How to prepare the following three most important chemical solutions in the Food Lab: Discover essential Food Analysis Lab Solutions. Learn to prepare key solutions in your lab for accurate results
1. 500 mL of approximately 0.20 M NaOH using solid NaOH;
- Because the desired concentration is known to be two significant figures, we do not need to measure precisely the mass of NaOH or the volume of the solution. The desired mass of NaOH is
0.20 mol NaOH/L×40.0 g NaOH/mol×0.50 L=4.0 g NaOH
To prepare the solution, place 4.0 grams of NaOH, weighed to the nearest tenth of a gram, in a bottle or beaker and add approximately 500 mL of water.
2 . 1 L of 150.0 ppm Cu2+ using Cu metal
- Since the desired concentration of Cu2+ is given to four significant figures, we must measure precisely the mass of Cu metal and the final solution volume. The desired mass of Cu metal is
150.0 mg Cu/L×1.000 M ×1 g/1000 mg=0.1500 g
To prepare the solution, measure out exactly 0.1500 g of Cu into a small beaker and dissolve it using a small portion of concentrated HNO3. Rinse the beaker several times with small portions of water, adding each rinse to the volumetric flask. Finally, add additional water to the volumetric flask’s calibration mark.
3. 2 L of 4% v/v acetic acid using concentrated glacial acetic acid (99.8% w/w acetic acid)
- The concentration of this solution is only approximate so it is not necessary to measure exactly the volumes, nor is it necessary to account for the fact that glacial acetic acid is slightly less than 100% w/w acetic acid (it is approximately 99.8% w/w).
Prepare: volume of glacial acetic acid is
4 mL CH3COOH/100 mL×2000 mL=80 mL CH3COOH
To prepare the solution, use a graduated cylinder to transfer 80 mL of glacial acetic acid to a container that holds approximately 2 L and add sufficient water to bring the solution to the desired volume.