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chemistry

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I know the formula is Ma x Mla / 1000 x Sa / Sb = Mb x Mlb / 1000



if 175 ml of KOH of unknown concentration with a methyl red indicator present is titrated with [0.275 M] H3PO4, the yellow solution turns red after 29.6 ml of the H3PO4 is added. What is the molarity of the KOH solution?

On the above problem I think it goes like this but i'm stumped...
0.172 x 27.4 / 1000 x 1/2 = Mb x 100 / 1000 ?? What do I do with the 1/2

also..

If 100 ml of HCl of unknown concentration with a methyl orange indicator present is titrated with [0.172 M] Ca(OH)2, the red solution turns yellow after 27.4 ml of the Ca(OH)2 is added, What is the molarity of the HCl solution?

Please Help I can't understand how to do this...

  • chemistry - ,

    moles H3PO4 = 0.0296 L x 0.275 M=0.00814

    the balanced equation is

    H3PO4 + 3 NaOH = Na3PO4 + 3 H2O
    the ratio between H3PO4 and NaOH is 1 : 3
    moles NaOH = 3 x 0.00814 =0.0244

    molarity of NaOH = 0.0244 mol/ 0.175 L=0.140 M

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