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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


Sagot :

Answer:

[tex]\boxed {\boxed {\sf B. \ 1.5 *10^{23} \ formula \ units}}[/tex]

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.

[tex]\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}[/tex]

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

[tex]0.250 \ mol \ KNO_3 *\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 \ mol \ KNO_3}[/tex]

The units of moles of potassium nitrate cancel.

[tex]0.250 *\frac {6.022*10^{23} \ formula \ units \ KNO_3}{1 }[/tex]

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

[tex]0.250 *{6.022*10^{23} \ formula \ units \ KNO_3}[/tex]

[tex]1.5055 * 10^{23} \ formula \ units \ KNO_3[/tex]

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

[tex]1.5 *10^{23} \ formula \ units \ KNO_3[/tex]

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