Open Ended Questions. National 5. Chemistry

Transcription

1 Open Ended Questions National 5 Chemistry

2 Open Ended Questions Advice The most important message is to write as much correct information as you can that relates to the question! Make sure you have answered the question! Don t be put off by the model answers they were written by someone who has been teaching a long time! Just do your best and try to write at least three points of correct information! If the question is about elements: Try to mention correct information about atomic number and mass number group in the periodic table, number of outer electrons elements in the same group have the same chemical properties as you go down a group the physical properties change whether they are solid, liquid or gas If the question involves molecules, compounds: bonding and properties (revise here etalsrev4.shtml) include conduction solubility, melting and boiling points (from the data book) If the question involves electricity: the electrochemical series (from the data book) an explanation of oxidation (loss of electrons), reduction (gain of electrons) how electrons flow from metals higher in the electrochemical series to lower in the electrochemical series any advantages or disadvantages about the environment (pollution, recycling, lack of availability of metals from the Earth s crust) If the question involves homologous series: functional groups (carbon to carbon double bonds C=C, hydroxyl OH, carboxyl COOH) formula molecular, structural increasing the number of carbons increase the boiling point and viscosity, decrease the volatility any advantages or disadvantages about the environment (pollution, recycling, use as fuels etc)

3 If the question is about Fertilisers: N, P and K essential elements Solubility Pollution Haber / Ostwald Natural v Synthetic If the question is about metals: Reactivity series Whether it is found combined (reactive element) or uncombined (silver, gold) Energy needed to extract the metal (cost) Pollution CO 2 formed to produce that energy Availability of metals is low as they are finite Properties and uses If the question involves acids and bases (alkalis are soluble bases): Neutralisation reactions o Acid + alkali Salt + water o Acid + carbonate salt + water + carbon dioxide Write balanced equations Names of salts ph H + ions in acids, OH - ions in alkalis If the question is about fuels: Combustion products usually CO 2 and H 2 O Pollution from sulphur (burns to make SO 2 ), soot (unburned hydrocarbons) E h = cmδt experiment CO 2 impact on Global Warming (this is not pollution) Examples from Specimen paper book: Specimen Paper 1 Q 2 (d)

4 In 1825 bromine had been isolated from sea waterby Liebig who mistakenly thought it was a compound of iodine and chlorine. Using your knowledge of chemistry, comment on why he might have made the mistake. Points to note: Cl, Br and I are in the same group of the periodic table and will have similar chemical properties They are all diatomic (Cl 2, Br 2 and I 2 ) They all have 7 outer electrons and a valency of 1 The formula of Iodine chloride would be ICl The gfm of ICl is and the GFM of Br 2 is 160 these values are very close All molecules are covalent so would not conduct electricity when solid, molten of in solution Could draw dot-cross bonding diagrams here for ICl and Br 2 When Liebig tests the bromine he would find that it would have similar chemical and physical properties to iodine chloride because Iodine, Bromine and Chlorine are all diatomic (I 2, Br 2 and Cl 2 ) and because iodine and chlorine have a valency of 1, iodine chloride would have the formula ICl. They would have similar GFM s (can show this), they are covalent molecules, they would not conduct electricity when solid, molten or in solution and because they are in the same column of the periodic table, they would have similar reactivity. Specimen Paper 1 Q10 Points to note:

5 Fertilisers are soluble salts containing the essential nutrients N, P or K Two neutralisation reactions to form salts: o Acid + alkali salt + water o Acid + carbonate salt + water + carbon dioxide o Write and balance the equation if you are confident State that it requires neutralisation There are various options you could pick to make the salt but the salt must have N, P or K in it. If you pick the potassium carbonate, you can tell the end point of the reaction as there will be no more gas given off. Need to talk about evaporating the water off at the end could draw a diagram here. The student should pick the acid and base that will give N, P or K in the product of the reaction. For example, they could react: Adding potassium carbonate and phosphoric acid will provide a neutral solution of the fertiliser potassium phosphate containing the essential elements K and P. During the reaction, ph paper can be used to test whether the solution is neutral if the ph paper is dipped in and it turns green then the sample can be evaporated to remove the water. CO 2 gas will be formed and when it stops forming this is also an indication that the acid is fully neutralised. The equation for the reaction is : 3K 2 CO 3 + 2H 3 PO 4 2K 3 PO 4 + 3H 2 O + 3CO 2 Adding potassium hydroxide and nitric acid will provide a neutral solution of the fertiliser potassium nitrate containing the essential elements K and N. During the reaction, ph paper can be used to test whether the solution is neutral if the ph paper is dipped in and it turns green then the sample can be evaporated to remove the water. The equation for the reaction is : KOH + HNO 3 KNO 3 + H 2 O I think it would be enough to select a pair of reactants, state why and comment that they have to be neutralised, how you would do this, then describe the evaporation. Correct pairs of reactants: Acids Bases Salt formed Nitric ammonium hydroxide ammonium nitrate Phosphoric ammonium hydroxide ammonium phosphate Phosphoric potassium hydroxide potassium phosphate or potassium carbonate Nitric potassium hydroxide potassium nitrate or potassium carbonate

6 Open Ended Questions 1. A student carried out an experiment to investigate the effect of temperature on the rate of reaction. The student concluded the only way to increase the rate of reaction is to increase the temperature. Using your knowledge of chemistry comment on the accuracy of the student s statement. 2. Fred says that Lithium chloride is ionic as it is a compound made from a metal and a non-metal. Using your knowledge of chemistry, explain how Fred could test this hypothesis. 3. Metals Using your knowledge of chemistry, describe how 4 metals could be placed in an order of reactivity. 4. Using your knowledge of chemistry, describe how you could distinguish between a solution that contains ethanoic acid and one which was pure water. 5. A new element is discovered. Using your knowledge of chemistry explain how you would decide whether it belonged in group 1, group 7 or group Two bottles, containing white powder, have lost their labels. One bottle contains potassium chloride the other contains glucose. Using your knowledge of chemistry, describe how you would decide which bottle is which.

7 7. The periodic table of the elements in its current form is an astonishing achievement with major contributions from famous chemists and other important scientists. Using you knowledge of chemistry, comment on 2 different elements comparing the properties and position of your chosen elements? 8. Aspirin is widely used as a medicine. The structure of aspirin is shown below. Using your knowledge of chemistry, comment on physical and chemical properties you would expect aspirin to demonstrate. 9. The labels have dropped off three bottles containing organic compounds. The chemistry technician has asked a National 5 chemistry class to identify these compounds. Using your knowledge of chemistry, comment on how would the class could identify the alcohol, alkene and carboxylic acid.

8 10. The lithium-ion batteries that power our laptops, smartphones and electric vehicles could produce a greater amount of energy if their graphite electrodes were to be replaced by lithium metal ones. Using your knowledge of chemistry, provide possible reasons for this increase in energy output and comment on the suitability of lithium for electrodes. 11. We are told that radioactivity is dangerous but there are over 200 radioisotopes used on a regular basis in medicine. Use your knowledge of chemistry, to comment on why radioisotopes can be used in medicine. 12. Aluminium can be extracted from aluminium oxide and iron from iron(iii) oxide. Aluminium oxide is more abundant than iron(iii) oxide yet aluminium is more expensive than iron. Use your knowledge of chemistry, to comment on why this is the case. 13. Dentists use an amalgam (an alloy of mercury, silver and tin). A person with an amalgam filling accidently touched a steel fork against it while eating and immediately felt a sharp pain in the tooth. A dentist said that the pain was caused by an electric current produced in the tooth and would have been more painful if they had touched the tooth with aluminium foil. Use your knowledge of chemistry, to comment on why this is the case. 14. A farmer tested his soil and found that it was lacking in nitrogen. He was concerned that fertilisers would make the soil too acidic. Use your knowledge of chemistry, to comment on how the accuracy of the farmers concerns.

9 15. The essential elements for plant growth are nitrogen, phosphorus and potassium. A student was asked to prepare a dry sample of compound containing two of these elements. The student was given access to normal laboratory equipment and the following chemicals: Using your knowledge of chemistry, comment on how the student could prepare the dry sample. 16. Electrochemical cells produce a voltage. An example is shown below: Using your knowledge of chemistry, comment on how the cell could be changed to create a larger voltage.

10 17. Burning ethanol as a fuel is better for the environment than burning petrol. Using your knowledge of chemistry, comment on the accuracy of this statement. 18. A student used a machine called a mass spectrometer to find the molecular mass of chlorine molecules. After looking at his databook he was expecting to get a reading of 71 amu, but his results showed three different masses, 70amu, 72amu and 74amu. Using your knowledge of chemistry, explain the results and how the student s misconception occurred. 19. A gem smuggler has tried to conceal some uncut diamonds in bags of salt crystals. Using your knowledge of chemistry, explain how the diamonds could be separated from the salt crystals if they looked very similar and were identical in size and shape, giving details of how their bonding explains their differences in properties. 20. Cars in Scotland rust very quickly when their paintwork is damaged, whereas in the Australian outback they show very little signs of rust even when they are old and badly damaged. Using your knowledge of chemistry, explain how rusting occurs and why there are these differences. 21. Leicester is a city in England that boasts that it is Britain s first nuclear free zone. Using your knowledge of chemistry, explain why this is unlikely to be true.