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 Zinc hydroxide, Zn(OH)₂. The base is Ammonium nitrate, NH₄NO₃.

(ii) Describe the observations for the reaction.
Ans: When Zinc hydroxide reacts with aqueous ammonia, a white precipitate, Zn(OH)₂, 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)  -> Na2SO4 (s) + 2H2O (l) + 2NH3 (g)

(ii) Describe a test for the gas.
Ans: Turns damn 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.
Ans: Ammonia, NH3

(ii) This is a confirmatory test for an anion. Name this anion.
Ans: Nitrate, NO3^-

(iii) Give a possible cation which gives the green solution.
Ans: Iron (II), 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.
Ans: This method, titration, is recommended because potassium sulfate is soluble and a Group (I) salt, and sulfuric acid and potassium hydroxide are colourless solutions, therefore titration method is needed with an indicator to determine the end-point of the neutralisation between sulfuric acid and potassium hydroxide before we prepare the salt.

(ii) Write an ionic equation for the reaction.
Ans: 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.
Ans: ZnCO3 (s) + 2H⁺ (aq) -> Zn²⁺ (aq) + H2O (l) + CO2 (g)
(ii) Why excess zinc carbonate is used?
Ans: 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.
Ans: After the hydrochloric acid is completely reacted with excess zinc carbonate until there is excess zinc carbonate solid left behind, filter to remove the excess unreacted zinc carbonate solid. Evaporate the zinc chloride solution to remove the water and make a saturated salt solution. The hot saturated solution form zinc chloride crystals when it is cooled.

Comments on friends! ;)

Cindy -  Very detailed and good information provided, simple and clear images. Good effort made in highlighting the keywords. Simple and nice blogskin. However, fonts can be bigger for people to read. overall, the blog is nicely done. Good effort. :p

XinHui - Nice pictures of yourself and your clique! Industrious blogskin, but dont know whether the person itself is industrious or not! ;p . Quite detailed information given, however, images can be clearer abit. Fonts are big enough for people to see clearer, well-done!

Janis - Information are fruitful, however, do not have the images of the atomic structure of sulfur atom and sulfide ion. Did not quote the website where she found her images. Nice pictures of her own and nice background. Overall is not bad.

Chemistry Assignment 1

1. What does an atom looks like?  What are the sub-atomic particles inside it.....(talk about electrons, neutrons, protons, electron shells, nucleus....)
Ans: An atom is made up of three different particles - protons, neutrons and electrons. Protons and neutrons are tightly packed together in the centre of an atom known as nucleus. Collectively,  protons which carry positive electric charge (+1) and neutrons which carry no electric charge are known as nucleons. Electrons which carry negative charge (-1) move rapidly around the nucleus on electron shells. Each electron shell must only contains 8 electrons, only the innermost shell contains 2 electrons.

2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
Ans:

The sodium atom was drawn according to the number of electrons it consists, the number of electrons also equals to the number of protons a sodium atom consists. However, a sodium ion has to lose one electron in order to complete its valence shell so as to make it stable, therefore, there will be one more proton than electron.

3. Draw the atomic structure of a sulfur atom and a sulfide ion....explain why you draw it this way.

Ans:

The sulfur atom was drawn according to the number of electrons it consists, the number of electrons also equals to the number of protons a sulfur atom consists. However, a sulfide ion has to gain two electrons in order to complete its valence shell so as to make it stable, therefore, there will be two less proton than electron.

4. Chlorine-35 atom and Chlorine-37 atom are called isotopes...Use these two examples to explain what is 'isotopes'

Ans: Chlorine-35 have 17 protons and 18 neutrons. Chlorine-37 have 17 protons and 20 neutrons.They have the same number of protons, however, they have different number of neutrons, 18 and 20 neutrons respectively. hence, they are isotopes.

5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??

Ans: Metals conduct heat and electricity, and sodium has these properties, thus, sodium is a metal. Non-metals do not conduct heat and electricity, and sulfur has these properties, thus, sulfur is a non-metal. Sodium is being classify in Group(I) as it loses one electron to become an ion whereas sulfur is being classify in Group(VI) because it gains two electron to become an ion.