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Purity by weight (percentage purity ) question...help please? :( Watch

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    A summary of the question is this.... 1g of boric acid has 50ml of water added to it as well as 15ml of glycerol. After boiling and cooling it was titrated with 1M NaOH using phenolphthalein as indicator and the titre value was 20.60 cm3.

    The question asks for the percentage purity.
    I tried working out by first finding the concentration of naoh and then using the equation B(OH)3 + NaOH--> NaB(OH)4 to find moles of boric acid and a whole bunch of stuff I've lost track of...I keep getting 1.27g as my answer for the supposedly pure mass which cant be as I had 1g in the beginning?? I'm definitely in need of help ...could someone kindly offer a solution please? Thank you!
 
 
 
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