Question

What is the mass of `3.2 × 10^24` atoms of nickel?

Answer 1

The mass is 310 g.

Explanation:

`3.2 × 10^24 color(red)(cancel(color(black)("atoms Ni"))) × (1 color(red)(cancel(color(black)("mol Ni"))))/(6.022 × 10^23 color(red)(cancel(color(black)("atoms Ni")))) × "58.69 g Ni"/(1 color(red)(cancel(color(black)("mol Ni")))) = "311.870 g Ni"` (to 6 digits).

You have to round this answer to 2 significant figures.

That is, you must drop all digits to the right of the red bar: `"31"color(red)(|)"1.870"`

When rounding, you examine the digit to the right of the red bar: the `1` that is just before the decimal place.

The digit you are examining is the first digit to be dropped.

If the first digit to be dropped is less than 5, drop it and all the digits to the right of it.

The rounded number becomes `310`.

Note: The trailing zero in `310` is not a significant digit.