1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. (i) Name the salt and the base. (ii) Describe the observations for the reaction. (iii) Write a chemical equation for the reaction (include state symbols). (iv) Write an ionic equation for the reaction.
Answer:
1. (i) The salt formed is ammonium nitrate and the base is zinc hydroxide.
(ii) When colourless zinc nitrate solution reacts with colourless ammonium hydroxide, white precipitate of zinc hydroxide is produced and is soluble, giving a colourless solution. A colourless solution of ammonium nitrate solution is also formed.
(iii) Zn(NO3)2 (aq) + 2NH4OH (aq) --> 2NH4NO3 (aq) + Zn(OH)2 (s)
(iv) Zn 2+(aq) + 2OH - (aq) --> Zn(OH)2 (s)
2. Ammonium sulfate is heated with sodium hydroxide. (i) Write a chemical equation (include state symbols) for the reaction. (ii) Describe a test for the gas.
Answer:
2. (i) (NH4)2 SO4 (aq) + 2NaOH (aq) --> Na2 SO4 (aq) + 2H2O (l) + 2NH3 (g)
(ii) Turns damp red litmus paper blue.
3. 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. (ii) This is a confirmatory test for an anion. Name this anion. (iii) Give a possible cation which gives the green solution.
Answer:
3. (i) The gas evolved is ammonia.
(ii) It is nitrate ions.
(iii) It is iron(II) ions.
4. 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. (ii) Write an ionic equation for the reaction.
Answer:
4. (i) Titration is used to prepare the salt reacted from Sulfuric acid and Potassium hydroxide because the salt is a Group (I) salt and it is soluble. The acid, alkali and salt are also colourless solutions. Hence, titration is used to prepare the salt.
(ii) 2H+ (aq) + 2OH- (aq) --> 2H2O (l)
5. 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? (iii) Briefly explain how the zinc chloride crystals can be obtained.
Answer:
5. (i) ZnCO3 (s) + 2H+ (aq) --> Zn 2+ (aq) + H2O (l) + CO2 (g)
(ii) Excess zinc carbonate is used to make sure that the zinc carbonate has react completely with the hydrochloric acid before filtering out the excess unreacted zinc carbonate solid from the zinc chloride salt solution.
(iii) Excess zinc carbonate solid is added to the hydrochloric acid until there is excess zinc carbonate solid left behind. Filter the excess unreacted zinc carbonate solid and evaporate the zinc chloride solution to remove the water and make a saturated salt solution. The hot saturated solution from zinc chloride crystals when it is cooled.
Thursday, September 22, 2011
Friday, July 8, 2011
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Ysabelle(01): I think her way of posting is interesting as it is filled with different colour of fonts which does not make readers feel bored when reading her anwsers. She puts in effort to make her answers detailed and well-explained. The blog is also simple and nice. Overall, good job done. :)
Chelsea(08): Her way of posting the answers is neat and clear. It is easier to read her answers rather than reading a whole chunk of paragraph with words squeezing together. The drawings of the atoms and ions are clear too and answers are well-explained. Good effort too. :)
Michelle(30): The size of the words are big enough to see clearly and easily. She explained well and even provided a table to show the two isotopes, chlorine-35 and chlorine-37. The blog is unique and nice too. Good effort put in. :)
Chelsea(08): Her way of posting the answers is neat and clear. It is easier to read her answers rather than reading a whole chunk of paragraph with words squeezing together. The drawings of the atoms and ions are clear too and answers are well-explained. Good effort too. :)
Michelle(30): The size of the words are big enough to see clearly and easily. She explained well and even provided a table to show the two isotopes, chlorine-35 and chlorine-37. The blog is unique and nice too. Good effort put in. :)
1. What does an atom look like? What are the sub-atomic particles inside it.....(talk about electrons, neutrons, protons, electron shells, nucleus....)
Ans: An atom is the smallest foundation unit or particle of an element. An atom is made up of three sub-atomic particles such as protons, neutrons and electrons. The nucleus of the atom is formed by the protons and neutrons and they are known as nucleons. Electrons move rapidly around the nucleus. All atoms are electrically neutral. It contains an equal number if positively charged protons and negatively charged electrons. The proton has a positive charge and it has a relative mass of 1 while the neutron has a no charge and it has a relative mass of 1. The electron has a negative charge and its mass is much lighter than that of a proton and neutron. The relative mass of an electron is 1/1840.
2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
Ans:
A sodium atom has an electronic configuration of (2,8,1). In order to achieve stability, the atom need to lose one electron to achieve a full shell (2,8). Hence, the formula of sodium ion is Na+.
3. Draw the atomic structure of a sulfur atom and a sulfur ion....explain why you draw it this way.
Sulfur ion:
A sulfur atom has an electronic configuration of (2,8,6). In order to achieve stability, the atom need to gain two electrons to achieve a full shell (2,8,8). Hence, the formula of sulfur ion is S 2-.
4. Chlorine-35 atom and Chlorine-37 atom are called isotopes....Use these two examples to explain what is 'isotopes'.
Ans: Isotopes are different atoms of the same element which have the same number of protons but different number of neutrons. Chlorine-35 and chlorine-37 have the same number of protons, which is 17 protons. Chlorine-35 has (35-17)=18 neutrons while chlorine-37 has (37-17)=20 neutrons. Since chlorine-35 and chlorine-37 belong to the same element, have different number of neutrons and same number of protons, they are called isotopes.
5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
Ans: Sodium is a metal because it will lose 1 electron to complete the valance shell while Sulfur is a non-metal because it will gain 2 electrons to complete the valance shell. Metals lose electron(s) and become positively charged ion which is also known as a cation. Non-metals gain electron(s) and become negatively charged ion which is also known as an anion.
Ans: An atom is the smallest foundation unit or particle of an element. An atom is made up of three sub-atomic particles such as protons, neutrons and electrons. The nucleus of the atom is formed by the protons and neutrons and they are known as nucleons. Electrons move rapidly around the nucleus. All atoms are electrically neutral. It contains an equal number if positively charged protons and negatively charged electrons. The proton has a positive charge and it has a relative mass of 1 while the neutron has a no charge and it has a relative mass of 1. The electron has a negative charge and its mass is much lighter than that of a proton and neutron. The relative mass of an electron is 1/1840.
2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
Ans:
A sodium atom has an electronic configuration of (2,8,1). In order to achieve stability, the atom need to lose one electron to achieve a full shell (2,8). Hence, the formula of sodium ion is Na+.
3. Draw the atomic structure of a sulfur atom and a sulfur ion....explain why you draw it this way.
Sulfur ion:
A sulfur atom has an electronic configuration of (2,8,6). In order to achieve stability, the atom need to gain two electrons to achieve a full shell (2,8,8). Hence, the formula of sulfur ion is S 2-.
4. Chlorine-35 atom and Chlorine-37 atom are called isotopes....Use these two examples to explain what is 'isotopes'.
Ans: Isotopes are different atoms of the same element which have the same number of protons but different number of neutrons. Chlorine-35 and chlorine-37 have the same number of protons, which is 17 protons. Chlorine-35 has (35-17)=18 neutrons while chlorine-37 has (37-17)=20 neutrons. Since chlorine-35 and chlorine-37 belong to the same element, have different number of neutrons and same number of protons, they are called isotopes.
5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
Ans: Sodium is a metal because it will lose 1 electron to complete the valance shell while Sulfur is a non-metal because it will gain 2 electrons to complete the valance shell. Metals lose electron(s) and become positively charged ion which is also known as a cation. Non-metals gain electron(s) and become negatively charged ion which is also known as an anion.
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