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Sunday, September 18, 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 Ammonium Nitrate and the base is Zinc Hydroxide.

(ii) Describe the observations for the reaction.

Before they were added together, both zinc nitrate and ammonia hydroxide are colorless solutions. When they are added together, the ammonium nitrate formed is a colorless solution and there are white precipitate formed which is the insoluble precipitate, zinc hydroxide. White precipitate starts to appear in the mixture when added together.

(iii) Write a chemical equation for the reaction (include state symbols).

ZnNO3 (aq) + 2NH4OH (aq) à Zn(OH)2 (s) + (NH4)2NO3 (aq)

(iv) Write an ionic equation for the reaction.

Zn2+(aq) + 2OH-(aq) à 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) à Na2SO4 (aq)+ 2H2O (l) + 2NH3 (g)


(ii) Describe a test for the gas.

Hold a piece of damp red litmus paper over the mouth of the test tube. The ammonia gas will turn the damp red litmus paper blue indicating its presence. Ammonia hydroxide is formed on the damp red litmus paper, as it has became an alkali, it turns the 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.

The gas is ammonia.

(ii) This is a confirmatory test for an anion. Name this anion.

It is nitrates.

(iii) Give a possible cation which gives the green solution.

Iron(II) ions



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.

This is because the salt that we want to prepare, potassium sulfate, is a group (I) salt and it is soluble. All the solutions used are also colorless solutions.Hence we need to use titration and indicator to determine the end point of the neutralization between the acid and alkali before preparing for the salt.

(ii) Write an ionic equation for the reaction.

H2SO4 (aq) + 2KOH (aq) à K2SO4 (aq) + 2H2O (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 (aq) + 2HCl (aq) à ZnCl2 (aq) + H2O (l) + CO2 (g)

(ii) Why excess zinc carbonate is used?

This is to ensure that zinc carbonate has fully and completely reacted with the acid before filtering out the excess unreacted solid from the salt solution.

(iii) Briefly explain how the zinc chloride crystals can be obtained.

Excess zinc carbonate will be added to the hydrochloric acid first until excess solid is left unreacted behind. Filtration is carried out to remove the excess unreacted solid. evaporation then takes place for the zinc chloride solution to remove water to make a saturated salt solution. this hot saturated solution is then left to be cooled to obtain the zinc chloride crystals.








Tuesday, July 5, 2011

Wendy Ng Sock Ling (28)
Your blog was very informative as it includes remarks after a given explanation. In addition, instead of saying "to make it stable" maybe you can say "to achieve stability" so that it is a more scientific term. You can also say that when an atom loses an electron during a chemical process, the number of protons remains the same and has more than the number of electrons after the bonding. this same concept goes for the gaining of electrons vice versa. Also, you can also add in exceptional cases for lemons and water in non-metal description.

Your blog was nice and simple. Simplicity is the most modern of all. Maybe you must include acknowledgements for copyright purposes. this is very important as we do not own the photos and pictures that we post. If you drew it its fine. Also, you can elaborate more on saying that cations and anions bond together to form a compound. You can also raise an example of Calcium Chloride where calcium is the positive charged metal ion and chlorine is the negatively charged non-metal ion. I like the way you say Chlorine istopes is of 75% abundance and 25% abundance, should learn from you. Moreover, you can also suggest that the number of shells have different maximum number of electron limit. like in the first shell, maximum is only 2 electron and so on.

I like your Blog skin very much, its is simple yet beautiful. You can add on saying that Metals are more stronger than Non-metals and are more withstand-able and not brittle. However, you can take note that plastic, ceramic are exceptionals. Also, you can add in saying that electrons orbit around the nucleus of the atom and that it is involved in chemical reactions to help the ion of the atom achieve stability. you can also add in saying that the different chlorine isotopes and for chlorine-37, there is 25% abundance in chlorine atoms and in chlorine-35, there is 75% abundance in chlorine atoms. Maybe you can also add in the definition of isotopes to give a clearer explanation as well. In conclusion, i like your blog and it also has pictures to refer in the questions.



Me and Valerie from Bukit Panjang Govt High School, we met during Youth Leaders Camp and stayed in the same apartment!


Me and HWEE LENG! my chemistry mate, biology mate and classmate!

Me and Joey! we met also from Youth Leaders camp! she is from CHIJ Toa Payoh. We were in the same apartment as well.

Youth Leaders Camp was i camp i attended in the June Holidays and had gained alot of leadership qualities. i also learned some of the things different schools are learning in their school. some even learnt Atomic bonding in Sec 1.
LONG LIVE SPARTANS!


Sunday, July 3, 2011






http://scienceaid.co.uk/chemistry/fundamental/images/atom.jpg
http://sixthsense.osfc.ac.uk/chemistry


Friday, July 1, 2011

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 the smallest part of matter that consist of subatomic particles. These sub-atomic particles consist of Protons, Neutrons and Electrons. The protons and neutrons are found in the nucleus of the atom. they make up the nucleus of the atom known as nucleons. They are the nucleon number or relative atomic mass found in the period
ic table.The Protons, on the other hand, are the proton(atomic) number found in the periodic table. Electrons are found in electron shells which move around in definite energy levels. They orbit around the nucleus of the atom. the outer-most shell are called the Valance shell, the electrons on it are the valance electrons, the valancy of an atom is the number of electrons on the valance shells. The Protons and Neutrons each have a relative mass of 1. An electron have a relative mass of 1/1840, which can be considered negligible. the first shell can hold up to 2 electrons, the second and following subsequent shells can hold up to a maximum number of 8 electrons. In the fourth shell, it can hold up to 18 electrons. The protons have a relative charge of +1, Neutrons 0, and Electrons -1. Electrons and Protons have the same number in a neutral atom, so they are electrically neutral.


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



An electrically neutral Sodium atom has one valance electron. hence, it will lose one electron from the outer-most shell to achieve stability.it then forms a positively charged ion. this is because there is one moer proton than electron as it has already lost one.


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


An electrically neutral Sulfur atom have 6 valance electrons, hence it will gain 2 more electrons to achieve stability and form a negatively charged ion. this is because there is two more electron gained in the valance shell compared to protons.


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

Chlorine-35 has a relative atomic mass number of 35, that is why it is named as chlorine-35. There is also a atomic(proton) number of 17, this explains why there are 18 neutrons, because the nucleon number is 35 consisting of protons and neutrons (35n&p-17P=18n). Chlorine-37 has a relative atomic mass of 37. there is an atomic(proton) number of 17, which then explains why it has 20 neutrons, because there is a nucleon number of 37 consisting of protons and neutrons (37p&n - 17p = 20n).Hence we can conclude that they have the same number of protons but different number of neutrons. chlorine-35 has 18 neutrons while chlorine-37 has 20 neutrons.by definition, isotopes are different atoms of the same element which have the same number of protons but different number of neutrons. hence, by the chlorine-35 and chlorine-37, we can conclude that isotopes are the different atoms of the same element, chlorine, except that they have different number of neutrons but same number of protons.


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

Sodium has a valance electron of 1, hence it will lose electron during a chemical process, becoming a positively charged ion. On the other hand, Sulfur has a valance electron of 6, hence it will gain electrons during a chemical process, becoming a negatively charged ion. Metals like sodium will become positively charged ions by losing electrons on the outer shell while non-metals like Sulfur will become negatively charged ions by gaining electrons on the outer shell. Metals have less than 5 electrons inthe valnce shell while non-metals have more than 4 electrons in the valance shells.Metals, for example, sodium, lie in the periodic table at group I where metals are grouped into groups I, II, III(except boron), with Germanium, Tin, Lead, Antimony, Bismuth and Polonium. Metals lying between the group II and II are transition metals. Non-metals are in groups VI(except Polonium), VII, 0, with Boron, Carbon, Silicon, Nitrogen, Phosphorus and Arsenic. Metals like sodium conduct electricity while non-metals do not conduct electricity except for special cases like water and lemon.



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Monday, June 27, 2011

please play the music below for a nicer environment for reading :D



:)





Aleen Tan (27)

XNPS
YHSS
Concert Band; Trumpet :)

Achievements:
1.EAGLE award 2008
2.Edusave scholarship 2009
3.Edusave scholarship 2010
4.Sports day 2010, 4X100m Silver lowersec girls relay
5.Sports day 2011, 1500m Silver uppersec girls

Upcoming Events:
1.17th July 2011 Botanical Gardens performance
2.20th July 2011 International Band showcase

Hobby:
1.Play my instrument
2.Side read pieces
3.Listening to songs
4.fishing
5.Doing my own study notes

Favourites:
1.White colour
2.Blue colour
3.Adidas

Hates:
1.insects

I am a talented person and i believe i am
I love Chemistry and hope to pass it with flying colours!



EMC
Kinetic Particle Theory
Chemical Formulars
States of Matter/ states symbol
Preparation of Salts
Colours
ABSO
Chemical Analysis
Mole
Collecting and Drying Gases
Methods of purification & seperating mixtures

Currently learning:
Metals






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