Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    20
    ReputationRep:
    1) What does weighted mean in this statement? : Relative atomic mass of an element is the weighted average atomic mass of the element relative to 1/12 the mass of an atom of the C12 isotope.

    2) Why do we use 1/12 the mass of an atom of the C12 isotope? (My teacher said its because it is thought to be stable)

    3) What does the relative atomic mass of chlorine (35.5) tell you about the relative abundance of the 2 naturally occurring isotopes of chlorine 37 and chlorine 35?
    • Thread Starter
    Offline

    20
    ReputationRep:
    bump
    • Thread Starter
    Offline

    20
    ReputationRep:
    pls
    Offline

    18
    ReputationRep:
    This is very simple GCSE knowledge, and simple maths.

    1) Weighted - depending on the abundance of certain isotopes in the world, the atomic mass is calculated as an average.
    It's the same maths used when calculating a mean in a frequency table in maths.

    2) Carbon-12 has a stable arrangement (6 protons, 6 neutrons, 6 electrons), is relatively common in the world, and is a solid at a normal temperature, so is easy to store and transport. So, it's convenient to use Carbon.

    3) 35.5 tells you that 75% of the world's Chlorine is Chlorine-35, and 25% of the world's Chlorine is Chlorine-37. The formula to work this out is = (Mass x Abundance) + (Mass x Abundance) ... (in this question there are only 2 isotopes), then divide that by the total abundance (usually 100%), giving you 35.5
    Offline

    17
    ReputationRep:
    1) weighted means its been compared to other isotopes of the same element and its abundances - to get an average mass for an atom of the element.

    2) Its because its Ar is "stable" (its Ar is a whole number - which is 12 so its easier to use to compare with other atoms because other atoms have an Ar with lots of decimals/ are odd numbers.)

    3) It tells us that theres 75% abundance of cl-35 and 25% abundance of cl-37 ((75x35)+(35x25) divide by 100 = 35.5)
    • Thread Starter
    Offline

    20
    ReputationRep:
    AnnaRainbows Ishan_2000 i didnt learn anything about abundance in year 10/11 literally 0, this is all new to me. we learnt basics of isotopes and how they differ but thats it. thanks ishan for helping and shohaib712
    Offline

    18
    ReputationRep:
    (Original post by sfaraj)
    AnnaRainbows Ishan_2000 i didnt learn anything about abundance in year 10/11 literally 0, this is all new to me. we learnt basics of isotopes and how they differ but thats it. thanks ishan for helping and shohaib712
    Oh, ok, that's a bit weird. Anyway, you have learnt it now.
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Sponsored content:

HEAR

HEAR

Find out how a Higher Education Achievement Report can help you prove your achievements.

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.