acid/base & solutions?

Question

11.what mass of Na4SO4 is needed to make 2.5 L. of 2.0 M solution?
(Na=23g; S=32g; O=16g)

14.the volume of 6.00M HCL needed to make 319mL of 6.80M HCL is?

16. the volume of alcohol present in 620 mL of a 40.0% (v/v) solution is ?

32. what is the molarity of HCL solution if 50.0mL is neutralized in a titration by 40.0 mL of 0.400M NaOH?

34. calculate the molarity of Ba(OH)2 solution if 1900 mL is completely titrated by 261 mL of 0.505 M HNO3

Answer 1

11. Use the molarity formula (M = moles/liters) to calculate how many moles of Na2SO4 are needed. Then convert moles to grams by multiplying by the molelcular mass of Na2SO4.

14. Remember and use the dilution formula (C1V1 = C2V2).
This works for any concentration unit (as long as C1 and C2 are the same unit) and any volume unit (as long as V1 and V2 are the same)

16. If the solution is 40% alcohol by volume, then 40% of the 620 mL is alcohol. ("of" means to multiply; don't forget to change the % to a decimal before multiplying!)

32. If your acid and base have equivalent numbers of H+ and OH- as in this problem you can use MaVa = MbVb where "a" refers to the acid and "b" refers to the base.
(they have "equivalent" numbers because the acid has 1 H+ and the base has 1 OH-)

34. Here your base has 2 OH-'s and your acid has only one H+ so they are not equivalent.

If you change the molarity of the acid to a unit of concentration called "normality" you can then get the "normality" of the base and then change it to "molarity". The relationship between molarity and normality is: N = M(#equivalents/mole).

For a rule of thumb, the "equivalents/mole" for an acid is the number of H+ in the acid (in your problem that would be 1)

For a base the "equivalents/mole" for a base is the number of OH- in the base (in your problem that would be 2).

So, the normatlity of the HCl is the same as the molarity

Using NaVa = NbVb solve for the Nb.

To change the Nb to molarity use

Nb = Mb(2)

Answer 2

use the M1V1=M2V2 equation to obtain the volumes and use reaction raitos to do Q.34