0.250 g KCN is dissolved in 50 mL of water, and added to 2 mL of NaOH then mixed with 48mL of water. What is the molar concentration of KCN?
I am stuck on this question.
So far I have:
0.250gKCN/0.050L= 5M(g/L)
Moles of KCN: 5M = mol/0.05L = 0.25mol KCN
I am not sure exactly where to go from here or if I am on the right track. The addition of NaOH threw me off. If you can point me in the right direction it would be much appreciated.
Do you want concn in M or g/L. I will assume you want molarity = M
mols KCN = grams/molar mass KCN = ?
Then ?mols/0.052 L = ? mols/L = M KCN. The NaOH just adds 2 mL to the total volume.
To determine the molar concentration of KCN, you're on the right track with finding the moles of KCN. However, the addition of NaOH does not affect the molar concentration of KCN in this case, so you can ignore it for now.
Here's what you need to do next:
1. Calculate the number of moles of KCN.
- We know that 0.250 g of KCN is dissolved in 50 mL of water.
- To find the moles, use the molar mass of KCN. The molar mass of KCN is the sum of the atomic masses of each element: potassium (K) has a molar mass of 39.10 g/mol, carbon (C) has a molar mass of 12.01 g/mol, and nitrogen (N) has a molar mass of 14.01 g/mol.
- Add up the molar masses: 39.10 + 12.01 + 14.01 = 65.12 g/mol.
- Convert the mass of KCN to moles: 0.250 g / 65.12 g/mol = 0.00383 mol.
2. Determine the final volume of the solution.
- The initial volume of water is 50 mL, and after adding NaOH it becomes 50 mL + 2 mL = 52 mL.
- However, after mixing with an additional 48 mL of water, the final volume will be 52 mL + 48 mL = 100 mL, or 0.100 L.
3. Calculate the molar concentration of KCN.
- Divide the moles of KCN by the final volume in liters: 0.00383 mol / 0.100 L = 0.0383 mol/L or 0.0383 M.
So the molar concentration of KCN in the solution is 0.0383 M.