Question Chain Thread !!! (3 Viewers)

[danz90]

A QUESTION

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

When using neutralisation to safely minimise damage in chemical spills, the following must be considered:

- It must be certain that ALL of the acid/base has been removed via neutralisation. In other words, the acid or base that is used to neutralise the chemical spill MUST be in excess, to ensure there is no remaining acid/base chemical. For example, NaHCO₃ is used effectively in chemical spills as it bubbles (because of release of CO₂. After the bubbling has completely stopped, it can be certain that there is no acid left, for example.

- The chemical spill should not be dispersed. For example, NaHCO₃ is effectively used in chemical spills because it is a fine powder, and thus ABSORBS spills, rather than dispersing them. This ensures that the chemical spill does not spread.

- Ensure that no corrosive/dangerous substances are used to clean up the spill. For example, if there is a spill of a base (such as NaOH), it would not be wise to pour concentrated H₂SO₄ over the spill. The H₂SO₄ would itself be a chemical spill and pose hazards such as burns and corrosion of floors, and as a liquid, would disperse the spill.

lol dunno if I attacked this question from the right angle.

Next: The solubility of Calcium Hydroxide is 0.12g per 100mL of water at 25 C. Calculate the maximum pH of a solution of calcium hydroxide, assuming that the addition of the solid changes the volume only negligibly.

 

[@who]

When using neutralisation to safely minimise damage in chemical spills, the following must be considered:

- It must be certain that ALL of the acid/base has been removed via neutralisation. In other words, the acid or base that is used to neutralise the chemical spill MUST be in excess, to ensure there is no remaining acid/base chemical. For example, NaHCO₃ is used effectively in chemical spills as it bubbles (because of release of CO₂. After the bubbling has completely stopped, it can be certain that there is no acid left, for example.

- The chemical spill should not be dispersed. For example, NaHCO₃ is effectively used in chemical spills because it is a fine powder, and thus ABSORBS spills, rather than dispersing them. This ensures that the chemical spill does not spread.

- Ensure that no corrosive/dangerous substances are used to clean up the spill. For example, if there is a spill of a base (such as NaOH), it would not be wise to pour concentrated H₂SO₄ over the spill. The H₂SO₄ would itself be a chemical spill and pose hazards such as burns and corrosion of floors, and as a liquid, would disperse the spill.

lol dunno if I attacked this question from the right angle.

Next: The solubility of Calcium Hydroxide is 0.12g per 100mL of water at 25 C. Calculate the maximum pH of a solution of calcium hydroxide, assuming that the addition of the solid changes the volume only negligibly.

wtf. ok ill try.

find moles of Ca(OH)2:
= 0.12 / Ca(OH)2

then find concentration of Ca(OH)2
Mol = moles/V
= moles/ 0.1
this gives [OH-] concentration
then calculate pH :

since [H+]x[OH-] = 10^-14 .
divide the [OH-] by 10^-14 to give [H+] . then find pH by -log[H+]
...
no offense but thats a pain in the ass crappy question for the HSC level

 

[danz90]

wtf. ok ill try.

find moles of Ca(OH)2:
= 0.12 / Ca(OH)2

then find concentration of Ca(OH)2
Mol = moles/V
= moles/ 0.1
this gives [OH-] concentration
then calculate pH :

since [H+]x[OH-] = 10^-14 .
divide the [OH-] by 10^-14 to give [H+] . then find pH by -log[H+]
...
no offense but thats a pain in the ass crappy question for the HSC level

Here's my solution, though I'm not sure if it's correct.

n(Ca(OH₂) = 0.12/74.08
n(Ca(OH)₂) = 1.62 x 10^-3

[Ca(OH)₂] = 1.62 x 10<sup>-3[/sup / 0.1L
=0.0162 mol.L-1 (max concentration of Ca(OH)₂ possible at 25C)

n(OH-) = 2 x n(Ca(OH)₂)
n(OH-) = 3.24 x 10-3

[OH-] = 0.0324 mol.L-1

[H+] = 10-14 / 0.0324

max pH = 12.5 at 25 C

Next: Account for the reasons why ethanol can effectively dissolve glucose and why it is miscible in water.</sup>

 

[@who]

Here's my solution, though I'm not sure if it's correct.

n(Ca(OH₂) = 0.12/74.08
n(Ca(OH)₂) = 1.62 x 10^-3

[Ca(OH)₂] = 1.62 x 10<sup>-3[/sup / 0.1L
=0.0162 mol.L-1 (max concentration of Ca(OH)₂ possible at 25C)

n(OH-) = 2 x n(Ca(OH)₂)
n(OH-) = 3.24 x 10-3

[OH-] = 0.0324 mol.L-1

[H+] = 10-14 / 0.0324

max pH = 12.5 at 25 C

Next: Account for the reasons why ethanol can effectively dissolve glucose and why it is miscible in water.</sup>

^{wait wait. So i was right>? cause u just filled in my method if u look closely.}

 

[danz90]

wait wait. So i was right>? cause u just filled in my method if u look closely.

yeah, pretty much actually, now that I look at ur answer lol.
good job

Just remember to multiply moles of calcium hydroxide by 2 to get moles of OH.

 

[Azreil]

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.
AgCl = 3.65g
35/143 * 3.65 = 0.9g Cl
0.9g/50mL
18g/L
1800ppm

Account for the reasons why ethanol can effectively dissolve glucose and why it is miscible in water.
Ethanol is miscible in water due to the -O-H section of the molecule, which creates a delta - and a delta +. This means that this section of the molecule is polar, and as like-dissolves-like, can mix with water. The molecule is not, however, polar enough to break ionic lattices.

The rest of the molecule, however, is distinctly linear and non-polar. It is for this reason that ethanol can dissolve some non-polar substances such as glucose.

In your studies you conducted an investigation into the molar heat of combustion of alkanols. Account for differences in your experimental values and literature values.

 

[axlenatore]

When using neutralisation to safely minimise damage in chemical spills, the following must be considered:

- It must be certain that ALL of the acid/base has been removed via neutralisation. In other words, the acid or base that is used to neutralise the chemical spill MUST be in excess, to ensure there is no remaining acid/base chemical. For example, NaHCO₃ is used effectively in chemical spills as it bubbles (because of release of CO₂. After the bubbling has completely stopped, it can be certain that there is no acid left, for example.

- The chemical spill should not be dispersed. For example, NaHCO₃ is effectively used in chemical spills because it is a fine powder, and thus ABSORBS spills, rather than dispersing them. This ensures that the chemical spill does not spread.

- Ensure that no corrosive/dangerous substances are used to clean up the spill. For example, if there is a spill of a base (such as NaOH), it would not be wise to pour concentrated H₂SO₄ over the spill. The H₂SO₄ would itself be a chemical spill and pose hazards such as burns and corrosion of floors, and as a liquid, would disperse the spill.

lol dunno if I attacked this question from the right angle.

Use an amphiprotic substance

 

[JasonNg1025]

In your studies you conducted an investigation into the molar heat of combustion of alkanols. Account for differences in your experimental values and literature values.

1) Not all heat was transferred to the water, i.e. heat lost from surroundings
.
2) Not standard conditions, where the theoretical values are found. In standard conditions, H₂O produced from combustion is in gas form, not liquid. In lab conditions, often water is produced in liquid form.

3) Incomplete combustion in lab, excess oxygen is given for complete combustion in literature value.

 

[mophead]

Use an amphiprotic substance

can you name an amphiprotic substance that would be useful in neutralisation, i know acids and bases but not amphiprotic ones

 

[danz90]

can you name an amphiprotic substance that would be useful in neutralisation, i know acids and bases but not amphiprotic ones

NaHCO₃ is amphiprotic, since the HCO₃^- ion is amphiprotic (will neutralise both H₃O⁺ and OH^-).

That's the only one I can think of at the moment that's used in acid spills.

 

[JasonNg1025]

Yes, NaHCO₃ is the best one...

NaHCO₃ + H₃O⁺ ---> Na⁺ + CO₂ + 2H₂O

NaHCO₃ + OH^- ---> H₂O + Na⁺ +... CO₃^2-?

Cause

NaHCO₃ + NaOH ---> Na₂CO₃ + H₂O

Actually I think I guessed that one

 

[danz90]

Yes, NaHCO₃ is the best one...

NaHCO₃ + H₃O⁺ ---> Na⁺ + CO₂ + 2H₂O

NaHCO₃ + OH^- ---> H₂O + Na⁺ +... CO₃^2-?

Cause

NaHCO₃ + NaOH ---> Na₂CO₃ + H₂O

Actually I think I guessed that one

yep, those are all correct. alot of people wouldn't know about that last equation though, since most of the time u see NaHCO₃ reacting with acids.

 

[lil-monkey]

Phosgene is preared from the reaction of carbon monoxide and chloride in the presence of a catalyst:

CO(g)+ Cl2(g) <-> COCl2(g) ΔH= 9.93kJ mol-1​

what set of conditions (pressure and temp) would produce the highest yield of Phosgene?

and explain why.

 

[JasonNg1025]

High pressure
High temperature

Based around Le Chatelier's principle. There are more moles of gas on the LHS, so when pressure increases, the system will favour the RHS (i.e. phosgene yield) for its lower number of moles

ΔH is positive, so the reaction is endothermic, meaning it absorbs heat. A higher temperature will cause the system to absorb more heat, favouring the forward reaction and increasing phosgene yield.

 

[Azreil]

Increasing pressure would cause a shift to the products side of the equillibrium as there are 2 moles of gas on the left and 1 mole of gas on the right. When pressure is applied, the equillibrium shifts towards the side with least moles of gas; hence high pressure results in higher yield.

An increase in temperature also leads to an increase in pressure if the volume of the reaction vessel is not increased. In this reaction, however, temperature also lies on the reactants side of the equation; hence increasing temperature causes a shift towards products. High temperature will thus produce higher yields of phosgene.

Assess the impacts of reducing the sulfur content of petrol on the environment.

 

[midifile]

Phosgene is preared from the reaction of carbon monoxide and chloride in the presence of a catalyst:

CO(g)+ Cl2(g) <-> COCl2(g) ΔH= 9.93kJ mol-1​

what set of conditions (pressure and temp) would produce the highest yield of Phosgene?

and explain why.

This reaction is endothermic, so higher temperatures would favour the forward reaction, shift equilibrium to the right, and increase yield

This is a reaction involving gases -there are fewer moles on the product side (1) than the reactant side (2), so increasing pressure would favour the forward reaction, shifting equilibrium to the right and increasing yield

 

[imqt]

can someone please do this 4 me



2007 paper q 22

In 2004, Australia’s Minister for the Environment announced that the allowableamounts of sulfur in unleaded petrol and diesel would be reduced over the next 5years.Currently sulfur in diesel is 500 parts per million (ppm) but it will be cut to 50ppm on 1 January 2006 and capped at 10 ppm from January 2009.


(a)Calculate the volume of sulfur dioxide produced when a full tank(capacity60kg) of diesel is consumed at 25°C and 100kPa in November2007.

 

[imqt]

anyone know where i can get worked answers for 2007 paper?

 

[danz90]

can someone please do this 4 me



2007 paper q 22

In 2004, Australia’s Minister for the Environment announced that the allowableamounts of sulfur in unleaded petrol and diesel would be reduced over the next 5years.Currently sulfur in diesel is 500 parts per million (ppm) but it will be cut to 50ppm on 1 January 2006 and capped at 10 ppm from January 2009.


(a)Calculate the volume of sulfur dioxide produced when a full tank(capacity60kg) of diesel is consumed at 25°C and 100kPa in November2007.

[Sulfur] = 50mg/kg (since nov 2007 level corresponds to 55pm in jan 06 level)

When 60kg of diesel is combusted, 50mg * 60 = 3g of Sulfur is oxidised.

S + O₂ ---> SO₂
mole ratio is 1:1:1

therefore, moles of SO₂ = 3g/32.07 = 0.093545 mol

n = V / V_M
V(SO₂) = 24.79 * 0.093545mol

V(SO₂) produced = 2.3L (2 sig. fig.)

 

[JasonNg1025]

I did question 22 in another thread, I think it was 2007 Questions by Aaron.Judd