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When were elements discovered and how did scientists try to classify them?
In the 19th century but scientists didn’t know about the structure of atoms + tried to find ways to classify them based on their properties & atomic weights.
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What did Newlands propose in 1863?
His law of octaves stating that similar properties are repeated every 8th element + put the 62 elements known at the time into 7 groups according to their atomic weights. The properties didn’t match well after Ca + other scientists didn’t accept his
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How did Mendeleev produce a better table in 1868?
He left gaps for undiscovered elements so that groups of known elements had similar properties. He predicted the properties of unknown elements & when these were discovered his predictions were accepted + scientists accepted his ideas = basis for mod
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When did scientists find out about protons and electrons?
Start of 20th century. Models of arrangement of electrons in atoms developed soon after. The elements were arranged in the periodic table in order of their atomic numbers + lined up in vertical groups.
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Why do the groups of elements have similar properties?
As atoms have the same number of electrons in their outer shell. For the main groups the no. of electrons in the outer shell are the same as the group no.
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What does the reactivity of the elements within groups depend on?
The total number of electrons. Going down a group, there are more occupied energy levels + the atom gets larger so that the electrons in the outer shell are less attracted to the nucleus.
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How does the reactivity down groups differ between metals and non-metals?
When metals react they lose electrons, so the reactivity increases going down a group. When non-metals react they gain electrons, so the reactivity decreases going down a group.
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What are group1 metals called and how do they react with halogens?
Alkali metals- all metals that react readily with air + water. Soft solids at room temp with low melting/boiling points that decrease going down the group. Low densities – Li, Na + K float on water. React with halogens to form salts (white/colourless
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How do alkali metals react with water?
Produce hydrogen gas + a metal hydroxide that is an alkali. They have 1 electron in their outer shell which they lose in reactions = ions with single pos charge (Na+). Compounds of alkali metals dissolve in water forming solutions (usually colourless
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Explain the reactivity trend in group 1.
Reactivity increases going down group 1 as the outer electron is less attracted to the nucleus as the no. of shells (occupied energy levels) increase + the atoms get larger.
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Where are the transition metals (all metals)/elements found in the periodic table?
Between groups 2 + 3. Except mercury, they have higher melting/boiling points than alkali metals. Malleable, ductile, good conductors. React slowly or not at all with O2 + H2O at ordinary temps. Most are strong + dense (useful as building materials).
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Name some additional characteristics of transition metals/elements.
Form positive ions with various charges (Fe2+, Fe3+). Compounds of transition metals often brightly coloured. Most transition metals + their compounds are used as catalysts for chemical reactions.
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What are halogens?
Non-metallic elements in group 7. Exist as small molecules made up of pairs of atoms. Low melting/boiling points. At room temp Fl = pale yellow gas, Cl = green gas, Br = red-brown like liquid + iodine = grey solid (vaporises to a violet gas)
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Explain how halogens bond with metals and non-metals.
Have 7 electrons in outer shell + form ionic compounds with metals in which the halide ions have a charge of 1-. Also bond covalently with non-metals forming molecules.
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Explain the reactivity trend for group 7.
The reactivity of halogens decrease going down the group. A more reactive halogen is able to displace a less reactive halogen from an aqueous solution of halide compound.
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What is soft water?
Water that lathers easily with soap. When water comes into contact with rocks, some compounds dissolve.
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Why does hard water use more soap to produce lather + wash effectively?
As it contains dissolved compounds (containing calcium + magnesium ions) that react with soap to form an insoluble solid called scum. Soapless detergents don’t react with hard water to form scum.
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What is temporary hard water?
Hard water that produces an insoluble solid called scale when heated –scale can be deposited in kettles, boilers + pipes (reduces efficiency of heating systems + causes blockages.
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Hard water is softened by removing the dissolved Ca + Mg ions that react with soap. How is temp hard water softened?
By boiling as when it’s heated, the hydrogencarbonate ions (HCO3-) decompose to produce carbonate ions, water + CO2. The carbonate ions react with Ca ions + Mg ions in the water to produce precipitates that are deposited as scale.
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Describe the first method of softening hard water.
By precipitating out the ions that cause hardness using i.e. washing soda (sodium carbonate) which reacts with the Ca +Mg ions to form solid CaCO3 + MgCO3 that can’t react with soap.
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Describe the second method of softening hard water (ion-exchange column).
Use an ion-exchange column packed with a resin containing sodium/hydrogen ions. When hard water is passed though the resin, the Ca + Mg ions become attached to the resin + sodium/hydrogen ions take their place in the water (don’t react with soap).
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How is drinking water often treated?
Often by sedimentation + filtration to remove solids, followed by disinfection (Chlorine) to kill microbes in the water.
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How can water filters be used to improve the taste of water?
Often contain carbon + an ion-exchange column to remove some soluble substances + i.e. silver to prevent the growth of bacteria.
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Why isn’t distillation used to make pure water on a large scale?
As it requires a lot of energy to boil the water + so would be expensive.
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What reactions occur between fuels/foods and oxygen?
Exothermic reactions. Calorimeter can be used to measure the amount of energy released when substances burn (in joules or calories - 1 cal = 4.2J).
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Describe the simplest calorimeter.
Doesn’t give accurate results as energy released heats surroundings but results can be used for comparison of energy released by diff fuels. Water in glass beaker/metal can. Temp rise of water depends on amount of energy released when substance burns
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How can a simple calorimeter be used to compare the energy released by burning different substances?
The energy change in kJ per gram or per mole. Energy change in kJ/mol calculated by multiplyingthe energy change in kJ/g byt the relative formula mass of the substance.
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What is the equation used to calculate the amount of energy transferred to the water in joules?
Q (amount of energy transferred in J) = M(*** of water in grams) × c(specific heat capacity of water J/g=C) × T (temp change in oC).
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What happens when a reaction takes place in a solution?
Energy is transferred to or from the solution. We can do the reactions in an insulated container to reduce energy transfers to the surroundings. When we calculate the energy change we assume that c=4.2J/goC + M= 1cm3=1g.
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What is the difference between endothermic and exothermic reactions?
Breaking bonds is endothermic because energy is taken in __()-- + so exothermic changes go up and exothermic changed go down--()__ as when new bonds in the product are formed energy is released + this is exothermic.
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What are catalysts and what is activation energy?
Catalysts increase rata of reaction by providing a diff pathway with a lower activation energy – by lowering the ‘minimum energy needed for the reaction to happen’.
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What makes an overall reaction endothermic or exothermic?
Energy is needed in chemical reactions to break bonds in the reactants. Energy is released when new bonds are formed in the products + it’s the difference in these energy changes – energy taken in in endothermic reaction, energy released in exothermi
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What is bond energy (measured in kJ/mol)?
Energy needed to break bond between two atoms. An equal amount of energy released when a bond forms between 2 atoms. We can use bond energies to calculate the overall energy change for a reaction.
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A balanced equation for the reaction is needed to calculate the energy change for a reaction. What do you then calculate?
Total amount of energy needed to break all bonds in reactants. Total amount of energy released in making all bonds in products. Difference between 2 totals.
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What are advantages of using hydrogen as a fuel?
Burns easily + releases a large amount of energy per gram. Produces no CO2 when burned only H2O. Produced from renewable sources + can be burned in combustion engines or used in fuel cells to power vehicles.
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What are the disadvantages of using hydrogen as a fuel cell?
Supply, storage and safety problems. Vehicles that use fuels cells need to match the performance, convenience + costs of petrol/diesel.
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Flame Test: Describe the flame colour for Li, Na, K, Ca and Ba.
The flame test is a test for positive ions. Lithium –crimson, Sodium –yellow, Potassium –lilac, Calcium –red + Barium –green.
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How can sodium hydroxide solution be used to identify some positive ions?
The hydroxides of most metals that have ions with 2+ or 3+ charge are insoluble in water --> a precipitate of the metal hydroxides form when sodium hydroxide is added to solutions of these ions.
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What colour precipitate is formed for aluminium, calcium and magnesium ions?
Aluminium, calcium + magnesium ions form white precipitates + when excess sodium hydroxide is added, the precipitate of aluminium hydroxide dissolves. Copper(II) hydroxide = blue. Iron(II) hydroxide = green. Iron(III) hydroxide =brown.
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Give an example of how we can show the reactions of positive ions with sodium hydroxide solution by balanced ionic equations.
Fe^3+(aq) + 3OH^-(aq) --> Fe(OH)3 (s)
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Test for negative ions: Describe the test for carbonate ions.
Add dilute HCl to the substance to see if it fizzes. If I does + the gas produced turns limewater milky, the substance contains carbonate ions i.e. 2HCl(aq) + CaCO3(s) -->CaCl2(aq) + H2O(l) + CO2(g)
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Test for negative ions: Describe the test for carbonate ions.
Add dilute HCl to the substance to see if it fizzes. If I does + the gas produced turns limewater milky, the substance contains carbonate ions i.e. 2HCl(aq) + CaCO3(s) -->CaCl2(aq) + H2O(l) + CO2(g)
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Test for negative ions: Describe the test for Halide ions.
Add dilute nitric acid and then silver nitrate solution. Chloride ions give a white precipitate, bromide ions give a cream precipitate + iodide ions give a cream precipitate i.e. AgNO3(aq) + NaCl(aq) -->AgCl(s) +NaNO3(aq)
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Test for negative ions: Describe the test for sulphate ions.
Add dilute HCl + Barium Chloride solution. If a white precipitate forms, sulphate ions are present i.e. BaCl2 + MgSO4 --> BaSO4 + MgCl2.
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What is the purpose of a titration?
When solution of acid and an alkali react to form a salt + water, a neutralisation reaction takes place + the volumes of the solutions that react can be found by using a titration.
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How do you do a titration?
Use pipette to accurately measure volume of alkali that’s put into a conical flask. Add indicator to alkali. Fill a burette with acid and gradually add acid to flask. When indicator changes colour, end point of reaction has been reached
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What do you do after you have completed the titration experiment?
Find the volume of acid from the initial + final burette readings. Titration can be done several times to improve repeatability of the results.
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What are qualitative and quantitative methods in chemical analysis?
Qualitative methods used to find out simply if a substance is in a sample. Qualitative methods can tell us how much of a substance is in a sample i.e. GCM, titrations, GC-MS.
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How is equilibrium reached in a closed system (where no product or reactants can escape)?
Equilibrium is reached when the rate of forward reaction I equal to the rate of the reverse reaction. At equilibrium, both reactions continue to happen but the amounts of reactants + products remain constant.
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The amounts of reactants + products for a reversible reaction can be changed by changing the reaction conditions. Give an example of this in the chemical industry.
E.g. increasing the concentration of a reactant will cause more products to be formed as the system tries to achieve equilibrium. If a product is removed, more reactants will react to try to achieve equilibrium + more product is formed.
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Describe how pressure affects the amount of product formed if the forward reaction produce MORE molecules of gas.
An increase in pressure decreases the amount of products formed, A decrease in pressure increases the amounts of products formed = if forward reaction produces more molecules of gas -->inverse proportion between pressure and amount of product formed
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Describe the relationship between the pressure and the amount of product formed if the forward reaction produces fewer molecules of gas.
Direct proportionality. Increase in pressure = increase in amounts of products formed. Decrease = decrease.
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Describe the relationship between temperature and amount of product formed if the forward reaction is exothermic.
Inverse proportion –and increase in temp decreases amount of product formed if the forward reaction is exothermic. Decrease in temp = increase in amount of product formed.
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Describe the relationship between temperature and amount of product formed if the forward reaction is endothermic.
Direct proportion – increase in temp increases amount of product formed when forward reaction = endothermic, decrease in temp = decrease in amount of product formed.
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Describe the Haber process.
Nitrogen (from air) + hydrogen (usually from natural gas) purified + mixed in the correct proportions. Gases are passed over an iron catalyst at a temp of 450oC + a pressure of 200 atmospheres.
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Why is the yield of ammonia only about 15% for the Haber process?
As it is a reversible reaction (N2(g) + 3H2(g) 2HN3(g)) and so some of the ammonia produced breaks down into nitrogen and hydrogen.
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What is done to the gases that come out of the reactor (Haber process)?
The gases are cooled so that the ammonia condenses and the liquid ammonia is separated from the unreacted gases. The unreacted gases are recycled so that they aren’t wasted.
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Why is a pressure of about 200 atmospheres used for the Haber process?
Compromise between the costs and the yield - the products have fewer molecules of gas + so the higher the pressure, the greater the yield of ammonia but the greater the expense of the process.
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Why does a higher pressure cost more (Haber process)?
The higher the pressure the more energy needed to compress the gas. Higher pressures also need stronger reaction vessels + pipes which increases costs.
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Why is a compromise temperature of about 450oC used for the Haber process?
To give a reasonable yield in a short time - forward reaction=exothermic + so the lower the temp, the greater the yield of ammonia but the reaction rate decreases as the temp is lowered + the iron catalyst becomes ineffective.
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What are homologous series?
Series of molecules that have a general formula. Alkanes + Alkenes are 2 homologous series made of only hydrogen + carbons atoms.
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Describe the first three members of a homologous series of alcohols.
Methanol, ethanol and propanol which: dissolve in water to form neutral solution, react with sodium to produce hydrogen, burn in air + are used as fuels/solvents + ethanol is the main alcohol in alcohol in drink. Contain functional group –OH.
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How can alcohols be oxidised?
By chemical oxidising agents (i.e. potassium dichromate) to produce carboxylic acids. Some microbes in the air can also oxidise solutions of ethanol to produce ethanoic acid which turns alcoholic drinks sour + is the main acid in vinegar.
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Describe the first three members of a homologous series of Carboxylic acids.
Methanoic acid, ethanoic acid and propanoic acid – structural formula of HCOOH, CH3COOH + CH3CH2COOH. Have the functional group –COOH.
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Describe some of the properties of carboxylic acids.
They 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.
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Why are carboxylic acids weak acids?
As carboxylic acids don’t ionise completely when they dissolve in water --> in aqueous solutions of equal concentration, weak acids have a higher pH + react more slowly than strong acids.
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Describe Esters.
Esters have the functional group –COO- & are volatile compounds with distinctive smells + are used as flavourings and perfumes. Ethyl ethanoate is the ester produced from ethanol and ethanoic acid.
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Card 2

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What did Newlands propose in 1863?

Back

His law of octaves stating that similar properties are repeated every 8th element + put the 62 elements known at the time into 7 groups according to their atomic weights. The properties didn’t match well after Ca + other scientists didn’t accept his

Card 3

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How did Mendeleev produce a better table in 1868?

Back

Preview of the front of card 3

Card 4

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When did scientists find out about protons and electrons?

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Card 5

Front

Why do the groups of elements have similar properties?

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