[biologyexpert]

Hi there, here are some chemistry questions that I really could use a helping hand in. I understand that theres alot of them, but I would truly appreciate it if any of you could take a stab at one or two of them if you do know the steps and the answer.
Thanks so much.
Here they are...

1.Ozone is a highly irritating gas that reduces the lung capability of healthy people in concentrations as low as 0.12 ppm. Older photocopy machines could generate ozone gas and they were often placed in closed rooms with little air circulation. Calculate the volume of ozone gas that would result in a concentration of 0.12 ppm in a room with dimensions of 5.0 x 4.0 x 3.0 m.

2. Write the net ionic equation for the reaction between aqueous solutions of barium chloride and sodium sulfate. Be sure to include the state of each reactant and product.

3.Write the net ionic equation for the reaction between aqueous sodium hydroxide and aqueous nitric acid. Be sure to include the state of each reactant and product.

4.What are the spectator ions when solutions of Na2SO4 and Pb(NO3)2 are mixed?

5. A sample of lemon juice was found to have a pH of 2.50. What is the concentration of hydronium ions in the lemon juice?

6.What is the pH of a solution in which 2.0 x 10^-4 mol of HCl is dissolved in enough distilled water to make 300 mL of solution?
&
7. What is the pH of a solution containing 2.5 g of NaOH dissolved in 100mL of water?

[Borek]

Please read forum rules.

[Ch3micat]

5.  pH litterally means opposite common log of H+ ions.  H+ and H3O are the same basically when in water.  So if the pH is 2.50, then the concentration of hydronium ions is 10^-2.50  (Common log is base ten, so to find the pH , you do -log(molarity) and to find molarity from pH it is 10^-(ph).)    [Also, it is important to note, that a pH of 1 is ten times more concentrated than a pH of 2, and 100 times more than a pH of 3, and so on]
 
3.  Net Ionic equations just show what's going on.  So first you'd start with half reactions.  OH (from the NaOH) + H (from the HCl) = H2O.  And technically Na + NO3 = NaNO3, but you probably don't need that because NaNO3 is extremely soluble.  Unless you boil the water you are basically left with Na+ and NO3- ions in solution.

4. Spectator ions are the ones that don't react. Typically, the real soluble ones.  Lead is going to react with sulfate to form a yellow lead sulfate precipitate, but Nitrate is basically just there so that you can easily get the lead in solution.   The Sodium is also there just to get the sulfate in solution.  Neither the nitrate nor the sodium is going to react at all, so they are considered spectator ions.  After the reaction, they remain unchanged.  They do not react, therefore they are spectators.

1. PPM = parts per million.  Meaning out of every million molecules, .12 of them are ozone.  You can do the math.

7. You need to know the molar mass of NaOH, and figure out how many moles are in 2.5 grams.  Then, when you know how many moles you have, divide it by .1 Liters (100 mL)  this is your molarity.  Then, do -log(molarity) which will give you pOH.  Take 14, and subtract the pOH from it, and you've got your pH.