how to work out percentage abundance chemistry

Watch
jellyandjam
Badges: 11
Rep:
?
#1
Report Thread starter 5 years ago
#1
1 (b) A naturally occurring sample of the element boron has a relative atomic mass of 10.8
In this sample, boron exists as two isotopes, 10B and 11B
1 (b) (i) Calculate the percentage abundance of 10B in this naturally occurring sample of boron.
[2 marks]
1
reply
username2224711
Badges: 18
Rep:
?
#2
Report 5 years ago
#2
(Original post by jellyandjam)
1 (b) A naturally occurring sample of the element boron has a relative atomic mass of 10.8
In this sample, boron exists as two isotopes, 10B and 11B
1 (b) (i) Calculate the percentage abundance of 10B in this naturally occurring sample of boron.
[2 marks]
Which exam board is this from?
0
reply
MA1998
Badges: 8
Rep:
?
#3
Report 5 years ago
#3
(Original post by ravioliyears)
Which exam board is this from?
AQA
0
reply
batoot
Badges: 11
Rep:
?
#4
Report 5 years ago
#4
it should give you the percentage abundance of other isotope - 11B?
0
reply
username2224711
Badges: 18
Rep:
?
#5
Report 5 years ago
#5
(Original post by MA1998)
AQA
Thank you!
(Original post by batoot)
it should give you the percentage abundance of other isotope - 11B?
Yeah, thats what I was thinking... o.O
0
reply
eleanorlittle
Badges: 5
Rep:
?
#6
Report 5 years ago
#6
80% boron11, 20% boron10
(0.8*11)+(0.2*10)=10.8
I think...
1
reply
Kozmo
Badges: 10
Rep:
?
#7
Report 5 years ago
#7
I've seen this very question from an AQA paper and no percentage abundance of either of the isotopes was given.

This can be solved through trial and error or algebraically.
The user above me is correct, there's 20% boron-10 and 80% boron-11
1
reply
baz221
Badges: 4
Rep:
?
#8
Report 5 years ago
#8
It's 80% 11B and 20% 10B, I find it kind of hard to explain but I'll give it a go.

If it was 50/50 the average mass would be 10.5, so to raise the mass you need a higher percentage of 11.

Another way of looking at it is 10x + 11y= 10.8

10x+11y=10.8
x+y=1 (ratio)

10x+11y=10.8
10x+10y=10

Take bottom away from top
y=0.8
x+y=1 therefore x=0.2

then multiply by 100 to get percentages as these are ratios

So there is 80% 11 and 20% 10

Hope this helped
6
reply
Kozmo
Badges: 10
Rep:
?
#9
Report 5 years ago
#9
(Original post by baz221)
It's 80% 11B and 20% 10B, I find it kind of hard to explain but I'll give it a go.

If it was 50/50 the average mass would be 10.5, so to raise the mass you need a higher percentage of 11.

Another way of looking at it is 10x + 11y= 10.8

10x+11y=10.8
x+y=1 (ratio)

10x+11y=10.8
10x+10y=10

Take bottom away from top
y=0.8
x+y=1 therefore x=0.2

then multiply by 100 to get percentages as these are ratios

So there is 80% 11 and 20% 10

Hope this helped
Yep, these are the ways in which I would have worked the question out. The former is trial and error and the latter is algebraically involving a simultaneous equation.
0
reply
Joosofsucksess
Badges: 0
Rep:
?
#10
Report 5 years ago
#10
x+y=1 (ratio)
y=1-x

10x+11(1-x)
10x-11x+11=10.8
-x=-0.2
x=0.2

Multiply by 100 to get a percentage and find other percentage:
0.2x100=20%
100-20=80%

20% boron-10 & 80% boron-11
0
reply
jellyandjam
Badges: 11
Rep:
?
#11
Report Thread starter 5 years ago
#11
(Original post by baz221)
It's 80% 11B and 20% 10B, I find it kind of hard to explain but I'll give it a go.

If it was 50/50 the average mass would be 10.5, so to raise the mass you need a higher percentage of 11.

Another way of looking at it is 10x + 11y= 10.8

10x+11y=10.8
x+y=1 (ratio)

10x+11y=10.8
10x+10y=10

Take bottom away from top
y=0.8
x+y=1 therefore x=0.2

then multiply by 100 to get percentages as these are ratios

So there is 80% 11 and 20% 10

Hope this helped
Thankyouuu!!
0
reply
jellyandjam
Badges: 11
Rep:
?
#12
Report Thread starter 5 years ago
#12
Thanks everyone!! Merrry christmas!
0
reply
abby76566
Badges: 0
Rep:
?
#13
Report 5 years ago
#13
aqa
0
reply
Sanssunny
Badges: 0
Rep:
?
#14
Report 4 years ago
#14
You have to solve this algebraically like this:
10.8= 10 (x) 11 (1-x)
So 10.8= 10x 11 -11x
So now you have to get the x's to one side:11 - 10.8= 10x - 11x ( note because it was 11 so to take it to the other side u have to do the opposite which is to subtract it)
Now solve: 0.2 = -1xNow divide both sides by x so:X= 0.2 0.2 x 100 because it's asking for a percentage so:X = 20 ;/;
so this means tht 10B= 20;/;
This means that 11B is 80;/; ( because 100-20 = 80)
0
reply
ConfusedDemon
Badges: 17
Rep:
?
#15
Report 6 months ago
#15
I did it in a different way. So what you would do, would be to create a table, with 10B and 11B at the top. Under those, write x, and 100-x. The reason for writing x is because thats the one we need to find out, but for 100-x it's because both of the values for "x" have to equal 100.

Seeing as the RAM is 10.8, you would work backwards.
10.8 = 10 (x) + 11 (100-x) /100. You would multiply the values of the Borons together with the x to get the unknown. Divide it by 100 to get the percentage.

After that, it's basic solving. I got 1080 = 10x + 1100 - 11x. (got the 1080 by multiplying it by 100). 10x-11x is -x.
1080=-x+1110
1080 - 1100 = -20
-20 = -x, therefore, x is equals to 20
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

How are you feeling now you've started university?

I'm loving it! (48)
13.41%
I'm enjoying it but I'm still settling in (93)
25.98%
I'm a bit unsure (63)
17.6%
I'm finding things difficult (124)
34.64%
Something else (let us know in the thread!) (30)
8.38%

Watched Threads

View All