Question

What is the molar concentration of the solution after adding 1 mL of 6.00 mol/L `"HCl"` to 499 mL of water?

Answer 1

The molar concentration of the dilute `"HCl"` solution is 0.0120 mol/L.

Explanation:

The critical thing to remember is that

`"moles of HCl before dilution = moles of HCl after dilution"`

The formula for molar concentration `c` is

`color(blue)(bar(ul(|color(white)(a/a)c = "moles"/"litres"color(white)(a/a)|)))" "` or `color(blue)(bar(ul(|color(white)(a/a)c = n/Vcolor(white)(a/a)|)))" "`

Moles of `"HCl"` in 1 mL

`n = "0.001 00" color(red)(cancel(color(black)("L HCl"))) × "6.00 mol HCl"/(1 color(red)(cancel(color(black)("L HCl")))) = "0.006 00 mol HCl"`

Molar concentration of the dilute `"HCl"`

There will still be 0.006 00 mol of `"HCl"` after you have added 499 mL of water.

∴ `c = n/V = "0.006 00 mol"/"0.500 L" = "0.0120 mol/L"`