Development Of Practical Skills

Question 1

What is a repeatable experiment?

Answer 1

If the same person, repeats the same experiment, with the same methods and equipment they will get the same results.

Question 2

What is a reproducible experiment?

Answer 2

If someone different, does the experiment using a slightly different method or piece of equipment, the results will be the same.

Question 3

In order to get good result what should you do?

Answer 3

Change only one variable and measure it’s effect on another variable.

All other variables should be controlled

Negative controls should be used

Repeat the experiment at least three times and calculate the mean results.

Question 4

What is a variable

Answer 4

A quantity that has the potential to change.

Question 5

What is an independent variable?

Answer 5

The variable that you change.

Question 6

What is the dependant variable?

Answer 6

The variable that you measure.

Question 7

Why must all the variables besides the independent and dependent be controlled?

Answer 7

To keep them constant so you know that only the independent variable is effecting the dependent.

Question 8

Why are negative controls used?

Answer 8

To check that only the independent control is effecting the dependent.

Question 9

What effect should a negative control have on the experiment.

Answer 9

None.

Question 10

What advantages do you get from repeating an experiment?

Answer 10

It reduces the effect of random error making your experiment more precise.

If your get similar results each time it shows your test is repeatable and is more likely to be reproducible.

Question 11

When planing a experiment do you have to decide?

Answer 11

What your going to measure and how often.

What apparatus, equipment and techniques are best for the experiment.

Question 12

When choosing apparatus for measuring what should you take into account?

Answer 12

Is it sensitive enough to measure the changes your looking for.

Question 13

What does the equipment and apparatus need to be?

Answer 13

Appropriate for the function it needs to perform.

Question 14

What technique should you use?

Answer 14

The one most appropriate for your experiment.

Question 15

How should you read the meniscus on the scale on a graduated pipette?

Answer 15

At eye level.

Question 16

When using a water bath what should you do?

Answer 16

Allow time for the water to heat to the correct temperature. The solutions you are using will also need time to get to the correct temperature.

Question 17

What should you do when using a data logger?

Answer 17

Decide what you are measuring and what type of logger you will need. Connect an external sensor to the logger if you need to.
Decide how often you want the data logger to take readings depending on the length of the process that you are measuring.

Question 18

How should you use techniques and apparatus to get precise results?

Answer 18

Use the techniques and apparatus in the correct way.

Make sure your measuring using appropriate units i.e. Minutes or seconds.

Make sure all techniques are performed carefully and any apparatus is set up correctly.

Question 19

In order to do a risk assessment what do you need to identify?

Answer 19

All the dangers in the experiment.

Who is at risk from these dangers

What can be done to reduce the risk.

Also all ethical issues should also be considered i.e. Using animals.

Question 20

How should you record your data?

Answer 20

In a table.

Question 21

How should you use a table?

Answer 21

Make sure you include enough rows and columns to record all the data. A column for processing data is also useful.
Make sure each colour has a heading
The units should be in the column heading, not the table itself.

Question 22

What should you do if some of your data doesn’t fit?

Answer 22

Investigate the result and if you can work out what happened you can ignore them when processing your results.

Question 23

What makes it easier to spot anomalous results?

Answer 23

Repeat your experiment.

Question 24

You process data to help interpret it how is this done?

Answer 24

Calculate the percentage change.

Use averages and range to summarise your data.

Use statistical tests to tell you whether you should accept or reject your hypothesis.

Watch out for significant figures.

Question 25

Why and how do you calculate percentage change?

Answer 25

It helps to quantify how much something has changed.

Percentage change = (final value - original value) / original value x 100

A positive value shows an increase a negative shows a decrease

Question 26

What must you do and what may you do with your results, after you’ve done repeats of an experiment, and how do you do this?

Answer 26

You must get a mean by adding all the numbers together and dividing by the total amount of numbers.

You may also need a median which is the middle result once they are in numerical order, or the mode, the number which appears the most within the results.

You may need the range to see how spread out the data is, do this by taking the largest number and subtract the smallest.

Question 27

Why may standard deviation be more useful than the range?

Answer 27

Because it tells you how values are spread about the mean rather than the total spread.
A small standard deviation means the results are similar and close to the mean so more precise

Question 28

What are statistical tests used for and what can they analyse?

Answer 28

They are used to analyse data mathematically.

They can be used to analyse quantitative (numerical) or qualitative (non-numerical) results.

Question 29

What can use the student t-test for? What does it test? What is done with the value obtained to tell us what?

Answer 29

It can be used when you have two sets of data you want to compare.
It tests whether there is a significant difference in the means of two data sets.
The value obtained is compared to the theoretical expected value, which helps decide how likely it is that the results or ‘differences in means’ were due to chance.

Question 30

What is spearman’s rank correlation coefficient used for and how is it given?

Answer 30

It tells you the degree to which two sets of data are related. It is given as a value between 1 and -1, 1 being strongly correlated, 0 not being correlated and -1 being strongly negatively correlated.

Question 31

What is the first significant figure in a number?

Answer 31

The first digit in a number that isn’t a 0.

Second , third, forth etc follow after even if they are a 0.

Question 32

If you’re doing calculations to a certain number of significant numbers what should you do and why?

Answer 32

Always give your answer to the lowest number of significant numbers that was used in the calculation.

This I because the fewer digits a measurement has, the less accurate it is. Your answer can only be as accurate as the least accurate measurement in calculation.

Question 33

When you have qualitative data (non-numerical) or discrete data (numerical data that can only take certain values in a range) what graphs or charts should you use?

Answer 33

Bar charts

Pie charts

Question 34

When you have continuous data (data that can take any value in a range) what graph or chart should you use?

Answer 34

Histograms

Line graphs

Question 35

When you want to plot one variable against the other what graph or chart should you use?

Answer 35

Scatter graph

Question 36

When ever you use a graph you should make sure you

Answer 36

Use the y axis (vertical) for the dependant variable.
Use the x axis (horizontal) for the independent variable.
Always label the axes, include the quality units, and choose a sensible scale.
The graph should cover at least half of the graph paper.
A line or curve of best fit should be drawn through or as close as possible to any points ignoring any anomalous results.

Question 37

What is the rate?

Answer 37

A measure of how much something is changing over time.

Question 38

When mat calculating a rate be useful?

Answer 38

When analysing your data.

Question 39

For a linear graph how can you calculate the rate?

Answer 39

By finding the gradient of the line.

Gradient = change in y / change in x

Question 40

How can the equation for a straight line be written?

Explain each component.

Answer 40

Y = mx + c

Y is the value of the y axis
m is the gradient
X is the value of the x axis
C is the y-intercept (the value of y when the line crosses the y-axis)

Question 41

How do you find a rate for a curved graph?

Answer 41

Draw a tangent

1) position ruler at the point where you want to know the rate.
2) angle the ruler so there is equal space between the ruler and the curve on either side of the point.
3) draw the line right across the graph to make the tangent.
4) calculate the gradient of the tangent to find the rate. (Y/x=m)

Question 42

How can a conclusion be valid?

Answer 42

If it answers the question that was originally asked.

Question 43

How can you draw a conclusion?

Answer 43

By looking at the correlation between two variables.

Positive - As one variable increases so does the other.

Negative - as one variable increases the other decreases.

No correlation - when there is no relationship between the variables.

Question 44

What do you have to be wary of if drawing a conclusion by looking at the correlation between two variables.

Answer 44

The correlation could be due to chance or a third variable having an effect.

Question 45

If there is a relationship between two variables and a change in one variable does cause a change in the other what is this called?

Answer 45

Causal relationship.

Question 46

How can it be concluded that a correlation is a causal relationship?

Answer 46

If every other variable that could possibly affect the result is controlled.

Question 47

When you make your conclusion how must you do it?

Answer 47

It must be very specific, without making broad generalisations and you can only conclude from what the results show.

Question 48

Why will the results you get not be perfect?

Answer 48

There is always a degree of uncertainty in measurements due to the sensitivity of the apparatus being used.

Question 49

what is the uncertainty value for something weighing 0.01g?

What does this mean?

Answer 49

+ 0.005g
- (minus right under plus)

It can be 0.005g smaller or larger than the result you have.

Question 50

What is the range in which the true value lies called?

Answer 50

The margin of error.

Question 51

How can you calculate the percentage error?

Answer 51

Percentage error= (uncertainty/reading) x 100

Question 52

How can you minimise errors in your measurements?

Answer 52

Buy the most sensitive equipment you can.

Measure a greater amount of something.

Question 53

What do you need to assess about your experiment and data for your evaluation?

Answer 53

Repeatability-
did you take enough readings? Would you do more repeats if you were to do it again? Would you get similar results if you did it again?

Reproducibility-
Have you compared your results with other people’s results? Were your results similar? Could other scientists gain data showing the same relationships that are shown in your data?

Validity-
Does your data answer the question you set out to investigate?

Question 54

What should you analyse about your method for your evaluation?

Answer 54

Is there anything you could have done to make your results more accurate and precise.
Were there any limitations in your method?
Should you have taken measurements more frequently?
Were there any sources of error?
Could you have used more sensitive apparatus or equipment?

Question 55

Once you’ve evaluated your experiment what can you do?

Answer 55

Decide how much confidence you have in your conclusion.

Question 56

A good experiment gives results that are

Answer 56

Precise- results don’t vary much and when they do it is by random error.

Repeatable and reproducible

Valid- results answer the original question.

Accurate- accurate results are really close to the true answer