How to prepare the following solutions:

1-Prepare a 0.050 M Cr(III) stock solution in a 100 mL volumetric flask. Use the solid reagent Cr(NO3)3 - 9H2O and distilled water.

2-Use Cr(III) stock solution and prepare Cr(III) standards: 0.0100M, 0.0200M, 0.0300M, 0.0400M and 0.0500M in 25 mL volumetric flasks. Dilute to the mark with distilled water.

3-Prepare a 0.200 M Co(II) stock solution in a 100 mL volumetric. Use the solid reagent Co(NO3)2 - 6H2O and distilled water.

4-Use the stock solution of Co(II) and prepare Co(II) standards: 0.0400M, 0.0800M, 0.1200M, 0.1600M and 0.2000M in 25 mL volumetric flasks.