I'm making different concentrations of
ethanol and I just wanted to check my calculations and method.

Making ethanol concentrations of:


To make the 0.40% ethanol from stock solution using 100ml volumetric flask:

(xg ethanol)/(100ml) x 100= 0.40%
xg= 0.4g ethanol

Then 0.4g ethanol solution is added to a 100ml volumetric flask with water in it already. After the addition of 0.4g ethanol into the flask whilst weighing it on a balance.

Then I take that 0.40% solution of ethanol and dilute it with

To get 10ml of 0.30% ethanol solution:
Find out how much of stock is needed to dilute
V1= 7.5ml ethanol

add that 7.5ml ethanol into a 10ml volumetric flask and add water to the line to get 0.3% ethanol solution

To get 10ml of 0.20% ethanol solution:
Find out how much of stock is needed to dilute
V1=5 ml ethanol

add that 5 ml ethanol into a 10ml volumetric flask and add water to the line to get 0.2% ethanol solution

same process for the below concentrations..just checking my calculations:

0.1% ethanol solution:
V1=2.5 ml ethanol

0.05% ethanol solution:
V1=1.25 ml ethanol

I'm not sure if I can use percentage for the dilution equation, or if I can even use grams for the creation of the original solution

Thanks very much


  1. 0
  2. 11
asked by ~christina~
  1. I vaguely remember us having a similar conversation previously. If you are preparing those ethanol solution to be w/v percent, then you have done it correctly. The ethanol is weighed and the total volume is in 100 mL (for the original solution). That will give you 0.40 weight/volume percent. BUT, since the density of the solution isn't too far from 1 (because it's a fairly dilute solution of 0.4 g ethanol per approximately 99.6 g H2O) it won't miss 0.40% w/w by far. If you definitely wish to prepare 0.40% w/w, you can add 0.4 g ethanol to a tared 100 mL flask, then add water to 100 g total solution. Your calculations look ok to me.

    1. 0
    posted by DrBob222
  2. O.O I don't remember...It might have been a more general question on solutions though.

    Ah, I was going to ask about the density but I forgot. I had to prepare 10% H2SO4 solution using stock and I was wondering about if I had to convert the grams to ml using density and I was told that it would be fine for that but not so much for ethanol.

    I'm not sure why taking ml's of ethanol instead of grams would be less accurate.

    Another question is that if I had a solution that I made by adding
    0.85018g of K2CrO7 and 40ml of concent H2SO4, then diluting that to 100ml, what solution did I just make? (in terms of moles etc.?)
    I'm used to say...0.5% x solution and 2.5M x solution, but I'm not sure how to label this solution. I made it but I just put..0.85018g K2CrO7 in 40ml of sulfuric acid and distilled H2O. (that is very strange to put on a label, I think)
    So how would I label a solution with different components?

    Thanks Dr.Bob

    1. 0
    posted by ~christina~
  3. I wonder how you weighed the 0.85018 g? With conc H2SO4, you almost are forced to use the density if you want to measure a volume for 1 mL does not have a mass of 1 g. And you are right for ethanol, it isn't so necessary since the density of ethanol is about 0.8 or so if I remember correctly. I would label the dichromate/H2SO4 soln as
    mols K2Cr2O7/100 mL in xx%H2SO4 or g K2Cr2O7/100 mL in xx%H2SO4.

    1. 0
    posted by DrBob222
  4. I weighed the K2Cr2O7 on an analytical balance. (solid)
    correction: needed 0.85015g
    actually weighed out: 0.8508g
    I actually used 0.8508g but I needed 0.85015g, I just hope it doesn't make the results funny...but I hear that it does not need to be accurate.(how it is..I don't know) (told that only the ethanol concentrations in this conway experiment need to be accurate)
    And the scale doesn't measure out to that many digits.

    We are using a UV/Vis spectrometer to determine the absorbance of the solution. Concentration of the ethanol solution is then determined with the beer lambert equation. A=abc since we find A and a is a constant and the cell length is known..we find c.
    [saying all that because I'm not sure if the concentration of the solution will affect the readings]

    Thank you

    1. 0
    posted by ~christina~
  5. The only reason I asked about the balance is that most analytical balances in use in schools weigh to the nearest 0.1 mg although that may have changed since I retired. There are semi-micro balances that weigh to 5 places and micro-balances that weigh to 6 places but those aren't usually available to beginning students. And PLEASE don't call them scales. We use scales to weigh sacks of potatoes; we use analytical balances to measure mass in analytical chemistry.:-).
    I am guessing that you are using the acidified dichromate solution to oxidize the alcohol and measuring the absorbance of the C=O group that is formed. As an added note about the balance, absorbance readings and spectrophotometric work usually is not accurate enough to justify four places for the oxidant (in this case the dichromate). Probably you could have used a triple beam balance just as well. Good luck on your experiment.

    1. 0
    posted by DrBob222

Respond to this Question

First Name

Your Response

Similar Questions

  1. biology

    If I had an experiment where I was testing how the membrane permeability is affected by ethanol, and by doing this had to observe thin onion slides with different ethanol concentrations and had to count how many nuclei were seen
  2. chemistry

    I wanted to double check how to go about creating a 1% solution and a 4% solution. I know that it is 1 part to 99 and 4 part to 96. so I add 1ml of solution and then water and the same for the four percent. I wanted to know if you
  3. to dr bob..chemistry

    bottle of wine contains 13.1% ethanol by volume. The density of ethanol (C2H5OH) is 0.789 g/cm3. Calculate the concentration of ethanol in wine in terms of mass percent and molality. mass percent _______% molality ______mol/kg
  4. Biostatistic

    An enzymatic method for determining alcohol in wine is evaluated by comparison with a gas-chromatography (GC) method. the same sample is analyzed several times by both methods with the following results (% ethanol). Enzymatic
  5. chemistry

    An enzymatic method for determining alcohol in wine is evaluated by comparison with a gas-chromatography (GC) method. the same sample is analyzed several times by both methods with the following results (% ethanol). Enzymatic
  6. chemistry

    There are four main methods of making salts: Acid + Metal, Acid + insoluble base, Acid + alkali and solution of salt A + solution of salt B. a. a student wanted to make some sodium sulfate. i. which method would be best to use?
  7. vapor pressure

    The total pressure in a flask containing air and ethanol at 25.7C is 878 mm Hg. The pressure of the air in the flask at 25.7C is 762 mm Hg. If the flask is immersed in a water bath at 45.0C , the total pressure is 980 mm Hg. The
  8. chemistry

    Shown below is a schematic representation of the water-ethanol phase diagram. Making reference to the phase diagram, explain in a few sentences how one could enrich a solution of 15 percent ethanol - 85 percent water to a
  9. science

    A standard addition method is used to determine the concentration of ethanol in an unknown sample. Six 10 mL aliquots of the unknown are drawn from the processing vat. An aqueous solution of ethanol is standardized to have 1.57
  10. Chemistry -repost thank you in advance

    I have a bottle of 95% ethanol purchased from the manufacturer. Normally, when it is not stated, does it mean 95% w/w ethanol? I need to prepare 100ml of 40% v/v ethanol solution from 95% ethanol. Please show me the calculation

More Similar Questions