Variables

• Chemistry
• Secondary Education
• Age 12,13

IGCSE Chemistry 0620

Variables in Chemistry

30 August 2023

Describe how you feel right now 

using an emoji.

😒🙁😐🙂😃

• remember the atomic numbers and symbols of elements correctly
• differentiate the three types of variables
• write a plan of a practical investigation project following the format given
• submit our group plan for marking and possible suggestions

I intend to:

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IGCSE Chemistry 0620

Variables in Chemistry

30 August 2023

• What did I learn last session?
• Does an investigation need all types of variables?

Review

30 August 2023, Wednesday

IGCSE Chemistry 0620

Variables in Chemistry

30 August 2023

Element Quiz 03

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T O  D O:

• Open your laptop.
• Go to https://play.blooket.com/play.
• Enter the code shown and type name.
• Play and learn.

WALT: Remember the atomic numbers and symbols of elements correctly

dashboard.blooket.com

Does an investigation need all types of variables?

Yes.

No.

Conducting an investigation

• A chemist causes a change and records the effect of that change.

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Scientific Method

• The process of thinking about scientific questions
• The scientific method is a cycle.
• By testing the hypothesis, we make new observations that require us to look for patterns, thereby formulating new laws that require new hypotheses that then need to be tested, etc.

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Scientific Method

1. making observations to accumulate information
2. deriving scientific laws by organising the information and looking for regularities or patterns
3. making a hypothesis to explain why the regularities or patterns exist
4. tesing the hypothesis by a suitable experiment and communicating the findings and probable explanations to others

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Observations

• Seeing is NOT the same as observing.
• Observation requires concentration, alertness, and all or most of our senses.
• Observations also include making measurements.
• Observations which are recorded are called scientific data.

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The senses a Chemist uses to make observations are:

• sight (safety: wear eye protection in the Lab)
• smell (safety: gently waft the smell to your nose using your hand)
• hearing (safety: keep a suitable distance if safe to do so)
• touching (safety: only touch if considered safe to do so)
• tasting (safety: NEVER taste anything you found or produced in the Lab!)

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Example of Observations: 

In a test tube, colourless dilute hydrochloric acid is added to a dark solid, which is iron(2+)sulfide (iron(II)sulfide).

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• sight : (a) bubbles appear in the solution originating at the surface of the iron(2+) sulfide (iron(II) sulfide) - (b) the amount of solid iron(2+) sulfide (iron(II) sulfide) diminishes over time
• smell : the odour of rotten eggs is detected
• hearing : a fizzing sound may be heard
• touching : the test tube becomes warm
• tasting : never taste anything you found or produced in the Lab!

IGCSE Chemistry 0620

Variables in Chemistry

30 August 2023

Experimental Design

An experiment is conducted to test a hypothesis.

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FEATURES OF A WELL-DESIGNED EXPERIMENT

• ⚛ A well-defined aim (goal or objective) = can be disproved by experiment.
• ⚛ Results that can be reproduced (precision).
• ⚛ Errors that can be analysed.

A. Defining the Aim of the Experiment

• The aim, goal or objective, of an experiment is to test the validity of a hypothesis.
  
• A hypothesis is a possible answer to a scientific question.
• Experiment is conducted = to decide whether the possible answer to the question is most likely to be "true" or not.
• A well-defined aim, goal or objective, will be one which can be tested experimentally and can be disproved.

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Example

• Scientific Question: What temperature does water boil at?
• Possible Answer (Hypothesis): Water boils at 100°C.

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Imagine this!

If you give a thousand city-dwellers worldwide with digital thermometers that read to the nearest 10°C, they would all report that water boils at 100°C.

But will you have proved that the hypothesis is correct?

Example

• Scientific Question: What temperature does water boil at?
• Possible Answer (Hypothesis): Water boils at 100°C

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If you performed the same experiment using digital thermometers that read to the nearest 0.1°C, you would find a huge range of temperatures reported for the boiling point of water.

Have you disproved the hypothesis?

Hypothesis

• An hypothesis is useful when it is a statement that can be disproved.
• Results of an experiment may support the hypothesis, but can rarely definitively prove the hypothesis to be true.
• Results of an experiment that do not support the hypothesis can be said to disprove the hypothesis.

30 August 2023, Wednesday

WALT: differentiate the three types of variables

B. Designing an Experiment so that Results are Reproducible

You are going to have to design an experiment so that:

•  you can control the all the possible variables
•  the results are reliable (can be reproduced).

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Typical Variables in Chemistry

• nature of a substance
• concentration
• volume
• mass
• temperature
• pressure

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• stirring rate
• particle size
• time
• electrical current
• voltage

WALT: differentiate the three types of variables

Sample applications in Chemistry

• A student wants to design an experiment to see if more salt can be dissolved in hot water than cold water.

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• What are some of the possible variables in this experiment?
• What are the quantities that could change in this experiment?

WALT: differentiate the three types of variables

Sample applications in Chemistry

A student wants to design an experiment to see if more salt can be dissolved in hot water than cold water.

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•  Nature of the salt (What salt is it? Is it sodium chloride, or potassium chloride, etc?)
•  Purity of the salt (if lots of impurities are present they might effect the results of the experiment)
•  Purity of the water (once again, impurities in the water might effect the results of the experiment)
•  Amount of the salt used (the amount of salt used may effect how long it takes to dissolve and how much dissolves)
•  Amount of water used (the amount of water used may effect how much salt can be dissolved)
•  Temperature (of the salt, of the water, of the salt water solution)
•  Pressure (atmospheric pressure, pressure in a closed vessel etc)
•  Rate at which the salt is added to the water
•  Rate at which the salt is stirred into the water
•  Size of salt particles (is the salt first ground to a fine powder, is it in cubes, etc ?)
•  Time (how long are you going to observe the process for?)

Independent variable

• the variable that the Chemist decides to change
• When the Chemist changes this variable, he/she will then observe the effect of this change on one of the other variables
• Variable X

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WALT: differentiate the three types of variables

Study the situations below.

1. A student wants to design an experiment to see if more salt can be dissolved in hot water than cold water.
2. A student wants to design an experiment to see if more sodium chloride can be dissolved in water than potassium chloride can be dissolved in water.
3.  A student wants to design an experiment to see if more salt can be dissolved in a large amount of water than in a small amount of water.

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WALT: differentiate the three types of variables

Dependent variable

• the quantity that responds to the change the Chemist has caused
• the variable that is observed to respond when the Chemist changes the independent variable
• Variable Y

30 August 2023, Wednesday

WALT: differentiate the three types of variables

Study the situations below.

1. A student wants to design an experiment to see if more salt can be dissolved in hot water than cold water.
2. A student wants to design an experiment to see if more sodium chloride can be dissolved in water than potassium chloride can be dissolved in water.
3.  A student wants to design an experiment to see if more salt can be dissolved in a large amount of water than in a small amount of water.

30 August 2023, Wednesday

WALT: differentiate the three types of variables

Constant variable

• All the other quantities in the experiment that could change but the Chemist keeps at constant values to ensure the experiment is a fair test.
• After the Chemist has decided which variable will be the independent variable, and which variable is the dependent variable in the experiment, all the other variables must be held constant. 

30 August 2023, Wednesday

WALT: differentiate the three types of variables

Study the situation below.

A student wants to design an experiment to see if more salt can be dissolved in hot water than in cold water.

30 August 2023, Wednesday

WALT: differentiate the three types of variables

• The constant variables, which must not change during the experiment, are all the other variables. What are the constant variables in the investigation above?

• Nature of the salt: only sodium chloride will be used for each experiment
• Purity of the salt: the sodium chloride will be taken from the same jar of reagent each time and a clean, dry, spatula will be used to transfer the sodium chloride to the water
• Purity of the water: collect distilled water in a clean, dry, bottle and use water only out of that bottle during the experiment
• Amount of water: Use 50.00 mL of water in each experiment
• Pressure: Conduct all the experiments in vessels open to the atmosphere so that the pressure is the same as atmospheric pressure in the laboratory (record this pressure)
• Stirring rate: If you don't stir the salt into the water to dissolve it, the stirring rate will always be 0, but if you do want to stir the salt into the water, you will need to use a mechanical stirrer and ensure the rate of stirring is always the same
• Size of the sodium chloride particles: You could use 1 cm3 cube of sodium chloride, or you could assume that all the particles that come out of the reagent jar are the same (you could place a spatula full of the sodium chloride under a binocular microscope and see if the particles are all about the same size).
• Time: must be long enough for the dissolving process to be completed for all the experiments

30 August 2023, Wednesday

WALT: differentiate the three types of variables

B. Designing an Experiment so that Results are Reproducible

Controlling Variables

1. Reduce the number of factors that can change during the experiment.
2. Make a list of all the variables that you can think of that could affect the results of the experiment before doing the investigation.
3. Identify your independent variable.
4. Identify your dependent variable.
5. Control ALL the other variables so that they do not change during the experiment.

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The Aim of the Investigation

• The aim of an experiment can often tell us which variable is the independent variable and which variable is the dependent variable.
• Any other variable must be a constant variable.

30 August 2023, Wednesday

WALT: differentiate the three types of variables

Example - Cause and Effect Investigation 

Aim: To determine the effect of variable x on variable y

Aim: To determine the effect of temperature on the mass of sodium chloride dissolving in water.

• Use the template given to plan for the investigative project.
• Collect ideas from all members of your team.
• Begin writing the required sections in the plan.
• Submit your work for correction and possible modifications.

Project Plan for Semester One

30 August 2023, Wednesday

WALT:  Write a plan of a practical investigation project following the format given

GROUP 1

• Khea MolVinnika
• Pring Solita
• Sea Noreak Puthesak
• Sovannary Patheany
• Hem Kimhouy

Project Groupings

30 August 2023, Wednesday

GROUP 2

• Yin Sereyratanak Rithya
• Chin Chanthonary
• Ung Sokharita
• Oeng Viya Vortey
• Meng Kimhorng

docs.google.com

Self-Assessment for Learning

30 August 2023, Wednesday

T O  D O:

• Identify two ideas you do not understand quite well in our sessions.
• Ask someone who can explain and write the explanations in your notebook.
• Verify your learning from a classmate by sharing it with the teacher.