catty p
Does anyone know what the molarity of 20 volume hydrogen peroxide should be, roughly? Would be very helpful, thanks 
20 volume means 1dm3 of the H2O2 solution will produce 20dm3 of oxygen, where:
H2O2 -> O2 + H2:
i.e 1:1 stoichiometry. At 298K and 1atm pressure, 1 mole of gas occupies 24.45dm3. So 20/24.45 = 0.818 mol. O2 produced, which means there were 0.818mol H2O2 in 1dm3. Therefore molarity is 0.818M at 298K.
Reply 4
Original post by cowsgomoo
Original post by cowsgomoo
no thats not right!!
the equation is 2H2O2 (aq) --> 2H2O (l) + O2 (g) for a start.
Hydrogen peroxide 20-volume solution contains 6% H2O2 (i.e. 60g of H2O2 in 1000g of solution). Mr of H2O2 = 34gmol-1. Therefore the concentration of 20-volume solution is about 60 ÷ 34 = 1.76moldm-3.
the equation is 2H2O2 (aq) --> 2H2O (l) + O2 (g) for a start.
Hydrogen peroxide 20-volume solution contains 6% H2O2 (i.e. 60g of H2O2 in 1000g of solution). Mr of H2O2 = 34gmol-1. Therefore the concentration of 20-volume solution is about 60 ÷ 34 = 1.76moldm-3.
Hi could you help me please? This question is the same as an exam question I'm doing: determine concenrtation of 20 volume H202
I've looked at the mark scheme but don't understand all the steps, the first is dividing 20 by 24 to find the moles of 02 produced, which is 0.83 moles.
But then they next multiply this answer by 2 to get the answer of 1.67 mol dm^-3
I don't understand this last step, I'm guessing it has something to do with the 2:1 ratio between 02 and H202 but also how can the value in moles suddenly become a concentration?
Reply 5
Original post by abcd1234abcd
Hi could you help me please? This question is the same as an exam question I'm doing: determine concenrtation of 20 volume H202
I've looked at the mark scheme but don't understand all the steps, the first is dividing 20 by 24 to find the moles of 02 produced, which is 0.83 moles.
But then they next multiply this answer by 2 to get the answer of 1.67 mol dm^-3
I don't understand this last step, I'm guessing it has something to do with the 2:1 ratio between 02 and H202 but also how can the value in moles suddenly become a concentration?
I've looked at the mark scheme but don't understand all the steps, the first is dividing 20 by 24 to find the moles of 02 produced, which is 0.83 moles.
But then they next multiply this answer by 2 to get the answer of 1.67 mol dm^-3
I don't understand this last step, I'm guessing it has something to do with the 2:1 ratio between 02 and H202 but also how can the value in moles suddenly become a concentration?
right.
so we know 2 moles of hydrogen peroxide produces 1 mole of oxygen.
"20 volume", means 1 dm3 of peroxide solution produces 20 dm3 oxygen.
20 dm3 oxygen is 20 / 24.47 = 0.817 moles (at 298K and 1 atm)
therefore, 1 dm3 of solution must contain 2 x 0.817 = 1.635 moles peroxide.
so "20 volume" hydrogen peroxide is 1.635M
(edited 13 years ago)
Reply 6
Where are you getting 24/24.47 from?!
Reply 8
Original post by Borek
Not 24/24.47 bout 20/24.47. 20 (dm3) is the volume of oxygen produced (thats what "20 volume" means), 24.47 dm3 is the volume of one mole of ideal gas at STP. 20/24.47 is number of moles of oxygen produced.
I imagine that the 'volume' measure refers to room temperature ...
... I don't know this for a fact, but it would seem more likely in a household solution.
Reply 10
Original post by charco
I imagine that the 'volume' measure refers to room temperature ...
24.47 dm3 per mole is at 298K and 1 atm.
298K is room temperature (at least in my house).
Reply 11
The reason why it "suddenly becomes a concentration" is because you take the moles (1.67 mol dm^-3) and divide it by the volume of hydrogen peroxide (1 dm3) to get the concentration! So since you're only dividing by 1, the number stays the same, and you can change the units!!
Reply 12
Original post by cowsgomoo
no thats not right!!
the equation is 2H2O2 (aq) --> 2H2O (l) + O2 (g) for a start.
Hydrogen peroxide 20-volume solution contains 6% H2O2 (i.e. 60g of H2O2 in 1000g of solution). Mr of H2O2 = 34gmol-1. Therefore the concentration of 20-volume solution is about 60 ÷ 34 = 1.76moldm-3.
the equation is 2H2O2 (aq) --> 2H2O (l) + O2 (g) for a start.
Hydrogen peroxide 20-volume solution contains 6% H2O2 (i.e. 60g of H2O2 in 1000g of solution). Mr of H2O2 = 34gmol-1. Therefore the concentration of 20-volume solution is about 60 ÷ 34 = 1.76moldm-3.
How do we know it has 6% H2O2?
Reply 14
The volume of H2 O2 and its strength numerical
Reply 15
Hi, without getting into equatuons can somebody tell me how much% is 20 volumes of H2O2? I am looking for 3% H2O2 and there is no mention of% in any bottle. Only that it is 20volumes. Thanks.
Original post by abcd1234abcd
Hi could you help me please? This question is the same as an exam question I'm doing: determine concenrtation of 20 volume H202
I've looked at the mark scheme but don't understand all the steps, the first is dividing 20 by 24 to find the moles of 02 produced, which is 0.83 moles.
But then they next multiply this answer by 2 to get the answer of 1.67 mol dm^-3
I don't understand this last step, I'm guessing it has something to do with the 2:1 ratio between 02 and H202 but also how can the value in moles suddenly become a concentration?
I've looked at the mark scheme but don't understand all the steps, the first is dividing 20 by 24 to find the moles of 02 produced, which is 0.83 moles.
But then they next multiply this answer by 2 to get the answer of 1.67 mol dm^-3
I don't understand this last step, I'm guessing it has something to do with the 2:1 ratio between 02 and H202 but also how can the value in moles suddenly become a concentration?
1.
Since one mole of any gas occupies 24dm3 at r.t.p., dividing 20 by 24, gives you the number of moles of O2 you have.
2.
You want to find the moldm-3 of H2O2, so by using stoichiometry we have a 2:1 ratio, so it's necessary to multiply by 2 to find the number of moles of H2O2.
3.
Then finally to get the concentration, you just divide by the volume of hydrogen peroxide they gave you in the first place converted to dm3.
There is no mention of percentages in my question, or in my spec so far, so I'm guessing this is the way to answer it if your question doesn't include percentages either. Hope this helps.
(edited 7 months ago)
Reply 17
To calculate the molarity of hydrogen peroxide (H₂O₂) at a concentration of 20 volumes, the following steps must be taken:
The volume concentration (in volumes) refers to the volume of gas at standard temperature and pressure (STP) that can be produced from 1 volume of liquid.
20 volumes of hydrogen peroxide means that 1 litre of solution can produce 20 litres of oxygen gas (O2) at STP when decomposed.
1: Determine the volume of gas produced
Gas produced: 20 volumes of gas = 20 litres of O2 at STP (standard temperature and pressure).
At STP, 1 mole of any gas occupies 22.4 L (molar volume).
2: Calculation of the moles of gas produced
Mol of O2 = volume of gas/molar volume at STP = 20 L/22.4 L/mol = approx. 0.893 mol
3: Decomposition of hydrogen peroxide
The balanced chemical equation for the decomposition of hydrogen peroxide is:
The equation shows that 2 moles of H2O2 produce 1 mole of O2.
Therefore, the number of moles of H2O2 can be calculated as follows:
Moles of H2O2 = 2 x moles of O2 = 2 x 0.893 moles = approximately 1.786 moles
4: Calculation of molarity
Let us assume that the concentration of the hydrogen peroxide solution is 1 L (for ease of calculation).
Molarity (M) is defined as moles of solute per litre of solution: Molarity (M) = moles of solute/volume of solution in litres.
We have 1.786 moles of H2O2 in 1 L of solution.
Molarity of H2O2 = 1.786 moles/1 L = 1.786 M
Conclusion: The molarity of hydrogen peroxide (H2O2) at a concentration of 20 volumes at 298 K and 1 atm is approximately 1.79 M.
As member sahil2832 correctly wrote in reply #12 above.
The volume concentration (in volumes) refers to the volume of gas at standard temperature and pressure (STP) that can be produced from 1 volume of liquid.
20 volumes of hydrogen peroxide means that 1 litre of solution can produce 20 litres of oxygen gas (O2) at STP when decomposed.
1: Determine the volume of gas produced
Gas produced: 20 volumes of gas = 20 litres of O2 at STP (standard temperature and pressure).
At STP, 1 mole of any gas occupies 22.4 L (molar volume).
2: Calculation of the moles of gas produced
Mol of O2 = volume of gas/molar volume at STP = 20 L/22.4 L/mol = approx. 0.893 mol
3: Decomposition of hydrogen peroxide
The balanced chemical equation for the decomposition of hydrogen peroxide is:
2 H2O2 ==> 2 H2O+ O2
The equation shows that 2 moles of H2O2 produce 1 mole of O2.
Therefore, the number of moles of H2O2 can be calculated as follows:
Moles of H2O2 = 2 x moles of O2 = 2 x 0.893 moles = approximately 1.786 moles
4: Calculation of molarity
Let us assume that the concentration of the hydrogen peroxide solution is 1 L (for ease of calculation).
Molarity (M) is defined as moles of solute per litre of solution: Molarity (M) = moles of solute/volume of solution in litres.
We have 1.786 moles of H2O2 in 1 L of solution.
Molarity of H2O2 = 1.786 moles/1 L = 1.786 M
Conclusion: The molarity of hydrogen peroxide (H2O2) at a concentration of 20 volumes at 298 K and 1 atm is approximately 1.79 M.
As member sahil2832 correctly wrote in reply #12 above.
(edited 7 months ago)
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