Preliminary 2012 Chemistry Marathon (4 Viewers)

[theind1996]

Hopefully a lot of people try and participate. Similar to the HSC thread. Post answers to the previous question and submit a question of your own. At the moment, please try to only submit questions for the Chemical Earth and Metals modules.

ALSO SUBMIT MATHEMATICAL QUESTIONS SUCH AS THE MOLE CONCEPT, REDOX EQUATIONS AND GRAVIMETRIC ANALYSIS.

Cheers.

To kick off the thread:

• Define a decomposition reaction and identify it as an intake OR release of energy.
  
• Provide 1 example each of a decomposition reaction involving:
• heat
• light
• electricity
• Give 1 example of a decomposition occurring in everyday life.

6 MARKS.

 

[skillstriker]

- decomposition is a reaction in which a compound is broken down into two or more simpler substances. It is an intake of energy.
- heat: heating copper carbonate to produce copper oxide and carbon dioxide
- light: photolysis (decomposition by light) of silver bromide
- electricity: electrolysis of water --> decomposes into hydrogen and oxygen
- everyday example: lightning initiates decomposition reactions in the atmosphere by providing electricity to gases

Describe the formation of an ionic compound.

 

[theind1996]

YEP, THAT SHOULD SECURE YOU A 6/6 MARKS. GOOD WORK. Just maybe mention the word endothermic if you want regarding the intake of energy.

ANSWER: An Ionic Compound involves atoms losing and gaining electrons in order to form an ion. Thus, the compound is formed as a result of the strong electrostatic attraction between the positive cations and the negative anions.

OH AND BTW, PLEASE STATE THE AMOUNT OF MARKS WORTH PER QUESTION IN THE FUTURE AND THE MARKS THAT YOU WOULD AWARD FOR YOUR ANSWERED QUESTION.

For the oxidation-reduction reaction between Aluminium and Sulphuric Acid, write a balanced formula equation, a net-ionic equation,the 2 half-equations for oxidation and reduction, and identify which substance is being oxidised and which is reduced, and which substance is the oxidising and reducing agent. 4 MARKS.

 

[superSAIyan2]

A decomposition reaction involves the breaking down of a chemical compound into its components (elements or simpler compounds) and generally requires an energy input (not quite sure on this, correct me if im wrong). Represented as AB --> A + B

Decomposition reaction involving:
- Heat : Thermal decomposition of magnesium carbonate produces magnesium oxide and CO2
- Light : Photchemcial decomposition of a silver halide (e.g. silver chloride) to produce deposits of silver metal and chlorine used in non digital photography
- Electricity : Electrolysis of water, electrolysis of aluminium ore in mining industries-
- Everday example is the decomposition of nitrogenous compounds in the soil by decomposers to allow plants to obtain nitrate ions (Lol biology)

Question : Justify the differences in energy requirements for the process of electrolysis and boiling of water. 3M

 

[theind1996]

A decomposition reaction involves the breaking down of a chemical compound into its components (elements or simpler compounds) and generally requires an energy input (not quite sure on this, correct me if im wrong). Represented as AB --> A + B

Decomposition reaction involving:
- Heat : Thermal decomposition of magnesium carbonate produces magnesium oxide and CO2
- Light : Photchemcial decomposition of a silver halide (e.g. silver chloride) to produce deposits of silver metal and chlorine used in non digital photography
- Electricity : Electrolysis of water, electrolysis of aluminium ore in mining industries-
- Everday example is the decomposition of nitrogenous compounds in the soil by decomposers to allow plants to obtain nitrate ions (Lol biology)

YES, THAT SHOULD BE 6/6 MARKS (not sure about everyday example since I don't do Bio, but I'm presuming that it is correct).

PLEASE SUBMIT YOUR OWN QUESTION AT ALL TIMES AFTER ANSWERING.

 

[bleakarcher]

YEP, THAT SHOULD SECURE YOU A 6/6 MARKS. GOOD WORK. Just maybe mention the word endothermic if you want regarding the intake of energy.

ANSWER: An Ionic Compound involves atoms losing and gaining electrons in order to form an ion. Thus, the compound is formed as a result of the strong electrostatic attraction between the positive cations and the negative anions.

OH AND BTW, PLEASE STATE THE AMOUNT OF MARKS WORTH PER QUESTION IN THE FUTURE AND THE MARKS THAT YOU WOULD AWARD FOR YOUR ANSWERED QUESTION.

For the oxidation-reduction reaction between Aluminium and Sulphuric Acid, write a balanced formula equation, a net-ionic equation,the 2 half-equations for oxidation and reduction, and identify which substance is being oxidised and which is reduced, and which substance is the oxidising and reducing agent. 4 MARKS.

2Al+3H2SO4->Al2(SO4)3+3H2

donno what a net ionic equation is lol

3H2SO4+6e(-)->3H2+(SO4)3
2Al->Al2+6e(-)
i couldnt be effed with the charges (looks messy enough already)

the sulphuric acid is being reduced, aluminium is being oxidised.

 

[skillstriker]

A decomposition reaction involves the breaking down of a chemical compound into its components (elements or simpler compounds) and generally requires an energy input (not quite sure on this, correct me if im wrong). Represented as AB --> A + B

Decomposition reaction involving:
- Heat : Thermal decomposition of magnesium carbonate produces magnesium oxide and CO2
- Light : Photchemcial decomposition of a silver halide (e.g. silver chloride) to produce deposits of silver metal and chlorine used in non digital photography
- Electricity : Electrolysis of water, electrolysis of aluminium ore in mining industries-
- Everday example is the decomposition of nitrogenous compounds in the soil by decomposers to allow plants to obtain nitrate ions (Lol biology)

Question : Justify the differences in energy requirements for the process of electrolysis and boiling of water. 3M

more energy required for electrolysis because you have to break the strong intramolecular forces (and its a chemical change) whereas weak energy required for boiling because you only need to break the weak intermolecular forces (and its a physical change)

Identify a situation where gravimetric analysis could be useful? (2 marks)

 

[theind1996]

2Al+3H2SO4->Al2(SO4)3+3H2

donno what a net ionic equation is lol

3H2SO4+6e(-)->3H2+(SO4)3
2Al->Al2+6e(-)
i couldnt be effed with the charges (looks messy enough already)

the sulphuric acid is being reduced, aluminium is being oxidised.

NET IONIC is writing all the individual charges of the ions and excluding the spectator ion (one that doesn't change from reactant to product, in this case, the Sulfate ion).

You forgot the oxidising and reducing agent. You also forgot the states. And not knowing net ionic (DW, you'll improve) will probs give you a 2.5/4

AS I SAID BEFORE, PLEASE POST YOUR OWN QUESTION.

 

[theind1996]

more energy required for electrolysis because you have to break the strong intramolecular forces (and its a chemical change) whereas weak energy required for boiling because you only need to break the weak intermolecular forces (and its a physical change)

Identify a situation where gravimetric analysis could be useful? (2 marks)

Gravimetric Analysis is useful for mining companies in order to determine the composition of a metal ore to decide whether or not it is economically viable to mine the ore.

Identify why ionic substances are conductors of electricity in the molten or aqueous state, but not the solid state? (2 marks)

 

[bleakarcher]

^ shit looks like i have to revise chem lol.

 

[bleakarcher]

also theind1996 can you post the full solution to the one i attempted?

 

[superSAIyan2]

Gravimetric Analysis is useful for mining companies in order to determine the composition of a metal ore to decide whether or not it is economically viable to mine the ore.

Identify why ionic substances are conductors of electricity in the molten or aqueous state, but not the solid state? (2 marks)

Ionic substances exist as ionic lattices, an orderly three dimensional array of cations and anions held together by strong electrostatic forces called ionic bonds. In the solid state, the ions are localised within the lattice and due to the absence of mobile charge carriers there is no electrical conduction. However, in the molten state, the ionic bonds are broken and the ions dissociate resulting in the presence of mobile charges and hence allows electrical conduction.

Question : Discuss the problems associated with waste disposals from the separation of crude oil. 3M

 

[skillstriker]

Gravimetric Analysis is useful for mining companies in order to determine the composition of a metal ore to decide whether or not it is economically viable to mine the ore.

Identify why ionic substances are conductors of electricity in the molten or aqueous state, but not the solid state? (2 marks)

Ionic substances are insulators when solid because of the ions are held together by electrostatic forces and thus there is an absence of mobile charge carriers. But when they are in the molten state, the ionic bonds are partially broken, meaning that there are mobile charge carriers and it is able to conduct electricity.

Contrast between ionic and covalent bonds (2 marks)?

 

[theind1996]

A decomposition reaction involves the breaking down of a chemical compound into its components (elements or simpler compounds) and generally requires an energy input (not quite sure on this, correct me if im wrong). Represented as AB --> A + B

Decomposition reaction involving:
- Heat : Thermal decomposition of magnesium carbonate produces magnesium oxide and CO2
- Light : Photchemcial decomposition of a silver halide (e.g. silver chloride) to produce deposits of silver metal and chlorine used in non digital photography
- Electricity : Electrolysis of water, electrolysis of aluminium ore in mining industries-
- Everday example is the decomposition of nitrogenous compounds in the soil by decomposers to allow plants to obtain nitrate ions (Lol biology)

Question : Justify the differences in energy requirements for the process of electrolysis and boiling of water. 3M

Electrolysis of water is a chemical change, whereas the boiling of water is a physical change.

During boiling: Only weak dipole-dipole, dispersion and intermolecular forces are broken which exist between the water molecules.
During electrolysis: All bonds are broken including those during the boiling of water as well as strong covalent bonds existing between the hydrogen and oxygen atoms.

During boiling: No new substances are formed as the substance remains a molecule, only in gaseous steam form.
During electrolysis: 2 new substances are formed as Hydrogen and Oxygen gases.

During boiling: Easily reversible, simply condense the steam to form liquid water.
During electrolysis: Much more difficult to reverse, as it requires the newly formed and gases need to be mixed together and ignited with a high temperature spark.

Describe the limitations of models used to represent bonding between substances. (3 marks)

 

[theind1996]

also theind1996 can you post the full solution to the one i attempted?

sure. just wait a minute or 2 since i'm using latex. i'll edit this post when i finish.

HOLY FUCK LATEX TAKES AGES, DW I'LL EVENTUALLY GET THERE...









Therefore, the Hydrogen Ions are the oxidising agent, while the Aluminium is the reducing agent.

 

[superSAIyan2]

more energy required for electrolysis because you have to break the strong intramolecular forces (and its a chemical change) whereas weak energy required for boiling because you only need to break the weak intermolecular forces (and its a physical change)

Identify a situation where gravimetric analysis could be useful? (2 marks)

Food companies - determining the percent composition of various ingredients and chemicals in their product. Important for people with health problems/ dietary requirements.

Question : A sample of sand, water, sugar and iron filings were separated using magnetism, filtration and evaporation and the percent composition of each component in the sample was calculated. Assess the suitability of each separation technique used in relation to the experiment 4M

 

[skillstriker]

magnetism is suitable for separating the iron filings (because it is the only substance that is magnetic in the mixture)
filtration is suitable as it can be used to extract the sand (due to differences in particle size)
evaporation can be used to evaporate the water and thus extract the sugar (due to differences in boiling point/volatility)
Thus, magnetism, filtration and evaporation are all suitable techniques for separating the mixture.

IS THIS CORRECT (please correct me if im wrong)

Question - name the three types of chemical bonding (3 marks)

 

[bleakarcher]

Ionic substances are insulators when solid because of the ions are held together by electrostatic forces and thus there is an absence of mobile charge carriers. But when they are in the molten state, the ionic bonds are partially broken, meaning that there are mobile charge carriers and it is able to conduct electricity.

Contrast between ionic and covalent bonds (2 marks)?

In ionic bonds, electrons are directly transferred from one atom, which becomes a positive ion (cation), to another atom, which becomes a negative ion (anion).
In covalent bonds, electrons are shared between the atoms in the bond.
Ionic bonds are involve the bonding of the atoms of a metal and a non metal where as covalent bonds are the bonding of the atoms of two non-metals.

define the mole.

 

[skillstriker]

^good. now post a question

 

[theind1996]

magnetism is suitable for separating the iron filings (because it is the only substance that is magnetic in the mixture)
filtration is suitable as it can be used to extract the sand (due to differences in particle size)
evaporation can be used to evaporate the water and thus extract the sugar (due to differences in boiling point/volatility)
Thus, magnetism, filtration and evaporation are all suitable techniques for separating the mixture.

IS THIS CORRECT (please correct me if im wrong)

Question - name the three types of chemical bonding (3 marks)

There are actually 4 types.

- METALLIC BONDING
- IONIC BONDING
- COVALENT MOLECULAR BONDING
- COVALENT NETWORK BONDING

Outline the uses of 3 metals in contemporary society and relate this use to their properties. (3 MARKS)