Vangioni G.

asked • 12/20/17

How many significant figures should it have to get correct answer?

Here is my question: 
 
Sodium has a density of 0.971 g/cm3 and crystallizes with a body-centered cubic unit cell. Determine the atomic radius of sodium atom.
 
How many significant figures should it have to get correct answer? So like assume that I'm going to calculate this question, how many significant figures should I solve with?

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Randall K. answered • 12/20/17

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Vangioni, density is not significant because it is a calculated (vs. measured) value.  If you use an atomic mass of 22.99 g/mol for the sodium atom and 6.022x10^23 for Avogadro's number, then you may report your answer in four sig. fig.'s.
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Vangioni G.

What if we use 22.99 or 23?
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12/20/17

Vangioni G.

So I mean should we use 22.99 or 23? Assume that we've used it as 23. What will happen?
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12/20/17

Randall K.

The atomic mass of sodium is not 23 g/mol.  22.99 g/mol better represents the atomic mass of the sodium atom.
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12/20/17

Vangioni G.

So we will use it as 22.99 g/mol. Now,  will I solve it by using 4 signficant fig.?
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12/20/17

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