released by fuels and foods.
Draw an energy level diagram to represent an endothermic reaction	Image: Bo1 (image/png)
Draw an energy level diagram to represent an exothermic reaction	Image: Bo2 (image/png)
describe the transfer of energy when bonds are made or broken	During a chemical reaction: ■ energy must be supplied to break bonds ■ energy is released when bonds are formed.
Describe why heat is released during an exothermic reaction ?	In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
Describe why heat is absorbed during an endothermic reaction ?	In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
Explain how catalysts help reactions occur?	Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
draw an energy level diagram showing the effect of an enzyme on activation energy	Image: Bo4 (image/png)
State 2 ways the H can be used in vehicles	Hydrogen can be burned as a fuel in combustion engines. hydrogen + oxygen ==> water It can also be used in fuel cells that produce electricity to power vehicles.
State the benefits of using H as a fuel	1. unlike petrol and diesel, hydrogen does not generate carbon dioxide when burnt hydrogen 2. fuel cells are very efficient
State disadvantages of using H as a fuel	1. few filling stations sell hydrogen 2. hydrogen must be compressed and liquefied, and then stored in tough, insulated fuel tanks 3. atmospheric pollution may be generated during the production of hydrogen 4. hydrogen fuel cells do not work at very low temperatures, and they may also require a platinum catalyst (expensive)
Flame tests can be used to identify metal ions. Lithium, sodium, potassium, calcium and barium compounds produce distinctive colours in flame tests:	■ lithium compounds = crimson flame ■ sodium compounds = yellow flame ■ potassium compounds = lilac flame ■ calcium compounds = red flame ■ barium compounds = green flame.
describe tests for Al, Ca and Mg ions	Aluminium, calcium and magnesium ions form white precipitates with sodium hydroxide solution but only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.
describe tests for Copper(II), iron(II) and iron(III) ions	Copper(II), iron(II) and iron(III) ions form coloured precipitates with sodium hydroxide solution. Copper forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate.
describe a test for carbonates	Carbonates react with dilute acids to form carbon dioxide. Carbon dioxide produces a white precipitate with limewater. This turns limewater cloudy.
describe tests for the halides	Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.
describe a test for sulfate ions	Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
What are the raw materials for the haber process and how are they obtained ?	The raw materials for the Haber process are nitrogen and hydrogen. Nitrogen is obtained from the air and hydrogen may be obtained from natural gas or other sources.
Describe the haber process	The purified gases are passed over a catalyst of iron at a high temperature (about 450 °C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen reacts to form ammonia. The reaction is reversible so ammonia breaks down again into nitrogen and hydrogen: nitrogen + hydrogen => ammonia On cooling, the ammonia liquefies and is removed.The remaining hydrogen and nitrogen are recycled.
describe a reversible reaction at equilibrium in a closed system	When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction.
describe how an increase in temperature effects the yield of a reversible reaction	If the temperature is raised, the yield from the endothermic reaction increases and the yield from the exothermic reaction decreases.
describe how an decrease in temperature effects the yield of a reversible reaction	If the temperature is lowered, the yield from the endothermic reaction decreases and the yield from the exothermic reaction increases.
how dose an increase in pressure effect a reversible reaction involving gases ?	In gaseous reactions, an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction.
Why not increase the pressure to 1,000 atm, and get lots of ammonia really quickly?	In the real world, it all comes down to money. Building high pressure chemical plant is expensive. Running the reaction at about 200 atm gives the highest return (the biggest profit) on investment capital
represent the structure of ethanol	Image: Ho1 (image/png)
represent the structure of ethanoic acid (a carboxylic acid)	Image: Ho2 (image/png)
what is the functional group of alcohols and what are the first 3 alcohols	Alcohols contain the functional group –OH. Methanol, ethanol and propanol are the first three members of a homologous series of alcohols.
state the properties of : Methanol, ethanol and propanol	■ dissolve in water to form a neutral solution ■ react with sodium to produce hydrogen ■ burn in air ■ are used as fuels and solvents, and ethanol is the main alcohol in alcoholic drinks.
How is ethanol converted to ethanoic acid ?	Ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by microbial action. Ethanoic acid is the main acid in vinegar.
What is the functional group of carboxylic acids ?	Ethanoic acid is a member of the carboxylic acids, which have the functional group –COOH.
State the properties of carboxylic acids ?	■ 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.
what is the functional grouop of esters	Ethyl ethanoate is the ester produced from ethanol and ethanoic acid. Esters have the functional group –COO–.
what are the properties of eters ?	They are volatile compounds with distinctive smells and are used as flavourings and perfumes.

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