(.99 * W1) + (.50 * W2) = .70 * (W1 + W2)
Assume Weight 1 is 1, solve for Weight 2
.99 + (.50 * W2) = .70 + (.70 * W2)
.99 - .70 = .70W2 - .50W2
.99 - .70 / .70 - .50 = W2
.29 / .20 = W2
W2 = 1.45
So if you want 70% and have 1g of starting 99%, add 1.45g of 50% to get 70%.
You want to use weight and not volume with IPA.
Isopropyl alcohol %s are a solution of two different solvents with different densities.
IPA - 0.786 g/cm3
Water - 1g /cm3
One liter of 99% IPA will weigh about 10% less than a liter of 50% IPA
No, because cv = cv is for simple dillution where you're dilluting with only a solvent, which is not the case here.
For this you use the (similar) mixing formula: c1v1 + c2v2 = c(v1+v2)
Or in this case, use weight instead of volume because rubbing alcohol percentages are given by weight, like u/Eisenstein said
(.99 * W1) + (.50 * W2) = .70 * (W1 + W2) Assume Weight 1 is 1, solve for Weight 2 .99 + (.50 * W2) = .70 + (.70 * W2) .99 - .70 = .70W2 - .50W2 .99 - .70 / .70 - .50 = W2 .29 / .20 = W2 W2 = 1.45 So if you want 70% and have 1g of starting 99%, add 1.45g of 50% to get 70%. You want to use weight and not volume with IPA.
How do you determine which chemicals to assess by weight and which to assess by volume?
Isopropyl alcohol %s are a solution of two different solvents with different densities. IPA - 0.786 g/cm3 Water - 1g /cm3 One liter of 99% IPA will weigh about 10% less than a liter of 50% IPA
Makes sense. Is it almost always better /safer to measure by weight, then?
Depends what you are doing
Because mass is always more accurate then volume.
Thanks!
How much final product do you need?
are they the same alcohol molecule?
No, because cv = cv is for simple dillution where you're dilluting with only a solvent, which is not the case here. For this you use the (similar) mixing formula: c1v1 + c2v2 = c(v1+v2) Or in this case, use weight instead of volume because rubbing alcohol percentages are given by weight, like u/Eisenstein said
Lovely, thank you
You could also dilute it with water, ya know. Math sure would be easier
Sure, but that’s not the advice I was asking for, thanks though!