Concentration

Solution: A homogeneous mixture

Solute: The one present in a smaller amount

Solvent: The one present in a larger amount

Concentration: Amount of solute/amount of solvent

Some Units for Con'c

g/mL, g/L, mg/L, mg/L, mg/mL, ug/L

Most Common (and useful) Units are

mol/L = Molarity = Molar Concentration

M= mol/L, mol = M.L, L= mol/L

The triangle method can be used in this situation

This can only be used for an aqueous solution, but not for gases

Example #1: If you dissolve 25.0g of NaNO3 in water to make 500mL of the solution, what is the concentration?

[NaOH3] = M= 1.0mol/0.500L = 2 mol/L

Example #2: Jacob Black needs to make 550.0mL of 0.65M AgCl in order to weaken a rogue werewolf. What mass of solid AgCl is required?

con'c--->mol--->Mass

0.65mol x 0.550L = 0.358mol x 143.4g = 51.34g is needed to weaken a rogue werewolf

MID-TERM IS DONE SON!

We'd be lying if we say ' that was easy'.

Empirical Formulas

• The difference between an Empirical Formula and a Molecular Formula, is that an Empirical Formula give the whole number ratio of elements in a compound, whereas a Molecular Formula give the actual numbers.
  

Empirical Formulas
Simplest Formulas

How do you find the Empirical Formulas?
Example:
A sample of an unknown compound is analyzed and found to contain 8.4 G of Carbon, 2.1 G of Hydrogen and 5.6 G of Oxygen.

*To fully understand an figure out what the Empirical Formulas are, think back to the chart we did in class. *



*If the ratio ends in a decimal of :
~ 0.5 multiply it be 2.
~0.33 or ~0.66 multiply it by 3.
~0.25 or 0.75 multiply it by 4.
~0.2, ~0.4, ~0.6, or ~0.8 multiply it by 5.

Percent mass of elements in compounds ( Nov. 12 '09)

Find the % of carbon by mass in ethane (C2H6)
2(12g/mol)+6(1.0g/mol) = 30 g/mol
% Carbon = 24g/30g = 80%
% Hydrogen = 6g/30g = 20%

Percent composition
- means the % mass of each element in a compound
Find the composition of K2Cr2O7
K2 x 39.1 = 78.2 (27%)
Cr2 x 52 = 104 (35%)
07 x 16 = 112 (38%)
======294.2

(leave 1 decimal place for accuracy)

Finding the mass of an element in a given mass of a compound.
Find the mass of Carbon contained in a 25.0 g sample of CO2
C1 x 12 = 12 (27.3%) --> .2727(25g) = 6.8 g
O2 x 16 = 32 (72.7%) --> .7272(25g) = 18.2 g
====== 44 ================== 25g

Find the mass of K, C, and O contained in K2CO3 if the sample is 450.0 g.
K2 x 39.1 = 78.2 ( 56.6%)(450g) = 254.7 g
C1 x 12 = 12 (18.7%)(450g) = 39.6 g
O3 x 16 = 48 (34.7%)(450g) = 156.2 g
====== 138.2===========450 g

other examples:
Percent composition of C3H8
C3 x 12 = 36 (81.8%)
H8 x 1 = 8 (18.2%)
===== 44=100%
Find the percent of 2H2O in CaCl-2H2O
Ca1 x 40.1 = 40.1
Cl2 x 35.5 = 71
44 x 1 = 4 (2.7 %)
O2 x 16 = 32 (21.8 %)
====== 147.1 == 24.5%

Density and Moles (cont'd)

Class Date: November 9, 2009
----------------------------------------------------------------------------------------------------
This class was spent as a review lesson. Mr Doktor basically went through a few examples and continued/redid his lesson on density and moles.

Density--(D= M/V)--Mass--(molar mass)--Moles--(6.02 x 10^23)--Molecules
Mass--( x 22.4 L)--Volume(@STP)
Molecules--( x subscripts)--Atoms

Here are a few of Mr. Doktor's examples:
1. 1.25L of an unknown gas has a mass of 3.47g. What is the molar mass if it is at STP?
1.25L x (1mol/22.4L) =0.0558mol >>
3.47g/0.0558mol=62.2g/mol

2. 250mL of a gas which is known to contain one sulphur atom and an unknown number of fluorides has a mass of 1.63 at STP. Find the molar mass (g/mol)
250mL x (1L/1000mL) = 0.25L x 1mol/22.4L = 0.0111mol >>
1.63g/0.0111mol = 146.85g/mol

Here are a couple examples from us:
1. Find the mass of 2.5mol of NO2
1N: 1(14)=14>>2O: 2(16)=32
= 46g/mol
NO2 ---> 46g/mol--->mol/46g(1/2.5) = 1/115g (reciprocal)>>
115g

2. Find the volume occupied by 0.060mol of I2 at STP
0.060mol x 22.4L/1mol = 1.34L

Density and Moles

MOLE UNIT CONVERTIONS CHART

Density--(D= M/V)--Mass--(molar mass)--Moles--(6.02 x 10^23)--Molecules
Mass--( x 22.4 L)--Volume(@STP)
Molecules--( x subscripts)--Atoms

Density --> mass per unit volume

D=M/V, M= D x V, V= M/D


Density of gasses at STP
1 mol of gas
D= M = Molar mass g/mol
V 22.4 L/mol

Calculate the density of O2 at STP
D= 32 g/mol = 1.43 g/L
22.4 L/ mol

Density of C2 at STP
D = 24 g/mol = 1.07 g/L
22.4 L/ mol

Cl2 --> DSTP
DSTP = mm = 71.0 g/mol = 3.17 g/L
22.4 L/mol

A mystery gas has a density of 1.696 g/L at STP
It is a diatomic element. Identify the gas.
MM= (1.696 g/L)(22.4 L/mol) = 38.0 g/mol (19 g/mol à fluorine)

The density of Boron(s) is 2.34 g/mL. How many molecules are in a 60.0 mL piece?
2.34g x 60.0 mL = 140.4g
1 mL
140.4 g x 1mol = 13 mol
10.8 g
13 mol x 6.02 x 1023 molec. = 7.83 x 1024 molecules
1 mol

Liquid mercury has a density of 13.55 g/mL
Find the volume occupied by 1.806 x 1027 atoms of H g
1.806 x 1027 molecules x 1 mol x 200.6 g = 601800 g
6.02 x 1023 molecules 1 mol
V = M = 601800 g = 44413 mL = 44.4 L
D 13.55 g/mL

A 5.00 mL(volume) sample of lead contains 0.274 mol (moles) of Pb(s).
Calculate the density of Pb.
Molà massà density
0.274 mol x 207.2 g = 56.7728 g
1 mol
D = M = 56.7728 = 11.35 g/mL
V 5.00 mL

Density of gaseous mixture of C8 H18 at STP
(C8x12 = 96) + (H18x1 = 18) = 114 g/mol
114 g/mol = 5.09 g/L
22.4 L/mol

Molar Volume Lab

Tuesday, Nov. 11, 2009

Labs are a Whole Bunch of Fun!

During this class we did a lab using:

• 
  
  Butane


• 
  
  Water


• 
  
  Sink


• 
  
  Weigh Scale


• 
  
  100mL Graduated Cyliner
  
  

The whole point of the lab was to find out the molar volume of Butane gas at STP

Butane = C4H10

The Molar Mass of Butane: 58g per mol

Then we had to convert that into L