# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: yuheng_wu on December 16, 2020, 02:45:48 PM

Title: Can someone tell me what I'm doing wrong here? (calculation)
Post by: yuheng_wu on December 16, 2020, 02:45:48 PM
Given:
- dioxide is being disolved in water.
- c=8mg/l
- Vwater=10,0 liters
- T = 25 °C = 298,15K
- p = 1013 hPa
The question is: 'how much volume dioxide kan disolve maximally in 10,0 liters of water at a temperature of 25°C and pressure of 1013hPa?
The answer is 61,1mL, however when I solve this problem my answer is 6,11mL. Could someone please tell me what I'm doing wrong?
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2F&hash=03ee70165653ed1fcf3a617a5e4320ea)

Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: mjc123 on December 16, 2020, 03:00:40 PM
First, O2 is dioxygen, not "dioxide".

You are using the concentration in mg/L, and working out the volume that dissolves in 1L. You are asked for the volume that can dissolve in 10L.
Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: yuheng_wu on December 16, 2020, 03:28:43 PM
First, O2 is dioxygen, not "dioxide".

You are using the concentration in mg/L, and working out the volume that dissolves in 1L. You are asked for the volume that can dissolve in 10L.
So c= ndissolved substance/Vsubstance here I can say that V substance = 10 liters? I though that this is incorrect since V substace is equal to Vwater+Vdioxygen = 10 liters + x liters or am I understanding this formula incorrectly? I do understand my mistake now but I don't understand this formula.
Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: AWK on December 16, 2020, 04:13:25 PM
Such a small amount of oxygen dissolved in water practically does not increase its volume.

You have calculated the volume of oxygen dissolved in 1 L of water in the longest possible way. How much oxygen will there be in 10 liters of water?
Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: yuheng_wu on December 17, 2020, 02:12:36 AM
Such a small amount of oxygen dissolved in water practically does not increase its volume.

You have calculated the volume of oxygen dissolved in 1 L of water in the longest possible way. How much oxygen will there be in 10 liters of water?
Ah yes the volume of oxygen would not really increase it's volume indeed, I understand. You said I have calculated the volume in a very inefficient way? How could I do this faster/more efficiently please?
Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: AWK on December 17, 2020, 02:17:46 AM
10·(0.008/32)·22400·(298.15/273.15)=
Title: Re: Can someone tell me what I'm doing wrong here? (calculation)
Post by: yuheng_wu on December 17, 2020, 02:50:55 AM
10·(0.008/32)·22400·(298.15/273.15)=

Thank you very much.