calculate the mass in mg of solid chromium nitrate needed to make 250 ml of an aqueous solution with a pH OF 4.00. The Ka of [cr(H2O)6]+3 IS 1.0*10-4.
To calculate the mass of solid chromium nitrate required, we need to consider the molar mass of chromium nitrate, the volume of the solution, and the concentration of [Cr(H2O)6]3+ (chromium hexaaqua ion) required for the given pH.
Here's how you can calculate it step-by-step:
1. Determine the concentration of [Cr(H2O)6]3+ required:
Since the pH is given, we know that the solution is acidic. The chromium hexaaqua ion is a weak acid, so we can use the Ka value to determine its concentration.
pH = -log[H+]
[H+] = 10^(-pH)
From the pH value, we can calculate the concentration of H+ ions by taking the antilog of -pH. Since [H+] is equal to the concentration of [Cr(H2O)6]3+, we can use this value directly.
[Cr(H2O)6]3+ = [H+] = 10^(-4.00)
2. Calculate the moles of [Cr(H2O)6]3+:
To calculate the moles, we need to multiply the concentration (in mol/L) by the volume (in L):
Moles = Concentration * Volume (in L)
Moles = [Cr(H2O)6]3+ * 0.250 L
3. Determine the molar mass of chromium nitrate:
Chromium nitrate is a compound composed of one chromium ion (Cr3+) and two nitrate ions (NO3-). The molar masses are:
Chromium (Cr) = 52 g/mol
Nitrate (NO3-) = 63 g/mol
Adding these masses together, we get:
Molar mass of chromium nitrate = (52 g/mol) + 2*(63 g/mol)
4. Calculate the mass of chromium nitrate required:
To calculate the mass, we use the moles calculated in step 2 and multiply it by the molar mass of chromium nitrate:
Mass = Moles * Molar Mass
Therefore, the mass of solid chromium nitrate needed to make a 250 ml aqueous solution with a pH of 4.00 can be calculated using the steps above.