# how to work out percentage abundance chemistry

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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]

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]

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#2

(Original post by

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]

**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]

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#5

(Original post by

AQA

**MA1998**)AQA

(Original post by

it should give you the percentage abundance of other isotope - 11B?

**batoot**)it should give you the percentage abundance of other isotope - 11B?

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#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

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

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#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

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

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#9

(Original post by

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

**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

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#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

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

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**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

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#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)

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)

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#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

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

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