what mass of water must be added to 425 g of formaldehyde to prepare a 40.0% (by mass) solution of formaldehyde? this solution, called formalin, is used to preserve biological specimens.
(hint:) substitute the known quantities into the definition for mass percent, and then solve for the unknown quantity (mass of solvent)
ohhh yes, you are right. thank you very much I see my mistake now thank you again. have a nice day (:
To find the mass of water that must be added to 425 g of formaldehyde to prepare a 40.0% (by mass) solution of formaldehyde, we can use the definition of mass percent.
The mass percent of a solution is defined as the mass of the solute divided by the total mass of the solution, multiplied by 100.
So, in this case, we have the following information:
Mass of formaldehyde (solute) = 425 g
Mass percent of formaldehyde = 40.0%
Mass of water (solvent) = Unknown (let's call it "x")
Using the definition of mass percent, we can set up the following equation:
40.0% = (mass of formaldehyde / total mass of solution) * 100
We need to solve for the total mass of the solution, which is the sum of the mass of formaldehyde and the mass of water:
Total mass of solution = mass of formaldehyde + mass of water
Substituting the known quantities into the equation, we have:
40.0% = (425 g / (425 g + x)) * 100
Now, we can solve for "x" (mass of water).
Let's simplify the equation:
40.0% = (425 / (425 + x)) * 100
0.4 = (425 / (425 + x))
Cross-multiplying:
0.4 * (425 + x) = 425
170 + 0.4x = 425
0.4x = 425 - 170
0.4x = 255
x = 255 / 0.4
x = 637.5 g
Therefore, 637.5 g of water must be added to 425 g of formaldehyde to prepare a 40.0% (by mass) solution of formaldehyde.
To find the mass of water that must be added to prepare a 40.0% solution of formaldehyde, we'll use the definition of mass percent.
The formula for mass percent is:
Mass Percent = (Mass of solute / Total mass of solution) x 100
In this case, the solute is formaldehyde and the solvent is water. We want to find the mass of water (solvent) to prepare the solution.
Given:
Mass of formaldehyde (solute) = 425 g
Mass percent = 40.0%
Let's substitute the known values into the mass percent formula and solve for the mass of water (solvent).
40.0% = (Mass of formaldehyde / (Mass of formaldehyde + Mass of water)) x 100
Now, let's rearrange the formula to solve for the unknown quantity, which is the mass of water:
(Mass of formaldehyde + Mass of water) = Mass of formaldehyde / (40.0% / 100)
Simplifying further:
(Mass of formaldehyde + Mass of water) = Mass of formaldehyde / 0.4
Now, let's substitute the given mass of formaldehyde:
(425 g + Mass of water) = 425 g / 0.4
Dividing 425 g by 0.4:
(425 g + Mass of water) = 1062.5 g
To isolate the Mass of water, subtract 425 g from both sides:
Mass of water = 1062.5 g - 425 g
Mass of water = 637.5 g
Therefore, to prepare a 40.0% solution of formaldehyde, you would need to add 637.5 grams of water.
The hint isn't quite right but close.
You want 40% formaldehyde (w/w) which means 40g HCHO/100 g solution =
40 g HCHO/(40g HCHO + 60 H2O)
[425g HCHO/x]*100 = 40%
Solve for x which is the TOTAL grams solution. The amount of H2O to add will be x-425 = ? or 637.5g H2O.
Check it to see if that will do it.
[425/(425+637.5)]*100 =
(425/1062.5)*100 = 40%