Question

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Calculating Mass Quick Check
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Question
Use the chemical equation to answer the question.

4K(s) + O2(g) → 2K2O(s)

The molar mass of potassium (K) is 39 g/mol. The molar mass of oxygen (O) is 16 g/mol. How many grams of potassium are needed in the reaction to produce 23.5 grams of potassium oxide (K2O)?

(1 point)
Responses

19.5 g
19.5 g

23.5 g
23.5 g

9.75 g
9.75 g

0.50 g
0.50 g

Answer 1

Molar mass K2O = 2(39) + 16 = 94 g/mol.
Moles K2O = 23.5 g / 94 g/mol = 0.25 mol.
From 4 K → 2 K2O, ratio K : K2O = 4 : 2 = 2 : 1, so moles K = 2 × 0.25 = 0.50 mol.
Mass K = 0.50 mol × 39 g/mol = 19.5 g.

Answer: 19.5 g.