Significant Figures! (sig figs)

what are significant figures you say?

well...

• they are often used in connection to rounding
• establish the value of a number

 Significant Digits

In a measurement, the last digit is known to be an uncertain digit, because it may turn out to be one digit higher or lower. You will never know!
  for instance, in the measurement 7.63cm "3" is uncertain and "7 and 6" are certain digits.


To count the number of significant figures you would have to include all the digits as well as the uncertain digit! To help find the number of sig figs here are a few pointers:
     a)count all the numbers starting at the first non-zero digit on the left
     b)for a number written in scientific notation count the digits in the coefficient 
ex 1.  2.43 > 3 sig figs
     2.  5.254 > 4 sig figs

Details:  

• Zeroes placed before other digits are not significant; 0.0095 has two sig figs
• Zeroes placed after other digits but behind a decimal point are significant; 7.090 has four sig figs
• Zeroes at the end of a number are significant only if they are behind a decimal point
• Zeros placed after other digits without a decimal point are not counted; 8500 has two sig figs  

Exact Numbers

Not every number is measured experimentally, some numbers are exact. They have an infinite number of significant digits and no rounding is needed.

  ex 1. a pair of earings; there cannot be 1.92 earings rounds to 2  

       2. 360 degrees in a circle

       3. 1m = 100cm

Rounding

Rounding is replacing the numbers value that is approximately equal but has a shorter or simpler representation. 

1. Determine what your rounding digit is and look to the right side of it. 
      ex. When asked to round to the closest tens - your rounding digit is the second number to the left   (ten's place)
2. If that digit is greater than 5, round one up
3. If that digit is lower the 5, dont change it, keep it the same
4. If that digit is equal to 5 and there are more numbers that are not zeros following it, round one up
5. If that digit is equal to 5 but ends at 5, round the digit before that to an even number (0,2,4)

ex. round to the nearest 10th

     a) 74.24   =   74.2

     b) 7.273   =   7.3

     c) 67.35   =   67.4

     d) 2.652   =   2.7

Adding and Subtracting

When adding and subtracting, the number of decimal places in the ANSWER should be the SAME as the number with the LEAST decimal places in any of the terms being added or subtracted. 

  2.548g (3 decimal places) 

  5.72g   (2 decimal places)

+1.1g     (1 decimal place)

  9.36g

the answer is: 9.4g because the lowest decimal place in the equation is 1; also DON'T FORGET TO ROUND IT!

Multiplying and Dividing

When multiplying or dividing numbers, the number of decimal points/significant figures in the RESULT is the same as the LEAST number of decimal points/significant figures in any of the multiplied or divided terms.

  12.54mm    (2 decimal points)

x    1.3mm    (1 decimal point)

16.302mm2

the answer is: 16.3mm2 because the lowest decimal place in the equation is 1; and then ROUND IT!

I know its alot to take in! but practice makes perfect! just keep going over the rules and you'll get it!

ENJOY

Naming Acids!

Naming acids is really quite easy.
First off, what are acids?

Acids are formed when a compound composed of hydrogen ions and a negatively charged ion are dissolved in water. This is a state called aqueous. (aq.)
Ions separate when dissolved in water.

So now that we know what acids are, on to how to name them!
With simple acids, all you have to do is remember these 3 simple steps.

1. Use "hydro" at the beginning.
2. Drop the last syllable of the non-metal and replace it with "-ic". 
3. Add "acid" at the end.

Pretty easy, right?

Let's try an example.

HF, which you know as Hydrogen Fluoride, now becomes Hydrofluoric Acid.

See what I did there? I changed the end of Fluoride, by replacing the "-ide" with "-ic", and then added Acid at the end. It's as simple as that!

Let's try naming complex acids now. 

Once again, there are only 3 rules you need to know for naming complex acids.

1. Replace "-ate" with "-ic". 
2. Replace "-ite" with "-ous".
3. Add "acid" at the end.

This may seem like something thats hard to remember, but it's really not. 

Here's something that Mr. Morrison taught Ms. Chen to teach us! 

"We ate ic-y sushi and got appendic ite-ous." 

Get it? You replace ate with ic, and ite with ous. 

For example, HCN. You may think that this is Hydrogen Cyanide. But if you take the steps as shown above, you'll now know that it's really Hydrocyanic Acid.

Now a harder one...

HNO2.

Pfft, harder? That's easy! 

Hydronitrite Acid? Right?

Wrong. With more complex acids, you need to DROP THE HYDRO.

The answer for this one is actually Nitrous Acid. "-ous", because the original ion ends with "-ite". Then just add acid at the end!

The only two elements that do not lose the last part of their names are Sulphur and Phosphur. 

They change to Sulphuric, Phosphurous, etc. 

Just in case this isn't really clicking for you, try checking out this video. 

Naming Acids

Hope this makes sense for you!

Lab Day!

Last class we looked at the different separation techniques! This class we did an experiment on chromatography!!

Our Lab today was called Separation of a Mixture by Paper Chromatography

Key words

• solute front ( ie. food coloring)
• solvent front (ie. water)
• Rf values (d1 over d2)
• d1 (distance traveled by solute)
• d2 (distance traveled by solvent)

Preparation

1. The first step in this lab, was of course to put all of our safety equipment on!
2. obtain 3 large test, and 3 Erlenmeyer flasks.
3. next we had to get 3 strips of paper, 22 cm each. 4 cm from the end we drew a line and trimmed the edge to make a point.
4. we placed water 2 cm deep in the test tube.

Starting the experiment

1. On our first piece of paper we placed either a red, yellow, or blue dot on the line we drewin the preparation stage.
2. we placed the strip of paper in a test tube (The flat surfaces are not aloud to touch the test tube)
3. Here we wait for 10 min writting notes on what happens 

• because that process takes so long, we moved on to part III of the experiment

1. take another of our strip and put a dot of green food colouring on the line
2. take our last strip and put the unknown mixture on the line
3. put both of the strips of paper in the last 2 test tubes

• After 20 mins and you are fully satisfied that nothing more will change, you remove all the strips from the test tubes

 The hard part!! 

Now it's time for the calculation part of the experiment!!!

1. when you've taken the strips out measure the distance traveled by the solute (label d1), and the solvent (label d2)
2. with your results now it's time to find the Rf value

• to calculate this you use the formula ( d1 divided by d2= Rf)

    3. then we put our results on the white board and compared our answers

Here is a video of another chromatography experiment!
It is different but the results are very similar to that of the one we did!
http://www.youtube.com/watch?v=Oy_yTOwyRLM&feature=related

Results

In this video you saw the separation of the ink, our results were the same. ours however separated into the primary colours. Our unknown separated into all 3 primary colours ( red, yellow, blue) and our green separated into yellow and blue.


This was our Lab of the day!


Next day we have our first test!!!
(ahhhhhhhh!!!)

Different Techniques for Seperation

Today we learned about different techniques to seperate mixtures. Sounds fun, right? Well, it is!

FYI: The more similar the properties are, the more difficult it is to seperate them

The basic techniques are:

-Filtration
-Flotation
-Crystallization
-Chromotography
-Distillation

Hand seperation is useful for mechincal or heterogeneous mixtures. You can boil away the liquid and the solid will remain. (Like boiling away water in a pot of pasta)

Filtration is useful for solids that haven't been dissolved and liquids. It passes a mixture that contains solid particles through a porous filter. (this can sometimes we done for drinking water) You can also use filter paper - residue left in the filter paper and the filtrate goes through the filler paper

Crystallization solids are seperated by filtration or flotation and the solid comes out as pure crystals. Crystals are then filtered from the remaining solvent.

Crystallized Snow

Gravity Seperation is for solids based on density. A centrifuge (device) whirls a test tube around at high speed forcing denser materials for to the bottom. But this works best for small volumes only.

A centrifuge can be used at university

video on centrifuges (Super cool experiment)



Solvent extraction is when a component moves into a solvent shaken with the mixture. It works best with solvents that dissolve only one component. For mechanical mixtures (solid and solid - like nickels and dimes) you can use liquid to dissolve one solid but not the other. That way, the solid you want is left behind or has dissolved.

Distillation is used for liquid in a liquid solution. Most bottled water you find will have been distilled to seperate any sort of dirt or bacteria from the water. You can heat the mixture to cause the low-boiling components to vapourize, and that way the volatilized components have been collected and condensed.

Evian (being modeled by a mermaid?) distills their water

Chromotography can seperate more complex mixtures like drugs and plastic and the analyses can be highly accurate. It is when a mobile phase sweeps the sample over a stationary phase to seperate the two. An example would be when the wind sweeps your wig to reveal that you are bald! (Like in the trident commercial) There are two types of chromotography, sheet chromotography and thin layer chromotography.

Writing and Naming Ionic and Covalent Compounds

What are Ionic Compounds?

Well, basically they are compounds where two or more ions are held together by electric attraction.
One of the ions are positively charged, and the other is negatively charged. When writing the compounds, always remember that the positively charged ion (metal) is always first! 

To make life easier, looking at the periodic table, the positively charged ions (metals) are on the left side and the negatively charged ions (non-metals) are on the right side.

Writing and Naming Ionic Compounds

The Cross over rule:

1)Write the symbols
2)Write the charges
3)Cross over the charges from top to bottom
4)Remove the chages

In example 1 we took their charges and "cross-over" from top to bottom. Remember, before writing the formula down make sure that charges are correct and the metal is written first. The reason we do this is because we want the resulting charge to equal zero!

Ex 2.  You will find yourself coming across an element that has 2 charges instead of 1, but dont panic! turn that frown upside down, it only takes one more easy step :)
For instance, take copper (Cu), it has a charge of +2 and +1. Just follow the same steps as example 1, but make sure you use roman numerals to tell us which charge you are using.

a) Copper (I) oxide    =      Cu2O

b) SnCl4    =    Tin (IV) Cloride


Also, under Ionic compounds are Complex ions: A group of atoms that behave as one atom.
You can find these ions behind the periodic table Ms. Chen distributed :)

*Writing these formulas only requires the same steps as the one given before.The underlined elements are complex ions and are found in the back of the periodic table or the picture shown above.

a) Calcium Hydroxide  =  Ca(OH)2    < when dealing with complex ions, put brackets to show the 2  goes into both O and H

b) Copper (II) Nitrite   =  Cu(NO2)2

What are Covalent Compounds?

It is a compound in which two atoms bond, they share electrons rather than transfer. Covalent compounds are formed when two non-metals bond to each other whereas ionic compounds form when metals bond to non-metals.
Diatomic Elements is another thing you got to watch out for in covalent compounds. They are a special group of molecules that consist of 2 identical atoms, which are:
                                                H2, O2, F2, Br2, I2, N2, Cl2



In covalent compounds we use greek prefixes to indicate the number of atoms
*memorize this for tests in the furture*
Mono - 1                           Penta - 5                        Octa - 8     
Di - 2                                 Hexa - 6                        Nona - 9      
Tri - 3                                Hepta - 7                       Deca - 10
Tera - 4

Writing and Naming Ionic Compounds: 

*The cross over process is not needed for writing ionic formulas

Ex  a) CO2     =     Carbon dioxide

      b) N2O4     =    Dinitrogen tetroxide

      c) Sulphur trioxide      =      SO3


VIDEOS! For all you visual learners, like me :)

Ionic Compounds:  http://www.youtube.com/watch?v=vscoYh6m46M
Covalent Compounds: http://www.youtube.com/watch?v=fxE1KOeNZXw

Enjoy :)

Lab Day!

Today was lab day!

Today's lab was The Heating and cooling curves of a pure substance

The pure substance we used today was - Dodecanoic Acid
ps. it did not smell good, it made me feel dizzy!

Like all labs our first step was to put on our lab apron and safety goggles

This is one of the most important steps, because you always have to put safety first!

Our objective for the lad was to:

1. investigate the heating process for solid dodecanoic acid
2. investigate the cooling process for liquid dodecanoic acid
3. determine and compare the melting and freezing points of dodecanoic acid

Our next step in this lab was
- decide which role you'll play (one person observes and the other records the data)
- next was to obtain our materials and our acid
Materials

• ring stand
• buret clamp
• hot plate
• test tube
• beaker
• thermometer

This was all the setting up part, next is the fun stuff!!

In our textbook it said to do the heating process first, but instead we did the cooling process first.

This picture represents what our set up looked like, although there was water in the beaker and a test tube in the clamp above the beaker.

It took us around 9 min for the dodecanoic acid to drop from 43'C to 25'C and 13 min for the temperature to get back up and reach 50'C.
We had to complete a table of the temperature at every 30 seconds and observations at every step, then we had to graph it.

It was a lot of Hard work, but it was a really cool experiment!

• The acid went completely solid and it turned white ( it started as a pale yellow clear color)
• Then during the heating process it turned to a white goo before it went to its original state.

:)

Textbook Summary

Summarizing for a part of the reading (25-34) from the textbook:


What are chemists?
Chemists specialize in matter:

• what it is
• how one kind differs form another
• what different kinds have in common
• how one kind can be changed to another
• how it can be kept the same

Water is one of the most familiar kinds of matter. The temperature at which matter changes from a liquid to a gas is called boiling point. 

A mixture is two or more kinds of matter that have separate identities. It is easily separated into component parts, and some people say it is impure. 

Mixtures can be heterogeneous mixtures or homogeneous mixtures. 

Heterogeneous mixtures- the substances in the kind of a mixture are not spread out evenly. 

Example: Salad Dressing

Homogeneous mixtures- the substances are spread evenly throughout, a homogeneous mixture is called a solution. 

Example: Vinegar

By adding things to pure water, you can quickly find that there are no mixtures that do not scatter light.

If table salt is added, it disappears. You can taste it, but it cannot be seen.
Therefore, the table salt does not scatter light.

Solutions - mixtures that look uniform throughout and do not scatter light.

Distillation - separates most mixtures.

Mixtures that CAN be separated: 

• household ammonia
• alcoholic beverages - for example, whiskey

Pure Substances have a constant boiling point. Mixtures ordinarily do not. 

Freezing Point - the temperature at which a liquid changes to a solid

Melting Point - the temperature at which a solid changes to a liquid

Density - a property of matter that describes its mass per unit volume

Chemical Changes - changes that produce a new kind of matter with different properties

Physical Changes - changes that change the appearance, but do not produce new kinds of matter

Decomposition - when one kind of matter comes apart (decomposes) to form two or more kinds of matter

Electrolysis - involves passing an electric current through a substance, causing it to decompose into new kinds of matter

The Law of Definite Composition: A compound always contains two or more elements combined in a definite proportion by mass

The Law of Multiple Proportions: The fact that two or more compounds with different proportions of the same elements can be made.

Check out this video called the Atom Song!
Skip to 30 seconds to get to the song.
The Atom Song!



Summarizing for you a part of the reading (36-39) from the textbook:


The general idea here is that matter is made of atoms.
The idea that matter is made of atoms did not become popular until the early 1800s.


Now, lets look at some terms:


Atom: The smallest possible piece of something, they vary in size and mass


Elements: Pure substances that cannot be broken down


Solid: Holds its shape since atoms are stuck together


Liquid: The temperature is increased and atoms will vibrate and flow past one another


Molecule: particles made up of more than one atom


Compounds: Made by combining elements in definite proportions (made of 2 or more types of atoms)


Ions: particles that have an electrical charge


Ionic: melt to form ions


Molecular: melt as molecules

A very large water molecule

A caffeine molecule

LSD (acid) molecule. Don't try this at home kids!

My Socials Teacher once told me that once you know the meaning of the terms, it makes the material much easier to learn. So hopefully this helps!


Here's a cool video about atoms and molecules, and the guy talking has braces! It's pretty funny.


Click here