Plan how you would make 100mL of a buffer solution with a pH of 10.80 to be made using only sodium carbonate, sodium hydrogen carbonate and water.
You should specify the amount of sodium carbonate and sodium hydrogen carbonate that you would use.
Use the Henderson-Hasselbalch equation.
pH = pk2 + log(base/acid)
10.80 = 10.33 + log B/A
B/A = 2.95
CO3^2- = 2.95*HCO3^-
Now you need to pick a number for HCO3^- that will dissolve in 100 mL H2O (say 1.00 g, convert to mols, and calculate g CO3^2- needed. Dissolve the two salts in 100 mL H2O. Plug those numbers back into the HH equation to make sure the pH is 10.80.
Also, look up the solubilities of NaHCO3 and Na2CO3 to make sure they will dissolve in 100 mL H2O.
To make a buffer solution with a pH of 10.80 using only sodium carbonate (Na2CO3), sodium hydrogen carbonate (NaHCO3), and water, you'll need to calculate the appropriate amounts of each ingredient based on their dissociation and pH properties.
1. Understand the pH range:
Buffer solutions are designed to resist changes in pH when small amounts of acid or base are added. In this case, we want a pH of 10.80, so the buffer solution needs to be slightly alkaline.
2. Understand the properties of sodium carbonate and sodium hydrogen carbonate:
Sodium carbonate (Na2CO3) is a strong base, while sodium hydrogen carbonate (NaHCO3) is a weak base. By mixing the two, we can create a buffer solution that can resist changes in pH with the addition of acid due to the weak base's ability to partially neutralize the acid.
3. Determine the molar amounts of sodium carbonate and sodium hydrogen carbonate:
To calculate the amounts of each compound, you need to use the Henderson-Hasselbalch equation for pH of a buffer solution:
pH = pKa + log([A-]/[HA])
In this case, we're using sodium carbonate (A-) and sodium hydrogen carbonate (HA) as the conjugate base and acid pairs. The pKa of carbonic acid (H2CO3) is 6.35. Additionally, the ratio of [A-]/[HA] should be chosen to achieve the desired pH.
4. Calculate the appropriate molar ratios:
Let's assume we want to use a 1:1 molar ratio of sodium carbonate to sodium hydrogen carbonate. This means that the concentrations of [A-] and [HA] should be equal.
Since pH = pKa + log([A-]/[HA]), and we know pH = 10.80 and pKa = 6.35, we can rearrange the equation to find the ratio [A-]/[HA]:
10.80 = 6.35 + log([A-]/[HA])
4.45 = log([A-]/[HA])
This means that the ratio [A-]/[HA] should be approximately 10^(4.45). Hence, the concentrations for both compounds should be equal.
5. Determine the molar amounts:
To determine the molar amounts, you'll need the molecular weights of sodium carbonate and sodium hydrogen carbonate. The molecular weight of Na2CO3 is approximately 105.99 g/mol, and the molecular weight of NaHCO3 is approximately 84.01 g/mol.
Let's calculate the amounts needed for a 100mL buffer solution:
- Sodium carbonate: (105.99 g/mol) * (x moles) = (10 mL) * (1 g/mL)
- Sodium hydrogen carbonate: (84.01 g/mol) * (x moles) = (10 mL) * (1 g/mL)
Simplifying the equations, we find:
x = 0.0932 moles Na2CO3
x = 0.119 moles NaHCO3
Therefore, you would need approximately 0.0932 moles of sodium carbonate and 0.119 moles of sodium hydrogen carbonate to make a 100mL buffer solution with a pH of 10.80.
Remember to dissolve the calculated amounts of each compound in water and adjust the total volume to 100mL.