Chemistry 5/11/2020
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Chemistry 5/11/2020 - Marcador
Chemistry 5/11/2020 - Detalles
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Preguntas:
13 preguntas
| 🇬🇧 | 🇬🇧 |
| What are the 7 steps for titration? | 1)Use a pipette to transfer 25cm3 sodium hydroxide soloution to a conical flask. Dont blow liquid out, let it drain out to avoid an incorrect volume 2)Add 5 drops of indicator (methyl orange) to alkali in conical flask 3)Place flask on white tile 4)Fill a buirette with sulfuric acid. Then begin adding it into the flask and swirl. 5)Once colour begins changing, add drop by drop until neutral (yellow to red) 6)Read buirette volume at bottom of meniscus 7)Repeat titration untill you get 2 results withing 0.1 cm3, take a mean for final volume. |
| What are the half equations at the electrodes in fuel cells? | Negative= 2H2 --> 4H+ + 4e- Positive= O2 + 4H+ + 4E- --> 2H2O |
| What happens in the fuel cell? | Hydrogen gets oxidised. |
| Compare hydrogen fuel cells and rechargable batteries? | 1)Hydrogen fuel cells will work as long as hydrogen is provided, rechargable batteries run out and need to be recharged 2)Hydrogen fuel cells dont get less efficient, rechargable store less electricity the more cycles they go through 3)Hydrogen fuel cells provide drinking water. 4)Hydrogen is explosive and difficult to store, rechargable have no dangerous fuels required 5)Hydrogen fuel cells produce less pd so more are needed. |
| Describe the temperature change practical. | 1)Mesure out 30cm3 dilute hydrochloric acid transfer to pelestyrene cup and place it in beaker 2)Mesure temp of acid with themometer 3)Mesure 5cm3 sodium hydroxide and transfer to cup 4)Add plastic lid with hole and place thermometer through 5)use thermometer to gently stir soloution 6)When reading on thermometer stops changing mesure highest temp reached 7)Repeat with 10cm3 sodium hydroxide soloution and keep increasing by 5cm3 until 40cm3 8)Repeat this entire experiment one more time and find mean, plot it on graph |
| In ionic compounds what forces hold the atoms together. | Strong electrostatic forces of attraction. |
| What happens at the elecrodes during electrolysis of molten compounds? | Cathode(negative)= 1)metal attracted to negative electrode, gains electrons. Reduction reaction Anode(positive= 2)non-metal attracted to positive electrode loses electrons. Oxidation reaction |
| Describe electrolosis of aluminium oxide? | 1) Aluminium is mixed with cryolite to reduce boiling point 2)At the cathode, Al3+ +3e- --> Al 3)At the anode, 2O2- --> O2 + 42e- ,the oxygen atoms pair up forming O2 so equation is doubled 4)The anode must be raplaced regularly as it reacts with oxygen forming CO2 5)Melting the compound requires energy, loads of energy is needed for electric curent |
| Describe the properties of ionic compounds? | 1)Every positive ion is surrounded by negative ions - GIANT IONIC LATTICE 2)This means they have very strong electrostatic forces of attraction which act in all directions. 3)They have very high melting and boiling points as their bonds take a lot of energy to break |
| Compare small covalant molecules and giant covalant structures? | Small molecules-Fixed number of atoms joined by covalant bonds Giant covalant structure-Many atoms joined by covalant bonds e.g. silica dioxide High melting and boiling point as covalant bonds are very strong |
| Describe small covalant molecules? | 1)Usually gasses or liquids at room temperature 2)Have low melting and boiling points - strong covalant bonds between atoms but week intermolecular forces between each molecule as you increase size of molecule the intermolecular forces increase. |
| Describ the history of the atomic model. | 1)19th century-John Dalton-solid spheres 2)1897-JJ Thomson-experiments of charge and mass showed they had electrons-plum pudding 3)1909-Ernest Rutherford-expering alpha scattering-alpha particles(+charge) at gold foil and went through (showed they had empty space), sometimes alpha particles were deflected (showed centre had a positive charge) and sometimes bounced straigh back (mass was concentrated in the centre), whith electrons around the edge 4)Niels Bohr-electrons contained in shells orbitting nucleus 5)Scientists discovered positive charge in nucleus is due to protons 6)James Chadwick discovered nucleus also had neutrons - neutral particles |