chemistry
Thursday, September 22, 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 zinc hydroxide Zn(OH)2 . The base is Ammonium Nitrate NH4NO3.
(ii) Describe the observations for the reaction.
A white precipitate of zinc hydroxide Zn(OH)2 is formed.
(iii) Write a chemical equation for the reaction.
Zn(NO)3(aq) + 2NH4OH(aq) --> Zn(OH)2(s) + 2NH4NO3(aq)
(iv) Write an ionic equation for the reaction.
Q2 Ammonium sulfate is heated with sodium hydroxide.
(i)Write a chemical equation for the reaction.
(NH4)2SO4 (aq) + 2NaOH (aq) -> Na2SO4 (s) + 2NH3 (g) + 2H2O (l)
(ii) Describe a test for the gas.
Ammonia gas will turn red damp litmus paper to blue in colour.
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.
Ammonia gas
(ii) This is a confirmatory test for an anion. Name this anion.
The anion is Nitrate (NO3-)
(iii) Give a possible cation which gives the green solution.
The possible cation is Iron(III) Fe2+.
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.
Potassium sulfate is a group (I) salt and is soluble.
(ii) Write an ionic equation for the reaction.
Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.
(i)Write an ionic equation for the reaction
(ii)Why excess zinc carbonate is used?
It is used to ensure that all the hydrochloric acid is completely reacted with the zinc carbonate.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
Step 1: Add excess zinc carbonate solid to beaker of dilute hydrochloric acid until there is excess white zinc carbonate solid left behind.
Step 2: filter to remove the excess unreacted zinc carbonate solid.
Step 3: evaporate the zinc chloride solution to remove water and make a saturated salt solution.
Step 4: the hot saturated solution form zinc chloride salt when it is cooled.
Sunday, July 3, 2011
On Cindy(02)-great effort! the points are very detail and image are very clear and easy to understand too! I think it is very good to highlight the keywords, i should also do so the next time round! For question 2 and 3 she even include the point that "losing 6 electron is difficult...& gaining 7 elecrons is difficult... respectively.", which very few people do so. I think it is good that she include this point which make us understand even clearer. The blogskin is very nice! you link up the people, i should do so soon!
On janis(09)-She put in effort doing it too! information detail as well, pictures are very clear and useful! It is good that she search for images, however she should acknowledge the source next time round. For question 2, i think she never include the blacket and put(+) charge. For question 3,she should also include the atomic structure of sulfur atom and sulfide ion, it should be sulfide ion instead of sulfur ion. I think maybe next time font can be more clearer and bigger so it will be easier to read! To conclude, she did well too!
On Jieen(13)-great effort as well! nice answer! it is easy to understand and pictures are very clear too! i have difficulties finding her mistake. i think the words can be bigger next time so it will be easier to read! nice and peaceful song that make me feel like continue reading your blog! is good that you link up the people too!
The centre of an atom is known as a nucleus. Protons and neutrons are the subatomic particles found inside the nucleus.
Each shell can contain only a fixed number of electrons. The first shell can only hold 2 electrons while the second and third shell can only hold 8 electrons.
Chloride-35 have 17 protons and (35−17=) 18 neutrons. While chloride-37 have 17 protons and (37−17=) 20 neutrons. They have the same number of protons (17p) but different number of neutrons (18 and 20 respectively). Therefore they are isotopes.
5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
Sodium (2.8.1) is a metal because it loss 1 electron to complete the valance shells to make it stable and it is in group (I). While sulfur (2.8.6) is a non-metal because it will gain 2 electrons to complete the whole shell to make it stable and it is in group (VI).
In the periodic table, Metals are generally in the groups(I),(II),(III) while non-metals are generally in the groups(IV),(V),(VI),(VII),(VIII).