Question #174560

**Q3.** The Trypsin-EDTA solution used in the experiment would contain 0.4% trypsin (w/v) and

0.03% EDTA (w/v). It is provided to you as a 10x stock solution.

(a) EDTA has a molecular weight of 292.24. What is the molarity of the EDTA in the 10X stock solution? (3 marks)

(b) What is the total final amount (in mg) of Trypsin which is added to the cells? (2 marks)

**Q4.** Following a 2-minute incubation, FBS solution is then added to the cells to deactivate the trypsin enzyme. The solution comprises 10% FBS, made up in 1x PBS. You decide to make up 50 ml of this solution using your 10 x PBS stock, and a 100% FBS stock.

(a) How much 10 x PBS will you need to use to make the 50 ml solution? (1 mark)

(b) How much 100% stock FBS would you need? (2 marks)

I also need the workings out for the answers to these questions. Thank you.

Expert's answer

**Answer #3**

**(a) **the molarity can be calculated by using the given below equation.

"\\boxed{M={n\\over V}={m \\over M_w V}}"

here, M=molarity,n=no. of moles, V=volume, m=mass, "M_w" =molecular weight

As given 10x solution contains 0.03% EDTA

therefore, 100ml solution contains 0.03 gm EDTA

from here;

"M(EDTA)={0.03g\\over(292.24gmol^{-1} *0.1 L) }=0 mol\/L=1.027mM"

(b) If 1 mL of solution is added to the cells, the final amount of trypsin will be:

"m=({0.4g\\over1oo})\/10=0.0004g=0.4mg"

**Answer #4**

**(a) **For preparing 50 mL of 10% FBS in 1*PBS;

V(PBS)"={50mL\\over10}=5mL"

As a result, % mLof 10 *PBS are needed.

**(b)** For preparing 50 mLof 10% FBS in 1*PBS

V(FBS)"={50mL\\over100}*10 \\%=5mL"

As a result , 5mL of 100% FBS are needed.

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