Question 4 Select the best answer by circling A B or C below

Question 4. Select the best answer by circling A, B or C below, and if applicable, fill in the number of grams.

a) You work as a summer student in a lab to help a postdoctoral fellow in her research. One day she left on your bench a small vial containing 6 g of vitamin Z powder and a note asking you to prepare 20 ml of a 1M solution while she attends a seminar (use water to make the solution, she wrote). You start this task by checking the molecular weight of Vitamin Z (300 g/mol). When the postdoc comes back from the seminar:

A You complain that there is not enough powder and you need ______ g more to prepare this solution.

B You give your solution to the postdoc and thank her for having calculated the exact amount of powder needed. (but you think that she could have told you that!)

C You return the leftover _____ g to the postdoc together with the solution.

b) if you used 6g of vitamin Z powder to make 20 ml of solution, what is the % concentration of this solution?

6g per 20 ml equivalent to 30g per 100 ml (multiply 20ml by 5 to get to 100 ml)

Solution

a). For 20ml of 1M solution we need:

(300/1000) x 20 = 6 g of Vitamin Z powder.

A You complain that there is not enough powder and you need 294 g more to prepare this solution.

B You give your solution to the postdoc and thank her for having calculated the exact amount of powder needed. (but you think that she could have told you that!)

C You return the leftover 0 g to the postdoc together with the solution.

b). 6g/20mL of Vitamin Z solution is 30% w/v solution