Density

• a physical property of matter that describes the ration of mass to volume.

Density = Mass/Volume

                 possible units: g/mL, g/L, g/cm^3, Kg/L

1cm^3 = 1mL

Float vs. Sink experiment

Density of Liquid > Density of object                  Float

Density of Liquid < Density of object                  Sink

For example:
       Say there is a filled water balloon filled with an unidentifiable liquid.  There is 350mL with a mass of 450g.  What is the density of the liquid in the balloon?

D= M/V
D= 450/350
= 1.28mL/g

WORD PROBLEMS

1.  A block of aluminum occupies a volume of 15.0 mL and weighs 40.5 g. What is its density?

2.  Mercury metal is poured into a graduated cylinder that holds exactly 22.5 mL. The mercury used to fill the cylinder weighs 306.0 g. From this information, calculate the density of mercury.

3.  What is the weight of the ethanol that exactly fills a 200.0 mL container?

 The density of ethanol  is 0.789 g/mL.

4.  A rectangular block of copper metal weighs 1896 g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper?  (hint:  find the volume of a block first)

5. What volume of silver metal will weigh exactly 2500.0 g. The density of silver is 10.5 g/cm³.

6. Find the mass of 250.0 mL of benzene. The density of benzene is 0.8765 g/mL.

7.  A block of lead has dimensions of 4.50 cm by 5.20 cm by 6.00 cm. The block weighs 1587 g. From this information, calculate the density of lead.

8. 28.5 g of iron shot is added to a graduated cylinder containing 45.50 mL of water. The water level rises to the 49.10 mL mark, From this information, calculate the density of iron.

Answers

1) 2.70g/mL

2) 13.6g/mL

3)  253g

4) 8.922g/cm^3

5) 238 cm^3

6) 219.1 g

7) 11.3g/cm^3

8)7.92g/mL

Measurement and Uncertainty

-no measurement is exact

-it's your best estimate

-if you count an object, it's the exact number. 

     ex. 10 pens stays as 10

Absolute Uncertainty

-uncertainty is expressed in the units of measurement not as a ratio

Method: 1- make at least 3 measurements. Get the average. Absolute uncertainty is the LARGEST difference between the average of lowest and highest of reasonable measurement

Ex.

                    Trial #                                            Mass of an object

                        1                                                         14.4g

                        2                                                         14.2g

                        3                                                         17.5g (remove)

                        4                                                         14.3g  

                        5                                                         14.1g

-Average: (of four reasonable measurements)

    =14.3g

-Difference between the average and low measurement:

    =14.3-14.1 = 0.2g

-Difference between high and average:

    =14.4-14.3 = 0.1g

Mass would be recorded as 14.3+0.2g

Method: 2- always measure to best precision as you can. So estimate to a fraction 0.1 of smallest segment on the instrument scale

ex. beaker: 25mL. Best precision is 2.5 mL

Relative Uncertainty & Significant Figures

Relative Uncertainty = Absolute Uncertainty

                                 estimated measurement

PRACTICE

Find the average, and the absolute uncertainty of these pictures

Significant Figures

Definitions:

• Precision: How easy it is to reproduce a measurement
• Accuracy: How close the measurement is to the actual value
• Significant Figures: Measured or meaningful digits. The higher number of significant figures = more precise number

Accuracy Vs Precision

More PowerPoint presentations from Chloe

Significant Figures

Part I:

• The last number is always uncertain as it can easily be a digit higher or lower
• Significant digits include all certain digits (known digits) plus one uncertain
• Eg: 3.87329 
• Certain/Uncertain
• 6 Sig Figs

Part II:

• Leading Zero's are NEVER counted
• Zero's at end, if they are after a decimal ARE counted. If no decimal, they ARE NOT.
• Eg:
• 0.00000006 = 1 SF
• 12.000 = 5 SF
• 12000 = 2 SF

Part III: Exact Numbers

• Some amounts are defined to an exact point - no rounding needed
• Other's have an infinite number of significant digits
• Eg:
• If you have two light bulbs, you have two whole light bulbs, not 1.899999934583 light bulbs

Part IV: The Rules of Rounding

• Usually rounded the same way as in math
• EXCEPTIONS
• if the digit is equal to 5, and there are more non-zero digits after it, round up.
• If the digit is equal to 5 and there are NO more non-zero digits after it, make the last digit even
• Eg:
• 9.86356 to 3 SF = 9.86
• 4.87625 to 4 SF = 4.8763
• 12.065 to 2 SF = 12.06
• 12.075 to 2 SF = 12.08

Part V: Connections with Math

• When Adding or Subtracting, round to the fewest number of decimals

• When Multiplying or dividing, round to the fewest number of significant digits.
• Cannot have any more than the least number of significant digits
• DO NOT ROUND UNTIL CALCULATION IS COMPLETE!!!

PRACTICE QUIZ

Significant Figures and Rounding Quiz

Writing name and formulas for Covalent and Ionic compounds

Ionic Compounds

For Ionic compounds with metals that have more then one possible charge; Roman Numerals need to be put after the metal.  For example: Lead (IV) Oxalate

Roman Numerals

1 = I

2 = II

3 = III

4 = IV

5 = V

6 = VI

7 = VII

8 = VIII

9 = IX

10 = X

Covalent Compounds



Pracitce Questions

 Name the following:

KHCO3

SiS2

ZnF2

SF3

P2O5

Write the formula for the following:

Tetracarbon decahydride

Chlorine gas

Calcium Sulphide

Aluminum nitrate

Sodium Iodide

Answers:

Potassium bicarbonate

Silicon desulphide

Zinc Fluoride

Sulfur trifluroide

Diphosphorous pentoxide

C4H10

Cl2

CaS

Al(NO3)3

NaI

Lab 3b: Separation of a Mixture by Paper Chromatography

Objectives
1. to assemble and operate a paper chromatography apparatus
2. to study the meanilng and significance of Rf values
3. to test various food colorings and to calculate their Rf  values
4. to compare measured Rf  values with standard Rf  values
5. to separate mixtures of food colorings into their components
6. to identify the components of mixtures by means of their Rf  values

Supplies
Equipment                                                                            Chemical Reagents
per class:                                                                                 set of food coloring
5 glass stirring rods                                                                  (yellow, green, blue, red)
several pairs of scissors                                                           unkown mixture of food colorings
per lab station:
3 large test tubes
     (25 mm x 200 mm)
3 Erlenmeyer flasks (250 mL)
metric ruler
pencil
chromatography paper strips
      (2.5 cm wide x 66 cm long)








Procedure
Part I: Setting Up
1. Get 3 Erlenmeyer flasks and put a test tube in each one.
2. Get 3 chromatography paper and draw a line across each strip 4cm from one end then cut a point from the end.
3. Put water on test tubes, about 2cm deep
Part II: Rf  Values of Individual Food Colorings
1. You get to test one food coloring to test. Get one of your chromatography paper and place a dot of food coloring on the line.
2. Put the strip in the test tube. Don't push the strip down too far, tip should just touch the bottom. Don't let the strip touch the wall of the test tube.
3. Observe.
4. Continue observing for 10 min. Try to identify 2 colors as they move up the paper.
5. After about 20 minute and there's no more color separating, immediately draw a line across the top edge of the water before it evaporates.
6. Measure d1 and d2 then record the values on tables 1 and 2. Then calculate the Rf  value.

Part III: Separation of Mixtures into Their Components

1. Second strip will be spotted with a sample of green coloring and the third will be spotted with an unknown mixture of food coloring.

2. Follow directions from part II from 2-6.

3. Record data on Table 3

4. Clean up.

Table 1 : Results for Lab Station

Table 2 : Class Results 

Table III

Acids

How acids are formed

H + Cl = HCl(g)
ionic "non-acid" hydrogen chlordie
HCl(g) + H2O(l) = H30(aq) + Cl(aq)
hydrochloric acid

Rules for naming simple acids
1. hydrogen becomes hydro
2. the last syllabe becomes "-ic"
3. acid is added at the end
ex.
H2S     =     hydrogen chlorate   =   chloric acid
HCl      =     hydrogen chloride   =   hydrochloric acid

Rules for naming complex acids
1. no more hydrogen (hydro)
2. if second element ends with "-ate" it becomes "-ic"
    if it's "-ite" it becomes "-ous"
3. acid is added at the end
ex.
HClO4     =     hydrogen chlorate     =      chloric acid
HlO          =     hydrogen hypochlorite =   hypochlorous acid
-a way to remember this is:
we ate - ic - y sushi and got appendic - ite - ous

Law of Definite Composition (Proust's Law)
The statement that is in a pure compound the elements are always combined in fixed proportions by weight/mass.

ex. H2O has 2 atoms of H and 1 atom for O for a total of 18g

Law of Multiple Proportion (Dalton's Law)

The same elements can combine in more than one proportion to form different compunds

Heating & Cooling Curve and Speperating Techniques

Heating Curve (added notes to diagram)

A -> B: 

heat energy converts to kinetic energy
particles vibrate faster, temperature increase

B: still solid

B-> C: 

solid-> liquid
temperature remains constant because heat used to overcome force of attraction
melting point- heat absorbed is called heat of fusion
C: liquid
(all solids have melted)
C->D
temperature and KE increases

Cooling Curve
P: Gas
particles have high energy and move quickly
P -> Q
KE decreases (particles getting closer)
temperature decreases
Q
condensation (stronger bonds formed)
temperature remains constant
heat energy released is call latent heat of vaporization
R: Liquid
R-> S
molecules loose energy
particles move slower and closer to each other
temperature decreases
S: starts to freeze to solid
S->T -Liquid to Solid
particles arranged in an ordered manner
freezing point
T->U
temperate decreases
U: Substance has reached room temperature


Separating Techniques


Strategy: devise a process that discriminates between components/properties

Seperation
-components in a mixture retain their identities
- more similar the properties, more difficult to seperate

Basic Techniques
Hand Separation (solid and solid)
- mechanical mixture can be separated by using magnet or sieve
Evaporation (solid dissolved in liquid)
- boil away liquid; solid remains
Filtration (solid (not dissolved) and liquids)
- pass mixture through porous filter
-use filter paper-residue left in filter; filtrate goes through
Crystallization (Solid in liquid)
- precipitation
- solids are then separated by filtration or flotation
- use a saturated solution of desired solid
- evaporate and cool-solid comes out as pure crystals.
Gravity Separation (Solids based on density)
- a centrifuge whirls the test tube at high speeds forcing denser materials on bottom, (better for small volumes)
Solvent Extraction
Mechanical Mixture: use liquid to dissolve one solid, not other
Solution: solvent is insolvable with solvent already present
Distillation (liquid in liquid solution)
- heating a mixture can cause low boiling point component to vaporize(volatized)
- collect condensed volatized components
Chromatography
- flow the mixture that retains some components more then others so different components flow over the material at different speeds (a mobile phase sweeps a stationary phase)
Paper Chromatography
-stationary phase is liquid soaked into sheep or strip of paper
-components appear as a separate spots spread out on paper after drying or "developing"
Thin layer Chromatography
-stationary phase is a thin layer of absorbent (sheet of plastic or glass)
-some components bonded to the absorbent strongly; others weakly

Physical and Chemical Change

Physical Change
-concerned with energy and states of matter
-does not produce a new substance
ex. crushing a can, melting an ice cube, and breaking a bottle










Chemical Change
-takes place on the molecular level
-makes a new substance
 ex. burning, cooking an egg, rusting an iron pan, and mixing hydrochloric acid and sodium to make salt and water

1. Label each process as a physical or chemical change:

a. perfume evaporating on your skin
b. butter melting
c. wood rotting
d. charcoal heating a grill
e. autumn leaves changing color
f. a hot glass cracking when placed in cold water
g. melting copper metal
h. burning sugar
i. mixing sugar in water
j. digesting food

2. Label each process as a physical or chemical change:

a. Moth balls gradually vaporize in a closet
b. hydrofluoric acid attacks glass (used to etch glassware)
c. A chef making a sauce with brandy is able to burn off the alcohol from the brandy, leaving just the brandy flavoring
d. Chlorine gas liquefies at -35 °C under normal pressure
e. hydrogen burns in chlorine gas