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Sunday, September 18, 2011
Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. (i) Name the salt and the base. The salt is Ammonium Nitrate and the base is Zinc Hydroxide. (ii) Describe the observations for the reaction. Before they were added together, both zinc nitrate and ammonia hydroxide are colorless solutions. When they are added together, the ammonium nitrate formed is a colorless solution and there are white precipitate formed which is the insoluble precipitate, zinc hydroxide. White precipitate starts to appear in the mixture when added together. (iii) Write a chemical equation for the reaction (include state symbols). ZnNO3 (aq) + 2NH4OH (aq) à Zn(OH)2 (s) + (NH4)2NO3 (aq) (iv) Write an ionic equation for the reaction. Zn2+(aq) + 2OH-(aq) à Zn(OH)2 (s) Q2 Ammonium sulfate is heated with sodium hydroxide. (i) Write a chemical equation (include state symbols) for the reaction. (NH4)2SO4 (aq) + 2NaOH (aq) à Na2SO4 (aq)+ 2H2O (l) + 2NH3 (g) (ii) Describe a test for the gas. Hold a piece of damp red litmus paper over the mouth of the test tube. The ammonia gas will turn the damp red litmus paper blue indicating its presence. Ammonia hydroxide is formed on the damp red litmus paper, as it has became an alkali, it turns the damp red litmus paper blue. Q3 An unknown green solution is heated with a piece of aluminium foil and sodium hydroxide solution. (i) The gas produced turns damp red litmus paper blue. Name the gas evolved. The gas is ammonia. (ii) This is a confirmatory test for an anion. Name this anion. It is nitrates. (iii) Give a possible cation which gives the green solution. Iron(II) ions Q4 Sulfuric acid is titrated with potassium hydroxide in the preparation of potassium sulfate salt. (i) Explain why this method is recommended for the preparation for this salt. This is because the salt that we want to prepare, potassium sulfate, is a group (I) salt and it is soluble. All the solutions used are also colorless solutions.Hence we need to use titration and indicator to determine the end point of the neutralization between the acid and alkali before preparing for the salt. (ii) Write an ionic equation for the reaction. H2SO4 (aq) + 2KOH (aq) à K2SO4 (aq) + 2H2O (l) Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt. (i) Write an ionic equation for the reaction. ZnCO3 (aq) + 2HCl (aq) à ZnCl2 (aq) + H2O (l) + CO2 (g) (ii) Why excess zinc carbonate is used? This is to ensure that zinc carbonate has fully and completely reacted with the acid before filtering out the excess unreacted solid from the salt solution. (iii) Briefly explain how the zinc chloride crystals can be obtained. Excess zinc carbonate will be added to the hydrochloric acid first until excess solid is left unreacted behind. Filtration is carried out to remove the excess unreacted solid. evaporation then takes place for the zinc chloride solution to remove water to make a saturated salt solution. this hot saturated solution is then left to be cooled to obtain the zinc chloride crystals. |
 Aleen Tan (27) XNPS YHSS Concert Band; Trumpet :) Achievements: 1.EAGLE award 2008 2.Edusave scholarship 2009 3.Edusave scholarship 2010 4.Sports day 2010, 4X100m Silver lowersec girls relay 5.Sports day 2011, 1500m Silver uppersec girls Upcoming Events: 1.17th July 2011 Botanical Gardens performance 2.20th July 2011 International Band showcase Hobby: 1.Play my instrument 2.Side read pieces 3.Listening to songs 4.fishing 5.Doing my own study notes Favourites: 1.White colour 2.Blue colour 3.Adidas Hates: 1.insects I love Chemistry and hope to pass it with flying colours! 3E5 Clasmates 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Mr Tan June 2011 July 2011 September 2011 Designer : Chili. x o x o |