[pure-silver] Re: baking soda as wash aid

  • From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
  • To: pure-silver@xxxxxxxxxxxxx
  • Date: Thu, 17 Feb 2005 18:41:35 -0500 (EST)

From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
Subject: [pure-silver] Re: baking soda as wash aid
Date: Thu, 17 Feb 2005 17:32:35 -0500

> In a solution of sodium bicarbonate the principal species is the HC03-
> ion.  There is a very small amount of CO3-2 ion present from further
> dissociation of HC03-.  My question is where on the HC03- ion are you
> intending to put the extra C02 that you say is absorbed?

You are switching the point. Extra gas will dissolve in water and make
more carbonic acid.

> I quote from the Food Chemicals Codex; "Its solutions, when freshly
> prepared with cold water, without shaking, are alkaline to litmus.  The
> alkalinity INCREASES as the solutions stand, are agitated or are
> heated."
> You will find a similar statement in any detailed discussion of sodium
> bicarbonate.

And you are quoting irrelevant parts? Amazing.

When bicarbonate is dissolved in absence of gas exchange with air, it
will have a certain pH. If you mix pure bicarbonate in pure water, pH
will be something like 8.x depending on the concentration. Over time,
in contact with air, the gas exchange will occur and eventually
equilibrate at a pH determined by the temperature, bicarbonate
concentration, and carbon dioxide concentration in air. That'll be
lower than the fresh solution.

If the starting pH is lower, as in the baking powder or other
mixtures, the pH will rise, but the pH will reach equilibrium from
high 6.x to low 8.x depending on the concentration.

Either case, your warning is an empty one, because pH will reach an
equilibrium below 8 point something, and there is no danger of
anything because of this.

Ryuji Suzuki
"Keep a good head and always carry a light camera."
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