The Chemical World (Summary Questions)

25. Write word equations for the overall chemical reactions of photosynthesis and respiration. Edit by yourself!!!

PHOTOSYNTHESIS AND RESPIRATION Photosynthesis Photosynthesis is the process in which plants, some bacteria and some protistans (the simplest eukaryotes - single or multicellular organisms) use energy provided by the sun, carbon dioxide and water to produce sugar (glucose). The plant cells then respire ("breathe") and convert these sugars to ATP (which is adenosine triphosphate) the 'fuel' used by all living things. Oxygen is released as a waste product from the splitting of water in the reaction (see the equations below). This is an essential component as it is this release of oxygen that created the concentration of oxygen in our breathable atmosphere we have today. A general balanced equation for photosynthesis is: 6 CO2(gas) + 12 H2O(liquid) + photons (sun energy) ----> C6H12O6(aqueous) + 6 O2(gas) + 6 H2O(liquid) carbon dioxide + water + light energy ---> glucose + oxygen + water This equation can also be presented in a more simplified form: 6 CO2(gas) + 6 H2O(liquid) + photons (sun energy) ---> C6H12O6(aqueous) + 6 O2(gas) carbon dioxide + water + light energy ---> glucose + oxygen The picture below shows a close-up of a leaf. Leaves are the primary site of photosynthesis in plants. You can see the cells in the leaf and the veins which transport the water into the leaf and the ATP back out to feed the rest of the plant. Figure 1: The Cells of a Leaf (Image source: http://en.wikipedia.org/wiki/Image:Leaf_1_web.jpg) Cellular Respiration This is the process that takes place inside a cell and involves the oxidising of food molecules, such as glucose, into carbon dioxide and water. Oxidation is the combination of a substance with oxygen and involved the LOSS of electrons from an element or compound. The most common or well known oxidation reaction is rust. In this case iron (Fe) loses electrons. The equation below explains this process: Fe(s) ---> Fe2+(aq) + 2e- This is an abbreviated equation just showing the iron's participation in the oxidation reaction. The 2e- in this equation is the two electrons that have been lost by the solid iron when it has reacted with oxygen. The energy released from cellular respiration is trapped in the form of ATP (adenosine triphosphate) for use by all of the functions of the cell which require energy. The process of cellular respiration happens in two phases: Glycolysis - this is the breakdown of glucose (sugar) into pyruvic acid (CH3COCO2H is an alpha-keto acid which plays an important role in biochemical processes) The complete oxidation of pyruvic acid into carbon dioxide and water Respiration can be described using the following word equation: glucose + oxygen---> carbon dioxide + water + energy C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O + energy A basic summary of this process is: Respiration: The release of energy from food Takes place in plant and animal cells Respiration requires: Glucose Oxygen Respiration Produces: Energy Carbon Dioxide Water The respiration of plants is fairly similar to how humans respire. Breathing in humans also happens in two phases called: Inspiration Expiration In inspiration oxygen is inhaled into the lungs and placed in microscopic air sacks called alveolus. It is in these sacks that respiration occurs. Basically there is an exchange of oxygen and carbon dioxide between the air and the blood. When we breathe out (or expire) the carbon dioxide is expelled from our bodies into the atmosphere.

26. What factors can increase the rate of rusting?

1. Oxygen: Like water, oxygen increases the rate of corrosion. Corrosion can take place in an oxygen-deficient environment, but the rate of the corrosion reaction (and destruction of the metal) is generally much slower. In immersed conditions, if an electrolyte is in contact with one area of metal containing more oxygen than the electrolyte in contact with another area of the metal, the higher oxygen-concentration area is cathodic relative to the remaining surface. An oxygen concentration cell then forms, which results in rapid corrosion. 2. Temperature: Corrosion reactions are electrochemical in nature and usually accelerate d with increasing temperature; therefore, corrosion proceeds faster in warmer environments than in cooler ones. 3. Chemical Salts: Chemical salts increase the rate of corrosion by increasing the efficiency (conductivity) of the electrolyte. The most common chemical salt is sodium chloride, a major element of seawater. Sodium chloride deposited on atmospherically exposed surfaces also acts as a hygroscopic material (i.e., it extracts moisture from the air), which then increases the corrosion in non-immersed areas. 4. Humidity: Humidity and time-of-wetness play a large role in promoting and accelerating corrosion rates. Time-of-wetness refers to the length of time an atmospherically exposed substrate has sufficient moisture to support the corrosion process. The wetter the environment, the more corrosion is likely to occur. 5. Pollutants: Acid rain (a chemical by-product from manufacturing and processing plants), and chlorides (in coastal areas) promote corrosion. Acid gases, such as carbon dioxide, can also dissolve in a film of moisture in contact with the metal.

8. Define a compound

A compound is a material made from two or more chemical elements that have bonded. The two main types of compound bonds are covalent bonds and ionic bounds.

21. What is a precipitate?

A precipitate is an insoluble solid that emerges from a liquid solution. The emergence of the insoluble solid from solution is called precipitation. Often the precipitate emerges as a suspension. Precipitates form when reactions produce salts with low solubility products.

2. Define an element

An element is a substance consisting of atoms which all have the same number of protons - i.e. the same atomic number. Elements are chemically the simplest substances and hence cannot be broken down using chemical methods.

13. Define a physical change.

Any change that occurs without altering the chemical composition of a substance is a physical change. Physical changes can include changing the color, shape, state of matter, or volume of a substance

14. Define a chemical change.

Chemical change is any change that results in the formation of new chemical substances. At the molecular level, chemical change involves making or breaking of bonds between atoms. These changes are chemical: iron rusting (iron oxide forms)

12. Describe the use and identify the date of discovery of the following elements and alloys: gold, copper, iron, steel, bronze, tungsten, oxygen, iodine, lead and helium.

Gold (chemical symbol Au; atomic number 79) is a transition metal. It is yellow, shiny, soft and easily shaped. It is a good conductor of electricity and slow to corrode (be destroyed by chemical action). It is one of the least reactive elements and is found in its elemental state in rocks and sediments. It also occurs naturally as an alloy with silver, copper and palladium. For millennia, gold's useful and attractive properties (as well as its rarity) have led to its being highly valued as a material for jewellery, art and coins. Today, it is no longer used for coinage, although gold bullion (bars and ingots) is often kept as an investment. A common industrial use of gold is as an electrical connector. Copper (chemical symbol Cu; atomic number 29) is a transition metal. It is orangey in colour, soft and easily shaped. It is also a very good conductor of heat and electricity. Copper slowly turns greenish when exposed to oxygen in the air, but this layer of copper oxide protects the copper below from damage—unlike the rust formed on iron. Copper is widely used as a pure metal, most commonly in electrical wires and devices, construction and machinery. It is also often combined with other metals to form alloys, such as brass (with zinc), bronze (with tin) and cupronickel (with nickel, widely used for coins). Copper is mined from the Earth's crust and can also be extracted from minerals such as chalcopyrite. Iron (chemical symbol Fe; atomic number 26) is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Along with nickel and cobalt, iron is one of three naturally occurring metals that are magnetic at room temperature. Iron is the fourth most common element in the Earth's crust, but it reacts easily with oxygen, so it is most often found as iron oxide minerals. Iron is obtained from these ores by heating them until they melt, a process called smelting. Tungsten, also known as wolfram (chemical symbol W; atomic number 74), is a transition metal. These metals are usually dense, shiny and make good electrical conductors. Tungsten has the highest melting point of all elements, at 3422°C (6192°F). It also has the highest tensile strength of all metals, meaning that it can be stretched to an extreme degree without breaking. The very hard man-made compound, tungsten carbide (containing tungsten and carbon), is used for industrial cutting tools, ammunition and the rotating balls in the tips of ballpoint pens. Tungsten alloys are used for the filaments in light bulbs, electrodes and radiation shields. Metallic tungsten does not occur in nature, but the element can be extracted from minerals such as wolframite. Oxygen (chemical symbol O; atomic number 8) is a non-metallic element that is a gas at room temperature. Colourless, odourless and tasteless, oxygen is one of the commonest elements on Earth. It makes up one-fifth of the atmosphere and is found in most minerals in the Earth's crust. Bonded with hydrogen, it forms water. Oxygen bonds easily with many other elements to form compounds called oxides in a chemical reaction called oxidation. Sometimes this is a slow process, as when iron turns to rust (iron oxide) in damp air. But if oxygen reacts very quickly, combustion (burning) takes place, with flames, light and heat given off. Oxygen is essential for all living things (except for a few specialized types of microbes): they must take in oxygen to stay alive. This is because oxygen is a vital part of chemical changes inside each microscopic living cell, which break apart food substances to obtain the energy for life. Iodine (chemical symbol I; atomic number 53) is a halogen. The halogens are non-metallic elements that are highly reactive (they bond easily with other elements) because they are missing an electron in their atoms' outer shell (they have seven). Iodine is a blue-black solid that becomes a purple gas at room temperature (iodine comes from the Greek iodes, meaning "violet"). Iodine is rare on Earth, but iodine compounds, in the form of salts, are found in seawater. We need iodine for the correct working of the thyroid gland, so iodine compounds are often given as dietary supplements. Iodine is also used in the chemicals industry. Lead (chemical symbol Pb; atomic number 82) is a poor metal, also called a "post-transition metal". Like the other poor metals, lead is soft. It is shiny silver-blue but quickly reacts with oxygen in air to become dull grey. Elemental lead is rare on Earth: lead is most often obtained from lead compound minerals, such as galena (lead sulphide). Lead is the heaviest non-radioactive element. Its density makes it useful as a shield from X-rays and gamma rays—for example, in lead aprons worn to protect other parts of the body during X-rays. Lead is also used in bullets, car batteries, ballast and weights, construction and electronics. Lead is poisonous to humans and animals, and so is no longer used in pipes and paints. Helium (chemical symbol He; atomic number 2) is a noble gas. The noble gases are sometimes called "inert" or "unreactive" gases because they do not easily form compounds with other elements. Helium has the lowest boiling point (-268.9°C / -452°F) of all the elements, so it is a gas except for in exceptionally cold conditions—or extremely hot conditions, when it becomes plasma. Helium gas is colourless, tasteless and odourless. Helium is the second most abundant element in the Universe, after hydrogen, although it is rare in the Earth's atmosphere. Most helium for commercial use is extracted from natural gas. The best-known use of helium is in balloons and airships, but it is chiefly used in cryogenics (creating very low temperatures) and in various industrial processes.

6. Describe the uses of 3 metals and non-metals related to their specific properties

Melting and boiling points of metals and non-metals Element Metal or non-metal Melting point / °C Boiling point / °C aluminium metal 661 2,467 gold metal 1,064 2,807 iron metal 1,535 2,750 tungsten metal 3,407 5,927 iodine non-metal 114 185 phosphorus non-metal 44 280 sulfur non-metal 113 445

5. Describe the properties of metals and non-metals (Check up photo, as space too small)

Property Metals Non-metals Appearance. Shiny Dull State at room temper. Solid About half are solids, about half are gases, and one (bromine) is a liquid Density. High Low Strengt. Strong Weak Malleable or brittle. Malleable Brittle Conduction of heat. Good Poor Conduction of electricity. Good. Poor Magnetic material. iron, cobalt,nickel. None Sound when hit. Ring sound. Dullsound

10. Compare the properties of magnesium, oxygen and magnesium oxide.

See photo

24. In the reaction of magnesium Metal with hydrochloric acid, list all the observations that indicate that this is a chemical reaction.

See photo, have you done the experiment? Any records?

7. Draw and label simple diagrams to show the differences in the Thompson, Rutherford and Bohr models of an atom

See photos

4. Write symbols for: iron, copper, zinc, silver, tin, iodine, lead, platinum, gold and mercury.

Some Elements Name Symbol iron Fe copper Cu zinc Zn silver Ag tin Sn iodine I lead Pb platinum Pt gold Au mercury Hg

19. Explain the difference between an exothermic and endothermic reaction.

The difference between endothermic and exothermic reactions lies in the words themselves. "Thermic" refers to heat, just as in the word "thermometer." "Exo" means "outside" and "endo" means "inside." Thus, an endothermic reaction pulls heat into an object or area, while an exothermic reaction expels heat.

3. Name and write Symbols for the first 20 elements in the periodic table, identifying metals and non-metals

The first 20 Elements Name Symbol hydrogen H Non (Non-metal) helium He Non lithium Li Metal beryllium Be Metal boron B Metal Lois carbon C Non nitrogen N Non oxygen O Non fluorine F Non neon Ne Non sodium Na Metal magnesium Mg Metal aluminium Al Metal silicon Si Metal Lois phosphorus P Non sulfur S Non chlorine Cl Non argon Ar Non potassium K Metal calcium Ca Metal

18. List the characteristics that may be observed that indicate a chemical reaction has taken place.

There are several observations that we can identify some chemical reaction have taken place with in a system 1. Change in temperature -usually when a reaction takes place heat will be absorbed or released which result in a temperature change. -eg: put a piece of sodium in water. you will feel or observe that the temperature is increased 2. Change in colour -Some times we see a colour change in the media when a reaction takes place. -eg:put NaOH and KMnO_4 solution to a river water sample.you will see the color will change to brown 3. Emission of gas -sometime when a reaction took place a gas can be removed from the system -eg:put a piece of sodium in water. you will observe that a gas is emitting by the forming of bubbles 4. smell or odor -When some reactions take place the formation of some substances can give us a smell or odor. -eg: Add HCl to a FeS solution. You will taste the strong odor of H_2S Other than this there are several clues we can identify that a chemical reaction had taken place. Change in PH Dissolving of reactants Forming of precipitates

22. Explain why a precipitate is an indicator of a chemical reaction.

Whentwoliquidsarecombined,a solid called a precipitate can form. The shells of animals such as clams and mussels are precipitates. They are the result of a chemical change involving substances in seawater combining with substances from the creatures.

17. Compare the reversibility of the water physical and chemical changes. Watch the video and describe inyour own words

http://study.com/academy/lesson/comparing-reversible-irreversible-physical-chemical-changes.html