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National 5 Chemistry

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Mrs Smith

on 24 February 2015

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Transcript of National 5 Chemistry

National 5 Chemistry
Unit 1: Chemical Changes and Structure

Section A: Rates of Reaction
Section B: Atomic structure and bonding related to properties of materials
Section C: Formulae and Reaction Quantities
Section D: Acids & Bases
Lesson 1: What is a Chemical Reaction?
A chemical reaction is a change involving the formation of a new substance.
We are going to carry out four small experiments to show different signs of a chemical reaction occurring.
(Use 1/3 of a TT of all solutions)
1. Add Magnesium to Copper Sulphate
2. Add Magnesium to Hydrochloric Acid
3. Add equal volumes of Barium Nitrate to Sodium Sulphate
4. Add Ammonium Nitrate to Water

In your classwork jotter, under the heading 'Signs of a Chemical Reaction', briefly describe whether you think a reaction has occurred in each case and what evidence you have to support this.
A chemical reaction is one in which one or more new substances are formed.

To identify that a chemical reaction has occurred, we can look for
A colour change
A change in temperature
A gas being produced (bubbles/effervescence)
A precipitate forming.
Some types of chemical reaction to think about
Neutralisation
Combustion
Precipitation
Displacement
The reaction of an acid with a base
The formation of an insoluble salt from the mixing of two ionic solutions
The reaction of a substance with oxygen to produce energy
the less reactive element in a compound is replaced by the more reactive one
Lesson 2: Different Rates for Reactions
Learning Outcomes:
To define 'chemical reaction'
To carry out experiments and discuss evidence for a chemical reaction occuring


Success Criteria:
I can define 'chemical reaction'
I can work safely with others
I can draw conclusions about experiments
Learning Outcomes:
To understand Collision Theory
To think about different ways reaction rates can be measured.


Success Criteria:
I can use diagrams to show my understanding of Collision Theory.
I can describe at least two ways reaction rates can be measured.
Some reactions happen very slowly
Rusting
The Formation of Oil
REVISION VIDEO
Other reactions are much faster
Fireworks
Collision Theory
DISCUSS:
What needs to happen for a reaction to occur in the first place?!
In order for a reaction to occur, reactant particles must collide with
the correct orientation
the correct energy
Link: http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/rocks_metals/7_faster_slower1.shtml
The rate of reaction can be found by measuring how much of reactant is used up, or how much product is formed, in a given time.
reaction rate =
change in concentration of reactant
time
Concentration is a measure of how much solute is dissolved in a solvent.

In chemistry we measure this in
moles per litre ( mol l-1)
Why do some reactions occur faster than others?
Lesson 3: Following the Course of a Reaction
To follow the course of a reaction by monitoring a change that takes place over time

Success Criteria:
I can identify different properties that could be monitored eg volume of gas released, concentration of either reactant or product.
I can plot a reaction rate graph
I can calculate rate from a graph of e.g change in volume of a gas v time
Learning Outcomes:
Set up the apparatus as shown in the diagram above. Measure out 50cm3 (4moll-1 hydrochloric acid GOGGLES), 10g of small marble chips
Prepare a results table in jotter
Total Mass (g)
Time (min)
Mass of gas released(g)
Use this information to construct a table of time (x-axis) and mass (y-axis)
The reaction is fastest at the start resulting in a
steep gradient
. As the reaction proceeds it slows down leading to a
shallow gradient
. When the reaction stops the graph levels out to a
horizontal section
.
How to draw a graph
Must use a pencil
Draw in your axes with a ruler
Label your axes and include units.
The independent variable goes on the x-axis.
The dependent variable goes on the y-axis.
Plot your points using a small x.
Look for the pattern:
If a curve: Join the points with a smooth freehand curve.
If a straight line: draw a line of best fit.
Lesson 4: The effect of particle size on reaction rate
Learning Outcomes:
To investigate how changing the size of marble chips alters the rate of reaction with hydrochloric acid using given experimental results

Success Criteria:
I can explain the effect of different particle sizes on reaction rate in terms of the collision theory
In this experiment we will look at the speed of the reaction when we change the particle size of the reactants in a chemical reaction.

A: Whole Tablet
1.Fill a clear beaker with 100cm3 of room temperature water.
2.Drop 1/2 an Alka-Seltzer tablet into the water. Measure and record the time to react.


B. Powdered Tablet
1.Place 1/2 Alka-Seltzer tablet into mortar and grind to a fine powder.
2.Transfer powder into a clear beaker (Note: It's important to have the powder in the cup before adding water.)
3.Add 100cm3of water to the beaker. Measure and record the time to react.
Although it is sometimes easy to determine which of two experiments reacted faster just by observation it is more accurate to measure the loss of reactants or the formation of products at different time intervals. This can be shown in the experiment below.
Using the set of results in the following table plot line graphs of 'mass of CO2(g) produced' versus 'time' for both the powdered calcium carbonate and the calcium carbonate lumps, using graph paper
Smaller reactant particles provide a greater surface area which increases the chances for particle collisions so the reaction rate increases.
As particle size decreases, what happens to the reaction time? What happens to the reaction rate?

Why do you think this was?
Try to draw a diagram to show what you mean.
Lesson 5: The effect of concentration on reaction rate
Learning Outcome:
To practically investigate how concentration affects reaction rate.

Success Criteria:
I can explain how changes in concentration affect reaction rate in terms of collision theory.

I can carry out an experiment safely, draw conclusions and evaluate the process.
In this experiment we will look at the speed of the reaction when we change the concentration of the reactants





Ensure that your apparatus is clean before use and that you clean, dry and put away all apparatus after use and then clean your work area. After this, wash your hands and THEN remove your goggles.


In this experiment we will react a substance called sodium persulphate (reactant A) with a substance called potassium iodide (reactant B).

We also need to add some starch as an indicator.

A colour change will show the end-point of the reaction.
1. Using the syringes provided measure out
10cm3 of Reactant A
and 1 cm3 of the starch solution into a clean dry beaker place upon a piece of white paper with an X marked upon it.

2. Fill another 10cm 3 syringe with reactant B. Quickly add this to Reactant A in the beaker
START YOUR TIMER
EXACTLY
WHEN B IS ADDED TO A. Record the time when the X can no longer be seen.

3.Repeat the experiment a further two times.

The second time: in step 1
use 8cm3 of Reactant A, 2 cm3 water
and 1 cm3 of the starch solution

The third time: in step 1
use 6cm3 of Reactant A, 4 cm3 water
and 1 cm3 of the starch solution
RECORD:

1. Create a suitable table to record your results

2. Write down your conclusions (these must refer to reaction rate)

3. Evaluate your experiment and your results
Increasing the concentration means that there is more chance that the particles will collide. The frequency of the collisions will be greater as we increase the concentration, and the reaction rate will increase.
Increasing the concentration increases the reaction rate.

Decreasing the concentration decreases the reaction rate.
Lesson 6: Investigation into the effect of changing temperature on reaction rate
Learning Outcome:

To carry out a practical experiment into the effect of temperature on reaction rate.


Success Criteria:

I can explain the effect of an increase in reactant temperature on reaction rate using the collision theory
Write up your experiment in the paper provided and then store it carefully in your PRACTICAL FOLDER ensure that your name and candidate number are on your investigation report
By heating chemicals, we raise the
energy
levels of the molecules involved in the reaction. Increasing the temperature means the molecules move faster so are more likely to collide successfully and the reaction rate increases.
Lesson 7: Using Catalysts
Learning Outcomes:
To define what a catalyst is and describe briefly how it speeds up a reaction.

Success Criteria:
I can safely carry out experiments involving catalysts.
I know examples of where catalysts are used in industry.

Catalysts are substances which speed up chemical reactions but are not used up in reactions.

They work by providing an alternative pathway for the reaction which requires less energy.

Biological catalysts are called enzymes.
Examples of catalysts:

Iron in the Haber process, which converts hydrogen and nitrogen into ammonia.

Platinum in the catalytic converters of cars.

Nickel in the manufacture of margarine.
1. Place 2 test tubes in a rack and pour in hydrogen peroxide to a depth of 2cm
2. To the first test tube, add half a spatula of manganese (IV) oxide.
3. To the second test tube, add a small piece of liver tissue.
4. Watch what happens!
Hydrogen Peroxide naturally decomposes (breaks down) into water and oxygen.

H2O2 --> H20 + O2

This can be seen by the presence of tiny bubbles in the hydrogen peroxide.
The enzyme catalase, which is present in liver, naturally speeds up the breakdown of hydrogen peroxide which is harmful to living things.

The chemical manganese dioxide also speeds up the breakdown of hydrogen peroxide.
Lesson 1: Revision of Atomic Structure and Nuclide Notation
Learning Outcomes

To revise theory from S3 on atomic structure and nuclide notation.

Success Criteria

I can describe the features of all the subatomic particles.
I can write nuclide notation for a range of different atoms.
I can define element, mass number and atomic number.
The structure of atoms.

Atoms are the smallest particles into which
matter can easily be broken down.
Atoms are made up of subatomic particles called protons, electrons and neutrons.
The name atom comes from the greek word atomos meaning ‘to cut’ because it was thought to be uncuttable / could not be anything smaller

http://www.keithcom.com/atoms/scale.php

Use your knowledge of subatomic particles to complete the table below.


The Atomic Number of an element is equal to the number of protons in the nucleus.

This will also equal the number of electrons in a neutral atom.

The Mass Number of an atom is equal to the number of protons plus the number of neutron in the nucleus.

Summary of Numbers

Atomic number = P = E
Mass number = P + N
N = Mass number - Atomic number
N = Mass number – P


Ask your neighbour:

What is an atom?

What is inside an atom?

What is an element?

Nuclide Notation Questions

Write nuclide notation for
1) an oxygen atom containing 8 neutrons
2) a fluorine atom containing 10 neutrons
3) an aluminium atom containing 14 neutrons
4) a sodium atom containing 12 neutrons
5) a hydrogen atom containing 0 neutrons
6) a silver atom containing 60 neutrons
7) a carbon atom containing 6 neutrons
8) a carbon atom containing 8 neutrons
ANSWER
Lesson 2: Isotopes and Relative Atomic Mass (RAM)
Learning Outcomes

To discuss atoms of the same element which have different numbers of neutrons

Success Criteria

I can define 'isotope' and 'relative atomic mass'
I can explain why RAM is rarely a whole number
Each of the different elements all have a unique atomic number which is equal to the number of protons present in the nucleus.
Not all atoms of the same element have the same mass. They have the same number of protons but different numbers of neutrons.

Atoms with the same number of protons but different numbers of neutrons are called ISOTOPES.
There are two types of chlorine atom.
They have the same numbers of protons and electrons.

Chlorine – 37 has two more neutrons than Chlorine – 35
This means that Chlorine -37 is heavier.

Atoms with the same atomic number but different mass numbers are called isotopes.

R.A.M
Most elements are made up of a mixture of isotopes.

The relative atomic mass of an element is the average mass of all the isotopes.

For this reason, the relative atomic mass is rarely a whole number.

Lesson 3 : Covalent Substances - Structures and Properties
Learning Outcomes
To understand covalent bonding and describe how it arises

Success Criteria
I can define covalent bonding
I can show covalent bonding using diagrams
I can compare and contrast covalent networks and covalent molecules in terms of structure and properties

Non metal elements are held together by covalent bonds.
A covalent bond is a pair of shared electrons.
If there are two pairs of shared electrons, this forms a double bond.
Three pairs gives a triple bond.
The nucleus of an atom is positive.
The atoms are held in place by the mutual attraction of the positive nuclei for the shared negative electrons.
IT'S ALL ABOUT SHARING!
A molecule consists of two or more atoms joined by covalent bonds.
The atoms could be the same type (an element) or different (a compound).
Identify the two elements which would form a molecule with the same shape as methane.
Covalent Molecules
Covalent molecules have defined shapes.










They are low melting point solids, liquids and gases.












They are generally insulators of electricity.












Many do not dissolve in water.







Examples include :
Methane
Ammonia
Carbon Dioxide
Water
Covalent networks are giant structures










They are very high melting point solids.












They are generally insulators of electricity.












They are insoluble in water.







Examples include :
Silicon Dioxide
Carbon in the form of diamond.

Covalent Networks
What about Graphite?
Graphite exists as a covalent network but only 3 of the 4 valence electrons are bonded. They 4th is delocalised and can carry charge. This explains why graphite can conduct electricity.
compare & contrast
HOMEWORK FOR TUESDAY


Give definitions for the following terms:
1. element
2. atom
3. isotope
4. compound
5. molecule
6. relative atomic mass
7. ion
8. proton
9. mass number
10. covalent bond.

Lesson 5 : Ionic Bonding
Learning Outcomes
To discuss how metal and non metal atoms combine.


Success Criteria
I can give a definition for 'ion'
I can describe ionic bonding.
I can describe the structure of ionic substances and give examples
When metals and non-metals react they do so using ionic bonding.


Metals form ions by losing electron(s).

Non-metals form ions by gaining electron(s).

Atoms form ions to achieve a stable (full) outer electron shell.
Ions are charged particles formed by the gain or loss of electrons.

The charge on an ion reflects the number of electrons gained or lost.

E.G. Li indicates that the lithium atom has lost one electron to become a 'one positive' lithium ion.
+
Ionic compounds exist as crystal lattices.

The lattice is held together by the attraction of the positive ions for the negative ions and the negative ions for the positive ions.
Ionic compounds are high melting point solids.

They do not conduct in the solid state but conduct well when molten or when dissolved as the ions are free to move.

Most ionic compounds are soluble in water.

Examples of ionic compounds include Sodium chloride, magnesium oxide, calcium chloride.
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