If 20.0 ml of ca(oh)2 with an unknown concentration is neutralized by 37.5 ml of 0.124 m hcl, what is the concentration of the ca(oh)2 solution? show all of the work needed to solve this problem.
ca(oh)2 + 2 hcl yields 2 h2 o + cacl2

You first need to write the balanced chemical reaction for what is going on.
Ca(OH)₂+2HCl→2H₂O+CaCl₂

After you make the balanced chemical reaction, First you find the moles of HCl used.  To do this multiply 0.0375L by 0.124M to get 0.00465mol HCl.  Then you multiply 0.00465mol HCl by (1mol Ca(OH)₂)/(2mol HCl) to get 0.002325mol Ca(OH)₂.  Finally to find concentration of Ca(OH)₂ used you divide 0.002325mol by 0.020L to get 0.116M Ca(OH)₂.
Therefore the concentration of the unknown solution of Ca(OH)₂ was 0.116M.

I hope this helps.  Let me know if anything is unclear.