13604706
| Question | Answer |
| How do lithium, sodium, and potassium react with water? | All alkali metals REACT VIGOROUSLY with cold water. In each reaction, HYDROGEN GAS is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down GROUP ONE - in other words, REACTIVITY of the alkali metals INCREASES as you go down in the group. LITHIUM When lithium is added to water, it FLOATS. It FIZZES steadily and becomes smaller, until it eventually disappears. SODIUM When sodium is added to water, it MELTS to form a ball that moves around on the surface. It FIZZES rapidly, and the hydrogen produced may burn with an orange flame before the sodium disappears. POTASSIUM When potassium is added to water, the metal MELTS and floats. It MOVES AROUND very quickly on the surface of the water. The hydrogen IGNITES instantly. The metal is also set on fire, with sparks and a lilac flame. There is sometimes a small explosion at the end of the reaction. |
| What are two characteristics of alkali metals? Name two alkali metals. | CHARACTERISTICS 1. soft 2. relatively low melting points EXAMPLES Lithium. Sodium. Potassium. Rubidium. Cesium. Francium |
| What color is bromine water usually? What happens when it is shaken with an alkene? | Bromine water is a dilute solution of bromine that is normally ORANGE-BROWN in colour, but becomes colourless when shaken with an alkene. Alkenes can decolourise bromine water, while alkanes cannot. |
| Why is there less CO2 gas in the atmosphere now than there was in Earth's earliest atmosphere? | CO2 GAS IN THE EARLY ATMOSPHERE DECREASED BECAUSE: it dissolved (1) in the oceans (1) •it was incorporated into marine organisms (1) •it formed carbonate rocks (1) •an increase in (green) plants and photosynthesis removed carbon dioxide |
| Name two greenhouse gases. What do they do? | Greenhouse gases such as CO2 and METHANE act like a blanket in the earth's atmosphere, absorbing and reflecting trapping heat radiation inside the earth's atmosphere. This GREENHOUSE EFFECT is causing GLOBAL WARMING. |
| Describe the composition of the earth's atmosphere. What are the two most abundant gases? What percent of the atmosphere is made of CO2? What percent is argon? | 78% nitrogen 21% oxygen 0.9% argon .037% CO2 |
| What is "cracking" in the hydrocarbon industry? Why is it important? | CRACKING turns long saturated (ALKANE) molecules into smaller unsaturated molecules like ALKENES. Shorter chain molecules are more useful(1) • There is a demand for shorter chain molecules (1) •Cracking meets this demand by reducing the excess of longer chain molecules (1) • Cracking produces alkenes (1) • Alkenes used to make polymers (1) |
| What is an alkene? | ALKENES are hydrocarbons that have a carbon-carbon double bond. The number of hydrogen atoms in an alkene is double the number of carbon atoms. For example, the molecular formula of ethene is C2H4, while for propene it is C3H6. Alkenes can act as monomers to form a polymer. |
| What is a polymer? Give some examples. | POLYMERS - plastics - are very large molecules made from many smaller molecules called MONOMERS. Alkenes are able to act as monomers because they contain a double bond. They can join end-to-end in a reaction called addition polymerisation. The polymers they form are called addition polymers. In general: A lot of monomers → a polymer molecule For example: ethene → polyethene propene → polypropene chloroethene → polychloroethene - also called polyvinylchloride or PVC |
| How did Mendeleev arrange elements into a periodic table? Why did he swap the positions of of iodine and tellurium in his table? | Mendeleev arranged the known elements in order of their relative atomic masses. Unlike other chemists who had tried this before, Mendeleev did not always keep to the order, and left gaps in his table so that chemicals of known similar properties could line up. He sometimes swapped the positions of elements if he thought that better suited their chemical properties. For example, fluorine, chlorine, bromine, and iodine are non-metals that do not easily react with oxygen. Tellurium is a metal that burns in air to form tellurium dioxide. Iodine has a lower relative atomic mass than tellurium, so Mendeleev should have placed it before tellurium in the table. Instead, he placed iodine after tellurium so that it lined up with fluorine, chlorine, and bromine-- all elements that shared chemical properties. He justified this swap by saying that the value for tellurium must be incorrect. |
| What were the key features of Mendeleev's periodic table? | Mendeleev arranged the known elements in order of their relative atomic masses. Unlike other chemists who had tried this before, Mendeleev did not always keep to the order, and left gaps in his table so that chemicals of known similar properties could line up. |
| Name three ways that human activity affects the level of CO2 of the atmosphere. | 1. The human population is increasing, so there are more people respiring so more CO2 is released. 2. More people means more ENERGY is required for lighting, heating, transport etc - humans get this energy by BURNING FOSSIL FUELS and releasing CO2. The average energy demand per person is also increasing, so the rate of CO2 release through burning of fossil fuels is increasing exponentially. 3. A larger human population also means that more LAND is needed to build houses and grow food (CROPS and LIVESTOCK). This space is often made by DEFORESTATION of the land, which reduces the CO2 absorbed - since trees are reduced, photosynthesis is reduced, so less CO2 is absorbed. |
| Name one way CO2 is released into the atmosphere that is not caused by humans or other living organisms | Volcanoes |
| Describe the evolution of the earth's atmosphere in the first billion years | 1. The Earth's surface was originally MOLTEN. 2. Eventually the surface cooled and a thin crust formed, but VOLCANOES kept erupting, releasing CO2, methane, steam, and ammonia. The atmosphere was mostly CO2 and WATER VAPOR at this time, with very little oxygen. 3. Then, the water vapor CONDENSED to form the OCEANS |
| Describe the evolution of the earth's atmosphere in the 2nd and 3rd billion years. | 1. Much of the CO2 in the atmosphere DISSOLVED into the OCEANS. 2. NITROGEN (N2) gas entered the atmosphere in two ways - formed by ammonia reacting with oxygen, and released by DENITRIFYING BACTERIA. 3. Then, GREEN PLANTS and ALGAE EVOLVED. As they PHOTOSYNTHESIZED, they removed CO2 and produced O2. 4. The amount of O2 in the air gradually increased and CO2 decreased, locked up in plant bodies, fossil fuels, and sedimentary rocks. |
| Describe the evolution of the earth's atmosphere in the last billion years. | 1. INCREASED O2 in the atmosphere killed off early organisms that couldn't tolerate it, and new, more complex, oxygen-breathing organisms evolved. 2. The oxygen also created the OZONE layer (O3) which blocks harmful radiation from the sun. 3. Today CO2 is only approximately 0.35% of the Earth's atmosphere. |
| What is THERMAL DECOMPOSITION? Give an example | THERMAL DECOMPOSITION is when a substance breaks down into at least two new ones when heated. It requires breaking strong COVALENT BONDS so a lot of energy is required. Often a CATALYST is used to speed up the reaction. Example - CRACKING |
| How is cracking done? Why does it require a lot of energy? | VAPORIZED HYDROCARBONS are passed over a powdered CATALYST at high temperatures and moderately high pressure. It requires a lot of energy because strong covalent bonds must be broken. |
| Why is carbon monoxide dangerous? | CARBON MONOXIDE is dangerous because it is colorless and odorless, so hard to detect. It binds with the hemoglobin in your blood and reduces its oxygen-carrying capacity. If you breathe it too much, you can faint or even die. |
| What is the difference between complete combustion and incomplete combustion? What are their products? Under which conditions does each occur? | Complete combustion of hydrocarbons occurs where there is plenty of oxygen. It releases a lot of energy and the main chemical products are CO2 and water. Incomplete combustion occurs when there is a limited supply of oxygen. In addition to energy, CO2, and water, incomplete combustion also produces CO (a toxic gas) and carbon in the form of soot, a dirty substance which can cause respiratory disease. |
| Name two other compounds released when fossil fuels are burned, and how they contribute to pollution. | SO2 (sulfur dioxide) and nitrogen oxides, both of which form acid rain, which kills trees and dissolves limestone. Nitrogen oxides can also cause photochemical SMOG which causes breathing difficulties, headaches, and tiredness. |
| Name the pros and cons of using hydrogen as fuel. | PROS: 1. Hydrogen burns very cleanly - the only chemical product of combusting hydrogen is water - no pollutants 2. Hydrogen is obtained from the electrolysis of water, which is a renewable resource - it can even be formed from the water produced by the fuel cell itself CONS 1. You need a special, expensive engine to combust hydrogen. 2. The manufacture of hydrogen requires energy, which often comes from burning fossil fuels 3. Hydrogen is hard to store 4. Hydrogen is not widely available |
| Why are shorter hydrocarbons easier to ignite than longer ones? | Shorter hydrocarbons are easier to ignite because they have lower boiling points, so tend to be gases at room temperature. The gas molecules easily mix with oxygen in the air to produce a gas mixture which bursts into flames if it comes into contact with a spark. Longer hydrocarbons are usually liquids at room temperature, with higher boiling points. |
| The longer the hydrocarbon, the ______ the viscosity. Name a very viscous fraction of crude oil | higher bitumen |
| Why do longer hydrocarbons have higher boiling points? Why are they more viscous than shorter chain hydrocarbons? | The INTERMOLECULAR FORCES of ATTRACTION break a lot more easily in small molecules than they do in bigger molecules. The forces between bigger molecules are much stronger than they are between smaller molecules. |
| What is a homologous series of compounds? Give an example | A homologous series is a family of molecules which have the same general formula and share similar chemical properties. They do not share the same physical properties, however. Alkanes are a homologous series in the form C n H 2n+2 |
| What is crude oil? What can it be used for? Name its fractions in order of increasing boiling point, and what they are used for. | CRUDE OIL is a fossil fuel (therefore nonrenewable) and the main source of our hydrocarbons. It is a complex mixture of lots of different hydrocarbons, mostly alkanes. 1.GASES - domestic heating and cooking 2. PETROL - fuel for cars 3. KEROSENE - fuel for aircraft 4. DIESEL OIL - fuel for some cars, trucks, trains 5. FUEL OIL - fuel for large ships and power stations 6. BITUMEN - surfacing for roads and roofs |
| What is natural gas? | Natural gas is a mixture of gases which forms underground, similar to crude oil. Its main component is methane. It is a nonrenewable resource. |
| Explain how crude oil is separated into fractions during fractional distillation. (5 marks) | Crude oil is heated until most of it turns into a gas (1). The gases enter a FRACTIONATING COLUMN and the liquid part / bitumen is drained off at the bottom (1). There's a TEMPERATURE GRADIENT in the column - hot at the bottom and cooler at the top (1). The longer hydrocarbons with high boiling points turn back into liquids and drain out lower down the column (1). Shorter hydrocarbons have lower boiling points, so rise higher up the column before they are condensed and drained off (1). |
| Explain how cars produce nitrogen oxides |
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