(TG): CHEM LAB

 DILUTING AND CREATING SOLUTIONS LAB!

Today in class we had a lab where we had to create a solution of Copper Chloride with a concentration of O.1 M and then compare to samples\ Mr.Doktor set up. The solution that matched the solution you create (in terms of colour/shade) is the winner!

Materials:

• Beaker
• Graduated Cylinders
• Stir Rod
• Test Tube Stand

Procedure:

1. Tke about 5g of Copper Chloride and place it into a plastic dish
2. Take your plastic dish and pour the copper chloride onto a piece of wax paper
3. Take the wax paper and place it on your weighing scale
4. Weigh and record the total mass of the copper chloride
5. Put 25 mL of water in a graduated cylinder
6. Take 0.336g from the recorded amount of copper chloride with your scoopula
7. Put 0,336g  of copper chloride into the 25mL of water
8. Slowly stir the solution with a stir rod
9. Compare with Mr.Doktors solution and choose the closest shade of blue that matches yours
10. Repeat the procedure 3 times for consistent results

NECESSARY MATH:

0.025L x (.1mol/L\) x (134.5g/mol) = o.336g

Dont have any copper chloride? Well you could always....

(NR) March 14, 2011: Acid-Base Reactions

• Strong Acids dissociate to produce H+ ions.
  - HCl, H2SO4, HClO4
• Strong Bases dissociate to produce OH- ions.
  - NaOH, Ba(OH)2, LiOH
• When the Strong Acids and Strong Bases mix they form H2O and an ionic salt
  (The total volume changes!)
  
  
  pH and pOH- pH is a measure of the hydrogen ions present in a solution     > pH = -log[H+]
  - pOH is a measure of the hydroxide ions present in a solution > pOH = -log[OH-]
  
  
  EXAMPLE!
  0.200L of 0.500 M HCl is added to 0.200L of 0.500M LiOH.
  What is the mass of water produced?
  
  
  LiOH + HCl  --> H2O  + LiCl
  
  
  .500mol/L x 0.200L x 1/1 x 18g/mol = 1.8g
  
  
  What is the mass of the salt produced?
  
  
  0.500mol/L x 0.200L x 1/1 x 42.4g/mol = 4.24g

(DA) Feb 28, 2011: Titrations

• A titration is an experimental technique used to determine the concentration of an unknown solution

Terms & Equipment

• Buret - contains the known solution. Used measure how much is added
• Stopcock - Valve used to control the flow of solution from the buret
• Pipet - Used to accurately measure the volume of unknown solution
• Erlenmeyer Flask - Container for unknown solution
• Indicator - Used to identify the end point of the titration
• Stock Solution - Known solution

Example

• Jon the chemist wants to determine the concentration of a Sodium Hydroxide sample so he does a titration with HCl. He gathers the following data. Determine [NaOH]

NaOH sample = 10.00 mL                      [HCl] = 0.75M

Trial                              1                             2                          3                        4
Final Reading (mL)      13.3                        26.0                     38.8                  13.4
Initial Reading (mL)       0.2                        13.3                     26.0                   0.60
Volume Used (mL)      13.1                        12.7                     12.8                  12.8
                                                                                                          Vaverage = 12.85 mL


0.75 mol x 0.01285 L x 1 = 0.0964 mol
      L                             1

0.0964 mol x 1     = 0.964 mol/L
                 0.010L

(DA) Feb 24, 2011: Solution Chemistry

Example

• 100mL of 0.250 M Iron (II) Chloride reacts with excess copper. How many grams of Iron are produced?
  
  FeCl2 + Cu -> CuCl2 + Fe
  
  0.100L x 0.250 mol x 1 x 55.8g = 1.40 g
                        L          1     1mol
  

• How many moles of Copper (II) Chloride are produced?
  
  0.100 L x 0.250 mol x 1 = 0.0250 mol
                         L          1
  
• Determine [CuCl2]
  
  0.0250 mol x 1 = 0.250 mol/L
                    0.100L

(DA) Feb 22, 2011: Solution Stoichiometry

Solutions

• Solutions are homogenous mixtures composed of a solute and a solvent
  - Solute is the chemical present in lesser amount (whatever is dissolved)
  - Solvent is the chemical present in greater amount (whatever does the dissolving)
• Chemicals dissolved dissolved in water are aqueous
  - NaCl(aq); H2SO4(aq)

Molarity

• Concentration can be expressed in many different ways
  - g/L, ml/L, % by volume, % by mass, mol/L
• The most common (In Chemistry 11 & 12) is mol/L which is also called Molarity
  - mol/L = M
  - [HCl] = concentration of HCl
  
  Molarity = Moles
                  Volume 

Examples:

• What is the concentration of Sodium Chloride solution made from 0.75 mol of NaCl dissolved in 250 mL of water
  
  0.75 mol = 3.0 mol/L                or 3.0 M
  0.250 L 

(NR) DILUTIONS - March 3rd, 2011

Diluting solutions

- When two solutions are mixed the concentration changes.

-  Dilution is the process of decreasing the concentration by adding a solvent (usually water)

- the amount of solute doesn’t change.  n1 = n2

- because concentration is mol/L 

   We can write…

                  

        C=n/V          AND          n= CV          AND          V=n/C

So… 

C1V1 = C2V2

(initial) = (final)

EXAMPLES

A 12.0 mL of 38 M of hydrochloric acid is diluted to a final volume of 380 mL. What is the concentration of the new solution?

*REMEMBER TO CONVERT mL to L!

C1V1   =   C2V2

(38M)(0.012L)   =   C2(0.380L)

0.456mol   =   C2(0.380L)

1.2M   =   C2

Therefore new solution has a concentration of 1.2M

Mr. Doktor the ALMIGHTY chemist is given a solution of 3.8M NaOH. After diluting the solution to a final volume of 0.12L the concentration is 0.83M. What volume of NaOH was Mr. Doktor the ALMIGHTY chemist initially given?

C1V1   =   C2V2

(3.8M)V1   =   (0.83M)(0.12L)

(3.8M)V1   =   0.0996mol

V1   =   0.026L