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Hint
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Answer
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describe the experiment to find the percentage of oxygen in the air using phosphorus
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2 ways: 1st way do same experiment like with copper but just replace copper with phosphorus
2nd way First light phosphorus with a hot wire, phosphorus is very reactive with oxygen but not water. Phosphorus is put on an evaporating dish and floats in the water, a bell jar is placed on top of it and then a bung is put on it. The water level will rise as phosphorus pentoxide is produced and the water rises up to fill the volume of oxygen lost. Record the initial water level and leave it until it is constant. Record the end water level, you will notice that if you subtract the final volume by the initial volume and divide by the initial volume then multiply by 100, we get about 20%. So the phosphorus reacts with the oxygen to produce a phosphorus oxide called phosphorus pentoxide ( C4H10 ). This reaction emits lots of light. |
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what is an acid
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a substance that forms hydrogen ions when dissolved in water
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what conditions does iron need to rust
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oxygen and water present
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do groups have similar properties
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yes
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if the salt is soluble, what question would you ask to find out what method you should use
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is the salt a potassium or sodium one
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what is the oxide that dissolves in water to produce limewater
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calcium oxide
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what is a precipitate
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an insoluble, ionic, solid product of a chemical reaction
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how much indicator should you add
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a few drops
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what do greenhouse gases cause
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greenhouse effect
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what is source of H+ ions
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acid
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what is the result of the greenhouse effect
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global warming
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what salt will sulfuric acid form
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sulfate
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why does reactivity increase as you go down group 1
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as you go down a group, period number increases. Period number determines the amount of shells an atom has. The more shells, the larger the atom, so the atomic radii gets larger meaning the distance between the valence electrons and the nucleus is larger. This results in a weaker force of attraction between the nucleus and valence electrons, this is because a force weakens over a longer distance. So now the nucleus cannot hold on to the outer electrons anywhere near it could with a smaller atom. Reactivity is just how easily an atom loses or gains electrons, so a higher period number in group 1 means the electrons are more easily lost, so it's reactivity increases.
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explain an experiment to obtain a pure, dry sample of a soluble salt starting from an acid and alkali
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Let's look at the reaction between hydrochloric acid and sodium hydroxide. So preparing pure, dry samples of sodium chloride from sodium hydroxide and hydrochloric acid. This gives us sodium hydroxide and water. First, we do our titration to find out how much acid is needed to neutralise 25cm3 of alkali, we do this with an indicator, collect the values and now we can begin. Now, pipette 25cm3 of alkali into a conical flask, accurately measuring it, ensuring no indicator is added since we don't need to as the titration has already been completed and indicator would contaminate our crystals. Using the titration values, titrate the volume of acid into the beaker containing the alkali, as we have done the titration before, the neutralisation will be exact and precise, so now we have a neutralised solution. Now transfer to an evaporating basin and heat it to make a nice, hot aqueous solution of sodium chloride. Allow solution to cool so hydrated crystals begin to form as the alkali is less soluble in cold water, so won't dissolve in the water and will actually form the crystals we want. Remove the crystals with filtration, then wash with distilled water to remove impuritites. Finally, dry the hydrated crystals so all the water evaporates, leaving us with pure, anhydrous crystals. This is the titration method and it uses titrations so the process could be reversed, we could have 25cm3 of acid and we need to find how much alkali neutralises it.
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what's a desiccator
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object which removes water from the surroundings using chemicals.
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how do you extract a metal that's below carbon in the reactivity series
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react it with carbon via a displacement reaction, so the carbon displaces the metal from it's compound forming carbon dioxide and the pure metal
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what happens when the concentration of greenhouse gases increase
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greenhouse effect intensifies
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describe the experiment to find the percentage of oxygen in the air using copper
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Copper is in excess so all the oxygen can be used up, so first of all, ensure copper is in excess, this copper reacts with the oxygen to form copper oxide, so all the oxygen is taken out of the air by reacting with an excess of copper, so the volume of air in our apparatus would decrease by about 20%. First, we put a bunsen burner beneath our apparatus to heat the copper so it can react, then air is passed back and forth over copper which is in the middle of a closed system containing 2 syringes which meet in the middle. Eventually this copper turns black, this is because copper oxide is being formed and copper oxide is black. If we start with 100cm3 of air, it'll decrease by around 20%, so we will end up with 80cm3 of air after all oxygen is used up by copper. Once you take the heat off, let it cool. This is because gases expand when heated, so the actual volume when it's just been taken off will be incorrect. We need to heat the copper as it's unreactive so the heat forces it to react with the oxygen in the air. We must ensure our apparatus is a closed system so no oxygen can get out or get in. This experiment doesn't take into account the air between the syringes so it's an estimate. We use copper powder or something with a high surface area so reaction is faster, also make sure you move bunsen burner around so it doesn't target one area and melt it.
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what is a valence electron
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outer shell electron
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how do you test for hydrogen
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use a lit splint, this produces a squeaky pop when hydrogen is present because the hydrogen reacts with the oxygen
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what are the most reactive group
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alkali metals
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what is limewater
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calcium hydroxide
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how do you test for chlorine
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use damp, blue litmus paper, this bleaches white if chlorine is present
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how does aluminium resist corrosion
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forms a thin but strong oxide layer
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how do you extract a metal that's above carbon in the reactivity series
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react it with a more reactive metal or use electrolysis
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if the salt is insoluble, what method do you use to extract it
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precipitation method
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an indicator remained colourless in acid what indicator is this
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phenolphthalein
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what is pH a measurement of
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hydrogen (H+) ions, so how basic or acidic an aqueous substance is
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when copper carbonate is thermally decomposed, what is produced and what colour are the reactants and products
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copper oxide and carbon dioxide. the copper carbonate is a green powder and when thermally decomposed it turns into copper oxide which is black powder so we can see a colour change.
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what are the main ways to prevent corrosion
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galvanising, sacrificial protection and coating
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when bases and acids combine, what happens
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they combine to give a neutral solution of water, so they have been neutralised to give a solution of pH 7.
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how do you test for oxygen
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use a glowing splint, this re-lights in the presence of oxygen
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in what conditions will the metal disappear in the reaction between a metal and an acid
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if the metal is the limiting reactant ( acid is in excess)
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state word equation for the reaction between a hydrogen ion and a hydroxide ion
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(H+) + (OH-) -------> H20
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how do you test for ammonium ions
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add sodium hydroxide to sample and warm it up. If ammonium ions are present then ammonia gas will form. To test for ammonia gas put damp, red litmus paper near sample, if ammonia gas is present the paper turns blue.
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how do you test for carbonate ions
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First add HCl. This HCl is not for removing impurities. If carbonate ions ( CO3 2-) are present then fizzing is noticed which is carbon dioxide being made. To ensure this is definitely carbon dioxide, bubble it through limewater, if it's present it turns from colourless to cloudy.
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what is low-carbon steel used in
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nails, cars, ships, girders
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what indicator turns pink in alkali
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phenolphthalein
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why is copper used in hospital surfaces
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antimicrobial properties, malleable
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what state is bromine at room temperature
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reddish brown liquid
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what is produced when a carbonate reacts with an acid
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carbon dioxide, water and a salt
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how do you test for sulfate ions
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add hydrochloric acid to remove impurities. add barium chloride, if sulfate ions (SO4 2-) are present then a white precipitate of barium sulfate will form.
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an indicator turned red in acid, what indicator could this be
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litmus paper or methyl orange
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what is an oxidising agent
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a substance that oxidises another substance, so it itself is reduced
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what does inert mean
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unreactive
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what do metal carbonates thermally decompose into
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carbon dioxide and a metal oxide
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when metals react with acids, a bubbling is observed, what is this
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hydrogen gas (H2)
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an indicator turned blue in alkali, name the indicator
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litmus paper
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when carbonates react with acids a fizzing is noticed, what is this.
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carbon dioxide (CO2)
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what is a sulfate ion
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SO4 2-
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why do we do titrations multiple times
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do get a specific and accurate result. first time is an approximate, but the times after is more careful as we want a very specific answer.
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why do we not use universal indicator in titrations
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because it has a wide range of colours depending on the specific pH, so the change is too gradual meaning it is hard to see when the exact end point of the titration is. It doesn't have 1 specific colour for an acid, neutral and alkali like other indicators.
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what colour flame does sodium burn with
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yellow-orange
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what is a nitrate ion
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NO3 -
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what does ductile mean
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a metal that can be drawn into a thin wire
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how do you carry out a flame test
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an inert wire loop with a high melting point like nichrome or platinum is placed in concentrated HCl to remove impurites, to test it's purity, hold it to a flame, if it's colourless then it's pure and we can move on. Dip wire loop into your salt sample so some sticks to it. Then stick this in the roaring part of the bunsen burner flame, the blue bit, because this is the hottest part. Then the colour is observed, metal cations burn with a unique colour.
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name the 5 group 7 elements in order of reactivity
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astatine, iodine, bromine, chlorine, fluorine
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another name for low-carbon steel
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mild steel
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why is aluminium used in power cables
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it is ductile and conducts electricity
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state the balanced chemical equation for the production of rust
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4Fe + nH20 + 302 -----------> 2Fe2O3 . nH20
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