Beginner stuff lol

Elements, Compounds, and Mixtures

Classifying Substances (1.8)

  • Substances can be classified as elements, compounds, or mixtures.

Pure Substances vs. Mixtures (1.9)

  • Pure substances have fixed melting and boiling points.
  • Mixtures melt or boil over a range of temperatures.

Separation Techniques for Mixtures (1.10)

  • Simple distillation
  • Fractional distillation
  • Filtration
  • Crystallisation
  • Paper chromatography

Chromatogram Information (1.11)

  • A chromatogram provides information about the composition of a mixture.

Rf Value Calculation (1.12)

  • R_f values can be used to identify components of a mixture.
  • R_f = \frac{\text{distance moved by the compound}}{\text{distance moved by the solvent}}

Practical Investigation (1.13)

  • Investigate paper chromatography using inks/food colorings.

Chemistry: The Study of Matter

  • Chemistry is the study of matter, encompassing everything that occupies space, both living and non-living.
  • It explains the behavior of materials by examining the atoms and molecules that constitute them.
  • Activities include making new substances and analyzing their properties and composition.
  • Practical work is essential for developing observational, explanatory, and concluding skills.
  • Examples of chemical reactions:
    • Reaction 1: Ammonium dichromate and heat
    • Reaction 2: Copper penny in concentrated nitric acid
    • Reaction 3: Lead nitrate and potassium iodide

Laboratory Safety

  • Laboratory safety is crucial to prevent accidents.
  • Identify hazards in the lab.
  • Establish a list of "do’s" and "don’ts" for laboratory conduct.

Chemical Hazards Symbols

  • Understanding hazard symbols is important for safety in the laboratory.
  • Knowing the symbols allows for appropriate safety precautions.

Chemical Hazard Symbols Summary

  • Some substances have warning signs called hazard symbols.
  • Flammable: Materials that catch fire easily.
  • Oxidising: Materials that help other substances burn by supplying oxygen.
  • Acutely toxic: Substances that can kill you.
  • Moderate hazards: Less dangerous substances.
  • Corrosive: Substances that can destroy or burn skin.
  • Health hazards: Substances that can cause allergic reactions or coughing.

Physical and Chemical Changes

Physical Change

  • No new substance is made.
  • Easily reversed.
  • Change of state (e.g., melting or boiling).
  • Temporary color change.
  • No change in mass.

Chemical Change

  • New substance(s) are made.
  • Not easily reversed.

What to look for:

  1. Gas being produced, a color change, light given off
  2. Giving out or taking in heat
  3. Fundamental change in physical properties
  4. Very difficult to reverse

Chemical Reactions

  • Reactants (starting materials) are changed into products (finishing materials).

Experiment: Physical vs. Chemical Changes

  • Demo: Heating paraffin wax (physical change).
  • Demo: Heating copper (II) nitrate (chemical change, harmful).
  • Investigate physical and chemical changes by mixing or heating chemicals in test tubes.
  • Record observations to determine the type of change.

Experiment Instructions

  1. Heat a little Copper (II) Sulfate (HARMFUL) in a test tube
  2. Heat a little ammonium chloride (HARMFUL) in a test tube
  3. Hold a piece of magnesium metal in metal tongs over a flame
  4. Add a small piece of magnesium metal to 2cm3 of dilute hydrochloric acid in a test tube (CORROSIVE)
  5. Put 2cm3 of potassium iodide solution in a test tube. Add 5 drops of lead (II) nitrate solution (TOXIC)
  6. Heat a little zinc oxide in a test tube
  7. GENTLY heat a little salol in a test tube
  8. Add a spatula of sodium chloride to 5cm3 of water in a test tube
  • Follow safety guidelines: wear goggles, use small amounts, avoid touching/spilling chemicals, and inform the teacher of any spills. Dispose of solids in a designated beaker and flush waste solutions down the sink.

Elements, Compounds, and Mixtures

  • Substances are made of atoms and can be divided into elements, compounds, and mixtures.

Element

  • Definition:
  • Examples:
  • Arrangement of atoms:

Compound

  • Definition:
  • Examples:
  • Arrangement of atoms:

Mixture

  • Definition:
  • Examples:
  • Arrangement of atoms:

Experiment: Reaction between Iron and Sulphur

  1. Describe the appearance of some iron filings:
  2. Describe the appearance of some sulphur:
  3. Mix the iron and the sulphur. Draw a picture to represent the atoms in the mixture:
  4. Can you separate the mixture? How would you do it?
  • Heat the mixture of iron and sulphur in a test tube. Draw a diagram of the experiment: Describe what you see during the heating:
  1. Can the iron and sulphur be separated now? Explain your answer.
  2. What is the name of the product you have formed?
  3. Test the product with a magnet, what happens?

Reaction

  • Write a word equation: Iron + Sulphur → Iron Sulphide

  • Write a symbol equation: Fe + S → FeS

  • Draw a diagram to show what happens to the atoms during the reaction.

  • Test the iron, sulphur and product with hydrochloric acid (CORROSIVE) and record the results below:

    • Iron
    • Sulphur
    • Iron sulphide

  • Are the properties of the reactants the same as the products? Explain your answer.

Elements Quiz

  1. Some Ancient Greek philosophers thought that everything in the world was made of four elements. What were they?
  2. What do you understand by the term element?
  3. Approximately how many elements are known?
  4. Have all the elements been found or will we discover new ones in the future?
  5. Do you think that there are undiscovered elements in outer space?
  6. Are most elements metals or non-metals? How could you tell which was which?
  7. Give an example of each of these types of elements that:
    • exist naturally in earth
    • exist only in compounds
    • are man-made
  8. Explain what is meant by a ‘man-made’ element?
  9. Some elements have been named after a country or place where they were discovered. Some have been named after the person who discovered them. Give an example of each.

Direct Combination Reactions

Reactants

  • Name of elements
  • Appearance of elements

Product

  • Name of compound
  • Appearance of compound

Examples

  • Hydrogen + Bromine
    • Word equation:
    • Symbol equation:
  • Aluminium + Iodine
    • Word equation:
    • Symbol equation:
  • Zinc + Sulphur
    • Word equation:
    • Symbol equation:

*Your teacher is going to demonstrate three reactions in which two elements join together to form a compound, these are called direct combination reactions.

Naming Compounds

  • The ending -ide means that the compound consists of two elements only e.g. sodium chloride, iron sulphide
  • the ending -ate means that oxygen is present too e.g. copper sulphate is a compound of copper, sulphur and oxygen.

Naming Compounds Q1.

Complete the table as shown in the example and see if you can name the compound (Hint: don’t let the numbers confuse you! Look at the symbols only…)

Name of compoundElements presentSymbols of elementsFormula
potassium manganatepotassium, manganese, oxygenK, Mn, O
aluminium oxide
zinc fluoride
nickel sulphate
lithium carbonate
lead iodide

Naming Compounds Q2.

Give the names of the elements present in the following compounds and write the symbols of these elements. (You do not need to know the formulae of the substances)

Element or compoundElements presentName of substanceFormula
MgCl_2magnesium & chlorinemagnesium chloride
Zn
CaCO_3
NaCl
KNO_3
CuSO_4
H_2
Fe2O3
N

Elementary My Dear Watson

The solution to the mystery that follows depends on your knowledge of chemical elements and their symbols. If a symbol is given, substitute the name of that element. If the name is given, substitute the symbol.

  • (Helium) He explained that the gentleman had purchased several pieces of (Ag) silver and (Au) gold jewellery for his wife (or mistress (Iodine) I surmised). This had disappeared during a street (Carbon + Argon) car ride. The victim interrupted with, “You must (Fe) find this out before the 24th Mr (Ho) Holmes! “(Holmium + Tungsten) How dare someone (Sulphur + Tellurium + Aluminium) steal from me!” By this time Lestrade seemed eager to (Beryllium) Be rid (Oxygen + Fluorine) of our pompous victim.
  • (Tungsten + Arsenic) As I (Indium) In private, the Inspector explained that he wasn’t personally (Sb) bothered, but just wanted the theft cleared (Uranium + Phosphorous) up quickly (Sulphur + Oxygen) so he could get (Oxygen + Nitrogen) on to matters more important than petty theft.
  • (Iodine) I agreed to help, not to save the Inspector more time and embarrassment (Tungsten + Helium + Nitrogen) when he failed (Arsenic) as I (Potassium + Neon + Tungsten) know he would, but because I had the (Calcium + Selenium) case already solved. Informed of this, the Inspector cried, “(Sulphur + Oxygen) So fast!
  • (Hydrogen + Oxygen + Tungsten) How?!” Watson, Use the Periodic Table to finish off the story…… Holmium

Reacting Molecules and Chemical Equations

Required Model Atoms

  • Black (Carbon) - 1
  • White (Hydrogen) - 4
  • Red (Oxygen) - 4

Reaction 1: Hydrogen and Oxygen

A: Take two oxygen atoms and join them together with two long bonds. Make sure that there are no empty holes or loose ends. You have made a model of an oxygen molecule. Draw a diagram to represent the oxygen molecule, O_2.

B: Now use four small white model atoms to make two model hydrogen molecules, H_2. Draw them.

C: Hydrogen reacts with oxygen to make water. Put the model molecules together and make the molecules 'react'. Break up the molecules of the reactants and join the atoms together in a new way to make molecules of the product. (Remember that all the holes should be used and that there should be no loose ends to the bonds.) Draw a diagram of the product molecules.

D: Draw a 'model equation' to show the reactant molecules (hydrogen and oxygen) on the left and the product molecules (water) on the right. Can you name this molecule?

Reaction 2: Methane and Oxygen

E: The natural gas we use for cooking and heating is methane. The formula for methane is CH4. Make a model of the methane molecule and also two model oxygen molecules, O2. Draw all the molecules below:

  • One Methane molecule
  • Two Oxygen molecules

F: When methane burns in air (oxygen), it is converted into carbon dioxide (CO2) and water (H2O)

  • Break up your model methane and oxygen molecules and join the atoms together to make the products of the reaction. Draw a ‘model equation’ to show the reactant and product molecules when methane reacts:

  • Using your model equations as a guide, write symbol equations for the 2 reactions you have drawn:

    1. the formation of water
    2. the burning of methane

Balancing Equations

  • In a balanced chemical equation there are the same number of each type of atom on both sides of the equation.
  • In a chemical reaction atoms are not created or destroyed, but the ways in which the atoms are bonded together changes.

Example

  • How do you balance the following equation?
    Mg + O_2 → MgO

Step 1

  • Determine the number of atoms for each element.
    Mg + O_2 → MgO
    Mg = 1, O = 2, Mg = 1, O = 1

Step 2

  • Pick an element that is not equal on both sides of the equation.
    Mg + O_2 → MgO
    Mg = 1, O = 2, Mg = 1, O = 1

Step 3

  • Add a coefficient in front of the formula with that element and adjust your counts.
    Mg + O_2 → 2MgO
    Mg = 1, O = 2, Mg = 1, O = 2

Step 4

  • Continue adding coefficients to get the same number of atoms on each element on each side.
    2Mg + O_2 → 2MgO
    Mg = 2, O = 2, Mg = 2, O = 2

Exercise

  • Try the following examples yourself, remember to follow the 4 steps every time:
    1. Determine the number of atoms for each element.
    2. Pick an element that is not equal on both sides of the equation.
    3. Add a coefficient in front of the formula with that element and adjust your counts.
    4. Continue adding coefficients to get the same number of atoms on each element on each side.
  1. ___ Ca + ___ O_2 → ___ CaO
    • Ca = Ca =
    • O = O =
  2. ___ N_2 + ___ H_2 → ___ NH_3
    • N = N =
    • H = H =
  3. ___ Cu_2O + ___ C → ___ Cu + ___ CO_2
    • Cu = Cu =
    • O = O =
    • C = C =
  4. ___ H2O2 → ___ H_2O + ___ O_2
    • H = H =
    • O = O =

Balancing Equations 2

*Balance each equation. Be sure to show your lists! Remember you cannot add subscripts or place coefficients in the middle of chemical formulae.

  1. Na + MgF_2 → NaF + Mg
    • Na =
    • Mg =
    • F =
  2. Mg + HCl → MgCl2 + H2
  3. Cl2 + KI → KCl + I2
  4. NaCl → Na + Cl_2
  5. Na + O2 → Na2O
  6. Na + HCl → H_2 + NaCl

Separating Mixtures

  • When substances are combined to form a mixture, they maintain their physical and chemical properties.
  • Can you think of an example?

Experiment: Separating sand and salt

  • Design a three-step experiment to separate a mixture of salt and sand using the provided apparatus.
    Apparatus:

    • 100cm^3 beakers;
    • stirring rod;
    • filter funnel;
    • filter paper;
    • Bunsen burner;
    • heat proof mat;
    • tripod;
    • gauze;
    • evaporating dish.

  • Draw diagrams for steps 1 and 3 in the process and explain what property of the substances you are using to separate them.

Step 1

  • Property:

  • Property:

  • Label the diagram:

    • Filter funnel
    • Filter paper
    • Conical flask
    • Residue
    • Filtrate

Step 3

  • Property:

Technique: Simple distillation

  • Aim: To separate water from a solution of copper sulphate

  • Diagram of set up:

  • What property of the two substances (water and copper sulphate) is utilised, why does this enable them to be separated?

Technique: Fractional distillation

  • Aim: To separate ethanol from a mixture of ethanol and water

  • Draw and label a diagram:

  • What property of the two substances (water and ethanol) is utilised? Why is fractional distillation used instead of simple distillation?

Technique: Paper chromatography

  • Aim: To obtain information about the composition of a mixture of dyes in the indicator called methyl orange

Instructions

  1. Draw a straight line in pencil roughly 1cm from the bottom of the strip of filter paper, draw a cross in the middle of the line.
  2. Using a capillary tube (a small, glass tube) place a small drop of methyl orange on the cross.
  3. Set up a beaker with a small amount of water in the bottom.
  4. Suspend the filter paper so that it just touches the water (the water must be below the pencil line)
  5. Leave the set up to stand until the water reaches roughly three quarters of the way up the filter paper.
  6. Record your results.

  • Diagram of set up:

  • Diagram of results:

  • What property of the dyes in the mixture results in them travelling different distances up the paper?

  • How does the solubility of the individual dye affect the distance travelled up the paper? Which of the dyes in the mixture is most soluble in water?

Technique: Crystallisation

  • Aim: To separate copper sulphate crystals from a solution of copper sulphate

Instructions

  1. Gently heat a solution of copper sulphate in an evaporating basin.
  2. Once the solution is hot dip a glass rod into the solution, remove the rod and examine it.
  3. Repeat step 2 until solid is seen to form on the glass rod.
  4. Stop heating the solution, crystals will form as the solution cools.
  5. The crystals can be dried by filtering off the excess solution and dabbing the crystals with filter paper, or by leaving the crystals in a warm place until all the water has evaporated.

  • Diagram of set up:

  • What property of the two substances (water and copper sulphate) is utilised, why does this enable them to be separated?

  • Why was heating stopped in step 4, rather than continuing to remove the water by heating?

CASE - Kent Drugs Bust

BRIEFING

  • Yesterday the Kent Police Anti-Drugs Squad raided a flat frequented by a suspected cocaine dealer.
  • Six individuals were arrested on suspicion of possession and dealing of a Class A drug, a substantial amount of white powder was seized from the flat.
  • Your job is to identify the white powder using TLC (thin layer chromatography).

BACKGROUND

  • Many types of chromatography exist, as well as being a useful technique for separating and purifying substances, it allows unknown substances to be identified. You will be identifying the unknown white powder by comparing it’s chromatogram to that of known samples of three drugs.

INSTRUCTIONS

  1. Locate the vial that contains a small amount of the white powder recovered from the suspects’ flat (labelled crime scene evidence).
  2. Add 1/4 pipette of ethyl ethanoate to the vial, Close it and shake gently to dissolve the samples.
  3. Handling carefully by the edges, prepare a TLC plate as instructed by your teacher (diagram above).
  4. Using capillary tubes, spot a sample from each of the vials onto the plate. Your teacher will demonstrate this process. Allow the spots to dry and repeat 3 more times until you have a spot of about 1-2 mm in diameter.
  5. Place your plate in the developing tank, ensuring that the pencil line is above the solvent. Put a lid on the tank and allow the solvent to rise up the plate to within 1 cm of the top.
  6. Remove the plate from the solvent and allow it to dry.
  7. Observe your plate under short wavelength UV and lightly mark the position of any spots you can see with a pencil. Do not look directly at the UV light - it can damage eyes and skin!
  • Thin-Layer Chromatography (TLC)
  • You will need to run a chromatogram of the white powder recovered from the suspects’ flat, together with samples of cocaine, heroine and an amphetamine. Do not inhale this solvent - it will irritate the eyes and respiratory system and is highly flammable!

Results

  • Sketch your chromatogram, marking on the solvent front and the distance each spot has travelled:
  • Looking carefully at your chromatogram. Was the white powder recovered from the suspects flat a Class A drug? If so, which one and how can you tell?
  • Do you think this substance is pure? Explain your answer.
  • None of the substances used in this experiment are Class A drugs.

Chromatography – Rf Values

  • Substances can be identified using chromatography either by comparing their chromatogram with those of known substances, or by calculating the R_f value and using a data base to match it to that of a known substance.

  • The Rf value is simple to calculate: Rf value = \frac{\text{distance moved by the compound}}{\text{distance moved by solvent}}

  • E.g. Here are the results of a chromatography experiment: A B

  • Using a ruler, calculate the R_f value for compound A.

  • R_f value = \frac{\text{distance moved by the compound}}{\text{distance moved by solvent}}

  • R_f value =

  • What does the position of compound B indicate about the solubility of B in the solvent?