Question

28. How many formula units are found in 0.250 moles of potassium nitrate?

2.41 x 1024 formula units
O 1.5x1023 formula units
4.15x10-25 formula units
O 6.022 x 1023 formula units

Answer 1

`\boxed {\boxed {\sf B. \ 1.5 *10^(23) \ formula \ units}}`

Step-by-step explanation:

1 mole of any substance contains the same number of particles. The particles can vary (atoms, molecules, formula units), but there are always 6.022*10²³ particles. In this case, the particles are formula units of potassium nitrate or KNO₃.

Let's create a ratio.

`\frac {6.022*10^(23) \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}`

Since we are trying to find the formula units in 0.250 moles, we multiply by that number.

`0.250 \ mol \ KNO_3 *\frac {6.022*10^(23) \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}`

The units of moles of potassium nitrate cancel.

`0.250 *\frac {6.022*10^(23) \ formula \ units \ KNO_3}{1 }`

The denominator of 1 can be ignored, so we can make a simple multiplication problem.

`0.250 *{6.022*10^(23) \ formula \ units \ KNO_3}`

`1.5055 * 10^(23) \ formula \ units \ KNO_3`

If we round to the nearest tenth, the 0 in the hundredth place tells us to leave the 5 in the tenth place.

`1.5 *10^(23) \ formula \ units \ KNO_3`

0.250 moles of potassium nitrate is approximately equal to 1.5*10²³ formula units of potassium nitrate and choice B is correct.