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22:[["$","$L31",null,{"feature":"flashcards"}],"$L32",["$","$L33",null,{"href":"/igcse/chemistry/edexcel/crude-oil/flashcards","label":"Crude oil","subjectCode":"igcse_chemistry","surface":"flashcards"}],["$","$L34",null,{"runner":["$","div",null,{"className":"min-h-0 flex-1 overflow-hidden bg-background","children":["$","$L35",null,{"decks":[{"id":"7f2563e1-16fc-4a92-a0b5-6d36559c1d65","title":"Crude oil Flashcards","topicId":"b1859bdc-fe34-5abd-9c11-63010d5cdf1f","topicSlug":"crude-oil","cards":[{"id":"c7a292d7-48cc-466b-996f-5c0b002eb2cd","cardType":"basic","points":1,"front":"Why can crude oil be separated without making new substances?","back":"It is a mixture, so substances are not chemically bonded.","mcqOptions":[{"text":"It is a mixture, so substances are not chemically bonded.","correct":true,"explanation":"The hydrocarbons in crude oil are physically mixed rather than joined by chemical bonds, so physical methods can separate them without producing new substances."},{"text":"It is a compound, so substances are chemically bonded.","correct":false,"explanation":"Compounds contain elements chemically bonded in fixed proportions and require chemical reactions for separation. Crude oil is a mixture whose components are not chemically bonded."},{"text":"It is an element, so it contains only one type of atom.","correct":false,"explanation":"Crude oil contains many different hydrocarbons, not one type of atom. It can be separated physically because it is a mixture of substances that are not chemically bonded."},{"text":"It is a solution, so all substances have identical boiling points.","correct":false,"explanation":"Being a solution would not mean that all components have identical boiling points. Crude oil is separable because it is a mixture whose substances are not chemically bonded."}]},{"id":"da924d05-7e1d-42fc-96a2-68600e6c4161","cardType":"cloze","points":null,"front":"A hydrocarbon contains [ ].","back":"A hydrocarbon contains hydrogen and carbon atoms only.","mcqOptions":[{"text":"hydrogen and carbon atoms only","correct":true,"explanation":"A hydrocarbon is defined as a compound containing only hydrogen and carbon atoms. Compounds containing any additional element are not hydrocarbons."},{"text":"hydrogen, carbon and oxygen atoms","correct":false,"explanation":"Including oxygen is a common confusion with fuels such as alcohols. A hydrocarbon contains hydrogen and carbon atoms only, with no oxygen or other elements."},{"text":"carbon and oxygen atoms only","correct":false,"explanation":"Carbon and oxygen alone form substances such as carbon oxides, not hydrocarbons. A hydrocarbon must contain hydrogen and carbon atoms only."},{"text":"hydrogen and oxygen atoms only","correct":false,"explanation":"Hydrogen and oxygen can form water, but carbon is essential in every hydrocarbon. The correct definition requires hydrogen and carbon atoms only."}]},{"id":"ba05aeef-5861-4535-aa1a-832a4bcc7c90","cardType":"basic","points":1,"front":"What type of hydrocarbon are most useful crude oil molecules?","back":"Alkanes.","mcqOptions":[{"text":"Alkanes.","correct":true,"explanation":"Most hydrocarbons in crude oil are alkanes, a homologous series of saturated compounds containing only carbon-carbon single bonds."},{"text":"Alkenes.","correct":false,"explanation":"Alkenes are unsaturated hydrocarbons usually produced by cracking larger alkane molecules. Most useful hydrocarbons obtained directly from crude oil are alkanes."},{"text":"Alcohols.","correct":false,"explanation":"Alcohols contain oxygen as well as carbon and hydrogen, so they are not hydrocarbons. Most useful hydrocarbon molecules in crude oil are alkanes."},{"text":"Carboxylic acids.","correct":false,"explanation":"Carboxylic acids contain oxygen and a carboxyl functional group, so they are not hydrocarbons. The relevant crude oil molecules are alkanes."}]},{"id":"72a4e96f-c785-4877-8a75-afcf115f10fc","cardType":"cloze","points":null,"front":"An alkane has only [ ].","back":"An alkane has only carbon-carbon single bonds.","mcqOptions":[{"text":"carbon-carbon single bonds","correct":true,"explanation":"Alkanes are saturated hydrocarbons because every bond between carbon atoms is a single covalent bond. Their general formula is $C_nH_{2n+2}$."},{"text":"carbon-carbon double bonds","correct":false,"explanation":"A carbon-carbon double bond identifies an alkene, not an alkane. Alkanes are saturated and have only carbon-carbon single bonds."},{"text":"carbon-carbon triple bonds","correct":false,"explanation":"A carbon-carbon triple bond identifies an alkyne rather than an alkane. An alkane contains only single bonds between its carbon atoms."},{"text":"carbon-carbon single and double bonds","correct":false,"explanation":"Including double bonds makes the molecule unsaturated, so it is not an alkane. Alkanes have carbon-carbon single bonds only."}]},{"id":"5bbd6b5a-62f2-4fdb-9e66-86e5182954a2","cardType":"basic","points":1,"front":"How does molecule size affect hydrocarbon boiling point?","back":"Larger molecules have higher boiling points.","mcqOptions":[{"text":"Larger molecules have higher boiling points.","correct":true,"explanation":"Larger hydrocarbon molecules have stronger intermolecular forces because they contain more electrons and have greater surface area, so more energy is needed to separate them."},{"text":"Smaller molecules have higher boiling points.","correct":false,"explanation":"This reverses the size-boiling point relationship. Smaller hydrocarbons have weaker intermolecular forces, while larger molecules require more energy and therefore have higher boiling points."},{"text":"Larger molecules have lower boiling points.","correct":false,"explanation":"Larger molecules do not boil more easily. Their stronger intermolecular forces require more energy to overcome, so larger hydrocarbons have higher boiling points."},{"text":"Molecule size has no effect on boiling points.","correct":false,"explanation":"Molecular size affects the strength of intermolecular forces. As hydrocarbon molecules become larger, these forces strengthen and their boiling points increase."}]},{"id":"7d2dc032-6c07-4472-8ebc-085ae6fa2041","cardType":"cloze","points":null,"front":"A fraction is a mixture of hydrocarbons with [ ].","back":"A fraction is a mixture of hydrocarbons with similar boiling points.","mcqOptions":[{"text":"similar boiling points","correct":true,"explanation":"Hydrocarbons collected in one fraction boil over a similar temperature range, allowing them to condense at a similar level in the fractionating column."},{"text":"identical boiling points","correct":false,"explanation":"A fraction contains several hydrocarbons, so they do not all have exactly the same boiling point. Instead, they have similar boiling points within a range."},{"text":"widely different boiling points","correct":false,"explanation":"Hydrocarbons with widely different boiling points condense at different levels and enter different fractions. One fraction contains hydrocarbons with similar boiling points."},{"text":"similar chemical formulae","correct":false,"explanation":"Hydrocarbons within a fraction may have related formulae, but fractions are defined by boiling ranges. Their shared property is having similar boiling points."}]},{"id":"a317dc43-d99d-4997-9433-8ad66612854c","cardType":"basic","points":1,"front":"What industrial process separates crude oil into fractions?","back":"Fractional distillation.","mcqOptions":[{"text":"Fractional distillation.","correct":true,"explanation":"Fractional distillation separates crude oil by exploiting differences in hydrocarbon boiling points within a fractionating column that has a temperature gradient."},{"text":"Simple distillation.","correct":false,"explanation":"Simple distillation is unsuitable for efficiently separating the many hydrocarbons with overlapping boiling ranges. Crude oil is separated industrially by fractional distillation."},{"text":"Catalytic cracking.","correct":false,"explanation":"Catalytic cracking converts long-chain hydrocarbons into shorter alkanes and alkenes, creating different molecules. Fractional distillation separates existing crude oil components without chemical change."},{"text":"Filtration.","correct":false,"explanation":"Filtration separates an insoluble solid from a fluid and cannot separate dissolved liquid hydrocarbons. Crude oil is separated into fractions by fractional distillation."}]},{"id":"1aef7a6a-6efe-42b2-bfb8-905d5fda08a3","cardType":"basic","points":2,"front":"What happens to crude oil before it enters the fractionating column?","back":"It is heated until most of it vaporises.","mcqOptions":[{"text":"It is heated until most of it vaporises.","correct":true,"explanation":"Heating supplies enough energy for most crude oil hydrocarbons to become vapours, which then rise through the column and condense at different temperatures."},{"text":"It is cooled until most of it condenses.","correct":false,"explanation":"Cooling before entry would keep the hydrocarbons liquid and prevent effective separation in the column. Crude oil is heated until most of it vaporises."},{"text":"It is heated until all of it combusts.","correct":false,"explanation":"Combustion would chemically convert hydrocarbons into new substances such as carbon dioxide and water. Crude oil is heated only until most of it vaporises."},{"text":"It is filtered until impurities are removed.","correct":false,"explanation":"Filtration cannot prepare the mixed liquid hydrocarbons for separation by boiling point. Crude oil is heated until most vaporises before entering the fractionating column."}]},{"id":"07464a2d-9b57-4a15-84c0-0ed11aea6543","cardType":"cloze","points":null,"front":"A fractionating column is [ ] and [ ].","back":"A fractionating column is hot at the bottom and cooler at the top.","mcqOptions":[{"text":"A fractionating column is hot at the bottom and cooler at the top.","correct":true,"explanation":"The column has a temperature gradient: it is hottest at the bottom and becomes cooler towards the top, allowing fractions to condense at different levels."},{"text":"A fractionating column is cool at the bottom and hotter at the top.","correct":false,"explanation":"The temperature gradient has been reversed. Heat enters at the bottom, so the correct description is hot at the bottom and cooler at the top."},{"text":"A fractionating column is hot at the bottom and warmer at the top.","correct":false,"explanation":"The top is not warmer than the bottom; it is cooler. The correct temperature pattern is hot at the bottom and cooler at the top."},{"text":"A fractionating column is cooler at the bottom and cool at the top.","correct":false,"explanation":"This option incorrectly makes both ends relatively cool and reverses the important gradient. The column is hot at the bottom and cooler at the top."}]},{"id":"6087bd02-3889-48ea-93c4-f4fc14503914","cardType":"basic","points":1,"front":"Where do lower-boiling fractions condense in the column?","back":"Near the top.","mcqOptions":[{"text":"Near the top.","correct":true,"explanation":"Lower-boiling fractions have weaker intermolecular attractions and condense at lower temperatures, so they rise higher before reaching a cool enough part of the column."},{"text":"Near the bottom.","correct":false,"explanation":"The bottom is hottest and is suitable for high-boiling fractions. Lower-boiling fractions rise further and condense near the cooler top of the column."},{"text":"Near the middle.","correct":false,"explanation":"Although some fractions condense in the middle, the lower-boiling fractions travel higher because they need cooler temperatures, so they condense near the top."},{"text":"At the base.","correct":false,"explanation":"The base is the hottest region, so it favours high-boiling fractions rather than lower-boiling ones. Lower-boiling fractions condense near the top."}]},{"id":"e370a3cf-aa3d-4c56-8b4d-9ad8b4564f8e","cardType":"basic","points":2,"front":"Why does a high-boiling fraction condense low in the column?","back":"It condenses at a higher temperature, found lower down.","mcqOptions":[{"text":"It condenses at a higher temperature, found lower down.","correct":true,"explanation":"High-boiling fractions require higher temperatures to condense. Higher temperatures occur lower in the column, so these fractions condense there."},{"text":"It condenses at a lower temperature, found lower down.","correct":false,"explanation":"The temperature has been confused with the fraction’s boiling point. High-boiling fractions need a higher temperature, and that region is lower down."},{"text":"It condenses at a higher temperature, found higher up.","correct":false,"explanation":"The temperature requirement is correct, but the location is reversed. Higher temperatures are found lower in the column, not higher up."},{"text":"It condenses at a lower temperature, found higher up.","correct":false,"explanation":"This describes a lower-boiling fraction instead. A high-boiling fraction condenses at a higher temperature, found lower down in the column."}]},{"id":"27b5f991-82af-4f22-9f4f-45daad57fdf3","cardType":"basic","points":1,"front":"Which fraction is collected at the very top of the column?","back":"Refinery gases.","mcqOptions":[{"text":"Refinery gases.","correct":true,"explanation":"Refinery gases contain the smallest hydrocarbon molecules and have the lowest boiling points, so they remain gaseous longest and are collected at the top."},{"text":"Petrol.","correct":false,"explanation":"Petrol condenses below the gases because its hydrocarbons have higher boiling points. The fraction collected at the very top is refinery gases."},{"text":"Kerosene.","correct":false,"explanation":"Kerosene contains larger hydrocarbons with higher boiling points, so it condenses lower down. Refinery gases are collected at the very top."},{"text":"Bitumen.","correct":false,"explanation":"Bitumen contains very large molecules and has a high boiling point, so it remains at the bottom rather than reaching the top. Refinery gases are collected there."}]},{"id":"5a175438-d6b4-4c9b-9745-d29596f94346","cardType":"basic","points":1,"front":"Which crude oil fraction is used as petrol for cars?","back":"Gasoline.","mcqOptions":[{"text":"Gasoline.","correct":true,"explanation":"Gasoline is the crude oil fraction used as petrol in cars. It contains hydrocarbons with suitable volatility and energy release for spark-ignition engines."},{"text":"Kerosene.","correct":false,"explanation":"Kerosene is mainly used as aircraft fuel, not petrol for cars. The crude oil fraction used as petrol is gasoline."},{"text":"Diesel oil.","correct":false,"explanation":"Diesel oil is used in diesel engines and is a different fraction from petrol. Cars using petrol require the gasoline fraction."},{"text":"Bitumen.","correct":false,"explanation":"Bitumen is a thick residue used for road surfaces and roofing, not as a car fuel. Gasoline is the fraction used as petrol."}]},{"id":"08693c84-c190-40a0-9e40-9c5fea993f98","cardType":"basic","points":1,"front":"Which crude oil fraction is used as aircraft fuel?","back":"Kerosene.","mcqOptions":[{"text":"Kerosene.","correct":true,"explanation":"Kerosene has the appropriate boiling range and combustion properties for use as aircraft fuel, often called jet fuel."},{"text":"Gasoline.","correct":false,"explanation":"Gasoline is used as petrol for cars and is more volatile than the fuel required for aircraft. Kerosene is the crude oil fraction used as aircraft fuel."},{"text":"Diesel oil.","correct":false,"explanation":"Diesel oil powers diesel engines, including some vehicles, but it is not the standard aircraft fuel fraction. Aircraft use kerosene."},{"text":"Bitumen.","correct":false,"explanation":"Bitumen is a heavy, viscous residue used for roads and roofing. It does not serve as aircraft fuel; kerosene is used instead."}]},{"id":"984f6bdc-c110-465f-ab65-fffa0e459c8a","cardType":"basic","points":1,"front":"Which crude oil fraction is used for road surfaces and roofing?","back":"Bitumen.","mcqOptions":[{"text":"Bitumen.","correct":true,"explanation":"Bitumen is the heaviest, most viscous crude oil fraction. Its waterproof and durable properties make it suitable for road surfaces and roofing."},{"text":"Fuel oil.","correct":false,"explanation":"Fuel oil is mainly burned as a fuel for ships and industrial heating. The thick fraction used for road surfaces and roofing is bitumen."},{"text":"Lubricating oil.","correct":false,"explanation":"Lubricating oil reduces friction in engines and machinery, whereas road surfaces and roofing use bitumen because it is durable and waterproof."},{"text":"Gasoline.","correct":false,"explanation":"Gasoline is a light, volatile fraction used as petrol for cars. It is not suitable for roads or roofing; those applications use bitumen."}]},{"id":"00aa3f6b-384c-49c6-8e5c-4fcbca6346b8","cardType":"cloze","points":null,"front":"From top to bottom in the column, hydrocarbon molecules get [ ] and viscosity [ ].","back":"From top to bottom in the column, hydrocarbon molecules get larger and viscosity increases.","mcqOptions":[{"text":"From top to bottom in the column, hydrocarbon molecules get larger and viscosity increases.","correct":true,"explanation":"Fractions collected lower down contain larger hydrocarbon molecules. Larger molecules have stronger intermolecular forces and flow less easily, so viscosity increases."},{"text":"From top to bottom in the column, hydrocarbon molecules get smaller and viscosity increases.","correct":false,"explanation":"The molecule-size trend is reversed: molecules become larger from top to bottom. Larger molecules cause viscosity to increase, so only the second term is correct."},{"text":"From top to bottom in the column, hydrocarbon molecules get larger and viscosity decreases.","correct":false,"explanation":"Molecules do become larger down the column, but larger molecules flow less easily because of stronger attractions. Therefore, viscosity increases rather than decreases."},{"text":"From top to bottom in the column, hydrocarbon molecules get smaller and viscosity decreases.","correct":false,"explanation":"Both trends are reversed. Moving down the column, hydrocarbon molecules become larger and the thicker fractions have increasing viscosity."}]},{"id":"0c46e425-21eb-4080-b8af-3f06f2f26c92","cardType":"basic","points":1,"front":"What does high viscosity mean for how a liquid flows?","back":"It is thick and flows slowly.","mcqOptions":[{"text":"It is thick and flows slowly.","correct":true,"explanation":"High viscosity means the liquid has a strong resistance to flow, so it is thick and moves slowly, like treacle compared with water."},{"text":"It is thin and flows quickly.","correct":false,"explanation":"This describes low viscosity, where a liquid flows easily. High viscosity means the liquid is thick and resists flow, so it flows slowly."},{"text":"It is thick and flows quickly.","correct":false,"explanation":"Thickness and rapid flow contradict each other here. A highly viscous liquid is thick because internal resistance is high, so it flows slowly."},{"text":"It is thin and flows slowly.","correct":false,"explanation":"A thin liquid usually has low viscosity and flows quickly. High viscosity produces a thick liquid with greater resistance to movement and slower flow."}]},{"id":"e13a66f8-c54f-4e9c-9d25-4e235ec57ee0","cardType":"basic","points":1,"front":"What carbon-containing product forms in complete combustion?","back":"Carbon dioxide, $CO_2$.","mcqOptions":[{"text":"Carbon dioxide, $CO_2$.","correct":true,"explanation":"Complete combustion supplies enough oxygen for all carbon atoms in the fuel to oxidise fully, producing carbon dioxide, $CO_2$."},{"text":"Carbon monoxide, $CO$.","correct":false,"explanation":"Carbon monoxide forms mainly during incomplete combustion when oxygen is limited. With enough oxygen, carbon is oxidised further to carbon dioxide, $CO_2$."},{"text":"Carbon, $C$.","correct":false,"explanation":"Solid carbon or soot can result from incomplete combustion. Complete combustion oxidises the carbon fully, forming carbon dioxide, $CO_2$."},{"text":"Methane, $CH_4$.","correct":false,"explanation":"Methane is a hydrocarbon fuel, not the carbon-containing product of its complete combustion. Complete combustion produces carbon dioxide, $CO_2$, and water."}]},{"id":"9c6cc272-7ea6-4e68-a7b1-e6f8f5448550","cardType":"cloze","points":null,"front":"Incomplete combustion happens when there is [ ].","back":"Incomplete combustion happens when there is not enough oxygen.","mcqOptions":[{"text":"not enough oxygen","correct":true,"explanation":"Incomplete combustion occurs when the fuel does not receive enough oxygen to react completely, so products such as carbon monoxide or soot may form."},{"text":"too much oxygen","correct":false,"explanation":"Too much oxygen favours complete combustion rather than incomplete combustion. The correct condition is not enough oxygen, which prevents the fuel burning fully."},{"text":"not enough fuel","correct":false,"explanation":"A shortage of fuel does not define incomplete combustion. It happens when there is not enough oxygen for the available fuel to burn completely."},{"text":"too much nitrogen","correct":false,"explanation":"Nitrogen is not the condition that causes incomplete combustion. The key requirement is not enough oxygen for complete oxidation of the fuel."}]},{"id":"4b8be979-331d-4aed-a7cd-02e32a51b406","cardType":"basic","points":1,"front":"Which poisonous gas can form during incomplete combustion?","back":"Carbon monoxide, $CO$.","mcqOptions":[{"text":"Carbon monoxide, $CO$.","correct":true,"explanation":"Limited oxygen during incomplete combustion can produce carbon monoxide, $CO$. It is poisonous because it interferes with oxygen transport in the blood."},{"text":"Carbon dioxide, $CO_2$.","correct":false,"explanation":"Carbon dioxide is the normal carbon product of complete combustion and is not the poisonous gas specifically formed by incomplete combustion. The answer is carbon monoxide, $CO$."},{"text":"Sulfur dioxide, $SO_2$.","correct":false,"explanation":"Sulfur dioxide forms when sulfur impurities burn, not simply because combustion is incomplete. The poisonous gas associated with incomplete combustion is carbon monoxide, $CO$."},{"text":"Nitrogen dioxide, $NO_2$.","correct":false,"explanation":"Nitrogen dioxide is an oxide of nitrogen formed at high engine temperatures. Incomplete combustion of fuels can instead produce poisonous carbon monoxide, $CO$."}]},{"id":"177c12ab-a6ea-450c-9d4e-59e0da9a29cd","cardType":"basic","points":2,"front":"Why is carbon monoxide poisonous?","back":"It reduces blood’s capacity to transport oxygen.","mcqOptions":[{"text":"It reduces blood’s capacity to transport oxygen.","correct":true,"explanation":"Carbon monoxide binds strongly to haemoglobin, reducing the blood’s ability to transport oxygen and potentially depriving body tissues of oxygen."},{"text":"It reduces blood’s capacity to absorb oxygen.","correct":false,"explanation":"The lungs absorb oxygen, whereas haemoglobin transports it around the body. Carbon monoxide binds to haemoglobin and reduces the blood’s capacity to transport oxygen."},{"text":"It reduces blood’s capacity to transport carbon dioxide.","correct":false,"explanation":"Carbon monoxide’s key danger is its strong binding to haemoglobin, which reduces oxygen transport. Carbon dioxide transport is not the specific poisonous effect tested here."},{"text":"It reduces blood’s capacity to digest oxygen.","correct":false,"explanation":"Blood does not digest oxygen. Carbon monoxide binds to haemoglobin and prevents it transporting oxygen efficiently to body tissues."}]},{"id":"65f38704-1c48-45a7-b4f9-5b36a5cbd379","cardType":"basic","points":2,"front":"Why can car engines form oxides of nitrogen?","back":"High temperatures make nitrogen and oxygen react.","mcqOptions":[{"text":"High temperatures make nitrogen and oxygen react.","correct":true,"explanation":"Normally nitrogen and oxygen are relatively unreactive, but the high temperatures inside car engines provide enough energy for them to react and form nitrogen oxides."},{"text":"High temperatures make nitrogen and hydrogen react.","correct":false,"explanation":"Hydrogen is not the relevant reactant in air for forming these pollutants. High engine temperatures make nitrogen and oxygen react to produce oxides of nitrogen."},{"text":"High temperatures make carbon and oxygen react.","correct":false,"explanation":"Carbon reacting with oxygen forms carbon oxides, not oxides of nitrogen. The nitrogen oxides in engines form when nitrogen and oxygen react at high temperatures."},{"text":"High temperatures make sulfur and oxygen react.","correct":false,"explanation":"Sulfur reacting with oxygen produces sulfur dioxide, usually from sulfur impurities in fuel. Oxides of nitrogen form when nitrogen and oxygen react in hot engines."}]},{"id":"084fca93-74b9-4bca-bd05-4b31d6160546","cardType":"basic","points":1,"front":"What pollutant forms when sulfur impurities in fuels burn?","back":"Sulfur dioxide, $SO_2$.","mcqOptions":[{"text":"Sulfur dioxide, $SO_2$.","correct":true,"explanation":"Sulfur impurities in fuels react with oxygen during burning, producing sulfur dioxide, $SO_2$, which can contribute to acid rain."},{"text":"Carbon dioxide, $CO_2$.","correct":false,"explanation":"Carbon dioxide is produced by burning carbon-containing fuels, not specifically by sulfur impurities. Burning sulfur impurities produces sulfur dioxide, $SO_2$."},{"text":"Carbon monoxide, $CO$.","correct":false,"explanation":"Carbon monoxide is associated with incomplete combustion caused by limited oxygen. Sulfur impurities burning in oxygen form sulfur dioxide, $SO_2$."},{"text":"Nitrogen dioxide, $NO_2$.","correct":false,"explanation":"Nitrogen dioxide is an oxide of nitrogen formed when nitrogen and oxygen react at high temperatures. Sulfur impurities burn to form sulfur dioxide, $SO_2$."}]},{"id":"2a3f87e2-c794-4be7-bc1c-4ab35246cf51","cardType":"cloze","points":null,"front":"Acid rain is caused especially by [ ] and [ ] dissolving and reacting in rainwater.","back":"Acid rain is caused especially by sulfur dioxide and oxides of nitrogen dissolving and reacting in rainwater.","mcqOptions":[{"text":"Acid rain is caused especially by sulfur dioxide and oxides of nitrogen dissolving and reacting in rainwater.","correct":true,"explanation":"Sulfur dioxide and oxides of nitrogen dissolve in rainwater and react to form acidic solutions, lowering the rainwater’s pH and causing acid rain."},{"text":"Acid rain is caused especially by carbon monoxide and oxides of nitrogen dissolving and reacting in rainwater.","correct":false,"explanation":"Carbon monoxide is poisonous but is not a main cause of acid rain. The relevant pollutants are sulfur dioxide and oxides of nitrogen, which form acids in rainwater."},{"text":"Acid rain is caused especially by sulfur dioxide and carbon dioxide dissolving and reacting in rainwater.","correct":false,"explanation":"Carbon dioxide can make rain naturally slightly acidic, but the pollutants especially associated with acid rain are sulfur dioxide and oxides of nitrogen."},{"text":"Acid rain is caused especially by carbon monoxide and carbon dioxide dissolving and reacting in rainwater.","correct":false,"explanation":"Neither carbon monoxide nor carbon dioxide is the pair tested for pollution-driven acid rain. Sulfur dioxide and oxides of nitrogen react in rainwater to form acids."}]},{"id":"d70cdef6-695d-4c51-af6b-031e482bf827","cardType":"basic","points":1,"front":"What damage can acid rain cause to limestone buildings?","back":"It damages them.","mcqOptions":[{"text":"It damages them.","correct":true,"explanation":"Acid rain contains acids that react with calcium carbonate in limestone, gradually dissolving the stone and damaging buildings made from it."},{"text":"It protects them.","correct":false,"explanation":"Acid rain does not form a protective coating. Its acids react with limestone, so the correct answer is that it damages the buildings."},{"text":"It strengthens them.","correct":false,"explanation":"Limestone is weakened rather than strengthened when acids react with its calcium carbonate. The correct answer is that acid rain damages limestone buildings."},{"text":"It polishes them.","correct":false,"explanation":"Acid rain causes chemical erosion, not controlled polishing. It reacts with and wears away limestone, so the correct answer is that it damages the buildings."}]},{"id":"e3308b81-a952-4dfa-a412-2d419aaaa543","cardType":"basic","points":2,"front":"Why is cracking needed in oil refineries?","back":"It makes more short-chain fuels from long-chain fractions.","mcqOptions":[{"text":"It makes more short-chain fuels from long-chain fractions.","correct":true,"explanation":"Cracking breaks large, less useful hydrocarbon molecules into smaller molecules, producing more short-chain fuels that are in greater demand."},{"text":"It makes more long-chain fuels from short-chain fractions.","correct":false,"explanation":"Cracking breaks long-chain hydrocarbons apart rather than joining smaller molecules together. It makes more short-chain fuels from long-chain fractions."},{"text":"It makes more alkanes from long-chain fractions.","correct":false,"explanation":"Cracking produces some alkanes, but its refinery purpose is specifically to make more short-chain fuels from long-chain fractions; it also forms alkenes."},{"text":"It removes all impurities from long-chain fractions.","correct":false,"explanation":"Cracking changes the size of hydrocarbon molecules and does not purify every impurity. Its purpose is making more short-chain fuels from long-chain fractions."}]},{"id":"03b520fb-ce92-423c-ba76-5e0146162f5d","cardType":"basic","points":1,"front":"What type of process is cracking?","back":"A chemical process.","mcqOptions":[{"text":"A chemical process.","correct":true,"explanation":"Cracking breaks chemical bonds in long-chain hydrocarbon molecules and forms new molecules, so it is a chemical process rather than a physical separation."},{"text":"A physical process.","correct":false,"explanation":"Distillation is a physical separation, but cracking forms new substances by breaking chemical bonds. Therefore, cracking is a chemical process."},{"text":"A reversible process.","correct":false,"explanation":"Reversibility is not the classification being tested here, and cracking is not normally reversed in the refinery. It is classified as a chemical process because new substances form."},{"text":"A purification process.","correct":false,"explanation":"Purification removes unwanted substances, whereas cracking changes long-chain molecules into different hydrocarbons. The correct classification is a chemical process."}]},{"id":"8efab894-5f55-458a-b9d1-cd36346d8c0e","cardType":"cloze","points":null,"front":"Catalytic cracking heats long-chain alkanes to [ ] over a hot [ ].","back":"Catalytic cracking heats long-chain alkanes to 600-700 °C over a hot catalyst.","mcqOptions":[{"text":"Catalytic cracking heats long-chain alkanes to 600-700 °C over a hot catalyst.","correct":true,"explanation":"Catalytic cracking uses a high temperature of 600-700 °C and passes the vapour over a hot catalyst, which speeds up the breaking of long-chain alkanes."},{"text":"Catalytic cracking heats long-chain alkanes to 100-200 °C over a hot catalyst.","correct":false,"explanation":"The catalyst is correctly included, but 100-200 °C is too low for catalytic cracking. The required temperature is 600-700 °C, which provides enough energy for cracking."},{"text":"Catalytic cracking heats long-chain alkanes to 600-700 °C over a hot steam.","correct":false,"explanation":"Steam can be involved in other industrial processes, but catalytic cracking requires a hot catalyst. The correct conditions are 600-700 °C over a hot catalyst."},{"text":"Catalytic cracking heats long-chain alkanes to 800-900 °C over a hot catalyst.","correct":false,"explanation":"A catalyst is required, but 800-900 °C is higher than the usual catalytic-cracking range. The correct temperature is 600-700 °C over a hot catalyst."}]},{"id":"434581c2-6773-423d-a178-cdf057af601c","cardType":"basic","points":1,"front":"Name one catalyst used in catalytic cracking.","back":"Silica or alumina.","mcqOptions":[{"text":"Silica or alumina.","correct":true,"explanation":"Silica and alumina are catalysts used in catalytic cracking. They provide a surface that helps long-chain hydrocarbon molecules break into smaller molecules."},{"text":"Nickel or iron.","correct":false,"explanation":"Nickel and iron are associated with other industrial catalytic processes, not the standard catalysts named for cracking. The accepted answers are silica or alumina."},{"text":"Copper or silver.","correct":false,"explanation":"Copper and silver are not the usual catalysts identified for catalytic cracking at this level. The correct examples are silica or alumina."},{"text":"Platinum or palladium.","correct":false,"explanation":"Platinum and palladium are familiar catalysts in catalytic converters, which can make them tempting, but catalytic cracking uses silica or alumina."}]},{"id":"c40fa040-450c-4937-9eb9-24dcd7ccc5dd","cardType":"basic","points":1,"front":"What useful non-fuel products are made by cracking?","back":"Alkenes.","mcqOptions":[{"text":"Alkenes.","correct":true,"explanation":"Cracking produces alkenes as useful non-fuel products. Their carbon-carbon double bonds allow them to undergo addition polymerisation and form polymers."},{"text":"Alcohols.","correct":false,"explanation":"Alcohols are not the characteristic non-fuel products formed directly by cracking hydrocarbons. The expected answer is alkenes, which contain carbon-carbon double bonds."},{"text":"Carboxylic acids.","correct":false,"explanation":"Cracking does not usually produce carboxylic acids because it breaks hydrocarbon molecules without adding the oxygen needed for that functional group. It produces alkenes."},{"text":"Proteins.","correct":false,"explanation":"Proteins are biological polymers and are unrelated to cracking hydrocarbons. The useful non-fuel products made by cracking are alkenes."}]},{"id":"3ecb08ff-eb94-4820-a95f-50aff92a3581","cardType":"basic","points":1,"front":"Why are alkenes useful after cracking?","back":"They are used to make polymers.","mcqOptions":[{"text":"They are used to make polymers.","correct":true,"explanation":"Alkenes contain carbon-carbon double bonds, which open during addition polymerisation so many alkene molecules can join together to make polymers."},{"text":"They are used to make alkanes.","correct":false,"explanation":"Alkenes are not mainly valuable because they make alkanes. Their carbon-carbon double bonds allow addition polymerisation, so they are used to make polymers."},{"text":"They are used to make metals.","correct":false,"explanation":"Alkenes cannot be converted into metals. Their important chemical use after cracking is undergoing addition polymerisation to make polymers."},{"text":"They are used to make limestone.","correct":false,"explanation":"Limestone is calcium carbonate and is not made from alkenes. Alkenes are useful because their double bonds allow them to form polymers."}]},{"id":"a5112c40-6cf3-433b-8337-b131c3489359","cardType":"basic","points":1,"front":"In $C_{10}H_{22} \\rightarrow C_8H_{18} + C_2H_4$, what alkene is formed?","back":"Ethene, $C_2H_4$.","mcqOptions":[{"text":"Ethene, $C_2H_4$.","correct":true,"explanation":"The products must conserve the atoms in the reactant. After forming $C_8H_{18}$, the remaining atoms are $C_2H_4$, which is ethene and an alkene."},{"text":"Propene, $C_3H_6$.","correct":false,"explanation":"Propene has three carbon atoms, so it would not conserve carbon in this equation. The remaining product is $C_2H_4$, which is ethene."},{"text":"Ethane, $C_2H_6$.","correct":false,"explanation":"Ethane has the correct number of carbon atoms but six hydrogens, leaving the hydrogen atoms unbalanced. The alkene formed is ethene, $C_2H_4$."},{"text":"Methane, $CH_4$.","correct":false,"explanation":"Methane contains only one carbon atom and does not account for the two-carbon fragment left after forming $C_8H_{18}$. The correct alkene is ethene, $C_2H_4$."}]}]}],"examCountdown":{"examDate":"2027-05-19","paperLabel":"Paper 1"},"heading":"Crude oil","title":"Crude oil Flashcards","topbar":{"backHref":"/igcse/chemistry/edexcel/flashcards"},"topicSidebar":"$L36"}]}],"topicId":"b1859bdc-fe34-5abd-9c11-63010d5cdf1f","walled":"$L37"}],"$L38","$L39"]