Chemical equation

Question

If 25.0g of potassium bicarbonate, KHCO3 has undergo complete decomposition, calculate the number of moles of potassium bicarbonate, KHCO3 decomposed

Answer 1

Molar mass KHCO₃ = 100.1 g / mol

moles KHCO₃ undergoing decomposition = 25.0 g x 1 mol / 100.1 g = 0.2498 mols KHCO₃

Rounding to 3 sig. figs. (based on 3 sig.figs in 25.0 g ) we get 0.250 moles KHCO₃

Answer 2

Since potassium bicarbonate undergoes complete decomposition, then you can say that all 25.0 grams of potassium bicarbonate has decomposed. The next step is to use the molar mass of potassium bicarbonate. You can google this molar mass if you like, but it is good to know how to calculate the molar mass using just a periodic table. Listed below are approximate molar masses of each element:

K: 39 g/mol

H: 1 g/mol

C: 12 g/mol

O: 16 g/mol

You can add the molar masses (make sure to multiply oxygen's molar mass by 3 since there are 3 oxygen atoms in potassium bicarbonate) to get the molar mass of potassium bicarbonate.

Using the molar mass of potassium bicarbonate, you can multiply or divide (check units!) the molar mass by the mass to get the number of moles. You may also need to round your answer to the correct number of significant digits.