# Chemistry A level questions

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#1
1. A sample of boron contains the isotopes 10B and 11B (I can't do subscript)

The relative atomic mass of the boron sample is 10.

What is the percentage of 11B atoms in the sample of boron?

2. What is the number of hydrogen atoms in 0.125 of C2H5OH?

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2 years ago
#2
(Original post by lovinglife302)
1. A sample of boron contains the isotopes 10B and 11B (I can't do subscript)

The relative atomic mass of the boron sample is 10.

What is the percentage of 11B atoms in the sample of boron?

2. What is the number of hydrogen atoms in 0.125 of C2H5OH?

1. If RAM is exactly 10 then the percentage of 11B would be 0 or too small to make a difference.

2. moles of C2H5OH= mass/Mr = 0.125/46 = 2.717e-3 mol
no. of C2H5OH molecules = moles* avagadros constant = 2.717e-3 * 6.02e23 = 1.636e21
No. of H atoms = 6 * 1.636e23 = 9.82e21

Hope this helps ^^
0
2 years ago
#3
(Original post by JoannaE)
1. If RAM is exactly 10 then the percentage of 11B would be 0 or too small to make a difference.

2. moles of C2H5OH= mass/Mr = 0.125/46 = 2.717e-3 mol
no. of C2H5OH molecules = moles* avagadros constant = 2.717e-3 * 6.02e23 = 1.636e21
No. of H atoms = 6 * 1.636e23 = 9.82e21

Hope this helps ^^
RAM of boron is 10.8 - I'll bet lovinglife302 just forgot the 8.

Likewise, without a unit on the 0.125, the question is in fact impossible to answer. Assuming the unit was meant to be grams, then your calculation looks fine.

My suggestion, though, is not to just do people's work for them. It doesn't really help them learn.
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