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Question Chain Thread !!! (2 Viewers)

zxcvbee

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aussiechick007 said:
oxygen free radical:
- is unstable, has a very short existence, mp and bp unknown.
- has 6 valence electrons in its outer shell, 2 of which are unpaired.

oxygen atom:
- colourless, bp of -183oC.
- is stable, has a low solubility in water.
- consists of 2 oxygen free radicals with their unpaired electrons in a covalent bond.
hehe i got you confused! lol. Oxygen atom and oxygen free radical are the same thing! there are no differences !!
The oxygen ATOM doesnt consist of 2 oxygen free radicals & is not stable..

(that was a multiple choice in our trial and i got it wrong cos i got confused too so i thought id share it with the rest of you all lol. its a sneaky question but!
 

danz90

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What volume of 0.005M KOH is required to neutralise 15mL of 5x10-4 mol.L-1 H2SO4?
 

zxcvbee

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yorkstanham said:
Fritz Haber’s discovery of a method to synthesise ammonia was extremely significant at that time in world history. It was during WWI that the British blockaded the German’s supply of nitrates from South America. This had devastating effects on Germany’s ammunition and crops. Haber’s process allowed Germany to produce up to 200 tonnes of ammonia a day, this allowed for fertilisers to be created which boosted crops and hence food for Germany and its troops, the ammonia was also used to create ammunition. Some historians say that the Haber process allowed Germany to prolong its time in the war by 2 years, significantly changing the course of history during the early 20<SUP>th</SUP> century.

NEXT Q:
The atmosphere contains acidic oxides of sulphur which have been increasing in concentration since the Industrial Revolution.ffice:eek:ffice" /><O:p></O:p>
Discuss the evidence for this statement, and include relevant balanced chemical equations. (4 marks)<O:p></O:p>
SO2 is released into the atmosphere natually by volcanoes & industrially by the buring of fossil fuels containing sulfur as impurities.
S + O2--> SO2
Or the smelting of sulfide ores in order to extract a metal:
PbS(s) + O2(g) --> Pb(s) + SO2(g)

This reacts with water to form sulfurous acid:
SO2 + H2O --> H2SO3
And impurties in the air futher catalysie the conversion into Sulfuric acid:
H2SO3 + O2 --> H2SO4

In the 1960's many forests were serioulsy damaged due to acidic nature of the rain, such as germany;s 'black forest.'
Water ways increased in acidity (lower pH), killing fish and disrupting food chains, such as in canada where many lakes were found dead in an ecological sense, erosion of marble & limestone statues in rome and environmental damage around Queenstown, Tas, by the release of SO2 from the Mt Lyrell copper mine & smelter, which has still not recovered 20 years down the tract.
 

imqt

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can someone OUTLINE 5 EXAMPLES OF STRONG/WEAK ACIDS AND 5 EXAMPLES OF STRONG/WEAK BASES
 

JasonNg1025

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imqt said:
OUTLINE 5 EXAMPLES OF STRONG/WEAK ACIDS AND 5 EXAMPLES OF STRONG/WEAK BASES
No need for capitals, mate

Strong Acids:

1) Hydrochloric Acid
2) Sulfuric Acid
3) Nitric Acid
4) Hydrobromic Acid
5) Hydroiodic Acid

The rarer ones are easy to remember, they're like HCl but with different halogens.

Weak Acids:

1) Ethanoic Acid
2) Citric Acid
3) Phosphoric Acid
4) Boric Acid (B(OH)3 or H3BO3)
5) Hydrofluoric Acid (dunno why... I think it is).

Strong Bases:

1) Sodium Hydroxide
2) Potassium Hydroxide
3) Calcium Hydroxide
4) Barium Hydroxide
5) Lithium Hydroxide

Weak Bases:

1) Ammonia
2) Ammonium Hydroxide
3) Pyridine (C5H5N)
4) Methylamine (CH3NH2)
5) Err... sodium hydrogen carbonate?
 

Trebla

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A student opens a bottle of carbonated soft drink that has been stored at room temperature. He places a thermometer into the bottle and into the soft drink.

The bottle is left unemptied and opened for a long period of time after the soft drink becomes ‘flat’. Assuming a constant room temperature and atmospheric pressure, explain any changes in temperature that will occur that will be detected by the thermometer.
 
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JasonNg1025

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Trebla said:
drink that has been stored at room temperature
Trebla said:
a constant room temperature
Trebla said:
explain any changes in temperature
I have a feeling you're tricking us... reason being, you already done your HSC.
So... are you?

The drink goes flat...

H2CO3 + heat <=> H2O + CO2

But I don't think that necessarily means that the drink itself goes cooler. Does it even change?
I'm confused xD
 

danz90

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Trebla said:
A student opens a bottle of carbonated soft drink that has been stored at room temperature. He places a thermometer into the bottle and into the soft drink.

The bottle is left unemptied and opened for a long period of time until the soft drink becomes ‘flat’. Assuming a constant room temperature and atmospheric pressure, explain any changes in temperature that will occur that will be detected by the thermometer.
The soft drink becomes more 'flat' as the following reaction is favoured to partially offset loss in CO2(g) (by leaving the bottle unopened):
heat + CO2(aq) ---> CO2(g)

Hence, as heat is absorbed/required in favourng the above reaction, the thermemoter will detect a drop in temperature of the soft drink.

Next: A 50.0mL water sample was being titrated with a solution of AgNO3 to determine the concentration of Cl- in the sample. If the mass of the dried precipitate was 3.65g, calculate the chloride ion concentration in the water sample in ppm.
 

Trebla

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danz90 said:
The soft drink becomes more 'flat' as the following reaction is favoured to partially offset loss in CO2(g) (by leaving the bottle unopened):
heat + CO2(aq) ---> CO2(g)

Hence, as heat is absorbed/required in favourng the above reaction, the thermemoter will detect a drop in temperature of the soft drink.
Yes, but after a while there may also be a rise in temperature back to room temperature as equilibrium is lost due to an open system. The cooled system will be warmed up eventually by surrounding heat trying to enter the system...:p
 
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danz90

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Here's a question from a topic test our school gave us on Acidic Environment:

A crusty white deposit around the rim of an irrigation pipe was thought to consist of a mixture of sodium chloride and sodium carbonate. To test for sodium carbonate, the following procedure was followed.

-A sample (mass = 2.50g) of the deposit was dissolved in water and then filtered.
-100mL of 0.125 mol.L-1 solution of nitric acid was added.
-The excess nitric acid was titrated against standardised 0.200 mol.L-1 NaOH (aq).
-The volume of NaOH(aq) required was 23.5mL.

Calculate the mass and percentage by mass of sodium carbonate in the sample.
 

JasonNg1025

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Dealing with 2 equations:

2HNO3 + Na2CO3 --> 2NaNO3 + H2O + CO2

HNO3 + NaOH --> NaNO3 + H2O

From information,

Moles NaOH = 4.7 x 10^-3 (n = CV)
=> Moles HNO3 in excess = 4.7 x 10^-3

From information,

Moles HNO3 initial = 0.0125
=> Moles HNO3 reacted = 0.0125 - 4.7 x 10^-3 = 7.8 x 10^-3

=> Moles Na2CO3 = 3.9 x 10^-3 (2 : 1)
=> Mass Na2CO3 = 0.413g

% by mass = 0.413 / 2.50 x 100%

This is equal to 16.5%.
 

danz90

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JasonNg1025 said:
Dealing with 2 equations:

2HNO3 + Na2CO3 --> 2NaNO3 + H2O + CO2

HNO3 + NaOH --> NaNO3 + H2O

From information,

Moles NaOH = 4.7 x 10^-3 (n = CV)
=> Moles HNO3 in excess = 4.7 x 10^-3

From information,

Moles HNO3 initial = 0.0125
=> Moles HNO3 reacted = 0.0125 - 4.7 x 10^-3 = 7.8 x 10^-3

=> Moles Na2CO3 = 3.9 x 10^-3 (2 : 1)
=> Mass Na2CO3 = 0.413g

% by mass = 0.413 / 2.50 x 100%

This is equal to 16.5%.
Well done, that's correct ;)
 

imqt

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hey guys, is the molar heat of combustion NEGATIVE? or if it isnt how do you know when it is, and what other reactions are negative? (i know exothermic reactions are)
 

JasonNg1025

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Exothermic is negative, endothermic is positive.

This is because when there's a negative enthalpy change, it means that heat has been lost, i.e. released. When there's a positive, heat has been gained, i.e. absorbed.
 

danz90

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imqt said:
hey guys, is the molar heat of combustion NEGATIVE? or if it isnt how do you know when it is, and what other reactions are negative? (i know exothermic reactions are)
yeah, it is, because all combustions are exothermic.
although when u find the molar heat of combustion, I don't think u actually have to write a minus in front of ur answer.
 

imqt

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danz90 said:
yeah, it is, because all combustions are exothermic.
although when u find the molar heat of combustion, I don't think u actually have to write a minus in front of ur answer.
oh thanks, because in the 2002 paper i think it was, the answer was negative in the HSC ONE SUCCESS but ive never actually put a negative b4
 

imqt

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A QUESTION

Discuss factors that must be considered when using neutralisation reactions to safely minimise damage in chemical spills
 

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