Question

what is the concentration of hcl when 55 ml of this hcl solution neutralize 15ml of .9m ca(oh)2

Answer 1

You can't be lazy and be a good student. It is inexcusable to start sentences with lower case and not show where sentences end with a period. You make it very difficult for someone to read your questions. We don't know where to start and where to end. hcl means nothing except three letters of the alphabet. Be means beryllium but be is a word. Get it?
2HCl + Ca(OH)2 ==> CaCl2 + 2H2O
How many moles base did you use? That is M x L = ?
? moles.
Use the equation to convert moles Ca(OH)2 to moles HCl. That will be
?moles Ca(OH)2 x [2 moles HCl/1 mole Ca(OH)2] = ? moles Ca(OH)2 x 2 = x moles HCl.
Now M HCl = moles HCl/L HCl. You know moles HCl and L HCl, solve for M HCl.