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.
White precipitate is formed.
(iii) Write a chemical equation for the reaction (include state symbols).
Zn(NO3)2(aq) + 2NH4OH(aq) - Zn(OH)2(s) + 2NH4NO3(aq)
(iv) Write an ionic equation for the reaction. (aq)
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.
(NH4)2SO4(aq) + 2NaOH(aq) - Na2SO4(s) + 2H2O(l) + 2NH3(g)
(ii) Describe a test for the gas.
Turns 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.
Ammonia.
(ii) This is a confirmatory test for an anion. Name this anion.
Nitrate.
(iii) Give a possible cation which gives the green solution.
Iron(III).
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.
The salt is soluble and is in group I hence titration is used to carry out this experiment.
(ii) Write an ionic equation for the reaction.
OH- (aq) + H+ (aq) - H2O (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 (s) + 2H+ (aq) - Zn2+ (aq) + H2O (l) + CO2 (g)
(ii) Why excess zinc carbonate is used?
To ensure that the hydrochloric acid is completely neutralised.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
Zinc carbonate reacts with hydrochloric acid to form salt and excess zinc carbonate is lefted behind. Filter to remove excess zinc carbonate and heat the filtrate to remove the water and make a saturated solution. The hot saturated solution forms zinc chloride crystals when cool.
Tuesday 20 September 2011
Thursday 7 July 2011
Comments:
Cindy- Simple and nice! She highlighted important words which make the point stands out, thus her work can be easily read and understand. The pictures are clear too. Shall improve in my work and add more details in it;D Great work!
Xinhui- Even though the pictures she used to explain isotope are blur, her work is clear and simple to read. The words are big enough and easy to read. Shall increase the size of my words. Thanks for the comment;D keep it up!
Jieen- Nice blog! Her work is neat and understandable. Nice picture too!;p I think that the background is great but somehow makes the words difficult to read. Splendid!
Cindy- Simple and nice! She highlighted important words which make the point stands out, thus her work can be easily read and understand. The pictures are clear too. Shall improve in my work and add more details in it;D Great work!
Xinhui- Even though the pictures she used to explain isotope are blur, her work is clear and simple to read. The words are big enough and easy to read. Shall increase the size of my words. Thanks for the comment;D keep it up!
Jieen- Nice blog! Her work is neat and understandable. Nice picture too!;p I think that the background is great but somehow makes the words difficult to read. Splendid!
Tuesday 5 July 2011
Sunday 3 July 2011
Q1. What does an atom look like? What are the sub-atomic particles inside it?
The atom is a basic unit of matter that consists of a dense which has a nucleus in the centre, surrounded by a cloud of negatively charged electrons. the atomic nucleus contains a mix of positively charged protons ad electrically neutral neutrons.
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The proton is a subatomic particle with a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons.
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The atom is a basic unit of matter that consists of a dense which has a nucleus in the centre, surrounded by a cloud of negatively charged electrons. the atomic nucleus contains a mix of positively charged protons ad electrically neutral neutrons.
The three main sub-atomic particles are protons, electrons and neutrons.
The electron is a subatomic particle carrying a negative electric charge.
The proton is a subatomic particle with a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons.
The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.
Q2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
Sodium atom has 11 electrons whereas sodium ion has 10 electrons. The electronic configuration of the sodium atom is (2.8.1), thus has one electron at the outermost shell. The sodium ion is stable thus loses one electron. Its electronic configuration is (2.8).
Q3. Draw the atomic structure of a sulfur atom and a sulfide ion....explain why you draw it this way.
The sulfur atom has 16 electrons, with electronic configuration of (2.8.6). The sulfur ion gained 2 electrons on the outermost shell, thus with the electronic configuration of (2.8.8).
Q4. Chlorine-35 atom and Chlorine-37 atom are called isotopes...Use these two examples to explain what is 'isotopes'.
Isotopes are different atoms of the same element which have the same number of protons but different number of neutrons. In this example, they are the same element, which have the same number of protons and different number of neutrons, thus they are isotopes.
Q5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
Sodium is a metal as it loses 1 electron to complete the valence shell. Sulfur is a non-metal shell as it gain 2 electrons to complete the valence shell.
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