Question

Suppose the half life of element K is 20 minutes. If you have 200 g sample of K, how much of element K will be left after 60 minutes?

Answer 1

`25color(white)(i)g`

Explanation:

Recall that the formula for half-life is:

`color(blue)(|bar(ul(color(white)(a/a)y=a(b)^(t/h)color(white)(a/a)|)))`

where:
`y=`final amount
`a=`inital amount
`b=`growth/decay
`t=`time elapsed
`h=`half-life

To find the amount of the sample left after `60` minutes, substitute your known values into the equation.

`y=200(1/2)^(60/20)`

Solve for `y`.

`y=200(1/2)^3`

`y=200(1/8)`

`color(green)(|bar(ul(color(white)(a/a)y=25color(white)(i)gcolor(white)(a/a)|)))`