In the awwa notebook for $\ce{Na2SiF6}$ determination, why it is required to wash the product sample in an alcoholised $\ce{KCl}$ solution before titration?

  • 2
    $\begingroup$ I think we need a bit more info to be able to answer this question. In general, you wash your sample to get rid of something unwanted. What this might be in your case, nobody can tell you without more details about the experiment setup. $\endgroup$ – Gerhard Apr 25 '15 at 6:23
  • $\begingroup$ It is true that this is not an academic question that can be answer with a notebook from high school. $\endgroup$ – Bruno Apr 25 '15 at 18:19
  • $\begingroup$ Here the summerised protocole 1. Wheight precise amount of sample to analyse, 2. Suspend sample in enough solution of KCl/carbonate/ethanol/water to keep the solution alcaline, 3. Filter solution in a paper filter, 4. Rince sediment with a solution of KCl/ethanol/water untill filtrate gets a neutral pH, 5. Dissolve filtered sediment in distilled water under heat, 6. When temperature of solution reach 80 C, start titrate with NaOH, 7. As solution is boiling, end titration when the solution is alcaline per phenilphtalein, 8. Amount of NaOH used correlate with amount of Na2SiF6 in sample.Thanks $\endgroup$ – Bruno Apr 25 '15 at 18:41

Your protocol gives you the answer: to make sure your sediment is neutral. After all, you titrate with NaOH afterwards, so any wrong starting point in terms of pH would skew your result.


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