A) You need to make 250ml of a 20x stock solution of NaCl to dilute later to a f

Question

A) You need to make 250ml of a 20x stock solution of NaCl to dilute later to a final concentration of 50 mM. The M.W. of NaCl is 58.44. How would you accomplish this?

      NaCl ___________ g

      Pure Water __________ ml

B) You need 3.5 L of 50 mM NaCl from your 20x stock. How would you accomplish this?

     20x stock ______ ml

     Pure water ________ ml

C) You need to make 20 ml of a 20% glucose solution. The M.W. of glucose is 180.16. How would you accomplish this?

     Glucose ________ g

    Pure water _______ ml

Explanation / Answer

A. Stock solution required is 250ml of 20X.

20X of 50mM = 20 * 50 = 1000mM ie; 1 M

58.44g of NaCl in 1000ml of water gives 1M

Therefore, [(58.44*250)/1000] g of NaCl in 250ml of water will give 1M.

Hence, the answer is NaCl - 14.61g and Pure water upto 250 ml.

B. A 1X (in this case 50mM) solution can be prepared from its 20X stock by mixing 1 part of 20X stock solution and 19 parts of pure water. Here the final volume of 1X solution is 3.5 L. Therefore, 3.5L contains one part of 20X solution ie; 3.5/19 = 0.185L of 20X solution and remaining 3.315 L of pure water (3.5L - 0.185L)

Hence, Answer is 20X stock - 0.185 L, Pure Water- 3.315L

C. 20g of Glucose in 100ml gives 20% glucose solution.

Therefore, [(20*20)/100] g of glucose in 20 ml will give 20% solution.

Hence, answer is Glucose 4 g, Pure water 100ml

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