Solutions and concentrations question

[510586]

Hi guys, so this is kind of a silly question so bear with me. The example question is from a chad's video quiz over solutions and concentrations.

"To what volume of water should 29g of KF be diluted to make a 4 M solution?"

I understand how to do all the stoichiometry, but I was wondering: If we are dissolving KF (or perhaps something else) in water, would we ever have to write out a balanced equation and take into account molar ratios and stuff? Does the concentration (molarity) of the "final" solution need to take into account molar ratios?

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[DAT Destroyer]

Hi guys, so this is kind of a silly question so bear with me. The example question is from a chad's video quiz over solutions and concentrations.

"To what volume of water should 29g of KF be diluted to make a 4 M solution?"

I understand how to do all the stoichiometry, but I was wondering: If we are dissolving KF (or perhaps something else) in water, would we ever have to write out a balanced equation and take into account molar ratios and stuff? Does the concentration (molarity) of the "final" solution need to take into account molar ratios?

Use the formula M = moles of solute/liters of solution. Simply take the grams and divide by the weight to get moles. Plug it into the formula.

Hope this helps.

Dr. Romano

 

[510586]

Thanks! So water as a solvent is the same as solution in volume? It doesn't change when adding stuff that dissolved?

 

[DAT Destroyer]

For a problem of this type this is all you would need. The question should have been worded what is the volume of the solution.

Notice how the phrase "of solution" keeps showing up. The molarity definition is based on the volume of the solution, NOT the volume of pure water used. For example, to say this:

"A one molar solution is prepared by adding one mole of solute to one liter of water."

is totally incorrect. It is "one liter of solution" not "one liter of water."

Be careful on this, especially when you get to molality.

Dr. Romano

 

[510586]

For a problem of this type this is all you would need. The question should have been worded what is the volume of the solution.

Notice how the phrase "of solution" keeps showing up. The molarity definition is based on the volume of the solution, NOT the volume of pure water used. For example, to say this:

"A one molar solution is prepared by adding one mole of solute to one liter of water."

is totally incorrect. It is "one liter of solution" not "one liter of water."

Be careful on this, especially when you get to molality.

Dr. Romano

Oh yea I understand that what I meant to ask was if adding solute to the 1 liter of water solvent changed the volume of the solution.