Mid-Term Exam BCH 4034 L (Biochemistry II Lab Time: 1.5 Hours Answer all questio

Question

Mid-Term Exam BCH 4034 L (Biochemistry II Lab Time: 1.5 Hours Answer all questions. Show calculations to obtain full credit 1. You have a 0.5 M stock of EDTA solution that is used to chelate divalent cations. You want to make 2 ml of 100 mM solution. What volume of water and stock solution will you mix together to obtain the diluted solution? Show your work. (5) 2. Name two aseptic techniques used in the lab. Explain how these techniques work. (5) You have a 70 mg/ml stock solution of ampicillin. In order to make a LB-Agar plate you with 0.2 mL of ampicillin stock. What is the 3. 100 mL of LB-Agar mixture nal concentration of the ampicillin solution on LB-Agar plate? Show your work. (5)

Explanation / Answer

Q1.

We need to apply dilution law, which is based on the mass conservation principle

initial mass = final mass

this apply for moles as weel ( if there is no reaction, which is the case )

mol of A initially = mol of A finally

or, for this case

moles of A in stock = moles of A in diluted solution

Recall that

mol of A = Molarity of A * Volume of A

then

moles of A in stock = moles of A in diluted solution

Molarity of A in stock * Volume of A in stock = Molarity of A in diluted solution* Volume of A in diluted solution

Now, substitute known data

M1V1 = M2V2

0.5*Vstock = (100*10^-3)(2)

Vstock =  (100*10^-3)(2)/0.5 = 0.4 mL required

Q2.

aseptic technique --> techniques used to avoid infections; they come from "cleaning your hands" "use of alcohols" "desinfectants" and other such as barrier equipment like gloves/eye protection, etc...

Q3

C = 70 mg/mL

V = 100 mL of Agar

V = 0.2 mL stock

Vfinal = 100+0.2 = 100.2

Cfinal = Vfinal/Vinitial * Cstock= 100.2/100*70 = 70.14 mg/mL

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