Welcome to Science
Specific Learning Outcomes
By the end of this unit you should be able to
recall basic laboratory rules
know how to conduct yourself safely in the laboratory
be able to name, draw and give the use of basic lab equipment
be able to carry out a practical experiment, record data and process it
recall some of the ways we observe the natural world
have some understanding of how scientific ideas compare with unscientific ones
recall the steps involved in a scientific investigation
define the term 'variable' as it is used in science
identify the independent variable, the dependent variable and controlled variables in an investigation
design a simple investigation to compare things (fair test) or find a pattern
make use during an investigation of the structure: aim, hypothesis, experiment/trial, results, conclusion and evaluation
explain what the difference is between quantitative and qualitative observations
describe why it is important that observations are repeated
outline ways to improve the reliability of results in an investigation (range: repeats, averages, dealing with outliers)
be able to create a results table from data
choose a suitable graph type and accurately plot a scientific graph of date (own or supplied)
interpret a graph and find and describe a pattern (if one exists) in the data
distinguish between an observation, an inference and a generalisation
make a suitable conclusion from a set of experimental results
Laboratory Rules
Rules are needed in the laboratory to keep everyone safe and to make sure that equipment is not damaged.
Some of the rules we use at Sacred Heart are:
Safety Rules
Always wear safety glasses when working with glass, chemicals or heat.
Long hair must be tied up during practical work
No schoolbags in the laboratory - place them in the cubbyholes at the entrance
Do not touch anything in the room on the side benches, unless instructed to by the teacher
Do not sit on the benches or side benches
Ensure you know the location of the emergency stop for GAS, WATER & ELECTRICITY (usually behind the teachers desk)
Always push your chair in when not using it
Report any breakages immediately
Do not bring food or drink in to the laboratory
Ask for help if you do not understand
take note of the location of the following safety features in the lab: Emergency Exit, Emergency Eye Wash; Fire Extinguisher, first aid kit and fire blanket.
ensure you are aware of any out of bounds areas
Courtesy Rules
Be on time to science
Do not talk when the teacher talks
Remain in seats during the science lesson unless instructed by your teacher
Bring all equipment with you to your lesson
Laboratory Equipment
Below are pictures of some of the common pieces of equipment we will be using through the year.
The Bunsen Burner
Bunsen burners are a common piece of heating equipment in a laboratory. They were invented by Michael Faraday but improved by Robert Bunsen.
A Bunsen Burner (often shortened to 'burner' in the lab) uses gas and premixes it with air so it can burn with a clean, sootless flame. Most burners have the ability to reduce the air supply so that the burner burns with a yellow flame which is easy to see but not used for heating because it leaves soot marks on the equipment. The parts of the Bunsen Burner are shown in the diagram below:
Lighting and using a Bunsen Burner
ensure you have a heat proof mat on the bench
connect the burner to the gas tap
adjust the collar until the airhole is closed
light your match or lighter and hold at the top of the burner
turn on the gas
withdraw the match or lighter when the burner shows a flame and adjust the flame height with tap if needed
Note that if you reverse steps 4 and 5 you run the risk of getting a mass of gas lighting in your face, which could be dangerous. For this reason you should always light the match before turning the gas on.
The flame at this point should be a yellow safety flame. The burner should be on a safety flame when it is not actually being used to heat something; this is because the heating flame is hard to see and a student might not notice and receive a burn by reaching through it,
Note: matches must be extinguished and should be disposed of in the bin at the end of the lesson; it can be a good idea to wet them to ensure there is no possibility of starting a fire in the rubbish
if your teacher uses lighters, these should be sat at the back of the bench when not in use (they are not toys and should not be used except to light burners)
When you are ready to heat with the burner, adjust it to a quiet blue flame by opening the airhole. If you open it too far, the burner will start to make a soft 'roaring' noise. This is caused by the burner going out and relighting several times a second, and happens just before the flame goes out altogether. A softly roaring flame is a bit hotter than a quiet flame and can be used for heating, but can go out very easily.
The yellow colour of the safety flame is caused by glowing particles of soot. This is why the safety flame leaves soot over equipment if you use it to heat. The hot soit particles normally burn away leaving no smoke, but if they touch cold glass they can't burn and remain behind.
Drawing lab equipment
When we draw diagrams of lab gear, we draw 2D diagrams as illustrated below
In this way, we can draw a diagram of apparatus which is used together. Below is shown a photo then a 2D drawing of a beaker, sitting on a tripod with gauze on a safety mat:
The simplified 2D drawing has the gauze and the burner omitted. In the exam it is OK to draw the simplified version but the parts you have shown must be labelled.
Measuring cylinder
These are for accurately measuring out small volumes of liquid. They are available in several sizes. The size you use should be close to the volume you are measuring e.g. you would use a 10 mL cylinder to measure 8 mL, not a 100 mL one. This is because the smallest cylinder that measures a volume is the most accurate.
When you use the measuring cylinder the top of the water makes a downward curve, called the meniscus. The measurement is taken from the lowest point of the meniscus, with your eye level with the water as shown in the diagram on the left. Having your eye above or below the water level gives a type of wrong measurement called parallax error.
Measurements are in millilitres, written as mL
These are the same size as cubic centimetres (cc or cm3 ); however, mL are the more correct way of writing this in science. 1000 mL = 1 L (on litre or one cubic decimetre, dm3 )
Note the mL is written with a lowercase m to start with and an uppercase L following. It is important you get into the habit of writing the units exactly
In science we "weigh" things on a balance. These can be electronic or mechanical like the one above. The balance above is called a triple beam balance and can accurately determine the mass of an object between 0.2 and 490 grams to an accuracy of about plus or minus 0.1 gram.
How to use a Triple Beam Balance
In a triple beam balance the mass on the pan is used to balance the weights on the three arms.
Each of the back two arms balances exactly the stated mass when it is in the 'slot' where it clicks into place.
Example: if you put a rock (actual mass 183.2 grams) on the pan, with all weights at the left, on zero. The pointer should be in the middle with nothing on the pan (if it isn't, ask the teacher to adjust it).
The right hand side of the beams goes up to the top, because the pan has gone all the way to the bottom with the weight of the rock.
Now move the middle weight - the hundreds - along. At 100 g, nothing happen. At 200 g, the right hand side suddenly drops to the bottom. The weight on the beams is now bigger than the weight of the pan. The rock has a mass of more than 100 grams but less than 200 g. Now you carefully move the hundreds weight back so it sits in the 100 gram slot. Your rock has a mass of "one hundred and something" grams.
The next step is to move the back weight - the tens - across. Again, nothing happens until you get to 90. This means that the rock has a mass of more than 180 g but less than 190. Again, we move the weight back until is sits exactly in the slot, and the pointer goes back up to the top. The rock has a mass of "one hundred and eighty something grams".
Finally you move the "ones" weight across until the pointer goes exactly to the middle:
You read the beam balance by adding the three figures together.
Common mistakes: the commonest mistake is to not put the big masses - the tens and hundreds - exactly into the slots. If they are between the slots, the mass measurement won't be accurate.
A problem with using the beam balance can be that it doesn't zero exactly. This shouldn't matter, because the most accurate way to use the balance is to weigh by difference. This is where you weigh your unknown in a container e.g. in a beaker. You then take it out and re-weigh the beaker without the unknown mass in it. You calculate the unknown mass from:
[mass of (container with unknown)] - [mass of (container only)] = [mass of (unknown)
Since both the mass of the container with and without the unknown is wrong by exactly the same amount, they cancel out and the mass of the unknown is exactly right.
Investigations
What is it that makes something "science"?
In ancient Roman times, people thought that horse hairs that fell on the ground turned into earthworms when it rained. They based this on some observations:
horses were common, and shed hairs
earthworms are found on the ground after rain
some things swell up when they absorb water (e.g. dried fruit, which the Romans knew about)
horse hairs might look like worms if they swelled up and absorbed water when they were wet.
Of course, we know they were wrong. The prediction 'horse hairs turn into worms when wet' hadn't been tested. Neither did they think of some logical flaws: you can find worms in places there are no horses; horse coats don't turn into a wriggling mass of worms when they are wet.
The Romans were doing something all humans do: trying to understand and make predictions about the world around them. However, their method was not scientific.
Modern Science
Modern science has come about as a way to get the best answers about the way we understand the world, using observations, experiments and logic.
Scientific theories and ideas have the following features:
they are based on real (and repeated) observations, not just stories which haven't been checked out
they makes useful predictions (not predictions which could never be observed)
those predictions must be able to be tested in some way, through more observations or experiments
they are supported by lots of different pieces of evidence, not just one
they are consistent with what is already known and understood
the theories can be modified to fit with new observations if they occur
the theory doesn’t invent any more 'new ideas' than is absolutely necessary (e.g. it doesn’t have to keep on inventing new things to explain every little observation that happens)
Observations, inferences and generalisations
Scientific observations are made using your senses, or scientific instruments which can detect things your senses can't directly detect. An example of such an instrument is an ammeter, which can detect and measure electric current (you can sense large currents if they give you a shock, but that isn't a good idea). Some instruments enhance our senses; for example, a microscope lets you see things too small for the naked eye, or a telescope things too distant.
There are several types of observations. Two important categories are
Quantitative observations, which can be measured and given a number. For example, saying that 'the mouse had a mass of 18 grams' is quantitative.
Qualitative observations. for example 'this chemical smells of almonds'. These can be described but are (usually) difficult to measure.
Some observations, such as colour, can be measured with special instruments but require a lot of preparation and special conditions . To measure colour, for example, you need to standardise the colour of the light used to illuminate the object before you start.
Observations are things that can be directly observed with the senses or indirectly observed using scientific instruments.
For example, you could feel an earthquake – that is observation with your senses. You could also detect an earthquake that might be too small to feel using an instrument called a seismometer. This is still an observation.
You could infer how far away the earthquake is from the seismic observations, because different earthquake waves travel at different speeds so the time-lag between them depends on the distance. Inferences are made using things that are known to be highly likely, and are therefore likely to be true.
In this case, you can't directly observe the distance to the earthquake but you can still work it out. That is what makes it an inference.
If you are working something out from an observation using ideas that are less certain, it would be a hypothesis. For example, if the earthquake I detected was 150 km under Taupo, I could make a hypothesis that it had occurred on the subducting Pacific Plat
A generalisation in science is something you work out as the result of an investigation which is true in most cases. For example, it is generally true that the smaller an animal, the faster its heartbeat.
In the pictures above, the cat will have a faster heartbeat than the horse. However, the sloth does not have a faster heartbeat than an elephant. This is because sloths have unusually slow heartbeats in order to conserve energy and lower the demand on how much food they need to eat. Generalisations only have to be true most of the time.
Variables
In a scientific experiment you usually want to compare or change things to find out what will happen. For example, you might want to find out if a Berocca tablet dissolves faster in hot or cold water. The things that change in the experiment are called variables. There are three types of variable in the experiment:
the variable you (the experimenter) are changing to find out what is going to happen. This is called the independent variable. In this case, it would be the temperature of the water you were dissolving the tablet into.
the variable you observe or measure to see what is going to happen. This is called the dependent variable. In this case you would be observing how long it takes for the tablet to dissolve.
things you have to keep the same to make the comparison fair are called controlled variables. In this case, you would want to make sure that you used the same sized tablet (because a bigger one might take more time to dissolve) and the same amount of water (because using more or less water might change things). You would probably also want to use the same size and shape container to hold the water and so on.
Data
Data is the results of an experiment, usually numbers. Since you do the experiment multiple times to see if your answers are consistent, you can wind up with an lot of numbers to deal with .
For example, the following data is from an experiment melting an ice cube in a cup of water and measuring the temperature of the water: Several students have collected the data for different trials on different bits of paper (this is not a good idea because they could easily get lost):
The students have made a few other mistakes as well.
They don't have a consistent way of writing their results down,
they haven't labelled which numbers are the minutes and which is the temperature (mostly). We can guess, in this case - but there are other experiments where guessing would be far too hard.
One of the trials is labelled "Fifth trial" but there only appear to be four trials; this is confusing.
A better way would be to put the results into a single table prepared in advance. When you plan out your experiments, you should try to draw up such a table in advance if you can. Below is an example
Here we have assumed the results of the 'fifth trial' are really the 4th. There are still a few problems.
We need somehow to show the pattern of results. To do this, the best way is a graph. But which set of results should be graphed?
The answer is all of them, but not as separate points. Instead we average the results. To do this, we add them together and divide but the number of results.
Be careful you average the correct direction. We want to average all the 1 minute temperatures for four trials, not all the temperatures of Trial 1.
The average of the one minute temperatures is: (17 + 18 + 17 + 17) divided by four = 17.25 degrees.
However, you might not want to graph to this many decimal places and might round this to 17 degrees.
We have a problem with the 5 minute result for Trial 4: should we include it in the average? The answer is usually no, as it appears to be a mistake. However, it should be checked out in case it isn't a mistake. A result like this is called an outlier and outliers are not included when we average results for analysis.
Below is the table of averaged data. We call this the processed data.
Now we can graph the results. Some graph rules for Science:
Science graphs are mostly line graphs - one quantitative variable against another.
A bar graph or pie graph could be used if one of the data sets is not quantitative
Science graphs should have a title explaining what the graph is about
Usually, the independent variable goes along the horizontal axis, which is called the x-axis
Both axes must be labelled and with units
not all graphs have to start at zero, but graphs should usually not have a 'break' in them
the numbers on the axes have to go up in even amounts
the data points are best plotted as a small cross (x)
a smooth line or curve should show the trend of your results.
A graph of results for the experiment above might look something like what is shown below:
Some important points about this graph
the title says what the graph is about
the label on the axes says what quantity is being measured; it must have units if they exist
the points are plotted at the co-ordinates given in your summary table
a graph should start at zero if the number 0 is important for the graph; otherwise either axis can start and finish where convenient
the scale of the axes should be big enough to show a pattern and not leave too much unused space on either axis
numbers on the scale have to go up in regular jumps ( e.g. 3, 6, 9)
the trend line should be a straight line or a smooth curve that comes as close to the points as possible. Ideally, equal numbers of points should be on either side of the line. This is because it is assumed that the fact they aren't exactly on the line is caused by random errors in the experiment. Do NOT just join the points up..
Below is a copy of the graph above on which I have annotated the bullet points above:
When you write up a method to do an experiment, you have to say what the aim of the experiment is, what the variables are, how you are going to control the variables and how you are going to measure or observe your results.