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.
I don't know where to start! Someone please help?
Read the part about pH and pI carefully. The answer is there. Remember that adding NaOH will form the Na salt and adding HCl can form the amine salt.
So with NaOH... it's a strong base... it denatured the protein so it eliminated the suspension? Adding acid to the original suspension didn't do anything because it didn't denature the protein?
In strong acid, the protein is exposed to the strong acid and the charge is neutral as the protein gains a proton. In strong base, the protein is exposed to OH- and postive (as a proton is being taken away).
???
No problem! Let's break down the situation step by step and understand what is happening.
1. Attempted dissolution in water: When a protein is mixed with water, it interacts with the water molecules. Proteins are made up of amino acids, and these amino acids contain ionizable functional groups, such as carboxyl (-COOH) and amino (-NH2) groups. In water, these groups can dissociate, resulting in the protein acquiring a net charge.
2. Suspension formation: The protein may not have dissolved completely in water due to factors such as hydrophobic interactions or insufficient solubility. These factors can lead to the formation of a suspension, where particles of the protein remain suspended in the water instead of being dissolved.
3. Drop-wise addition of NaOH: NaOH is a strong base, and when it is added drop-wise to the protein suspension with stirring, it increases the pH of the solution. As the pH increases, the concentration of hydroxide ions (OH-) increases. The hydroxide ions can react with the carboxyl groups of the proteins, which are usually negatively charged under normal physiological pH conditions. This reaction results in the carboxyl groups being deprotonated and becoming negatively charged (-COO-). The increased negative charge on the protein allows it to repel other protein molecules, facilitating their solubility and ultimately eliminating the suspension.
4. Addition of acid to the original suspension: When acid is added to the original protein suspension, it lowers the pH of the solution. However, unlike the strong base, the acid does not have a significant effect on the charge of the protein. Since the suspension was not affected by the addition of acid, it suggests that the protein is not significantly charged at acidic pH conditions.
In summary, the pH affects the charge on a protein by altering the ionization state of its functional groups. Increasing the pH with a strong base, such as NaOH, can neutralize the negative charge of the protein and make it more soluble. Lowering the pH with acid does not have a strong impact on the charge of the protein and, therefore, does not affect its solubility in this specific case.