20.0 mL of 0.10 M hydrochloric acid (HCl) reacts with 20.0 mL of 0.30 M potassium hydroxide (KOH) solution - VCE - SSCE Chemistry - Question 13 - 2005 - Paper 1

Similarly, for KOH: $ext{moles}_{ ext{KOH}} = 0.30 ext{ M} imes 0.020 ext{ L} = 0.006 ext{ moles}$

The balanced reaction is:

After reaction: $ext{moles}_{ ext{KOH remaining}} = 0.006 - 0.002 = 0.004 ext{ moles}$

The total volume after mixing the two solutions is: $ext{Total Volume} = 20.0 ext{ mL} + 20.0 ext{ mL} = 40.0 ext{ mL} = 0.040 ext{ L}$

The concentration of K+ ions is given by: ext{Concentration}_{ ext{K}^+} = rac{ ext{moles}_{ ext{KOH remaining}}}{ ext{Total Volume}} = rac{0.004 ext{ moles}}{0.040 ext{ L}} = 0.10 ext{ M}