B (Salters) F331 (Chemistry for Life) 22nd May 2015 [Official Thread]

All you have to know for our specification is that in radiocarbon dating, carbon 14 is used to measure how old an object is. The theory behind this is that when plants photosynthesise, they take in a small amount of carbon 14, therefore when animals eat these plants, they also gain a small amount of carbon 14, this amount of carbon 14 is then let back out into the atmosphere (due to aerobic respiration), therefore all living materials are constantly replenishing the amount of carbon 14 inside of them to match the value in the atmosphere. Therefore when an organism dies, this carbon 14 inside of them decays and we can thus measure how old the organism is: the less the amount of carbon 14, the more old it is. This is because we know the half life of carbon 14 and the half life is constant for that given isotope.

However, there are flaws in this, for example how do we know that the decay was constant, there could've been environmental changes which affected the decay and the amount of carbon 14.

Hope this helps ^_^

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Reply 3

vuvuzela

OP

Original post by MuslimaSheikh

All you have to know for our specification is that in radiocarbon dating, carbon 14 is used to measure how old an object is. The theory behind this is that when plants photosynthesise, they take in a small amount of carbon 14, therefore when animals eat these plants, they also gain a small amount of carbon 14, this amount of carbon 14 is then let back out into the atmosphere (due to aerobic respiration), therefore all living materials are constantly replenishing the amount of carbon 14 inside of them to match the value in the atmosphere. Therefore when an organism dies, this carbon 14 inside of them decays and we can thus measure how old the organism is: the less the amount of carbon 14, the more old it is. This is because we know the half life of carbon 14 and the half life is constant for that given isotope.

However, there are flaws in this, for example how do we know that the decay was constant, there could've been environmental changes which affected the decay and the amount of carbon 14.

Hope this helps ^_^

Posted from TSR Mobile

Yeah the flaws are stuff like;

Parent/daughter isotope could me removed/added, therefore not same age as organism.
The half life may not be constant
If the half life is large, and far exceeds the age of the specimen, then the change in count rate will be small and difficult to detect.
Count caused by other isotopes.
Pretty much what the above poster said.

Reply 4

barbiex

How about archaeological dating? could someone please explain that in depth too :smile:

Reply 5

MuslimaSheikh

The same concept applies for archaeological dating :smile:

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Reply 6

NapkinofDestiny

Could anyone state some of the Molar Calculation formulae we need for this exam?

Im not inept at maths but lets just say its not my cup of tea, I cant seem to get my head around it at all :thumbdown:

Thankyou

Reply 7

username1673577

Original post by NapkinofDestiny

Could anyone state some of the Molar Calculation formulae we need for this exam?

Im not inept at maths but lets just say its not my cup of tea, I cant seem to get my head around it at all :thumbdown:

Thankyou

The 2 we need to know are:

1. moles = concentration (in moles per dm^3) times volume (in dm^3)

2. moles = mass (in grams) divided by formula mass

(:

Reply 8

NapkinofDestiny

Original post by Meloddymaybe

The 2 we need to know are:

1. moles = concentration (in moles per dm^3) times volume (in dm^3)

2. moles = mass (in grams) divided by formula mass

(:

Thankyou

)

Reply 9

Resitting this exam cause i got a D last year, I'm so **** at chemistry :/

Reply 10

Marli-Ruth

How did everyone do on F333 Skills test :smile:

Reply 11

Original post by Marli-Ruth

How did everyone do on F333 Skills test :smile:

I got an A on it last year (85%)

Reply 12

vuvuzela

OP

Original post by Marli-Ruth

How did everyone do on F333 Skills test :smile:

Everyone should be done for F333 next year we should help each other out. Some people do skills before and after others so a few pointers could be given if you know what I mean

Reply 13

Marli-Ruth

Original post by GianluigiBuffon

I got an A on it last year (85%)

An A was 53/60?
According to the grade boundaries so you got 88%? No?

That's really good! I got just on the A boundary so I'm chuffed!

Reply 14

Original post by Marli-Ruth

An A was 53/60?
According to the grade boundaries so you got 88%? No?

That's really good! I got just on the A boundary so I'm chuffed!

I got 51/60 UMS which is 85% and around 55/60 raw marks and thats really good!!! keep up the good work

Reply 15

Tajwar786

The light and electron chapter is really confusing like, I know how to describe how absorption and emmision spectra looks like (colour line on black bg or black lines on colour bg) when passes through a prism, but what is the idea behind this??? Why do we use prism or what this lines actually means and why the gaps of lines get smaller at higher frequncy. Thanks in advance :smile:

Reply 16

Original post by Tajwar786

The light and electron chapter is really confusing like, I know how to describe how absorption and emmision spectra looks like (colour line on black bg or black lines on colour bg) when passes through a prism, but what is the idea behind this??? Why do we use prism or what this lines actually means and why the gaps of lines get smaller at higher frequncy. Thanks in advance :smile:

Basically electrons absorb a certain wavelength of light which corresponds to a particular colour and at a specific frequency. So this is why we get the lines innit

Reply 17

vuvuzela

OP