...Relaxing ...

Saturday, September 17, 2011Y

Acid, Bases, Salts

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.

(i) The salt is ammonia nitrate and the base is zinc hydroxide.
(ii) Aqueous ammonia and zinc nitrate are aqueous solutions mixed together. After the reaction, a solid precipitate (ammonia nitrate) and an aqueous solution (zinc hydroxide) is formed.
(iii) Zn(NO3)2 (aq)   +   2NH4OH (aq)   =   2NH4NO3 (aq)   +   Zn(OH)2 (s)
(iv) Zn2+ (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.

(i) (NH4)2SO4 (aq)   +   2NaOH (aq)   =   Na2SO4 (aq)   +   2H2O (l)   +   2NH3 (g)
(ii) The gas (ammonia gas) will turn 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.

(i) Ammonia gas.
(ii) Ammonium hydroxide.
(iii) Iron(II).

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.

(i) Potassium sulfate is a Group(I) soluble salt. Therefore, titration is the best way to prepare this salt.
(ii) OH- (aq)   +   H+ (aq)   =   H2O (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.

(i) (CO3)2- (aq)   +   2H+ (aq)   =   H2O (l)   +   CO2 (g)
(ii) It is because the salt (zinc chloride) is a transition metal souble salt. Therefore, the method to prepare this type of salt is excess solid + acid method. Zinc carbonate is a solid, so hence, it is used.
(iii) Add the excess zinc carbonate to a beaker of hydrochloric acid, until it cannot react anymore and leaves the zinc carbonate unreacted. Heat the acid while doing so. Next, when there is excess zinc carbonate, filter it to remove the unreacted solid. Evaporate the filtrate to form a saturated salt solution. The saturated solution will form zinc chloride crystals upon cooling.

ends at Saturday, September 17, 2011

Monday, July 04, 2011Y

#1 - Comments

These are the comments for some of my friend's post. (:

#12 - Lek Shu Yu

For Shu Yu, her answers are very clear and easy to understand. She has put in some photos to make them look interesting and easy to understand. She has used different colours in the blog for different questions, to make them look clearer. She has even took the effort to draw out the electronic structure of the atoms and ions and upload them on her blog. She has also credited the photos. She has done a great job and her blog is wonderful.

#16 - Ng Wan Ling

For Wan Ling, her blog is remarkable. It has all the point shown clearly in point form, which is easier to read and understand. She covered most of the things that had been taught these few days. She has also put the information in different colours, which highlights the important key words. Her pictures are also clear and easy to understand. Wan Ling has also acknowledged the source of the photos. She has done a great job for her blog. I have nothing else to say except that I should learn from her and use her blog as a reference when exams are near.

#26 - Tan Yi Jin

For Yi Jin, her blog has clear pictures that shows clearly the protons, neutrons and electrons inside the carbon atom. It also has a clear picture of the Sodium ion. The picture for how the sulfur atom changes into sulfur ions is very clear and easy to understand. Her blog consists of only pictures, but they are clear and easy to understand. She could do more improvements such as adding some words to allow better understanding of them.

ends at Monday, July 04, 2011

Sunday, July 03, 2011Y

#1 - Atomic Structure

1. What does an atom looks like? What are the sub-atomic particles inside it.....(talk about electrons, neutrons, protons, electron shells, nucleus....)?

An atom is made up of sub-atomic particles, which includes protons, neutrons and electrons. Inside each element or molecule, there are atoms. Protons and neutrons are found inside the nucleus of the atom, while the electrons are found on the electronic shell.

The number of protons and the number of electrons are the same, thus, all the atoms in the periodic table are neutral atoms. Neutrons have zero charges, protons have one positive charge while electrons have one negative charge. The maximum number of electrons in the first shell is 2. The maximum number of electrons in the second to the fourth shell is 8. For any atom with more than 20 electrons when drawing the atomic structure, only the valence shell is needed to be drawn.

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

The atomic structure of a sodium atom is drawn with 11 electrons, as, according to the periodic table, it has 11 protons. Since the atoms in the periodic table are neutral, the number of electrons is equal to the number of protons. Thus, it has 11 electrons. Since there can only be a maximum of 2 electrons in the first shell, the remaining electrons are in the second shell. However, there can only a maximum of 8 electrons in the second to fourth shell, thus, there is 1 valence electron in the last shell. As for the sodium ion, it has already given away it's 1 valence electron, thus, there is 1 less electron. It loses the electron to make it stable and achieve a full shell. Since it has given away 1 electron, there is more protons than electrons now. Thus, the sodium atom is now no longer neutral. As it has 1 proton more than the number of electrons, it has a positive charge of +1. Therefore, since the electron in the valence shell has been given away, there is only 2 shells left.

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

The atomic structure of a sulfur atom is drawn with 16 electrons, as, according to the periodic table, it has 16 protons. Since the atoms in the periodic table are neutral, the number of electrons is equal to the number of protons. Thus, it has 16 electrons. Since there can only be a maximum of 2 electrons in the first shell, the remaining electrons are in the second shell. However, there can only a maximum of 8 electrons in the second to fourth shell, thus, there is 6 valence electron in the last shell. As for the sodium ion, it has already gained 2 valence electron, thus, there is 2 more electron. It gains the electron to make it stable and achieve a full shell. Since it has gained 2 electron, there is more electrons than protons now. Thus, the sulfur atom is now no longer neutral. As it has 2 electron more than the number of protons, it has a negative charge of -2.

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

Chlorine-35 has 17 protons and 18 neutrons, while chlorine-37 has 17 protons and 20 neutrons. Therefore, I can conclude that chlorine-35 and chlorine-37 have the same number of protons (17 protons). However, chlorine-35 have 18 neutrons while chlorine-37 have 20 neutrons. Since chlorine-35 and chlorine-37 are isotopes and the only difference between chlorine-35 and chlorine-37 is the number of neutrons (18 neutrons and 20 neutrons respectively). Therefore, isotopes are different atoms of the same element which have the same number of protons, but a different number of neutrons.

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

Sodium has an electronic configuration (also known as electronic structure) of 2.8.1, while sulfur has an electronic configuration of 2.8.6. Atoms that lose electrons to complete the valence shell and to make it stable are metals. Atoms that gain electrons to complete the valence shell and to make it stable are non-metals. Sodium is a metal because it will lose 1 electron to complete the valence shell and to make it stable. Sulfur is a non-metal because it will gain 2 electrons to complete the valence shell and to make it stable.

(Acknowledgement: http://www.google.com.sg/imghp?hl=en&tab=wi)

ends at Sunday, July 03, 2011

Thursday, June 30, 2011Y

Phuket Trip

Phuket Trip: 24 December 2010 ~ 26 December 2010

That holiday, my family and I went to Phuket, Thailand. We went via Tiger Airlines. That wasn't my first time on the plane, but it was my longest flight yet. The Phuket trip was fun. We went for swims in the ocean near our hotels, went shopping and even went to sea! It was my first time on a speedboat. Unfortunately, since it was my first time, I was sea sick. I vomited. Due to that, I missed out the chance of going snorkeling underwater for corals. But, I did went to an island, where I saw monkeys! Overall, the trip was fun! I also went elephant-riding! It was my first elephant ride and it was fun, though my butt ached a lot after the 1-hour long ride! My parents went brought us up to worship the Buddha, up on a hill which is very high - a lot higher Bukit Timah, the highest hill in Singapore. It is called 佛山. Up there we could see almost everything! It was picturesque! However, it wasn't finished yet. My parents said that they would return back to Phuket again when the Buddha is completed. Here are some photos: