Density

Density is a physical property of matter that describes the amount of mass to a unit of volume.

We use the formula below to calculate the density.



 In this formula, D equals M divided by V where D stands for Density, M stands for mass, and V stands for Volume.

Some of the possible units for density are; g/mL, g/L, g/cm³, kg/L

 If an object is less dense than the liquid, it SINKS

 

If an object is more dense than the liquid, it FLOATS

Here's the video showing what happens if you put an egg into two liquids with different density(water&salt water)

 

 

Example Question:

A substance has a mass of 44.1g and a volume of 12.6cm³. What is it's density?

 

Use the formula to calculate the density.

　　　D=M/V

  　　　 =44.1g/12.6cm³

   　　　=3.5g/cm³

So, its density is 3.5g/cm³.

 

 

 

Here's something you can do using different densities the substances have.

 

 

 

 

 

 

Measurement and Uncertainty

No Measurement is exact,

measurement is a best estimate which has some degree of uncertainty.

We can only be certain of an amount when we count.

 

Here are some of the methods to determine the degree of uncertainty:

Absolute Uncertainty

Expressed in the units of measurement, not as a ratio.

Method 1: Make at least 3 measurements and calculate average.

                  The absolute uncertainty is the largest different between the average and lowest or

                  highest reasonable measurement. Discard the unreasonable data.

e.g. 5.9, 5.8, 5.9, 6.0, 6.5 <- the 6.5 here would be an unreasonable data that we don't need

now find the average: 5.9+5.8+5.9+6.0 = 23.6 -> 23.6 / 4 = 5.9

final answer: 5.9 ± 0.1 <- absolute uncertainty

Method 2: Determine uncertainty of instrument

                   Always measure to the best precision,

                   estimate to a fraction 0.1 of the smallest segment of the instrument scale

e.g. Smallest division: 1 cm, measure to 0.1 cm

Relative Uncertainty = Absolute Uncertainty ÷ Estimated Measurement x 100

a ± b  ->  b ÷ a x 100 = ___% relative uncertainty

Or use sig figs,

 number of sig figs indicates relative uncertainty

Here is a video to help understand this lesson better:

Significant Figures and Rounding

Accuracy -  how close the measurement is compared to the actual value
Precision - to what value does measuring the same object under the same conditions show the same result

An instrument can be very precise but not accurate
Example- a ruler could have precision down to the milimeter but if the ruler does not have to necessarily be accurate with its measurements.

Significant Figures or Meaningful Digits

• The more significant figures a measurement has, the more precise the measurement is
• The last significant digit in the measurement is uncertain
• All of the other significant digits are certain
• Significant digit contains all the certain digits and only the FIRST uncertain digit
• Any zero between a decimal and a significant digit do not count if the number is smaller than 1
• Zeros after significant digits count if there is a decimal
• Zeros between two significant digits also count

This example shows when zeros do not count as significant digits

•  0.00023
• Only 2 and 3 count as significant digits
• The four zeros in front DO NOT count  

These zeros count as significant digits

• 3000 = 1 significant digit
• 1.01 = 3 significant digits
• 1.1000 = 5 significant digits

To help you understand scientific notation better, here is a QUIZ on it:

Exact Numbers/ Rounding

Some numbers are exact and so are not to be rounded

• The number of people in your family
• Amount of pencils in a pencil case
• A dozen = 12

Rounding:
When Rounding, you will round up when the digit is five or up and you will round down if digit is 4 and under
HOWEVER: if the digit 5 is the last digit, then you would round to the nearest even number (zeros after the five follow this rule too)

Math and Significant Figures
When adding or subtracting significant figures, round the answer to the least amount of decimal digits shown in the question.

Example:

  23000

  15600

+33120

  71720

However, because there are certain digits that you are unsure of, 71720 is NOT your final answer. The question would actually be something like this:

  23???

  156??

+3312?

  71???

Since we know that hundreds place is a 7, we would round our answer up and so the answer to this addition question, with consideration of significant figures would be: 72000

Multiply and Dividing

When multiply or dividing, we round the answer to the least amount of significant figures present in the question.

Example:

135x1 = 100

This is because 1 only has one significant digit and so when the product is 135, we round it so it would only have 1 significant digit (the hundreds) and so it becomes 100.

23.56/1.12 = 21.0

Since 1.12 only has three significant figures, the answer to this question will only have 3 significant figures as well.

Naming Ionic, Covalent Compounds and Acids

Naming Ionic Compounds:
When naming ionic compounds:

1. write the name of the positive ion element (usually metal)
2. write the name of the negative ion element (usually non-metal) and change the ending to "ide"
3. State the charge of the elements in brackets with roman numerals after the name of the element if has more than one charge

Examples:
FeO = Iron (II) oxide
NaCl = Sodium chloride

Prefixes

Naming Covalent Compounds:

When naming covalent compounds:

1. Write the prefix for the amount of element in the compound
2. Write the name of the first element (do not put prefix "mono" if it's only one for the first element)
3. Write the name of the second element and change the ending to "ide"



Example: 

CO₂ = carbon monoxide

P₂O₅ = diphosphorus pentoxide

CF₄ = carbon tetrafluoride

 

Naming Acids

Acids are always dissolved in water.

HCl is not an acid by itself. When HCl is added to water, a hydronium ion will form (H₃O). This combined with the chlorine ion will form hydrochloric acid.

Rules for Naming Simple Acids:





Lemon is acidic


• Hydrogen is changed into hydro-
• The last syllable in the name of the non-metal is replaced with "ic"
• The word acid is added to the end

Examples:

HF(aq) = hydrofluoric acid

HBr(aq) = hydrobromic acid

Rules For Naming Complex Acids:

• The word hydrogen is completely dropped
• If negative ion ends with "ate" replace it with "ic"
• If negative ino ends with "ite" replace it with "ous"
• add the word "acid" to the end

Examples:

HNO₃(aq) = hydrogen nitrate(compound name)

                 = nitric acid (when dissolved in water)

H₂SO₃(aq) = sulphurous acid



John Dalton



Law of Definite Composition (Proust's Law)

Chemical compounds always have the same proportion of element by mass

Example: C₆H₁₂O₆

Law of Multiple Proportions (Dalton's Law)

Same element can combine in more than one proportion to form different compounds

Example: CO and CO₂

Lab 3-B Paper Chromatography

Today, we had a lab based on paper chromatography. We dotted food colouring on strips of paper and then dipped them into different test tubes that had water. These dots and the water would slowly travel up the strip of paper. Eventually, the dots and water would stop moving and then we would take out the strips of paper and measure.

1. Measure the distance from the starting line to the solvent front (where the water stopped) (D₂)
2. Measure the distance from the starting line to the middle of where the dot ended up (D₁)
3. 
   

   D₁ ÷D₂
4. This will give you the R_f value for the colour

By finding out the R_f value, we can find out what the mixture (if it is a mixture) is made up of

Example: A green dot will separate into yellow and blue

              Therefore, green is composed of yellow and blue

Heating & Cooling Curves / Separation Techniques

Heating & Cooling Curves

These are the basic terms for the changes of state of elements.

  

• This graph shows a heating curve of a pure substance.When the temperature increases, particles of  the substance move faster and kinetic energy increases as well.
• At point A, the substance is a solid.
• B--C is the melting point
• C indicates that the substance has finished melting and is now liquid.
• A slope of zero shows that the temperature stays the same because heat is used to overcome forces of attraction that holds the particles together.
• The heat absorbed is called a latent heat of fusion. 
• It occurs as a substanse changes its states.
• D--E is the boiling point
• E is when the substances has turned completely into gas.



 

• This graph shows a cooling curve of a pure substance.
• The substance starts out as a gas at point P and as the temperature decreases, the particles will come closer and lose energy.
• The heat energy released from Q to R is called latetn heat of vapourization.
• R is when the substance completes its change into a liquid state.
•  S--T is its freezing point
• The substance turns into solid at point T and then stays at room temperature

Separation Techniques

Components in a mechanical mixture retain their identities. Those mixtures that have different components can often be separated by devising a process that discriminates between components with different properties. The more similar the properties are, the more difficult to separate them.

Different properties that the components might have are:

• high density / low density
• volatile / non-volatile
• soluble / insoluble
• reactive / inert
• magnetic / non-magnetic
• polar  /non-polar

Some of the Basic Separation Techeniques

   

 1.Filteration

• separates solids that are not dissolved in liquids
• passing a mixture through a filter paper 
• residue left in filter = solid
• substance filtrate through = liquid

     

2.   Evapolation

• liquids & solids
• boiling away the liquid to retrieve a solid

Hand Separation

• Solid & solid
• separating mixture by using a  magnet or sieve

  

 3.  Crystallization

• Separates solid in liquids (precipitation) 
• solid is dissolved in liquid to form a saturated solution
• then, th substance is slowly evaporated and the solid will come out as crystals
•  the crystals can then be filtered out      

 4. Solvent Extraction

• Use a liquid to dissolve one solid but not both
• The desireable solid will be left behind or dissolved
• Since the sample separates, it is then possible to separate the components

   5. Gravity Seperation

• separates solid based on a difference in density
• a centrifuge whirls the test tube around at high speeds forcing the denser materials to the bottom

6. Distillation (based on boiling point)

• Heating mixtures can cause low-boiling components to volatilize
• then, collect and condense the evaporated material

    7.  Chromatography

• flowing of the mixture over a material that retains some components more than others, so different components flaw over the material at different speeds.