Chem CLass- December 15, 2009

Today, we missed some class time because of a presentation in a gym for the whole school. We did take notes on chemical equations, however.

CHEMICAL EQUATIONS
- Shows the chemicals used up (reactants) and produced (products) during a chemical reaction
- The numbers in front of the symbols are called coefficients and they refer to the number of moles

BALANCED CHEMICAL EQUATIONS
- There are the same number of each type of atom on each side of the equation
- Mass, atoms and charge are conserved

Ex: Sn + O2 -----> SnO
= 2 Sn + O2 -----> 2SnO

Ex: Na + H20 -----> NaOH + H2
= 2 Na + 2 H20 -----> 2NaOH + H2

Ex: NH3 + O2 -----> NO + H20
= 4 NH3 + 5 O2 -----> 4 NO + 6 H2O

For some extra help, here's a video on balancing chemical equations:

Chem Class- December 11, 2009

Today we got our tests back! We hope everyone did well.

• We got a new outline for our new unit. We are are going to be learning about chemical reactions!
• Mr. D showed uss a small lab with hydrochloric acid (PH of -1)
• He added bromothemal blue and the hydrochloric acid turned a light yellow colour
• Then he added ammonia to the mixture. The top of the mixture turned blue. He added more ammonia and the blue stayed on top of the acid.
• Mr. D turned on the gas valve and we found out that someone hadn't turned it off. It stunk really bad!
• If he lit a match, there would be an explosion
• Next, he showed us another experiment where he mixed in potassium iodie with iron iodide. It made the mixture turn yellow
• He also got out the match and burned magnesium. We saw a spectacular light, but were not supposed to look directly at it. Apparently this was how fireworks were made.
• Finally, he dipped a piece of paper in salt water and alcohol and put it through the bunsen burner. Flames appeared for a short instant but it did not burn the paper. The alcohol was burning.

<---burning magnesium


Signs of a chemical Reaction: colour change, property change, energy change, temperature change, precipitate forming, gas production, heat and light produced...

Chem Class- December 4, 2009

For chem we did our lab on Dilution and Creating Solutions.

 

Basically, the procedure goes like this:

1. Measure desired amount of water
2. Measure needed amount of copper (II) Chloride (__mol/L x ___L = # of mol x ___g/ 1 mol = # of g)
3. Add to the water and stir until it dissolves
4. Compare results to 5 testubes (labelled a, b, c, d, e) for the best match (lighter shades of blue to darker shades of blue)

Copper (II) Chloride

  

We also went over the make up of the upcoming test. It will consist of:

• The mole
• The moles conversions chart
• % composition, % mass, empirical formulas
• Mass of elements in compounds
• Concentration
• Molar volume
• Dilution
• Density
• Molecular Formulas

Chem Class- December 2, 2009

After going over questions #25-28 from our Unit 2 Homework Questions, we took notes on Giving Directions and Dilution of Solutions.

GIVING DIRECTIONS

Outline for experimental procedures

---------> simply find the mass you need.

It isn't hard. You just convert from con'c---->moles---->mass

Remember that C=n/v (Concentration = number of moles over volume)

Then you give the directions like so, filling in the missing information:

a) Measure (Volume in L or mL) of Water

b)Weigh (mass in g) of (element or compound)

c) Add (element or compound) to water and stir until dissolved.

Example: Lizzy is asked to make a 3.00 M solution of NH4Cl.  If she needs 1.00 L, what procedure should she use?

3.00 mol L x 1.00 L = 3.00 mol

3.00 mol mol x 53..5 g/1 mol = 161 g

a) Measure 1.00 L

b) Weigh 161 g of NH4Cl

c) Add NH4Cl to water and stir until dissolved

___________________________________________________

 DILUTION OF SOLUTIONS

When you add water, the con'c decreases. If the volume is doubled, the con'c is halved. If the volume is halved, the concentration is doubled.

6.0 L = 2.0 mol/L (Start out with)

12.0 L = 1.0 mol/L (Multiply the volume by 2, divide the volume by 2)

48.0 L = 0.25 mol/L (Multiply the volume by 4, divide the volume by 4)

The number of moles is doesn't change though (In this case 12.0 mol)

Remember that C1V1 = C2V2 (Where C1 is equal to the initial concentration, C2 is equal to the final concentration, V1 is equal to the initial volume and V2 is equal to the final volume)

Ex: If 20.0 mL of  0.75 M HBr is diluted to a total volume of 90.0 mL, what is the molar concentration of the HBr in the resulting solution?

V1 = 20.0 mL

C1 = 0.75 M

V2 = 90.0 mL

C2 = ?

(0.75) (20) = C2 (90)

C2 = 0.17 M

Here's a video on calculating Dilution of Solutions for some more help: