On preparation of a solution of protein, you attempted to dissolve the substance in water, but a suspension resulted. Drop-wise adition of NaOH solution, with stirring, eliminated the suspension. Addition of acid to the original suspension had no effect. Think about how pH affects the charge on a protein and explain the phenomenon.
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so the protein in acidic solution did not dissolve. acidic solution have a + charge and take away electrons/bonds. if the protein side chains are acidic (NH3+), then nothing would happen as they're both acidic?
if the protein is in basic solution and it dissolved...and the protein side chains are acidic, then the protein would dissolve as the - charge on the OH- would form new bonds with the protein side chains that are +.
Can you please check my reasoning? it somehow makes sense in my head but i don't know if i used technical science terms or anything. Thank you!
Yes, you have it.
Your reasoning is partially correct, but let's dive into a more detailed explanation of how pH affects the charge on a protein and why the observed phenomena occurred.
Proteins are composed of amino acids, and each amino acid contains functional groups such as carboxyl groups (-COOH) and amino groups (-NH₂). These functional groups can be ionized depending on the surrounding pH.
In an acidic solution, the concentration of hydrogen ions (H⁺) is high. The excess of H⁺ ions can protonate the carboxyl groups (-COOH) of the protein, converting them into charged carboxylic acids (RCOOH → RCOO⁻ + H⁺). Similarly, the amino groups (-NH₂) can gain an extra H⁺ to become charged ammonium ions (RNH₂ → RNH₃⁺). As a result, the overall charge of the protein becomes positive.
Now, when you attempt to dissolve the protein in water, the positively charged protein molecules are attracted to the negatively charged water molecules, forming a suspension. The attractive forces between the protein's positive charges and the water's negative charges are relatively weak, leading to the formation of a suspension rather than a fully dissolved solution.
When you added NaOH solution drop-wise with stirring, NaOH dissociated to produce hydroxide ions (OH⁻). These hydroxide ions react with the positively charged protein molecules, neutralizing their charges. The process can be represented as RCOO⁻ + OH⁻ → RCOOH + OH⁻. As a result, the protein becomes uncharged, and the suspension is eliminated. The neutralized protein can dissolve more readily in water because there are no longer strong positive charges to attract negative water molecules.
On the other hand, when you added acid to the original suspension, there was no notable effect. This lack of effect is because the acidic solution already contained an excess of H⁺ ions. Since the protein was already positively charged in the acidic environment, the addition of more H⁺ ions did not significantly alter the protein's charge or its ability to dissolve.
In summary, the observed phenomenon can be explained by the change in the protein's charge due to the surrounding pH. In an acidic solution, the protein becomes positively charged and forms a suspension. When a basic solution (NaOH) is added, the hydroxide ions neutralize the protein's positive charges, allowing it to dissolve. However, adding acid to the original suspension does not alter the protein's charge significantly and therefore has no effect on its solubility.