6.25 L of a propanoic acid-propanoate buffer must be prepared. The pH of the buffer needs to be 5.05. The solution will be 0.120M in propanoic acid. If the propanoate ion comes from the strontium propionate Sr(C3H5O2)2 then how many grams of strontium propanoate are needed?
To determine the number of grams of strontium propanoate needed to prepare the buffer, we need to consider the molar ratio between propanoate ion (C3H5O2-) and strontium propanoate (Sr(C3H5O2)2).
The formula weight of strontium propanoate can be calculated by adding the atomic masses of its constituent elements: Sr (strontium), C (carbon), H (hydrogen), and O (oxygen). The molecular formula of strontium propanoate (Sr(C3H5O2)2) indicates that it contains 2 propanoate ions, so we'll need to multiply the molecular weight of propanoate ion (C3H5O2-) by 2.
Here are the steps to calculate the grams of strontium propanoate needed:
1. Determine the molar mass of propanoate ion (C3H5O2-):
- 3 carbon atoms: 3 * atomic mass of carbon = 3 * 12.01 g/mol
- 5 hydrogen atoms: 5 * atomic mass of hydrogen = 5 * 1.01 g/mol
- 2 oxygen atoms: 2 * atomic mass of oxygen = 2 * 16.00 g/mol
- Total molar mass of propanoate ion = sum of the above masses
2. Multiply the molar mass of propanoate ion by 2 to account for the 2 propanoate ions in strontium propanoate.
3. Calculate the number of moles of propanoate ion required in the buffer solution. To do this, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, the propanoic acid (HA) is present at a concentration of 0.120 M. Since the buffer is prepared in a 6.25 L solution, the total number of moles of propanoic acid (HA) is 0.120 M * 6.25 L.
Rearranging the Henderson-Hasselbalch equation, we can calculate the ratio of [A-] to [HA].
4. Finally, multiply the number of moles of propanoate ions calculated in step 3 by the molar mass of strontium propanoate (including the 2 propanoate ions).
This calculation will give us the total grams of strontium propanoate needed to prepare the buffer solution.