- Chemsitry ;

Monday 26 September 2011

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

i) Name the salt and the base.

Ammonium Nitrate (NH₄NO₃). The base is Zinc Hydroxide .

ii) Describe the observations for the reaction.

White ppt. is formed.

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

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

iv) Write an ionic equation for the reaction.

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) -> 2NH₃(g) + 2H₂O (l) + Na₂SO₄(aq)

ii) Describe a test for the gas.

Use red litmus paper by holding it over the ammonia gas. The red litmus paper will turn 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.

Ammonia gas

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

Nitrate ion

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.

It is because sulfuric acid, potassium hydroxide and potassium sulphate salt are soluble.

ii)Write an ionic equation for the reaction.

2H⁺ (aq) + 2OH^- (aq) -> H₂O

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) -> H₂O (l) +CO₂(g) + Zn²⁺

ii) Why excess zinc carbonate is used?

It is to ensure that all the hydrochloric acid is completely reacted to form the chloride salt.

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

Add excess zinc carbonate to hydrochloric acid. Filter out all the excess zinc carbonate after that. Boil the solution in a evaporating dish. Control the fire to prevent the salts from “jumping” out. Heat until there is little fluid left. Let the solution cool under the fan. Zinc chloride crystal is formed after it dries.

Blogged @ 08:13
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Sunday 10 July 2011

repost of image that can't be seen in answer

Blogged @ 03:35
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requested by MR TAN!

Blogged @ 03:26
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Jun Wei
Jun Wei's answer is detailed and there are pictures to make the explaination easier. Although his blog is a little annoying as u can't scroll up and down, he did well in his answers.

Grace
Her answers are detailed, like Q1, but for Q2, she should make a spacing between the explaination for Ions and Atoms. She made some spelling and grammer mistakes, but overall, it is good.

Shinyoong
Her answers are detailed and there are pictures to make the explaination easier, even though it is somehow too long. She even went through the trouble of taking a picture and transferring it into the computer and upload it. Overall, her answers are detailed but it is too lengthy.

Blogged @ 02:47
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Monday 4 July 2011

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

Atoms are made up of 3 types of particles electrons , protons and neutrons . These particles have different properties. Electrons are tiny, very light particles that have a negative electrical charge (-). Protons are much larger and heavier than electrons and protons have a positive charge. Neutrons are large and heavy, however neutrons have no electrical charge. Each atom is made up of a these particles.

In atoms, the number of protons and the number of electrons is always the same. The number of neutrons is about the same as the number of protons, but sometimes it has more. The number of protons in an atom is called the atomic number.The total number of protons and neutrons added together is called the relative atomic mass.

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

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The sodium atom is drawn this way because it electronic configuration is (2.8.1). Therefore, only 1 electron lies on the 3^rd shell.

Sodium ion is drawn this way as it only has 1 electron on the 3^rd shell, it is hard to make a full shell as it needs another 7 electrons. It can either gain 7 electrons or lose the 1 electron so that the 3^rd shell becomes the full. Since it is too hard to gain 7 electrons during chemical bonding, it loses its electron.

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

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https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgLf2cahnvIZBdNDYCvLnDhNte5CxpQoVJaIFRtunQ3s7FNXtfxal-ird2BJyr2JRVoFTTY-FdYr7dlSTRo7vX3vevdlcXe3BZbN-Um5YhjhyphenhyphenUnHMOMzM55Dnp7ajRQz5DCDq5Zj1ex3R7-/s200/Untitled-4jpg.jpg

Sulfur atomic structure is drawn this way as the 1^st shell could only contain 2 electrons, 2^nd shell could only contain 8 electrons, therefore the remaining 6 are placed this way in the 3^rd shell.

Sulfur ion structure is drawn this way because its electronic configuration is (2.8.6). It is easier to gain 2 more electrons than to lost 6 , hence the sulfur ions is drawn like this.

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

Isotopes mean different atoms of the same element which have the same number of protons but different number of electrons. Chlorine-35 and Chlorine-37 are both chlorine, but they have different number of neutrons. Chlorine-35 has 18 neutrons, while Chlorine-37 has 20 neutrons. Their proton numbers are the same. Hence, Chlorine-35 atom and Chlorine-37 atoms are called isotopes.

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

Sulfur is a non-metal as it is in group (VI) in the periodic table. The non-metals are mostly on group (IV),(V),(VI) and (VII). Sodium is a metal as it is on group (I) in the periodic table.

Sulfur is a non-metal as it is not capable of forming a positive charge. Most metals form positive charge.

Metals are solid and malleable and capable of forming positive charges. Sodium is solid and malleable and capable of forming positive charges, therefore it is a metal.

Non-metal form oxides that are acidic, and sulfer reacts with oxide to form sulfer dioxide, which is acidic (acid rain), thus it is a non-metal. Whereas, metals form oxides that are basic, and sodium reacts with oxide to form sodium oxides which is a basic oxide.

Blogged @ 02:40
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Friday 1 July 2011

this is only for chem -.-

Blogged @ 06:44
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