You are working in the laboratory and are given a 1.0 times 10^-2 M erythrosine
ID: 530239 • Letter: Y
Question
You are working in the laboratory and are given a 1.0 times 10^-2 M erythrosine dye solution. You are then asked to make 100.0 mL of a 3.2 times 10^-6 M erythrosine dye solution. Describe with words and calculations how you would make this solution using only glassware and equipment that is available in the Chem 216 laboratory. (ii) Describe how you would make 10.0 mL of a 4.0 times 10^-4 M solution of KSCN using solid KSCN Note that your experimental procedure should produce minimal errors and that only glassware and equipment used in Chem 216 can be used.Explanation / Answer
For calculating concentration of erythrosine, we can use the following formula
M1V1=M2V2
where M1 is the concentration of stock erythrosine given (1*10-2M) and V1 has to be found
M2 and V2 is are the concentration and volume of the solution has to be prepared (3.2*10-4M and 100 mL respectively)
Thus on substituting in the above equation
1*10-2M*V1= 3.2*10-4M *100 mL
V1=3.2 mL
that is, take 3.2 mL of the stock solution make up to 100 mL
b). Number of moles in one liter is the defined as molarity
mass required can be calculated by the formula
Mass in grams = (Molecular mass of the compound * molarity of the solution has to be prepared* volume of the solution in mL)/1000
Molecular mass of KSCN is 97.18 g/mole
Mass of KCN needed = (97.18* 4*10-4*10)/1000
=3.887 *10-4 g
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