Chemistry Questions (1 Viewer)

[nsbrando]

Cl2 + 2I <--> 2Cl + I2

 

[someth1ng]

Re: Which one is oxidant and reductant

Cl2 + 2I <--> 2Cl + I2

Are those ions? If they are ions, you MUST put it in.

 

[nsbrando]

name species undergoing oxidation

a. Cu + Cl2 <--> CuCl2
b.Zn + Pb^2+ <--> Zn^2+ + Pb

 

[someth1ng]

Re: name species undergoing oxidation

Cu undergoes oxidation to become CuCl2 because the oxidation state changes from 0 to +2 - that is, it loses electrons to the Cl2.
Zn undergoes oxidation to become Zn2+ because the oxidation state changes from 0 to +2 - that is, it loses electrons to Pb2+.

 

[BlugyBlug]

Re: Which one is oxidant and reductant

oxidant = causes oxidation. - therefore is the one that undergoes reduction. the ion that undergoes reduction (gain of e-) is the chlorine.

reductant = causes reduction=undergoes oxidation=loss of e- = iodine

 

[nsbrando]

half life multiple choice

1. Which sample will decay least over a period of 30 days?

a. 10g of I-131
b. 10g of P-32
c. 10g of Rn-222
d. 10g of Au-198

2. A sample of ^131 I decays to 1.0 gram in 40 days, What was the mass of the original sample?

a. 8.0g
b. 16g
c. 32g
d. 4.0g

3. What is the number of half-life periods required for a sample of a radioactive material to decay to one-sixteenth its original mass?

a. 8
b. 16
c. 3
d. 4

4. In how many days will a 12-gram sample of 131 / 53 I decay, leaving a total of 1.5 grams of the original isotope?

a. 24
b. 8.0
c. 16
d. 20

5. As a sample of the radioactive isotope ^131 I decays, its half-life

a. decreases
b. increases
c. remains the same

 

[Riproot]

1 - C
2 - Haven't done it yet.
3 - D
4 - See 2
5 - A?

 

[DamTameNaken]

Re: half life multiple choice

1. One with the longest half life (ignore mass for this one). You won't be expected to memorise the half lives in the HSC, and you should probably find the answer by googling it.

2. C 40 days = 5 half lives. i.e. original mass was 1 x 2^5. = 32 g

3. D. The formula is 1/(2^n) where n is the number of half lives

4. A. 1.5 is one eight of 12, which means there were 3 half live periods

5. C. Half life is always the same, in one period of half life you will always lose 50% of to radiation its just that remaining 50% gets smaller and smaller.

 

[someth1ng]

Re: half life multiple choice

1 - C
2 - Haven't done it yet.
3 - D
4 - See 2
5 - A?

1 is B - not really a HSC question but if it were to go into HSC, they'd give you 3 radioisotopes and 1 non-radioisotope. In this case, all 3 are radioactive and hence, you really need to search out each half-life to determine how much each decays.
5 is C - the half life of an element is the half life of an element, it is a property of an element that won't change. It's like how molar mass of water will be the molar mass of water (18g/mol) but the mass of water depends on the sample.

 

[golgo13]

Re: half life multiple choice

Is it me or are only 3 and 5 the only questions that are applicable to exams. Because 1,2 and 4 all need to give you a constant (half life value)

 

[someth1ng]

Re: half life multiple choice

Is it me or are only 3 and 5 the only questions that are applicable to exams. Because 1,2 and 4 all need to give you a constant (half life value)

Yeah, 1 can also be used IF they give only 1 radioisotope and 3 stable nuclei.

 

[nsbrando]

mola heat of combustion

The molar heat of combustion of 1-propanol is 2021 kJ mol-1. Assuming no heat loss, what would be the final temperature of the water???

Mass of 1 Propanol burnt: 0.60g
Mass of water heated: 200g
Initial temp of water: 21.0 degrees celcius

 

[kunal96]

Re: mola heat of combustion

change in H=m*C*change in temp
4.18*200*change in temp=836*change in temp
=0.836*change in temp

moles of fuel=grams of fuel/MM of fuel
moles of fuel=0.6/60.094
=0.001

Molar heat of combustion=2021 kJ/mol
and, we know molar heat of combustion is kJ/(mol of fuel) or enthalpy change/moles of fuel
therefore 2021 kJ/mol=(0.836*change in temp)/0.001 <--- (since we calculated previously enthalpy change in kJ was 0.836*change in temp whilst the moles of fuel are 0.001 (3 DP)
Rearranging the equation we get (2021*0.001)/(0.836)=change in temp
therefore change in temperature is 24.14 degrees Celsius. However that is the CHANGE in temp from intiial temp. so, final temp is 24.14+21=45.14 degrees Celsius

 

[kunal96]

Re: mola heat of combustion

i hope you got the first part of the calculation, that is yr 11 stuff.

 

[someth1ng]

Re: mola heat of combustion

kunal96, don't forget your units during the calculation.

 

[kunal96]

Re: mola heat of combustion

kunal96, don't forget your units during the calculation.

sshhh.