Crystallisation, Separating Funner & Sublimation 29/1/13

Crystallisation - Lab Experiment

Lab worksheets

Separating Funnel

Simple Diagram of Concept behind Separating funnel

Example: Oil and Water.

--> Separate Immiscible Liquids

Sublimation

Simple Examples

Crystallization 28/1/13

Crystallization ( refer to slides handout given)

Different from Distillation:

End Product:

Distillation --> solution

Crystallization --> Solute

• Sodium Chloride ( normal salt solution )  -> CANNOT  ->  same solubility over different temperature.

You need a saturated solution to carry out crystallization.

different from concentrated solution

• contains the maximum amount of solute dissolved in a given volume of solvent at a particular temperature
• A concentrated solution: A solution that contains lots of solute dissolved in it.

Speed of Crystallisation And The Size of Crystals Obtained

• Rapid cooling of saturated solution

        - small and ill-shaped crystals formed

• Slow evaporation of a cold saturated solution

        - large and well-defined crystals obtained.

graph showing Concentration vs Temperature during Crystallisation

Lab Experiment - Separation Techniques 26/1/13

Chromatography- Food Colouring Experiment ( Individual Work)

Experiment Process: 

Learning Points:

• Locating Agents can be used to convert colourless chemicals into coloured, such that it is possible to separate a mixture of colourless chemicals by chromatography
• Factors affecting the Rf of a chemical:

            - Temperature: When temperature is higher, the dye is more soluble, hence it will travel higher up.

           - Paper: When the paper changes, it may absorb the dye better, hence the rf value is lowered.

           - solvent : type of solvent will affect the distance travelled by the dye, rf value higher/lower ( depending on the the amount of chemicals it dissolves

• Uses of Rf value:

           - Identify the individual components in dye

           - estimate/ predict the element.

Chromatography as a SYSTEM:

All the components must be present in order for the chromatography to work. It is made up of different parts with different functions to serve one common purpose -> identify and separate the mixture.

Principle: More Soluble -> travel farther than less soluble

       --> difference in solubility ; enables separation

Chromatography almost done! 

Separation Techniques 24/1/13

Pre-lab Questions on Distillation:

• What is the purpose of the boiling stones/chips?       

A boiling chip or boiling stone is a tiny, uneven shaped piece of substance added to liquids to make them boil more calmly. Boiling chips are frequently employed in distillation and heating. When a liquid becomes superheated, a particle of dust or a stirring rod can cause flash boiling. This very rapid boiling can be extremely violent and cause reagents to splatter, possibly causing severe burns, ruining an experiment, and damaging equipment. Boiling chips work by providing nucleation sites so the liquid boils smoothly without becoming superheated or bumping

• What is smooth boiling?

( refer to answer above ^)

1. What is the purpose of the thermometer and condenser?

condenser: to convert the gas form of a substance into a liquid. If the temperature and boiling points are kept constant, then the substance with the lower boiling point will be able to be evaporated and condensed, thus separated. The condenser ultimately just cools the gas form of the substance so it may return to the liquid state.

Thermometer: The thermometer on top measures the temperature of the vapor right before it condenses (boiling point).

1. Why does the water comes in from the top and out from the botton? (main purpose and purpose of position)

If water enters from the bottom of the condenser, it will always be completely filled with cold water which ensures efficient cooling. During distillation, vapors are formed in the heated distillation flask. The condenser cools these vapors condensing them back to liquid droplets that flow down the condenser into the receiver flask. A completely filled condenser provides maximum cooling therefore allowing for maximum recovery of the purified liquid during distillation.

Is it due to the concept of hot air rises and cold air sinks? ( Not Sure)

Theory Lesson:

Separation Techniques: mainly on Chromatography & Simple and Fractional Distillation

refer to slides on 'Separation Techniques Introduction'

references: - --http://www.chem.ualberta.ca/~orglabs/Techniques%20Extra%20Info/Distillation.html#same  - wikipedia

Mixture & Compound.Alloy.Separation Techniques 1 21/1/13

Revision: Element, Compound & Mixture

Example of a mixture of elements

Example of a mixture of compounds

Alloy:

• MIXTURE
• Mixture of metals with other elements
• Stronger. Not malleable

* STEEL

   STAINLESS STEEL

   BRONZE

   COPPER   MUST KNOW-S!

Separation Techniques

• Used only for Mixture
• Physical Means

1.          Magnetic Attraction
2.          Filtration
3.          Use of separatin funnel
4.          Distillation
5.          Crystallization
6.          Evaporation
7.          Sublimation

Method used depends on element's properties. e.g. soluble/insoluble

Mixture needs to be separated into pure substance for...

• Characterization (identify properties)
• Identification ^
• Production of useful substances such as medicine

Paper Chromatography

• separate a mixture of solutes with different solubility and degree of absorption
• The method uses a solvent moving over a porous or absorbent medium

Solvent : Water / ethanol

Principle ( Uncompleted)

• As solvent travels up the paper, the dyes dissolved
• some dyes are more soluble, so they travel faster up the paper
• dyes that are less soluble remain as the bottom of the paper (own comment)

example of a paper chromatography experiment

Sub-Atomic Particles 18/1/13

Sub-atomic Particles

• Protons
• Electrons
• Neutrons

All types and sizes of atoms consist of the same type of sub-atomic particles but of different numbers.

• Sub atomic particles CANNOT be used to identify/ distinguish elements. -->  All elements have the same type of sub-atomic particles

STRUCTURE OF AN ATOM

Proton:                                    

Carries a charge of +1

Relative mass of 1

Found in the nucleus -> centre of atom

Symbol : p

Neutron:

Carries no charge = 0

Relative mass of 1

Found in the nucleus -> centre of atom ( together with proton ^)

Symbol : n

Electron:

Carries a charge of -1

Negligible mass of 1/1840

Found in shells which surround the atom

Symbol : e

Relative Mass:

• Particles in atoms are VERY LIGHT
• proton weighs about 1.67x10^-27kg
• Hence scientists measure massess of atom against standard unit called atomic unti mass (anu)
• 1 amu = 1.67x10^-27kg  , which is also known as relative mass 
• When you say relative mass of 1, dont put units. ( SAME THING)

• All atoms are electrically neutral. ( negative charge of electron and positive charge of proton)
• An atom contains an equal number of proton and electron

Proton and Nucleon Number:

• Number of proton = proton number --> used to arrange elements in periodic table  
• ^ ALSO KNOWN AS THE ATOMIC NUMBER
• symbol = Z
• tell us the number of electrons in the atoms too!

Example: Proton number of nitrogen is 7

   A nitrogen atom has seven protons and seven electrons.

Different atoms have different proton number

each element has a unique proton number! -> only thing thats different from element to element

• Atoms of different elements have different numbers of protons.

Example: Carbon has a proton number of 6. 

Any atom with 6 protons must be a carbon atom

Nucleon Number:

Also known as the mass number.

• The mas of an atom depends on the number of protons and neutrons in an atom.
• Electron's mass = negligible!
• Symbol = A
• Nucleon Number = number of protons = neutrons

!! Nucleon Number and Mass number DO NOT mean the same thing, but coincidentally, the value is the same.

Representing Proton and Nucleon number:

An element can also be represented using only the nucleon number:

    e.g.: sodium-23 or 23-NA

Biography of Scientist who made notable contributions to the world of atoms:

Read up articles about:

John Dalton

Ernest Rutherford

George Johnstone Stoney

Dmitri Mendeleev

:>

Elements, Molecules & Compounds. 15/1/13

Comparing Element , Compound and Mixture. Partner: Emma :>

Element: 

• A Substance that cannot be spilt into two or more simpler substances by chemical reaction 
• Simplest kind of matter

Compound:

• A substance made up of two or more elements chemically combines together.

Mixture:

• Two or more substance which are not joined together chemically
• may be made up of elements, compounds or both
• May be solid, liquid or gas

Procedure and Observations:

Elements:

Appearance( Colour and State) of iron fillings: Slivery-grey powder

Appearance of sulfur powder: Yellow powder

Mixture:

Observations:
 

• Place a spatula of iron filings and a spatula of sulfur powder ona piece of filter paper. Mix them together. To form a mixture, can the iron filings and sulfur be mixed in any proportion?

       To form a mixture, the iron fillings and sulfur can be mixed in any proportion.

• Feel the mixture ( from the bottom of the filter paper.) Does it feel warm?

         The mixture remains cold  . mixture = no change in temperature

• Move a magnet under the paper. Does the magnet separate the mixture of elements?

         The magnet is able to separate the mixture of elements. Magnetic iron fillings. Non-magnetic sulfur

• Add the iron and sulfur mixture into a test-tube of water. Stir the mixture and let it stand of a while. Draw and label what you see.    Results: both are insoluble       
• Does water separate the mixture of elements?

          The water does not easily separate the mixture of elements. - Insoluble. cannot be separated easily           

• Do the iron filings and the sulfur act as separate substance of a single substance with water?

           The iron filings and the sulfur act as separate substances.      
Conclusions:

1. The substances in a mixture can be mixed in any proportion.
2. When a mixture if formed, heat and light are not usually taken in or given out.
3. The mixture can be separated by physical means.
4. The mixture has/ retain the properties of its constituent substances.

* constituent = individual substance that make up the mixture/ compound

Mixture of Compound

1. Mix one spatula of sulfur and half a spatula or iron filings in a crucible.
2. Cover the crucible with a lid and heat for 10 min. using strong flame
3. When the crucible has cool down, open the lid and observe the residue left. Describe the appearance of the residue. How is it different from the original iron fillings or sulfur
   • The new residue is heard and black solid. ( red= more sulfur. blue-= more iron)

   
   
4. Scrape out some reside from the bottom of the crucible on a filter paper and test it using a magnet. Does the residue separate into iron and sulfur with a magnet                                                  No. New residue has lost magnetic property (iron's property) -> New property. including new melting and boiling point.
5. Add the residue to water. Stir and allow the mixture to stand. Draw and label what you see.

6. Conclusion. Do you think the residue formed is a mixture / compound. Explain your answer

• Compound. Properties of a compound have a different physical property as its constituent element. 
• A compound cannot be separated by physical means. A chemical reaction takes place when a compound is form when there is a energy change -> heat content change/ heat transfer

Questions

1. A student decided to repeat the Part B of this experiment. But instead she used one spatula of sulfur and a spatula of iron filings. Predict what will this student observe with regards to ...

  

• Appearance of the residue in the crucible                                                                                  Mixture and black powder and excess grey iron filings

• Magnet test                                                                                                                                       Magnet os able to separate iron filings from black powder

• Residue in water test                                                                                                                              Grey iron filings and block powder will remain insoluble in water

• Explain your prediction                                                                                                                   Both iron and new compound are insoluble in water, producing a suspension as observed

Extension Question:

You are given a solid mixture of common salt, sulfur powder and iron filings. Describe how you will separate these 3 substances.

1. Use magnet to separate the iron filings from the mixture.
2. Add water to the salt and sulfur power mixture and stir. ( ensure that salt dissolved)
3. Filter the mixture (separate insoluble and soluble)
4. Evaporate the salt and water mixture to dryness ( remove all water)
5. Squeeze dry the sulfur and water mixture using the filter paper.

Periodic Table, Atoms and Molecules 14/1/13

Metals

characteristics used to classify metals in periodic table

• Colours
• Conductivity ( good conductor of heat = good conductor of electricity)
• malleable / ductile / brittle
• density

Overview of lesson:

Refer to Slides hand-out given.

Molecules (enrichment only)

• Hydrogen (H2) is a diatomic molecule
• Ozone (O3( is triatomic molecule
• Molecules consisting of a few atoms = Polyatomic molecule

Periodic Table 

Left = metals

Right = non-metals

Hydrogen: 

• only has 1 electron ( unique sub atomic particle)
• tend to lose electron -> Similar property to metal
• NOT CLASSIFIED !

Bunsen Burner 11/1/13

Lab Experiment- partner Emma :>

1)  Light a busen burner using 2 different lighters.

Procedure:

• Attach the gas intake tube to the gas tap.
• Close the air-hole by adjusting/turning the collar
• Have the lighter ready; positioned at the top of the barrel.
• Turn the gas tap on completely and strike the lighter immediately and continuously if the burner is not lit.
• Turn the gas tap until the flame is about 5cm tall (approx.)
• Adjust/turn the collar until the air hole is opened.

<-picture of a non-luminous flame 

2) Understanding the Busen Burner flame

Find out which part of the (blue) Busen flame is hottest by designing a simple experiment.

Prediction/Hypothesis: 

The inside of the blue core is the hottest, as the inside appeared the most blue-ish when lighted , and the non-luminous flame has a higher temperature than the luminous flame.

Planning:

apparatus--> bunsen burner. lighter. metal tongs. thin wires (copper wires). stopwatch

Light the busen burner with the lighter. Using the metal tongs, hold the thin wires in the inside of the blue core. Measure the time taken for the wire to turn red, with the stopwatch. Repeat the whole experiment once, now holding the wire at the tip of the blue core 

-> SHOULD HAVE DONE THE PROCEDURE THRICE, MEASURING THE TIME TAKE ABOVE THE BLUE CORE TOO!!

(assuming the thickness of the wire is constant, however heating cause thickness to change)

diagram of busen flame, showing the hottest part of flame

<-wire at the top of blue core

Table of results:

independent variabledependent variable

Should have taken results time taken when the wire is placed above the blue core

Claims and Evidence:

Our hypothesis was incorrect because the inside of the blue core was actually unburnt gas and air, which is not as hot as the tip of the blue core, but is hotter than the luminous flame above the blue core.

Conclusion:

In this investigation, I have learned how to light a bunsen burner and also have a better understanding of the busen burner. For example, The luminous flame has a lower temperature compared to the non luminous flame, the tip of the blue core is the hottest part of the bunsen burner, etc.

Notes of busen burner :D

Reflections: I really enjoyed myself during the whole process of this experiment as i got to try out something new (lighting the bunsen burner) and learn more interesting facts about the bunsen burner. Although i had learned about the bunsen since learning primary science, but i never had a chance to try lighting it and even know so much about it. Hence, this was a eye-opening experience to me.

Questions:

• Why is the luminous and non-luminous flame orange and blue respectively? What makes them into this colour? Or is it just a natural reaction due to the combustion of the flame?

Useful links: http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/carbon_chem/7_using_carbon_fuels2.shtml

http://tinyurl.com/aagsvjy (periodic table of elements)

Claims	Evidence

Introduction to Particles 10/1/13

ACTIVITY: classify the diagrams in as many ways as possible to explain each classification system used e.g. by sizes, colours, bonded or unbonded etc..

Grp members: Annette, arika and me. (Group 4)
We grouped the particles according to their size and whether they were conjoined or in twos. Also, we tried identifying the criteria used by the other two groups to group the particles.

Class discussion: Questions to think about

1) Which one(s) do you think comes from the same type of substance? Why?
- same size particles.

• different types of particles bond together -> same type of particles

• different types of particles DONT bond -> different type type particles

2) Which two do you think come from the same substance? Why?
- same size
- same colour

3) Which one(s) is/are gases? Why?

Gas particles-> particles that are far apart.

• The forces of attraction between gas molecules is too weak for them to mantain any kind of definitive shape.
•   Indefinite shape and volume.

4) What do you think each particle represent?

                           Particles 
                 atoms                 Molecules
                 (single)                (two/three)
                   O                       oo


F particles occupy more space than M = higher density.

VS

Of equal space, F particles (on the left) occupies more space than M particle( on the right).


Atoms Useful link