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Lost days, pictures fade.
Friday, 23 September 2011

mr tan i dont know why my blog is like that...


Prepare for EYE : 5 Questions on Ionic Equations, Colours of Cations & Anions, Acids, Bases, Alkalis, Salts

Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. 
(i) Name the salt and the base.
The name of the salt is ammonia nitrate and the base is zinc hydroxide.

(ii) Describe the observations for the reaction.
White precipitate of zinc hydroxide will be form with ammonium hydroxide. This precipitate will dissolve in excess aqueous ammonia to form complex zinc ion, which give you a colourless solution.

(iii) Write a chemical equation for the reaction (include state symbols).
ZnNO3 (aq) + NH4OH (aq) -> ZnOH (s )+ NH4NO3 (aq)

  (iv) Write an ionic equation for the reaction. 
  Zn 2+ (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 (aq) + 2H2O (l) +  2NH3 (g) (ii)  Describe a test for the gas.
Use a damp red litmus paper over the cloud of gas released. If it turns blue, it is ammonia gasQ3 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 gas

 (ii) This is a confirmatory test for an anion.  Name this anion. 
Nitrate ion  (NO3-).

 (iii) Give a possible cation which gives the green solution.
Iron(III) ion
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. 
 (ii) Write an ionic equation for the reaction.

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) + H+ (aq) > Zn+ (aq) + H2O(L) + CO2(g)

 (ii)  Why excess zinc carbonate is used?
To ensure that zinc carbonzte has fully reacted with hydrocloric acid.

 (iii) Briefly explain how the zinc chloride crystals can be obtained.Filter out the excess Zinc carbonate with the filter paper first from the solution so that zinc chloride solution will be left. to obtain the crystals, heat the solution gently to evaporate the water leaving us a saturated solution. When there is only little water left, take the saturated solution away from the fire, allowing it to cool down to form the zinc chloride crystals.
H+ (aq) + OH- (aq) > H2O (L)

 It is soluble Group I salt and hence by using titration method, we will be able to get the salt.


Friday, 8 July 2011

mr tan i did my blog already!!! I did put in effort to this even though its a last minute work, a very last minute. done it!!!


comments?!

Shu Yu (12)
your answers are great and clear. Other than that your answers are clear and straight to the point like the notes given by Mr Tan.

Wan Ling (16)
your answers together with your diagrams are really clear and nice to see. your answers are easy to understand. your diagrams are very neat and elaborate.

Xueting ( 19)
 your answers are not to short and not to long either. you are straight to your point. your diagrams are very neatly done.


:D




End of assignment!

From the periodic table, there is an invisible "staircase". Above the "staircase" are elements that are non-metal, and below it are elements that are metal. Sulfur is found above the "staircase", therefore it's a non-meatl. Sodium is found below the "staircase" , therefore it's a metal.
Besides referring to the periodic table to know that sodium is a metal and sulfur is a non-metal as the elements in Group (I), (II) and (III) of the periodic table is metal and Group (IV),(V),(VI) and (VI)  from the periodic table is non-metal. We could also refer to the number of electrons of the element.
Sodium (2.8.1) is a metal because it will lose 1 electron to complete the valence shell( to make it stable) and conduct electricity. Sulfur(2.8.6) is a non-metal because it will gain 2 electrons to complete the valence shell (to make it stable) and it does not conduct electricity.
Additionally,  Group (III) is also known as transition metal or coloured metals. Group (0)/group (III) is known as the noble gas as they can stabilise themselves.


question 4


Isotopes are atoms of the same element with the same number of protons but different number of neutrons. Isotopes of the same element  have the same number of electrons. thus, isotopes have the same proton number but different nucleon number. Most element that commonly occur are made up of isotopes. For an example. chlorine consists of two isotopes as what you can see from the picture above. A sample of chlorine gas consists of 75% chlorine-35 and 25% chlorine-37. The neutron number is added together then divided into 2.



question 3.
Sulfur atom needs 2 more electrons in the outermost shell to be stabilized. Thus, sulfide ion will be negatively charged. The number of electrons take by 2 for the third shell to be full but the proton number did not change.



Sulfur has 16 electrons. The first and second shell is full therefore the third (outermost) shell has 6 electrons. The maximum number of electron in the first shell is 2. The maximum number of electron in the second and third shell is 8 on each shell.


 question 2.



Sodium gives away an electron and becomes positively charged. Then number of electron has decrease by one but the number of proton did not change. After losing an electron at the outermost shell, sodium will be stabilize. It has eleven electrons but after giving away one electron, the total number of electron of a sodium ion is 10. The outermost shell have only 1 electron is because the first and second shell is full. The first shell can only have two electron maximum and 4 pairs of electron for the second and third shell.




Sodium has eleven electrons ( 2.8.1). The first and the second shell is full, therefore the third shell (outermost) have 1 electron. The first shell can only have two electrons and the maximum number of electrons in the second and third shell is eight.


question 1. What does an atom looks like?


All atom of the same element are alike.An atom has particles concentrated in the centre called nucleus. The nucleus consists of two types of particles- namely protons and neutrons. Collectively. protons and neutrons are known as nucleus. Surrounding the protons and neutrons are electrons. The protons have a positive charge while the neutrons do not have any charge as they are neutral. Both neutron and proton have a relative mass of 1. The electron carries one negative electric charge. The electron has a relative mass of 1/1800. The electrons move rapidly around the nucleus. The first two electrons nearest to the nucleus circulate in an elliptical path. These two electrons are constantly in motion in the fixed path. This path is known as the first electron shell and can hold at most two electrons. Any other electron will have to go on to the second shell. The second shell can hold at most 8 of electrons which are constantly circulating in pairs. Once the second shell is full with 8 electrons, the electrons move to the third shell which can also hold at most 8 shells. The number of protons in the nucleus is the atomic number. For an atom, the number of protons is equal to the number of electrons. The number of neutrons plus protons in the nucleus is known is the nucleon number or relative atomic mass.