Questions on Ionic Equations, Colours of Cations & Anions, Acids, Bases, Alkalis, Salts

Ans:

Q1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.

(i) Name the salt and the base.

Salt: Ammonium Nitrate | Base: Zinc Hydroxide

(ii) Describe the observations for the reaction.

A white precipitate (Zinc Hydroxide) forms when Zinc Nitrate solution is added to aqueous Ammonia solution.

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

Zn(NO₃)₂ (aq) + 2NH₄OH (aq) --> 2NH₄NO₃ (aq) + Zn(OH)₂ (s)

(iv) Write an ionic equation for the reaction. 

Ionic:  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.

(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 gas.

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 evolved is Ammonia gas.

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

It is Nitrate.

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

Iron (II) 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.

This is because Potassium Sulfate is a colourless soluble salt and there is no suitable metal, metal oxide, metal hydroxide or metal carbonate that is insoluble in water to react with it. Therefore, titration is the only way to prepare it.

(ii) Write an ionic equation for the reaction.

H⁺₂ (aq) + 2OH^- (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 (s) + 2H⁺ (aq) --> Zn²⁺ (aq) + H₂O (l) + CO₂ (g)

(ii) Why excess zinc carbonate is used?

This is to ensure all the Zinc Carbonate has reacted with the Hydrochloric acid to form Zinc Chloride.

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

The Zinc Chloride that has been formed is dissolved in water. To obtain the solid crystals, gently heat the Zinc Chloride solution, that has been filtered so that there is no more excess Zinc Carbonate, to evaporate the water. When there is little to no water left, allow the solution to cool to obtain the Zinc Chloride crystals.

 Posted on 9/21/2011, 5:30 PM before deadline (Yes! We *car horn sound* did it :D). 

Well, heres my humptydumpty's drop.

Well, I ,now, hate being captured eternally so this is the only pictures i shall post. That shall be the end of this matter. (No offences)

Comments for Chemistry Assignment 1.

So, this is what Mr. Tan meant?

IN NO DIRECT ORDER!!!

On Ze Wei's blog:
Wow, so hard to comment, well since this is the first blog so I'm gonna post here but you should get a chat box for easier commenting. I like the idea of a different colour for the text it really differentiates it from the question. You could probably do better if you added some pictures of what an atom looks like and well it could be easier to show what an atom is if you used a table. Hope this helped (p.s. I can't comment on the others cause I need the reference) Sign: Xin Kang

On Helmi's blog:
Ciaossu, this is Xin Kang (obvious...ly). So, hmm comment...where to begin? where to begin? Ahh! Yes, your answers are information packed but you could organize them in a simpler way. For Q.5, you did something I haven't yet see and that is classify them! *evil and maniacal laugh* that is very unique. Oh! and like my error, you forgot to include brackets for your ion diagrams. Well overall, much better than mine T_T

On Su's blog:
Freaking word limit...so I'm gonna be very...brief(in a way) and you can delete the previous ones. For your Q.1, there is alot of text, you could summarize them ...oh maybe not, although you could...underline all the important points, but I would've never though of adding a picture *thumbs up* well theres nothing more to type.

I hope this is right, but oh well, doesn't matter!!!
sign: Xin Kang

Atomic Structure Assignment (Ans: Q1)

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 looks like a nucleus surrounded by (an) orbital electron shell/s. The sub-atomic particles within are its protons, neutrons and electrons. Protons and neutrons can be found in the nucleus while electrons are found in its electron shell. Protons are positive (+1 charge) with a relative mass of 1, neutrons are neutral with a relative mass of 1 while electrons are negative (-1 charge) with a relative mass of roughly 1/1836.

Atomic Structure Assignment (Ans: Q2)

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

The sodium atom is drawn this way as its electronic configuration is (2.8.1) only possessing one electron on its last shell. The sodium ion however is stable and has lost its 1 electron on the outermost shell causing its electronic configuration to be (2.8) only.

Atomic Structure Assignment (Ans: Q3)

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

The sulfur atom has an electronic configuration of (2.8.6) so its last shell only has 6 electrons. The sulfur atom is stable and has gained 2 electrons giving it a full last shell, its electronic configuration is (2.8.8).

Atomic Structure Assignment (Ans: Q4)

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

Chlorine-35 has 35 as its nucleon number. Thus it has 17 protons (all the time) with 18 neutrons.
Chlorine-37 has 37 as its nucleon number. Thus it has 17 protons (all the time) with 20 neutrons.

Isotopes are same atoms of the same element but with different number of neutrons. Chlorine in this case has 18 and 20 neutrons respectively. Because of this the nucleon number is different for both cases and therefore, they are isotopes.