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Daniela_5535
#1 Posted : Monday, June 08, 2020 2:34:04 PM
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Hello,

I’m confused on an AAMC question (Chemical and Physical Foundations of Biological Systems - Passage 3), it states that in a solution of NiSo4 is dissolved in enough water to make 50 ml of a green solution and 7 g of Na2CO3 is dissolved in enough water to make 50 ml of a colourless solution. The two solutions are mixed and a green precipitate forms. The resulting slurry is divided into two portions and one portion is added an excess of 6 M HCL, which results in the disappearance of the precipitate and a rapid evolution of a gas. To the second portion is added a few mm of 6 M NH3. The precipitate dissolves and a blue solution forms.

If red litmus paper is dipped into NA2 CO3 solution it will :

- turn blue because carbonate reacts with water to produce OH- .

However, I chose “turn blue, because sodium ions form sodium hydroxide in water” and was wondering why it was incorrect?

Thank you.
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INSTR_Molly_59
#2 Posted : Monday, June 08, 2020 5:34:58 PM
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Hi Daniela, its because in water, strong acids/bases such as NaOH would ionize to form Na+ and OH- ions, and would not form the compound NaOH. Weak bases will indeed protonate in presence of water, which generates OH- ions that contributes to the basicity of the solution.

Hope this helps! :)
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