Question Chain Thread !!! (3 Viewers)

[yorkstanham]

pH = 1.53 (2.s.f)

working?

 

[danz90]

working?

n(H⁺) = 2 * (0.1*0.014)
= 2.8 x 10^-3 mol

n(OH^-) = 0.12*0.016
= 1.92 x 10^-3 mol

excess H⁺ = 2.8 x 10^-3 - 1.92 x 10^-3
= 8.8 x 10^-4 mol

[H⁺] = 8.8 x 10^-4 mol / 0.030 L
= 0.0293 mol.L^-1

pH = -log(0.0293)

= 1.53

 

[JasonNg1025]

Next question:

State your local catchment area.

 

[SkimDawg]

Sigh I missed the 2 H ions at the start, and got the base in excess. Silly mistakes ftw.

 

[danz90]

Was the pH calculation correct??

To jason's question:

Warragamba Catchment Area involves the Warragamba Dam and surrounding creeks and rivers that feed into the main water supply.
?
meh

 

[JasonNg1025]

I have no idea. Is it correct?

I'll check dot point

EDIT: Dot point says - "Sydney has four main catchments west and south-west of the city. The largest is around Lake Burragorang. This is the lake formed by Warragamba Dam and is fed by the Cox, Wollondilly and Kowmung Rivers."

Outline the procedure you used to measure the sulfate content of lawn fertiliser and explain the chemistry involved

 

[Pwnage101]

pH = 1.53 (2.s.f)

isnt that 3sf?

 

[danz90]

isnt that 3sf?

Significant figures for pH figures are counted AFTER the decimal point, since its a log function.

 

[Azreil]

isnt that 3sf?

For pH, sig figs are counted after the decimal place.

 

[JasonNg1025]

danz90 post a question

 

[danz90]

danz90 post a question

LOL

Outline the effect of the above compound in the stratosphere and troposhere. Also, describe the bonding within the molecule.​

 

[JasonNg1025]

THIS IS OZONE YARR. In the stratosphere, ozone is beneficial to human beings. It blocks out harmful UV rays that can mutate cells and cause cancer and sunburns.
In the troposphere, however, ozone is a pollutant. It irritates eyes and airways, causes coughing and causes chest pain, being toxic at >1ppm.
Ozone consists of 3 oxygen molecules. Two of these are held together by a double coordinate covalent bond. The third oxygen molecule is attached to one of the pair via a covalent bond, where the central O atom shares the whole pair of electrons.

EDIT: Outline the procedure (briefly) you used to perform esterification, and justify this procedure

 

[danz90]

THIS IS OZONE YARR. In the stratosphere, ozone is beneficial to human beings. It blocks out harmful UV rays that can mutate cells and cause cancer and sunburns.
In the troposphere, however, ozone is a pollutant. It irritates eyes and airways, causes coughing and causes chest pain, being toxic at >1ppm.
Ozone consists of 3 oxygen molecules. Two of these are held together by a double coordinate covalent bond. The third oxygen molecule is attached to one of the pair via a covalent bond, where the central O atom shares the whole pair of electrons.

EDIT: Outline the procedure (briefly) you used to perform esterification, and justify this procedure

4mL of Methanol was mixed with 5g Salicylic Acid, in a round-bottom flask. Several boiling chips were added to the mixture, to promote even boiling. An upright reflux condenser was set up, and attached to the round bottom flask.
The apparatus was then secured to a retort stand, and the round-bottom flask dipped into a water bath (to avoid direct heating which could lead to spitting of reactants). A few drops of concentrated sulfuric acid was added, to promote a reasonable rate of reaction.

The mixture was heated under reflex, so that any volatile reactants that evaporated, would be condensed in the upright condenser, and drop down back into the flask to participate in the reaction. This minimses wastage, and promotes a higher yield. Also, heating under reflex prevents the escape of dangerous volatile reagents (such as methanol - can cause blindess), as well as sulfuric acid, out into the surroundings, causing a hazard for students.

This is sort of brief though.. would go into more detail for a 6 marker.

Identify the nature of the oxides of non-metals and describe the conditions under which they behave in this nature.

 

[JasonNg1025]

Wait wait waittt

talk about why you used sulfuric acid, (2 reasons), why you used water bath in the justification area.

Also, you're not meant to use a water bath..... water bath means that the max temperature you can get the mixture to is 100^o C, in which case you wouldn't need a reflux. We just plonked ours on a hotplate.

For your question - what type of nature? Acidic?

Oxides of non-metals are generally acidic oxides. The non metals up the top right corner of the periodic table form more acidic oxides. Group VIII, the noble gases, do not form oxides. Oxides of non metals are acidic when in solution, where they react with water / ionise forming H₃O⁺ ions.

 

[danz90]

Wait wait waittt

talk about why you used sulfuric acid, (2 reasons), why you used water bath in the justification area.

Also, you're not meant to use a water bath..... water bath means that the max temperature you can get the mixture to is 100^o C, in which case you wouldn't need a reflux. We just plonked ours on a hotplate.

For your question - what type of nature? Acidic?

Oxides of non-metals are generally acidic oxides. The non metals up the top right corner of the periodic table form more acidic oxides. Group VIII, the noble gases, do not form oxides. Oxides of non metals are acidic when in solution, where they react with water / ionise forming H₃O⁺ ions.

well we actually did use a water bath (it prevents superheating/overheating for safety issues).. it worked out well, and we did produce the methyl salicylate.

I just stated that Sulfuric Acid was a catalyst used to promote a reasonable rate of reaction (by lowering activation energy required), and another thing you could say is, since Sulfuric Acid is a dehydrating agent - it removes water from the right side of the equilibrium, thus promoting the forward reaction, producing more ester and thus increasing ester yield.

---

You could also say that dry deposition may occur, where acidic oxides react with carbonates (in statues for example) directly:

2CaCO₃(s) + 2SO₂(g) + O₂(g) ---> 2CaSO₄(s) + 2CO₂(g)

 

[JasonNg1025]

well we actually did use a water bath (it prevents superheating/overheating for safety issues).. it worked out well, and we did produce the methyl salicylate.

I just stated that Sulfuric Acid was a catalyst used to promote a reasonable rate of reaction (by lowering activation energy required), and another thing you could say is, since Sulfuric Acid is a dehydrating agent - it removes water from the right side of the equilibrium, thus promoting the forward reaction, producing more ester and thus increasing ester yield.

Yes that's right
Our trial had this question on the uses of sulfuric acid during esterification, and it was worth 2 marks, so you had to put 2 reasons

EDIT: Discuss the benefits and problems with the use of radioisotopes in an identified industry

 

[hoochiscrazy]

Wait wait waittt

talk about why you used sulfuric acid, (2 reasons), why you used water bath in the justification area.

Also, you're not meant to use a water bath..... water bath means that the max temperature you can get the mixture to is 100^o C, in which case you wouldn't need a reflux. We just plonked ours on a hotplate.

For your question - what type of nature? Acidic?

Oxides of non-metals are generally acidic oxides. The non metals up the top right corner of the periodic table form more acidic oxides. Group VIII, the noble gases, do not form oxides. Oxides of non metals are acidic when in solution, where they react with water / ionise forming H₃O⁺ ions.

Even though max temp is 100 degrees reflux apparatus still needed as Boiling Temps of the liquids used maybe lower than 100.

Edit: How does the mixing of gases in the troposphere compare to that in the stratosphere?

 

[yorkstanham]

For your question - what type of nature? Acidic?

Oxides of non-metals are generally acidic oxides. The non metals up the top right corner of the periodic table form more acidic oxides. Group VIII, the noble gases, do not form oxides. Oxides of non metals are acidic when in solution, where they react with water / ionise forming H₃O⁺ ions.

Some do eg, Xenon. Xenon tetroxide (XeO4). Xenon tetroxide dissovles in water to produce perxenic acid, hence it is an acidic oxide.

 

[JasonNg1025]

Even though max temp is 100 degrees reflux apparatus still needed as Boiling Temps of the liquids used maybe lower than 100.

Boiling points are >100^o C..

Some do eg, Xenon. Xenon tetroxide (XeO4). Xenon tetroxide dissovles in water to produce perxenic acid, hence it is an acidic oxide.

Ahhh ok
Thanks

 

[alez]

Even though max temp is 100 degrees reflux apparatus still needed as Boiling Temps of the liquids used maybe lower than 100.

Edit: How does the mixing of gases in the troposphere compare to that in the stratosphere?

in troposphere, temp decreases with altitude, so the warm air is constantly moving to the top, causing a lot of mixing of gases
in stratosphere, temp increases with altitude, so there is little movement of gases

outline some examples of the occurrence, production and use of esters