Chemistry

Electrolysis of solutions Ions are free to move in solution of the compounds. But sometimes we cannot get a metal because of its highly reactivity. This is because of water in the solution. Water molecule effects the electrolysis. When solutions are electrolyzed, hydrogen being a non – metal, is deposited on cathode. Because hydrogen is an exceptional case, donate 1 electron per hydrogen atom. H +          +      e -        à          H But hydrogen is a diatomic molecule So 2H +          +      2e -        à          H 2 Why is hydrogen given off? We know water molecules are present in solution. Take any solution from table 7.6, For example calcium nitrate, water molecule will also split into H + &   OH -        H 2 O                      H +       +        OH - So hydrogen is deposited at cathode along with calcium. Calcium is more reactive & stable than hydrogen, replaces it & kicks o

Extraction of Aluminum: Aluminum is highly reactive metal and it will be electrolyzed. Aluminum has many useful properties like: Low density Conduct heat & electricity Resistance to corrosion (as forms Aluminum oxide layer on extraction that protects it from corrosion) Getting the Ore: Aluminum is extracted mainly from its ore called Bauxite (Al 2 O 3 ) Electrolysis of Aluminum oxide Aluminum is melted & then electrolyzed. To save energy, Aluminum oxide is dissolved in a chemical Cryolite (Na 3 AlF 4 ) At the cathode:     Al 3+          +      3e -      à     Al At the anode:     2O 2-          -      4e -      à     O 2 This oxygen reacts with hot carbon anodes making carbon dioxide gas & burns away. This needs to be replaced.                      Class Assessment 1.   Aluminum is highly reactive metal. T 2.   Oxygen reacts with hot carbon anodes      making carbon dioxide gas & burns away. T 3.   Aluminum is extracted mainly from its

Unit 4  Lesson 2: Weather and Climate Lesson target: Students will recognize different elements that affect the change in climate Lesson objectives: 1) Differentiate between weather and climate 2) Define the elements which affect the change in climate   What does the word weather refer to? What about climate? What are some machines that might help in detecting weather changes?   The weather and the climate are both part of Earth’s atmosphere. They both change according to the changing conditions of the atmosphere. Yet, they have some differences. The difference between weather and climate.   Weather Changes within a short time (24 hours or less) Changes from day to day Climate Constant over a long period (it does not change from one day to another) Characterizes the general atmosphere of a place over a long period     The 4 elements that affect the climate are and the effect of each is: Temperature   Temperature (heat) is one of the most important

  G9.CHY MCQ Postmortem  

  Chemistry Basic Definitions 1. Solid changing into a liquid Melting 2. Liquid changing into a solid Freezing 3. Gas/vapour changing into a liquid Condensation 4. Liquid changing into a gas/vapour Evaporation 5. Temperature at which a solid turns into a liquid Melting Point 6. Temperature at which a liquid changes into a solid Freezing Point 7. Temperature at which a liquid changes into a vapour at atmospheric pressure Boiling Point 8.   The random movement of particles from an area of a high concentration to an area of low concentration Diffusion 1.   A single substance Pure substance 2.   The unit particle of an element Atom 3.   The number of protons in one atom of the element Proton number 4.   A volatile compound easily changes into a vapour. It has a low boiling point Volatile 5.   A mixture of a solute, usually a solid, dissolved in the solvent, a liquid Solution 6.   A substance that reacts with colourless spots on a chromotogram and makes them visible as coloured spots

Electrolysis of Molten Compounds: As shown in the diagram of experiment 7.5 Lead bromide is melted & on passing electricity, lead as a metal will be collected on cathode while bromine being a non-metal will be collected on anode.        PbBr 2           à         Pb          +         Br 2 At the cathode: Lead, Pb 2+ , gains 2 electrons forming lead atoms     Pb 2+          +        2e -         à          Pb At the anode: 2 bromide, Br - , each loses 1 electron forming bromine molecule Br 2 2Br -          -      2e -           à           Br 2                    Class Assessment 1.   Lead as a metal will be collected on cathode. T 2.   Bromine being a non-metal will be collected on anode. T 3.   Lead, Pb 2+ , gains -------- electrons forming lead atoms. a) 2 b) 4 c) 6    

  Sulfur  in its yellow, powdery form is an octahedral ring. The meaning of  PLASTIC SULFUR  is sulfur in an amorphous form obtained usually by pouring boiling sulfur into cold water LIQUID  sulfur  is well known to become highly viscous when heated above 160° C

Unit 4  Lesson 1: Earth’s Atmosphere Lesson target: Students will recognize the different components of air and the different layers of Earth’s atmosphere. Lesson objectives: 1) Identify the components of air 2) Identify the different layers of earth’s atmosphere   Importance of air for all living things without any exceptions. What might the air we breathe consist of? The elements of air. Atmosphere is a mixture of gases. The different layers of Earth’s atmosphere. Which appears to be the widest? (The ozone layer). Do you think that each layer has an effect on our Earth’s temperature? (Answer: It should have an effect on the temperature) ultraviolet radiation   a. Air is mostly nitrogen. (true) b. The ozone layer is the thickest layer in the   atmosphere. (false)   Exercise 1:  Name the 3 gases that form the air . 1. 78% Nitrogen 2. 21% Oxygen 3. 1% Other gases Exercise 2:  List the layers of Earth’s atmosphere. 1. Troposphere 2. Str

What are Simple molecular structures? Simple molecular structures: Methane, CH 4 as an example It has a very low boiling point -161 0 C Substances, with low melting points and boiling points have simple molecular structures. Simple molecular substances have strong covalent bonds joining their atoms within each molecule. However, they only have weak forces between individual molecules. We say that they have weak inter-molecular forces.                                           Class Assessment 1.    Substances, with low melting points and boiling points have simple molecular structures. T 2.    Simple molecular substances have strong covalent bonds joining their atoms within each molecule. T 3.    CH 4 has a very ----------- boiling point                           a) high b) low c) both 4. The mutual sharing of electrons, is called a covalent bond. T