Reagent Preparation Practice ANSWERS Reminder: How to do calculations for making
ID: 479036 • Letter: R
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Reagent Preparation Practice ANSWERS Reminder: How to do calculations for making laboratory solutions A. A molar solution: 1 M 1 mole of substance dissolved in 1 liter of solvent (water in our B. Weight/volume Percentage A g of substance (solid) in 100 ml total volume C Volumenolume Percentage A ml substance (liquid) in 100 ml total volume D. Dilution of stock solutions: Civi Czva Question 1. Calculate how to make 100 ml of "Alkaline Phosphatase Reaction Buffer", a buffer containing several ingredients. Final MgCI2 (solid, MW 95.2 Da) 5 mM MgCl2 5 M NaCl 0.1 M NaCl 1 M Tris pH 9.5 0.1 M Tris, pH 9.5 20% Tween-20 0.3% Tween-20 You also have some stock solution of acid and base. Question 2: Indicate whether the two statements below are true or false. You work with two amino acids. Tryptophan (Mw 204 Da) and Methionine (MW-149 Da). You make various solutions of each amino acid separately and compare them. T When you compare two solutions at the same percentage concentration (e.g.1%),there are more moles of Tryptophan in solution than moles of Methionine because the molecular weight of Tryptophan is higher. E When you compare two 1-iter solutions containing these amino acids at a 10mM concentration, there is the same number of amino acid molecules in each solution. Question 3 Your professor asks you to make a staining solution to stain and observe specimen under the microscope. You are told by to prepare 100 mL of staining solution containing 40% methanol, 1x hematoxylin dye and 0.01 M calcium chloride (CaCl2). In the histology lab, you find a stock of 100% pure methanol (liquid), a 10x hematoxylin dyestock solution (liquid), plenty of water and a stock solution of 5M Cacl2. There are also all kinds of pipets, cylinders and beakers to measure volumes. a) Describe how you make the staining solution? b) on your following trip to the histology lab, you realize that all the pipets to accurately measure volumes smaller than 1 ml are broken. What alternative method do you need to use to avoidExplanation / Answer
Answers:
1. To prepare the solution: 100mL
MgCl2: For 1M solution: 95.2 grams in 1000mL
So, for 100mL, we require (95.2/1000)*100 = 9.52 g
For 5mM, we require (9.52/1000)*5 = 0.0476g
NaCl: V1S1=V2S2
So, 5000 * V1 = 0.1 * 100
V1 = 0.002 mL
Tris: V1S1=V2S2
1000 * V1 = 100 * 0.1
V1 = 0.01 mL
Tween 20: V1S1=V2S2
20 * V1 = 0.3 * 100
V1 = 1.5 mL
2. (a) False. The molecular weight of tryptophan is more is more than that of methionine. 1% of each solution contain 1gm of each in water. Since the molecular weight of tryptophan is more than methionine, the number of moles of tryptophan is less than that of methionine in the solution.
(b) True. Same molar concentration of two solutions contain same number of molecules.
3. (a) To prepare 100mL of the staining solution: (Calculations using V1S1=V2S2)
Methanol: 100 * V1 = 40 * 100
V1 = 40 mL
Hematoxylin: 10 * V1 = 1 * 100
V1 = 10 mL
CaCl2: 5 * V1 = 0.01 * 100
V1 = 1/5 = 0.2 mL
(b) If all the pipets (micropipets) are broken, we can use finely caliberated dropper for the measurements.
4. Molecular weight = 300 g/mol, Amount given = 6g
To prepare: 20mL of 1M solution
For 1M 20mL solution, he requires (300 * 20)/1000 = 6g
So, correct answer is option (B).
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