Monday, September 19, 2011
Q1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. i) Name the salt and the base. Ans: The salt is Ammonium Nitrate (NH4NO3) and the base is Zinc Hydroxide . ii) Describe the observations for the reaction. Ans: White ppt. is formed. iii) Write a chemical equation for the reaction (include state symbols). Ans: Zn(NO3)2 (aq) + 2NH4OH (aq) --> Zn(OH)2 (s) + 2NH4NO3 (aq) iv) Write an ionic equation for the reaction. Ans: : Zn2+ (aq) + 2OH- (aq) -->Zn(OH)2 (s) Q2. Ammonium sulfate is heated with sodium hydroxide. i) Write a chemical equation (include state symbols) for the reaction. Ans: (NH4)2SO4 (aq) + 2NAOH (aq) --> 2NH3 (g) + 2H2O (l) + Na2SO4 (aq) ii) Describe a test for the gas. Ans: Use a moist red litmus paper and hang it over the ammonia gas , it will turn the red litmus paper to 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. Ans: Ammonia gas ii) This is a confirmatory test for an anion. Name this anion. Ans: Nitrate ion iii) Give a possible cation which gives the green solution. Ans: Iron (II) ion 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. Ans: As sulfuric acid, potassium hydroxide and potassium sulphate salt are soluble. Hence, this method is recommended for the preparation of the salt. ii)Write an ionic equation for the reaction. Ans: 2H+ (aq) + 2OH- (aq) --> H2O Q5. Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt. i) Write an ionic equation for the reaction. Ans: ZnCO3 (s) +2H+ (aq) --> H2O (l) +CO2 (g) + Zn2+ ii) Why excess zinc carbonate is used? Ans: It is to ensure that all the hydrochloric acid is completely reacted to form the chloride salt. iii)Briefly explain how the zinc chloride crystals can be obtained. Ans: Add excess zinc carbonate to hydrochloric acid then filter out all the excess zinc carbonate. Boil the solution in a evaporating dish, control the fire to prevent the salts from “popping” out. Finally, let the solution cool under the fan and zinc chloride crystal is formed.
Thursday, July 7, 2011
Comments:
05. Shin Yoong
She did very well. She explained everything in detail and even put pictures in. Her blog is nice decorated too, with ample imformation about herself. However her answer is too "wordy" maybe she can summarise her answer and highlight the main point to shorten her answer.
06. Ei Ei
Her blog is very nice looking. She did very well to decorate her blog. All answers is answered clearly and neatly. She even took the effort to highlight the main point, good job on that. She also took pictures of her work and post it on her blog, her effort deserved to be praise. Overall, she did very well.
38. Jun Wei
Interesting blog for chemistry, "FLYWITHYOUUU CHEMISTRY BLOG." All question is answered very well. Maybe you could change the blogskin, because it is a bit silly looking but overall is okay. And good job with the answers.
1. What does an atom looks like? What are the sub-atomic particles inside it.....(talk about electrons, neutrons, protons, electron shells, nucleus....)
Ans: Atoms are made up of 3 types of particles electrons , protons and neutrons . These particles have different properties. Electrons are tiny, very light particles that have a negative electrical charge (-). Protons are much larger and heavier than electrons and have the opposite charge, protons have a positive charge. Neutrons are large and heavy like protons, however neutrons have no electrical charge. Each atom is made up of a combination of these particles.
In all atoms, the number of protons and the number of electrons is always the same. The number of neutrons is very roughly the same as the number of protons, but sometimes it's rather more. The number of protons in an atom is called the atomic number and it tells you what type of atom you have. The total number of protons and neutrons added together is called the relative atomic mass.
2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
Ans:
Ans:
4. Chlorine-35 atom and Chlorine-37 atom are called isotopes...Use these two examples to explain what is 'isotopes'.
Ans: Isotopes means different atoms of the same element which have the same number of protons but different number of electrons. Chlorine-35 and Chlorine-37 have the same number of protons, but different number of neutrons. Chlorine-35 has 18 neutrons, while Chlorine-37 has 20 neutrons. Hence, Chlorine-35 atom and Chlorine-37 atoms are called isotopes.
5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
Ans: Sulfur is a non-metal because on the periodic table it is in group (VI). And the non-metals usually fall on group (IV),(V),(VI) and (VII). While sodium is a metal because on the periodic table it fall on group (I). And most of the metal fall in group (I),(II) etc.
Sulfer is non-metal is also beacause it is an element incapable of forming simple positive ions in solution. Where most of the metal is positively charge.
Metals are non-brittle and malleable. And sodium is non-brittle and malleable, in conclusion it is a metal. Whereas, sulfer is brittle and non-malleable, hence it is a non-metal.
Non-metal form oxides that are acidic, and sulfer reacts with oxide to form sulfer dioxide, which is acidic (acid rain), thus it is a non-metal. Whereas, metals form oxides that are basic, and sodium reacts with oxide to form sodium oxides which is a basic oxide.