1. How many moles are present in 20 g of glucose (MW = 180.2)? 2. How many grams

Question

1. How many moles are present in 20 g of glucose (MW = 180.2)?

2. How many grams of NaCl are required to make 1 liter of a 15 % (w/v) solution?

3. What is the molar concentration of 70 % (v/v) ethanol (density of 100% ethanol= 0.798 g/ml; MW = 46.07)?

4. What volume of 70 % ethanol do you need to prepare 1.0 liter of 25 % ethanol?

How many moles are present in 20 g of glucose (MW = 180.2)? How many grams of NaCl are required to make 1 liter of a 15 % (w/v) solution?page5image22664 page5image22824 page5image22984 page5image23144 3. What is the molar concentration of 70 % (v/v) ethanol (density of 100% ethanol= 0.798 g/ml; MW = 46.07)? 4. What volume of 70 % ethanol do you need to prepare 1.0 liter of 25 % ethanol?

Explanation / Answer

1) no. of moles = 20/180.2 = 0.11 moles

2) Mass-volume percentage, (weight-volume percentage % w/v) describes the mass of the solute in g per 100 mL of the resulting solution.

Since the concentration of your solution is 15% w/v, this means that 100 mL of the solution contains 15 g NaCl

so 1 liter or 1000mL of the solution require 150 g of NaCl

3)(v/v)=volume (of reagent) per final solution volume

70% (v/v) =70 ml of ethanol per 100 ml of solution

mass of ethanol =density*volume=0.798*70

mass of soution =100mL=0.1L

molar concentration =(70*0.798/46.07)/(0.1) =12.12 M

4) 70% ethanol conatins 70 grams of ethanol per 100 mL

or 700 grams of ethanol per liter

25% ethanol needs 250 grams of ethanol in 1 liter

so (250/700)*1000=357.1 mL

so 357.14 mL of 70% ethanol is needed

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