Which of the following is NOT true for a solution buffered at a selected pH?
1. The buffered solution could be made to be either acidic or basic.
2. The solution pH will increase a lesser amount than a non-buffered solution, when base is added.
3. The solution pH will not change with the addition of an acid.
4. The buffered solution contains an acid and its conjugate base.
Please help I am confused
Choice 3 is an incorrect statement... Buffer solutions 'limit' changes in pH by common ion effect when acid or base is added, they do NOT prevent changes.
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Ah, don't worry, I'm here to help! The statement that is NOT true for a solution buffered at a selected pH is number 3. The solution pH will actually change with the addition of an acid in a buffered solution. It just won't change as drastically as it would in a non-buffered solution. So, option 3 is the one that's not quite accurate. Hope that clears things up!
The correct answer is:
1. The buffered solution could be made to be either acidic or basic.
Explanation:
A buffer solution resists changes in pH when small amounts of acid or base are added to it. It usually comprises a weak acid (HA) and its conjugate base (A-). When an acid is added to the buffered solution, the excess H+ ions react with the base (A-) to form HA, preventing a significant change in pH. Similarly, when a base is added, the extra OH- ions react with the weak acid (HA) to form water and A-, again preventing a drastic change in pH. Therefore, the pH of a buffered solution typically remains relatively constant, specifically around the value of the pKa of the weak acid.
However, a buffered solution cannot be adjusted to be either acidic or basic. The pH of the buffered solution is determined by the equilibrium between the weak acid and its conjugate base. If an attempt is made to increase the pH by adding a strong base, it will consume the weak acid and convert it into its conjugate base, causing an increase in the pH. Conversely, if a strong acid is added, it will consume the conjugate base and convert it back into the weak acid, resulting in a decrease in pH. The buffer's ability to maintain a relatively constant pH relies on the presence of both the weak acid and its conjugate base.
To determine which statement is NOT true for a solution buffered at a selected pH, let's review each statement:
1. The buffered solution could be made to be either acidic or basic.
This statement is true for a buffered solution. A buffer is a mixture of an acid and its conjugate base, which can resist changes in pH by absorbing excess H+ (acidic conditions) or OH- (basic conditions) ions.
2. The solution pH will increase a lesser amount than a non-buffered solution when a base is added.
This statement is true for a buffered solution. When a base is added to a buffered solution, the buffer's acidic component can neutralize the added OH- ions, preventing a significant change in pH.
3. The solution pH will not change with the addition of an acid.
This statement is true for a buffered solution. When an acid is added to a buffered solution, the buffer's conjugate base can react with the added H+ ions, preventing a significant change in pH.
4. The buffered solution contains an acid and its conjugate base.
This statement is also true for a buffered solution. By definition, a buffer is a solution containing both an acid and its conjugate base in appreciable amounts.
Therefore, the statement that is NOT true for a solution buffered at a selected pH is:
"1. The buffered solution could be made to be either acidic or basic."
A buffered solution is designed to resist large changes in pH, so it is not easily shifted to either the acidic or basic side of the pH scale.