Question

1)what is the molarity of a solution prepared by disolving 10.7g NaI in 0.250L?

2) the oxygen gas emitted from an aquatic plant during photosynthesis is collected over water at 20.0C and a total pressure of 452mmHg. What is the partial pressure of the oxygen gas in atm?

3)how many grams of a 23.4 by mass NaF solution is needed if you want to have 55.9g of NaF?

4)What volume (in mL) of a 12.0 M HCl stock solution is required to dilute and make 75.0mL of 3.5g of HCl?

5) if the molarity on an NaOH solution is 3.50M and you have a volume of 225mL, calculate the mol solute? What is the mass in g of solute?

Answer 1

1.

         Molarity    = W/G.M.Wt*volume of solution in L

                        = 10.7/150*0.25    = 0.285M

2. vapor pressure of water at 20c = 17.5mmHg

Total pressure   = partial pressure of O2 + water vapour pressure

           452         = partial pressure of O2 + 17.5

partial pressure of O2   = 452-17.5   = 434.5mmmHg

partial pressure of O2   = 434.5/760    = 0.57atm

3.

23.4% mass of NaF solution means 23.4g of NaF present in 100g of solution

      100g of solution contains 23.4g of NaF

    55.9g of solution contains = 23.4*55.9/100    = 13.1g of NaF

4.   molarity = W*1000/G.M.Wt* volume of solution in ml

                    =3.5*1000/36.5*75    = 1.278M

    Before dilution                                                    After dilution

   M1   = 12M                                                          M2   = 1.278M

   V1     =                                                                 V2   = 75ml

               M1V1    =   M2V2

                V1        = M2V2/M1

                              = 1.278*75/12    = 7.98ml

5.

molarity   = no of moles /volume of solution in L

3.5            = no of moles /0.225

no of moles = 3.5*0.225    = 0.7875moles

mass of solute = no of moles * gram molar mass

                         = 0.7875*40   = 31.5g