How can you precipitate BaCrO4(s) from a solution of barium nitrate and potassium dichromate? I don't get it.. it's a question from a lab we did on chromate-dichromate equilibrium.
There is an equilibrium represented as follows:
2CrO4^2- + 2H^+ ==> Cr2O7^2- + H2O
So in acid solution the Cr2O7^2- predominates and in neutral or basic solution the CrO4^2- is the main ion.
Barium ion forms a ppt with CrO4^2- but not with Cr2O7^2-. So to get BaCrO4 you are depending upon the equilibrium conditions to help you get enough CrO4^2- to exceed the Ksp of BaCrO4.
Thank you! :D
To precipitate BaCrO4(s) from a solution of barium nitrate (Ba(NO3)2) and potassium dichromate (K2Cr2O7), you'll need to follow a few steps. Here's how you can do it:
1. Write down the balanced chemical equation for the reaction:
Ba(NO3)2 + K2Cr2O7 --> BaCrO4 + 2KNO3
2. Determine the stoichiometric ratio between the reactants:
From the balanced equation, you can see that one molecule of Ba(NO3)2 reacts with one molecule of K2Cr2O7 to form one molecule of BaCrO4.
3. Calculate the required amounts of reactants:
Determine how much BaCrO4 you want to precipitate. Let's say you want to precipitate 10 grams of BaCrO4. From this, you can calculate the amount of Ba(NO3)2 needed using its molar mass.
4. Prepare the reactant solutions:
Dissolve the calculated amount of Ba(NO3)2 in distilled water to make a known volume solution. Similarly, dissolve the calculated amount of K2Cr2O7 in a separate container of distilled water.
5. Mix the solutions:
Slowly add the Ba(NO3)2 solution to the K2Cr2O7 solution while stirring continuously. Make sure to add them in stoichiometric proportions. A yellow precipitate of BaCrO4 will start to form.
6. Filter and wash the precipitate:
Once the precipitate has settled, pour the mixture through filter paper using a filtration apparatus. Collect the solid precipitate (BaCrO4) and wash it with distilled water to remove any impurities.
7. Dry and weigh the precipitate:
Transfer the washed precipitate onto a watch glass or a suitable container and let it air-dry. Once dry, weigh the precipitate on an analytical balance to determine its mass.
By following these steps, you should be able to successfully precipitate BaCrO4 from the barium nitrate and potassium dichromate solution. Remember to always follow laboratory safety protocols and work under the supervision of a trained instructor.