Calculate the Quantity of substance in a Titrated solution: A flask contains 20 mL of a solution with an unknown amount of HCl. This solution is titrated with 0.207 M NaOH. It takes 4.47 mL NaOH to complete the rection. What is mass and the molority of the HCl?
Strategy: Convert the volume of NaOH to moles of NaOH (using the molar of NaOH). Then convert moles NaOH to moles HCl, using the chemical equation. Finally, convert moles HCl to gram HCl and molaruty HCl.

Explanation

Step 1. Converting volume NaOH to moles NaOH
`n_(NaOH)=V_(L)xxM`
`=4.47xx10^(-3) L NaOH "soln"xx(0.207 mol NaOH)/(1 L NaOH "soln")`
`=0.000925 mol NaOH`
`=9.25xx10^(-4) mol NaOH`
Step 2. According to the balanced equation `(NaOH+HCl rarr NaCl+H_(2)O)`, the number of moles of HCl is the same as that os NaOH:
`n_(HCl)=9.25xx10^(-4) mol NaOHxx(1 mol HCl)/(1 mol NaOH)`
`=9.25xx10^(-4) mol HCl`
Step 3. Dividing the number of moles of HCl by the volume gives the molarty of HCl:
HCl molarity`=("Moles" HCl)/V_(L)`
`=(9.25xx10^(-4) mol HCl)/(20xx10^(-3) L HCl)`
`=0.0462 M HCl`
Step 4. Multiplying the number of moles of HCl by the molar mass of HCl gives the mass of HCl:
`mass_(HCl)=n_(HCl)xx Molar mass_(HCl)`
`=(9.25xx10^(-4) mol HCl)((36.5 g HCl)/(1 mol HCl))`
`=0.0338 g HCl`