The concentration of stomach acid, HCl, is approximately 0.10 M. What volume of stomach acid contains 0.25 mg of HCl?

Question

Please include step by step how to answer this question including any conversions you may have to do and the formula.

Answer 1

There are several ways to approach this problem, depending on what units you want to use in your final answer. You could report the answer in liter, milliliters, microliters, etc.  The solution below is shown for milliliters and microliters.

0.10 M HCl = 0.1 moles HCl/liter

molar mass HCl = 36.5 g/mole

How many moles or mmoles of HCl is 0.25 mg?  

0.25 mg x 1 mmole/36.5 mg = 0.00685 mmoles

0.10 M = 0.1 mol/L = 0.1 mmoles/ml

(0.1mmoles/ml)(x ml) = 0.00685 mmoles

x = 0.0865 ml = 68.5 ul