13hasane
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I’m really struggling on this question... the answer is sodium but I’m really not sure how... would really appreciate some help

A sample of gallium, Ar=69.7, was analysed and was found to consist of 65% of 69 Ga and one other isotope.
Determine the mass number of the other isotope in the sample of gallium
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username3249896
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The answer is 71, not sodium
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13hasane
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Yes you’re right
How did u get that answer
I read the mark scheme wrong
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username3249896
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(Original post by 13hasane)
Yes you’re right
How did u get that answer
I read the mark scheme wrong
There are only 2 isotopes, so if the abundance of one is 65%, the abundance of the other is ....
Then write an equation to find the mass number of the unknown isotope
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13hasane
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The abundance of the other is 35%
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13hasane
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What is the equation
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username3249896
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(Original post by 13hasane)
What is the equation
You should be able to write it

 \dfrac{69 \times 65 + x \times 35}{100} = 69.7 where x is the mass number of the other isotope
You need to solve for x (x = 71)
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13hasane
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Thank you very much, I understand now
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