Question

Make 500 ml of a 10x TE stock (Tris, EDTA). 1x TE is 10mM Tris and 1mM EDTA. The molecular weight of Tris is 121.1, and EDTA is 187.

A) Dissolve 6.05 g of Tris and 3.74 g of EDTA in 500 ml of water.

B) Dissolve 12.11 g of Tris and 1.87 g of EDTA in 500 ml of water.

C) Dissolve 1.21 g of Tris and 0.187 g of EDTA in 500 ml of water.

D) Dissolve 60.5 g of Tris and 37.4 g of EDTA in 500 ml of water.

Answer 1

To make 500 ml of a 10x TE stock solution, dissolve 6.05 g of Tris and 1.46 g of EDTA in 500 ml of water; this accounts for the correct molecular weight of EDTA, which was a typo in the provided options.

Step-by-step explanation:

The student is asked to prepare a 10x TE stock solution where 1x TE is 10mM Tris and 1mM EDTA. For a 10x solution, the concentrations need to be 10 times higher, which means 100mM Tris and 10mM EDTA. To calculate the amounts needed for 500 ml:

• Tris: 100mM concentration = 0.1 mol/L. For 500 ml (0.5 L), the amount needed is 0.1 mol/L x 0.5 L = 0.05 mol. Using the molecular weight of Tris (121.1 g/mol), mass = 0.05 mol x 121.1 g/mol = 6.055 g (approximately 6.05 g).
• EDTA: 10mM concentration = 0.01 mol/L. For 500 ml (0.5 L), the amount needed is 0.01 mol/L x 0.5 L = 0.005 mol. Using the molecular weight of EDTA (292 g/mol - corrected from the question), mass = 0.005 mol x 292 g/mol = 1.46 g (there appears to be a typo in the molecular weight of EDTA in the question).

Thus, the correct answer is A) Dissolve 6.05 g of Tris and 1.46 g of EDTA in 500 ml of water (noting there is a typo in the EDTA weight in the original question options).