Thursday, October 28, 2010

Accuracy and Precision

Accuracy-->how reproducible a measurement is compared to other similar measurements
     -->can be described as the correctness of a measurement

Precision-->how close the measurement (or average measurement) comes to the accepted or real value
     -->can be described as the exactness of a measurement

*no measurement is exact
-every measurement is only one's best estimate, as it has some degree of uncertainty
-measurements are only exact when they are counted
  eg. a family of 4

  Absolute Uncertainty

-Uncertainty is expressed in the unit of measurement, not as a ratio or fraction
-there are 2 methods:
Method 1:
1. Make at least 3 measurements
2. Calculate the average between the measurements
3.Calculate the different between the average and the lowest or highest reasonal measurement. The largest difference will be the absolute uncertainty.

Method 2:
1. Make the best precise measurement, estimate to a fraction 0.1 if the smallest segment on the instrument scale.

Relative Uncertainty and Sig. Figs.

Relative Uncertainty=Absolute uncertainty/estimated measurement
-relative uncertainty can be expressed as a percent, or with sig. figs.

Practice reading scales, and identifying the uncertainty of each measurement using method 2.

Watch this video! It'll help. (:
How to Read a Ruler

Written by Jialynn

Tuesday, October 26, 2010

Significant Figures - Isabelle Cheng

Isabelle Cheng
October 26,2010
Block 2-2 Chemistry 11
Ms. Chen
Significant Figures
Significant figures are the number of significant digits in an answer to a calculation. They are approximate answers and the more digits it has the more accurate it may be. 
More facts about significant figures: 
non- zero numbers are significant - for example: 355 has three significant digits, and 24.35 has four digits
however with zeros there are different rules:
zeros put between other digits are always significant
zeros put after another digit but behind a decimal are significant
zeros put before other digits are not significant
zeros at the end of a number are significant only when they are after the decimal point
leading zeros aren’t counted though
Exact numbers - Ex. there are exactly 14 dogs. You can’t have 14.34 dogs. 
Inexact numbers - Ex. the length of the table is 124.34 mm then it is an inexact number. 
Rounding numbers - round answers to the approximate - Example: if the number is over 5 then round it to a high number and if it is under five keep it that number. If the number equals to five the put a five
Adding and Subtracting Significant Digits:
round up to the fewest numbers of the decimal places
ex. 14.982+4.2 would be looking like 14.982 = 19.182
+   4. 2 
same thing for subtracting!
round to the thousands place for the first uncertain digit
ex. 24500+7000 = 31,900 - you have to change it to 34,500 = 34,000
Multiplying and Dividing Significant Digits:
round to the nearest number significant digits 
ex. 32.96 x 2.4 = 79.104 - multiplying
ex. 14.59 ÷ 5 = 2.918 - dividing
Some exercises of significant figures:
Write how many significant figures there are!
1.00 x 1000000

Wednesday, October 20, 2010

Lab 3B; Oct 19th, 2010; by: Mandy Xiao

Separation of a Mixture by Paper Chromatpgraphy

Some vocabularies you should know:
Rf value: the ratio of the distance traveled by the solute to the distance traveled by the solvent
Formula: Rf=d1/d2
D1 = distance traveled by solute
D2 = distance traveled by solvent
*Rf values vary from 0 to 1
capillary action: in this case: when water is moving up the paper

solute front: (in this experiment) food colouring
solvent front: (in this experiment) water

Lab procedure:
Part 1: Setting Up
3 large testubes & 3 Erlenmeyer flasks. Label A, B, C
22cm chromatography paper
Use pencil to draw a line across strips 4cm from one end
Trim the end of the strip
Place 2cm deep water into each test tube

Part 2: Rf values of individual food colourings
Use a glass stirring rod to spot the strip with the colour
Write the colour at the top of the strip
Insert strip in test tube A
Observe the sample spot as the water goes up
Observe solute front and solvent front
Remove strip from the test tube. Immediately draw a pencil line across the top edge of the solvent front
Measure d1 and d2 calculate Rf for sample and record

Part 3: Separation of Mixtures onto Their Components
2nd strip with green colour, 3rd strip with unknown LABEL!
Insert strip in test tube B&C (see procedure in Part 2)
Record data on table 3!

Further Information: 
  The substances (solutes) to be analysed must dissolve in the solvent, which is called the mobile phase because it moves. The paper or thin layer of material on which the separation takes place is called the stationary or immobile phase because it doesn't move.

INTERESTING! Paper chromatography Art!

Sunday, October 17, 2010

How to Separate Mixtures (by Bev)

-basis: different components & properties
-come up with a process that differentiates between components with different properties
     ex. high density/low density

-a substance comprised of more than one substance that is not chemically bonded
-the mixture’s components keep their identities
-the more different the properties are, the easier it is to separate them

-filtration: chooses components by particle size
-flotation: chooses components by density
-crystallization & extraction: chooses components by solubility
-distillation: chooses components by boiling point
-chromatography: chooses & absorbs components at different rates in a fluid mixture
Hand separation
-for solids
-mechanical/heterogeneous mixture can be separated with magnet/sieve
-evaporation: a solid dissolved in a liquid solution
                -liquid evaporates (from boiling) & the solid is left
-for solids that are not dissolved in liquids
-using a permeable filter, pass a mixture with solid particles through
-the solid particles stay on top of the filter because they are bigger than the pores
Filtration Apparatus Diagram
-the filtrate permeates but the residue remains in the filter
-a solid in a liquid
-precipitation: from physical/chemical change, a solute (dissolved substance) is converted into a solid
-flotation/filtration separate the solids
-the desired solid becomes a saturated solution, containing the maximum amount of solute (which the liquid can no longer dissolve
-evaporate/cool: solid becomes pure crystals, which are filtered
Gravity separation
-for solids based on density
-centrifuge rapidly spins a test tube & separates substances of different densities, forcing the denser materials to the bottom
-works best with small quantities
Solvent extraction
-a component moves to a solvent shaken with a mixture
-works best with solvents that dissolve only one component
-mechanical mixture (2 solids): only one solid dissolves in the liquid & the desired solid is left behind
-solution: the solvent is insoluble because it is already present.  It dissolves at least 2 substances & the unwanted substances remain
                -if shaken in the separatory funnel, the liquids from layers
-for a solution of 2 liquids
-heating the mixture triggers the low-boiling components to volatize (vapourize)
-evaporated components collect & condense
-the liquid with the lowest boiling point boils first, the vapour ascends to distillation flask & enters condenser, gas cools to a liquid, & distillate (condensed liquid formed from boiling) is dropped as a purified liquid
-a mixture is passed over a material that absorb some components more than others
-different components pass over the material at different speeds
-mobile phase: sweeps the sample over the stationary phase (ex. Wind sweeping swarm of bees over flower bed)
-can separate extremely complex mixtures
                Ex. Drugs, plastics, flavourings, foods, pesticides
-using very small sample sizes, the analysis can be highly accurate & precies
-the separated components can be collected individually
Sheet/paper chromatography
-stationary phase is a liquid soaked into sheet of paper & mobile phase is a liquid solvent
-some components spend more time in the stationary phase than others
-components appear as separate spots spread out on the paper after drying/”developing”
Thin layer chromatography
-the stationary phase is a thin layer of absorbent (often SiO2 or Al2O3) coating a sheet of plastic/glass
-some components bond to the absorbent strongly; others, more weakly
-components appear as spots on sheet

Practice Problems: Separate!
1)      Coins: by hand
2)      Sand & copper sulphate: solvent extraction with filtration
3)      Salt in water: evaporation/distillation
4)      Sulphur 8 iron fillings: magnet (by hand)
5)      Ink: chromatography

Friday, October 15, 2010

How to name acids (by Bev)

-ACID: a covalent (non-metal + non-metal) bond formed from a negatively charged ion & a hydrogen ion dissolved in water
     -when dissolved in water, ions separate
     -chemical formula for an acid starts with a H (hydrogen)

1) prefix: "hydro"
2) the last syllabe of the non-metal is replaced with the suffix "ic"
3) add the word "acid" at the end

ex. HF = hydrofluoric acid
HCl = hydrochloric acid
HBr = hydrobromic acid

1) "-ate" of the polyatomic anion is replaced with the suffix "-ic"
2) "-ite" of the polyatomic anion is replaced with the suffix "-ous"

3) add the word "acid" at the end

*REMEMBER (this actually works!): "We ate ic-y sushi & got appendic -ite-ous."

ex. HCH3COO = acetic acid
HClO3 = chloric acid
HNO2 = nitrous acid
HClO4 = perchoric acid

beware the exception!
HCN = hydrocyanic acid (it is a simple acid!)


Thursday, October 7, 2010

Lab 2C: Melting & Freezing Points of Pure Substances (by Bev)

In the experiment, liquid dodecanoic acid (C12H34O2) was cooled in cold tap water until it reached a temperature of 25 degrees Celsius, and observations and temperature readings were taken every 30 seconds.  The same process was used for the heating process, except the solid dodecanoic acid was placed in 55 degrees Celsius water.  The purpose of the lab was to find the melting and freezing point of this substance (40 degrees Celsius) by graphing the results and finding the intersection between the heating and cooling processes.  It was also discovered that melting point and freezing point are the same and interchangeable terms.

Writing and Naming Ionic and Covalent Compounds - Isabelle Cheng

Isabelle Cheng
October 7, 2010
Block 1-2 Chemistry 11
Writing and Naming Ionic and Covalent Compounds 
composed of two or more particles (ions) --> oppositely changed
held together by electrostatic forces
electrons are transferred from a metal to a non-metal
Ex. Li+1     O-2
= Li2O
Ex. Ti has 4+ or 3+
Titanium (IV) fluoride ---> TiFl4
Ex. Complex Ions: a group of atoms that behave as one atom.
Na2SO4 ---> Sodium Sulphate
Na3PO4 ---> Sodium Phosphate

share electrons
non-metal with non-metal
- use GREEK prefixes to indicate the number of atoms
*Diatomic molecules: H2,O2,F2,Br2,N2,Cl2,I2
mono - 1
di - 2
tri - 3
tetra - 4 
penta- 5
hexa - 6
hepta - 7
octa - 8
nona - 9
deca - 10
a) CO2 - Carbon dioxide
b) N2O4 - Dinitrogen Tetraoxide

Monday, October 4, 2010

Finding Out About Matter

Science requires increasingly precise observations and detailed inferences. Observation takes too much time that science must be separated into different specialization. Individuals study matter in chemistry. One way to get a better understanding about matter is that you can carefully observe familiar substances, classify and generalize them on regular bases.

We learnt that few of the ways to identify matter is by their colour and taste. The characteristics of matter can also be recognized by the temperature at which matter changes from a liquid to a gas (boiling point) A mixture is twp or more kinds of matter that have separate identities. (impure) The idea of mixture and pure substance are used to describe matter.

Scatter light will appear if one shines a strong light on impure water and solutions Adding alum and lime to the water, then remove suspended particles from water. The water will not appear to have scattered lights Solutions are mixtures that look uniform throughout and do not scatter light Solutions such as sugar and salt in water are to be separated into their component parts using distillation
New techniques are still being developed in order to meet the environmental problems concerning today’s society. Pure substances have constant boiling point

Characteristics of Pure Substance
·         Have a constant boiling point & melting (or freezing) point, unlike most ordinary mixtures
o   Ex. As pure methanol is heated, the temperature gradually rises to 65C & begins to boil.  The temperature remains constant throughout boiling.  However, a mixture of 25% methanol & 75% water boils at around 86C, but the temperature continues to rise as it boils.
Chemical & Physical Changes
·         Chemical changes: produce a new kind of matter with different properties
o   Ex. When sugar is heated in a test tube, it bubbles & forms a black solid while a colourless liquid forms on the walls of the test tube.  The black solid & colourless liquid is both formed from an irreversible process of decomposition that forms new substances with new properties. 
·         Decomposition: type of chemical change when one kind of matter decomposes decomposes (comes apart), forming at least 2 types of matter.
·         Physical changes: no new substances produced
o   Ex. Melting, boiling, & freezing are types of physical changes because the substance has all the same properties after a change of state, and the process is reversible.
Compounds & Elements
·         Element: pure substances that cannot be decomposed
o   Smallest particle: atom
·         Compound: chemically combined elements & can be decomposed
o   Smallest particle: molecule

p.36-39 Macroscopic observations are observations from what an individual can see, feel or smell. Whereas melting point, boiling point, heat of fusion, temperature and mass are all called macroscopic properties. On the other hand, microscopic model is to explain the performance of matter. Matter is made up of atoms. Atoms are usually expressed as spheres because chemists use spheres to help them
understand the microscopic world. Elements only contain one kind of atom. If the particles in an element vibrate, temperature will increase, therefore, an element can exist as a solid, liquid, or gas. Particles made of more than one atom are called molecules. The more outsized the particle is, the higher the boiling point will be. Energy such as heat and electricity are used to break down compound
Compounds can be formed by molecules or ions. Chemists need to check their conductivity in order to determine rather the compound is ionic or molecular.

Sunday, October 3, 2010


Compounds will have a definite composion
Eg. H2O will be H2O anywhere (always have 2 Hydrogen & 1 Oxygen)
When 2 or more compounds with different proportions of the same elements can be made
Eg. CO2 x2 ->C2O4

Heating Curve of a Pure Substance Notes

Figure 1

·       Solid: below melting point
·       Particles are very closely packed together in an orderly manner
·       Strong forces
·       Can only vibrate at a fixed position
·       When heated: heat -> kinetic energy -> increase -> molecules vibrate faster about their fixed position -> temperature increases
·       Still solid –melting has begun -> liquid
·       Temperature remains the same
·       melting point
·       exists: solid &liquid state
·       temperature remains constant because the heat that id supplied to it is used to overcome the forces of attraction that holds the particles together
·       constant temperature = melting point
·       heat energy overcomes the intermolecular forces id named as the latent heat of fusion
·       all has completely melted
·       solid -> liquid
·       liquid state
·       more heat energy = temperature increase
·       particles move faster because kinetic energy increases
·       liquid starts to boil
·       molecules have got enough energy to overcome the faces of attraction between the particles in the liquid
·       some particles will start to move freely
·       liquid -> gas
·       liquid & gaseous states
·       the temperature unchanged
·       heat energy absorbed to overcome intermolecular forces between the particles of the liquid rather than increase the temperature
·       boiling point
·       all of the liquid has turned into gas
·       gas particles continue to absorb more energy & more faster

Here’s a chart that explains the heating and cooling of water:
Figure 2

KINETIC ENERGY is the energy that molecules possess as a resulr of their motion
      there are 3 types of Kinetic energy which a molecule can possess
1. rational energy: causes a molecule to rotate around one of its axes; bond lengths ans bond angles don't change
2. vibrational energy: changes the bond lengths and/ or angles between atoms in a molecule
3. tanslational energy: causes the molecule to travel in a straight line from place to place, but has no effect on bond lengths and angles

eg. MICROWAVE OVENS supply energy which causes the water molecules in food and liquids to vibrate. As molecules absorb energy ans bump into each other, the food "heats up".