Question

How many moles of potassium are in 0.256 g?

Answer 1

`n~~0.00655mol`

Explanation:

Recall that the formula for moles is:

`color(blue)(|bar(ul(color(white)(a/a)n=m/Mcolor(white)(a/a)|)))`

where:
`color(magenta)n=`number of moles
`color(orange)m=`mass (grams)
`color(teal)M=`molar mass (grams/mole)

Since you already have the mass of potassium, `color(orange)(0.256g)`, and the molar mass, `color(teal)(39.1g/(mol))`, which can be determined by looking at a periodic table, the only variable left to solve for is `color(magenta)n`, the number of moles. Thus:

`color(magenta)n=color(orange)m/color(teal)M`

`color(magenta)n=color(orange)(0.256g)/color(teal)(39.1g/(mol))`

`n=0.256g*(mol)/(39.1g)`

`n=0.256color(red)cancelcolor(black)g*(mol)/(39.1color(red)cancelcolor(black)g)`

`n=0.006547314578mol`

`color(green)(|bar(ul(color(white)(a/a)n~~0.00655molcolor(white)(a/a)|)))rArr`rounded off to `3` significant figures