Question #29ef3

2 Answers
Feb 20, 2017

Answer:

The empirical formula is #K_2O#

Explanation:

21.7 g of potassium is 0.555 mol (#21.7g -:39.1 g/"mol"#)

4.44 g of oxygen is 0.2775 mol (#4.44g-:16.0 g/"mol"#)

This change to moles is necessary, because we need to compare quantities using a unit that refers to a number of atoms rather than a total mass.

Now, look for a whole-number ratio between these two values. If it is not obvious, try dividing both by the smaller. This will give you a ratio in which one term is a one, and should be easier to recognize.

Oxygen: #0.2775-:0.2775 = 1.0#

Potassium: #0.555-:0.2775 = 2.0#

So, the ratio in the compound is 2 atoms of K for each 1 atom of O, giving a formula #K_2O#

Feb 20, 2017

Answer:

#K_2O# is the #"empirical formula"#.

Explanation:

The empirical formula is the simplest whole number ratio that represents constituent atoms in a species. Given masses of constituent atoms, we simply divide thru by the atomic mass:

#"Moles of potassium"=(21.7*g)/(39.10*g*mol^-1)=0.555*mol#

#"Moles of oxygen"=(4.44*g)/(15.999*g*mol^-1)=0.278*mol#

And if I divide thru by #0.278*mol#, clearly I get #K_2O#. Capisce?