[HersheyChocolates]

The density of Be(OH)2 is 1.92g/ml. Calculate the molar concentration of the OH- ions found in a 4% mass/mass Be(OH)2 solution.

Please show all steps and answer. Thanks in advance!

[Schrödinger]

Please show us your attempt at the question.

[HersheyChocolates]

Don't really know what to do at all or even how to start the question...thats why i posted here for help lol

[opti384]

Let's say you have 1L of Be(OH)2. How many mols of Be(OH)2 will be in that 1L?

[DevaDevil]

4 % by mass means there is 4 grams of Be(OH)₂ for every 100 grams of total solution




for the concentration: assume you have 1 liter (=volume of water + volume of Be(OH)₂)

water and Be(OH)₂ have a combined mass of M

Water is 1 kg / liter (approximately)

then you know that the mass % is 4%, so the mass of Be(OH)₂ divided by the combined masses of water and Be(OH)₂ = 0.04.

the final equation is the density; mass per volume of Be(OH)₂) = 1.92 g/ml

this gives you 5 equations with 5 unknowns, and is solvable.

[Borek]

1.92 g/mL doesn't sound right as a density of 4% solution; much too large for me.

[DevaDevil]

borek, I assumed it to be the density of the solid

[Borek]

If so, it is unrelated to the question.

http://www.chembuddy.com/?left=concentration&right=percentage-to-molarity

[DevaDevil]

very true, the answer should then have been
[OH^-] = 10^-7, as Be(OH)₂ does not (negligibly) dissolve in neutral water.
And if it does dissolve there will be no volume increase due to the adding of it to the water, rendering the density of the solid obsolete

I assumed wrong there, my bad