molarity Problems! Heeeeelp?

Question

1.The density of a 40.0% by weight aqueous solution of NaOH is 1.432 g/cm. What is the molarity of NaOH?(Atomic weights: Na = 22.99, O = 16.00, H = 1.008)

2. The density of a 32.0% by weight aqueous solution of acetone is 1.0425 g/cm. What is the molarity of the compound?(Atomic weights: C = 12.01, H = 1.008, O = 16.00)

3. A protein solution is prepared by dissolving 40 mg of protein in 10 mL of water. A .5mL sample of this solution is diluted to a volume of 20mL. How many mg of protein will be in 2 mL sample of the diluted solution?

4. What is the molality of a K2CrO4 solution with a mole fraction of 0.0161?(Atomic weights: K = 39.10, Cr = 52.00, O = 16.00, H = 1.008)


5. Concentrated HCl is 37% HCl by mass and has a density of 1.19g/mL. How many milliliters of this solution are required to prepare 125mL of 1.5M HCl solution?

I wish i could but my teacher doesn't go through these questions ... it's depressing iknow

Answer 1

You need to be better aware of the concepts of density, volume, mass and mole weight. These problems are not all that hard.

1. Take a liter of solution. Its mass is 1432 grams. 40% of this mass is NaOH. Find the NaOH and divide by the mol weight of NaOH to get your answer.
2. This is the same routine.
3. Just follow the bouncing ball. You start with 40 mg in 10 mL. You remove 0.5 mL of this. How much protein is in the removed volume? Now you dilute it (this doesn't change the mass in the removed volume, just spreads it out) to 20 mL. If you remove 2 mL, you have removed 10% of the volume. Guess what percent of the protein mass you have removed?
4. If the potassium chromate is 0.0161, the solute (water) is going to be the other 0.9839 moles. Find the volume of that many moles of water. Then divide 0.0161 by that volume and make sure your final result has a volume in Liters.
5. Work this from the end back. How many moles is 1.5M HCl in 125 mL solution. Once you know that, the MASS of HCl is coming from your concentrate. So convert the moles in the 125 mL solution to grams. In the concentrate, each mL has a weight of 1.19 grams of which 37% by MASS is HCl. So figure the mL of concentrate that provides the HCl for the 125 ml solution.

Answer 2

if she's in love with somebody else, then you definately can no longer substitute that. i know it might desire to be heartbreaking, yet you do no longer choose a female buddy who does not love you, do you? there is is the alternative of attempting to win her back via attempting to be as advantageous as you would be to her and giving her the help or love she desires, yet im no longer ensuring that it will artwork. wish it works out for you. each so often in existence, love does harm.

Answer 3

well this is probably your homework and my suggestion is look at your notes because that's what i do when i'm working on my chemistry.

Answer 4

6250.62L