Thursday, December 17, 2009

Balancing Equations

Today, we learned about chemical equations!

- Formulas must be correct or nothing will be right

there are different types of reactions:


combustion: when oxygen combines with another compound to form carbon dioxide and water
C3H4 + O3 ---> CO2 + H2O

synthesis: when two compounds combine to form a more complicated one
A + B --> AB

decomposition: when a complex molecule breaks down to make simpler ones
AB --> A + B

single replacement: When one element trades places with another in a compound.

A + BC --> AC + B (if A is a metal)
A + BC --> BA + C (if A is non-metal)

double replacement: When metals and non metals of an element switch places
AB + CD --> AD + CB

Acid-Base Neutralization: When an acid and base react to make a salt and water
HBr + NaOH ---> NaBr + H
2O


We balanced equations.... here's how!!
1. make sure all formulas are correct with correct subscripts
2. count how many of each element there is on each side
3. place coefficients beside compounds (and individual elements, if any) to make each element have the same number of each side
4. if oxygen is one of the elements present, do it last
5. check your answers!!!

here are a few examples

___ NaNO3 + ___ PbO ---> ___ Pb(NO3)2 + ___ Na2O
becomes

2 NaNO3 + PbO ---> Pb(NO3)2 + Na2O

AgI + Fe2(CO3)3 --> FeI3 + Ag2CO­3

becomes

6 AgI + Fe2(CO3)3 --> 2 FeI3 + 3 Ag2CO­3


C2H4O2 + O2 --> CO2 + H2O

becomes
C2H4O2 + 2 O2 --> 2 CO2 + 2 H2O






heres a worksheet!

Monday, December 14, 2009

Intro to Chemical Reactions

well firstly we went over our test from last class before we started our new unit today which is unit four- types of chemical reactions

we looked at some eqamples of when acids and bases neutralize each other


we talked about some supporting evidence that shows us when a chemical reaction has taken place:
  • change in colour
  • change in smell
  • percipitate is formed

remember that changes in state do not always mean chemical reaction has occured, although it may seem like it ( think ice to water to water vapour)

we also saw a demonstration from mr. doktor about magnesium and how when it burns, it gives of a lot of radiant light and thats why its used in fireworks. this video clip uses a lot more magnesium than what we used in class but you get the idea :P




thats pretty much all we did today!

Saturday, December 5, 2009

Copper (II) Chloride Lab

This class all we did was learn about dilution. For the next class we will be doing a cupric chloride lab. What we're will be doing is diluting a solution of copper II chloride. The lab is individual but you will be work in a group. The procedure is simple but we need to find the mass of copper II chloride we will be using. To find the mass here are a few examples we did in class.

1) Peter is asked to make a 250mL solution of K2SO4 with a concerntration of 0.55M. What steps will he follow? The conversions used here are: concentration - mole - mass
(0.55/1L)(0.25L)= make sure to convert mL into Litres!
(.1375mol)(174.3g/1mol)=
23.97grams

Dilution of Solutions:
When you add water concentration decreases. If volume is doubled, concentration is halved.
6.0L 2.0mol/L 12.0mol
12.0L 1.0mol/L 12.0mol

For the lab, the problem is how you can make a 0.300M Solution of Copper II Chloride?
In my solution I will be using 60mL of water. To know how much mass of Cooper II Chloride I will need for my solution I will use the conversions: concentration - mole - mass
(0.300mol/L)(.06L)=.018mol
(.018mol)(134.5g/mol)=2.421grams


for a dilutions worksheet, click here

Tuesday, December 1, 2009

Concentration

Today, we learned about the wonderful world of.....................concentration!!!!

Solution: A homogeneous mixture
Solute: The component present in the smaller amount
Solvent: The component present in the larger amount
Concentration: Ratio of solute to solvent and can be determined by the following equation:

Amount of Solute
Amount of Solvent

Possible units:
g/mL, g/L, mg/mL, micrograms/mL, m/L, % by mass, % by volume

con'c = concentration

The most useful units for con'c is mol/L which is also known as molarity (M)

molarity=

moles of solute
litres of solution

C = n/v
n = cv
v = n/c

n=
number of moles
c= concentration
v= volume

***********THOSE 3 FORMULAS LISTED ABOVE CAN ONLY BE USED FOR LIQUID SOLUTIONS

if a compound formula is in bracket, [like this], it means it is the concentration of the substance.
e.g. [HCl] = 6.0 mol/L


The concentration of HCl (Hydrochloric acid) is 6.0 mol/L



EXAMPLES
What is the molarity of a solution in which 0.45 grams of sodium nitrate are dissolved in 265 mL of solution?

Sodium Nitrate = NaNO3, molar mass = 84.99 g/mol

0.45 g x 1 mol/84.99 g = 0.005 mol
265 mL x 1L/1000mL = 0.265 L


molarity = 0.005 / 0.265 = 0.01998 mol

the molarity of NaNO3 in 265 mL of solution is 0.020


What will the volume of a 0.50 M solution be if it contains 25 grams of calcium hydroxide?
calcium hydroxide = Ca(OH)2
molar mass = 74.093 g/mol

25 g x 1 mol/74.093 = 0.3329 mol

v = n/c
= 0.3329 / 0.50 M
= 0.6658 L
=0.67 L

How many grams of ammonia are present in 5.0 L of a 0.050 M solution?

Ammonia = NH3
molar mass = 17.031 g/mol

n = cv
= (0.050)(5.0)
=0.25 moles

0.25 moles x 17.031 g/1mol = 4.26 g
= 4.3g

for a worksheet click here