Normality and Molarity     Chapter 7

 

Molarity is moles per liter of solution. 

   M = moles
            liter

We use Normality when discussing solutions especially acids and bases.

   HCl   + Na(OH)        ---->  NaCl   +  HOH
   acid        base                          salt     water 

If I had 100 milliliters of a 1 M HCl acid, how many moles of H+ would I have?

 

If I had 100 milliliters of a 1 M Na(OH), how many moles of (OH)- would I have?

 

Let's look at H2(SO4)   

   H2(S04)     ------->    2 H+    +    1 (SO4)=

Each molecule of H2(SO4)  would give  2 H+   and  1 (SO4)=

If I had 100 mL of a 1 M H2(SO4)

I would have 0.10 moles of H2(SO4)
 "  "        "     0.10 moles of (SO4)=
 "  "        "     0.20 moles of H+        Why?   1 mole of H2(SO4) has 2 moles of H+ 

 1 liter of  a 1 M Na(OH) would have 1 mole of (OH)-
  l liter of  a 1 M H2(SO4)  would have 2 moles of  H+ 

If I mixed 1 L of 1 M Na(OH) with 1 L of 1 M H2(SO4) I would have an acid solution.   Why? 

 I have  2 times as much  H+'s as I have  (OH)-'s. 
1 liter of 1 M NaOH has 1 mole of Na and 1 mole of (OH)-
 1 liter of  1 M H2(SO4) has 1 mole of  (SO4) and 2 moles of  H+ 

When using acids and bases we use Normality (N) instead of Molarity (M).

1 M HCl   =    1 N HCl
1 M H2(SO4)  =  2 N H2(SO4)
1 M H3(PO4)  =   __ N H3(PO4) 

H2(SO4)  +  2 Na(OH)  ------>  Na2(SO4) + 2 HOH

 

If I had 100 milliliters of a 1 M H2(SO4), how many moles of H+ would I have? 

 a 1 M H2(SO4) solution is a 2 N H2(SO4) 
for every mole of sulfuric acid, you would get 2 moles of H+

1 M Ca(OH)2   =   _____ N Ca(OH)2
For every mole of calcium hydroxide, would get 2 moles of hydroxide ions.
 

HCl has only 1 hydrogen 
 

H2SO4  has 2 hydrogens 

a 1 M HCl is a 1 N HCl 

a 1 M H2SO4 is 2 N H2SO4

 Examples 

What is the normality of 3 M H2(SO4)?

      1 M H2(SO4)      =      2 N H2(SO4)
     3 M H2(SO4)      =       x N H2(SO4)

    1         =        2            criss cross multiply
   3                    x 

    x  =  6 

What is the molarity of 6 N H3(PO4) ? 

   1 M H3(PO4)        =       3 N H3(PO4)
    x                         =        6 N H3(PO4) 

       1         =       3 
       x                  6

       x = 2

 

Problems

 

Determine the normality of  

1.5 M HNO3

0.55 M H2SO4 

0.0023 M Ca(OH)2 

Determine the molarity of 

0.9 N NaOH 

1.3 N HCl 

0.06 N H2SO4 

0.3 N H3PO4

12 N Ca(OH)2

 

Neutralization   

If I had 50 H+'s how many (OH)- s would I need to neutralize it? 

If I had 50  H+, how many (OH)- would I need to neutralize it? 

We frequently use the term EQUIVALENTS or MILLIQUIVALENTS when discussing hydrogen ions or hydroxyl ions.

You can think in terms of moles of H+ or moles of OH- when using the term equivalent.

Equivalents =  Normality x Liters              Molarity   =  moles
                                                                                           L

                                                                  moles    =   Molarity
                                                                     L

                                                                    moles    =  Molarity x L 

                                                               Equivalents  =  Normality x L

Milliequivalents  =   Normality  x   Milliliters

If I had 50 mL of a 2 N H(SO)4 how many milliequivalents of H+ do I have? 

How many milliequivalents of hydroxyl would I need to neutralize it?

meq H+            =  meq (OH)- 

   N1V1   =  N2V2 

  (N) (mL)     =     (N) (mL)

1. How many milliliters of a 0.02 N NaOH would be needed to neuralize  35milliliters of a 0.15 N HCl? 

 

2. What is the normality of a solution of HCl, if 50 mL of the HCl were neutralized by 30 mL of a 0.15 N NaOH? 

Dilutions   

Suppose I had 12 N HCl and wanted to make up 200 mL of 0.1 N solution.  How many milliliters of the concentrated solution would I need to make up 200 mL of the dilute solution?

 

How many milliequivalents of H+ would I need in 200 mL of 0.1 N HCl

Meq =   (N) (mL)    

So how many milliequivalents would I need to take out of the concentrated HCl solution?

 

How many milliliters would have that number of milliequivalents?

Formula for dilutions

      meq          =       meq    
    (N) (ml)     =   (N) (mL) 

 How many milliliters of a 6 N NaOH would I need to make up 100 mL of a 1 N NaOH? 

  Problems 

1.  How many milliliters of 2N HCl would be needed to make 100 mL of  0.1 N HCl?

 

2.  What is the Normality of a NaOH solution if it took 25 mL of  a 0.1 N HCl to neutralize 10 mL of the NaOH? 

 

3.  How many milliequivalents of H+ are there in 200 mL of 0.25 N solution? 

 

4.  What is the normality of a HCl solution if 10 mL of 12 N HCl were brought up to a 1 L volume? 

 

5.  How many milliequivalents of NaOH are needed to neutralize 50 mL of a 0.2 N HCl solution? 

 

6.  How many grams of NaOH are needed to make  100 mL of 0.5 N NaOH? (hint: N = M for NaOH     M = grams/ MW) 

 

7.  How many grams of H2(SO4) are present in 50 mL of a 0.1 N H2(SO4)?

                                                                    PROBLEMS

 

1. Calculate the mass percent of solute in 25.0 g of KNO3 in 850 grams of H2O. 

 

2. Calculate the mass, in grams, of solute needed to prepare 24.0 grams of a 13.5% by mass sucrose (C12H22O11) (MW 342) solution. 

 

3. Calculate the volume percent of solute in 75.0 g ethylene glycol in enough water to give 200 mL of solution.

 

4. What is the percent by volume of isopropyl alcohol in an aqueous solution made by diluting 20 mL of pure isopropyl alcohol to a volume of 125 mL. 


5. Calculate the mass/volume percent of magnesium chloride of 1.0 g MgCl2 in enough water to give 45 mL of solution. 


6. How many grams of NaCl are present in 15 mL of a 2.0% solution? 

 

7. How many grams of solute are present in 375 mL of  7.5 M CaCl2 solution? 
 

8. Given a 2.0 M solution of NaCl.  How many milliliters of the solution would be needed to get 1.0 gram of NaCl? 

 

9.   5.85 grams of NaCl wer dissolved in water.  The final volume was 100 mL.  A) What is the molarity?  B) What is % w/v?

 

10.  Concentrated HCl is 12 N.  How many milliliters of the concentrated acid wuld be needed for 100mL of a 0.15 N solution?

 

11. How many grams of sulfuric acid H2(SO4) are in 1 liter of a 1.50 N solution? 

 

12. How many meq of H+ are ther in 29 mL of a 2 N solution of HCl? 

 

13. What is the normality of a HCl solution which contains 50grams of HCl per liter?

 

14. What is the normality of a 4 M H2SO4? 

 

15. How many mL of a 0.3 N NaOH solution would be required toneutralize 50 mL of a 0.4 N solution of H2SO4? 

 

16.  How many milliequivalents are persent in 15 mL of a 2 N solution?

  

17. How many milliquivalents of acid are requird to neutralize 20 milliequivalents of base?

 

18. How many mL of a 0.15 N HCl would be required to neutralize 40 mL of a 0.20 N NaOH.


19. It took 35 mL of an acid of unknown normality to neutralize 25 mL of 0.12 N NaOH.  What is the normality?

 

20. How many milliliters of a a 0.20 M H2SO4 would be required to neutralize 80 mL of a 0.10 N NaOH?

 

21. How many mL of a 12 N HCl solution would be needed to make  100 mL of a 0.15 N solution?

 

 22. 15 mL of a 10 N NaOH solution was diluted to a volume of 1 liter.  What is the normality of the new solution.?

 

 23.  Given 3.92 grams of H2SO4, (MW 98) in 250 mL of solution.
        a) What is the Percent solution?
        b) What is the Molarity of the solution?
        c) What is the Normality of the solution?

Wednesday, March 21, 2007 01:28:03 PM