Question

Find the empirical formula of a compound containing 26.56% potassium, 34.51% chromium, and the remainder oxygen.

Answer 1

K₂Cr₂O₇

Step-by-step explanation:

Finding % of O

• % O = 100% - % K - % Cr
• % O = 100% - 26.56% - 34.51%
• % O = 73.44% - 34.51%
• % O = 38.93%

Steps

1. Change % of each element into grams.
2. Convert grams of each element into moles by dividing grams by molar mass.
3. Divide all moles by the smallest number of moles.
4. If the moles are all whole numbers, then you’re done and that’s your empirical formula.
5. If not, multiply all moles by number such that everything is a whole number.

Solving

We have 26.56g of K, 34.51g of Cr, and 39.93g of O

• Moles of K, n(K) = 26.56/39.0983 = 0.68 moles
• Moles of Cr, n(Cr) = 34.51/51.9961 = 0.66 moles
• Moles of O, n(O) = 38.93/15.9994 = 2.43 moles
• K = 0.68/0.66 ≈ 1 x 2 = 2
• Cr = 0.66/0.66 = 1 x 2 = 2
• O = 2.43/0.66 = 3.5 x 2 = 7

The empirical formula is K₂Cr₂O₇