Scientific Processes Summarized Notes #Two

Learning Objectives

- explain and use the relationship between length, surface area and volume and their units on metric scales
- identify the correct Sl unit and derive units (see annexe E)
- explain and use multiple prefixes (kilo) and submultiple prefixes (deci, centi, milli, micro) of units
- use standard notation
- use acceptable methods of stating units, e.g. metres per second or m per s written as m/s or m s-¹
- identity sources of error and suggest possible improvements in procedures
- handle and process experimental observations and data, including dealing with anomalous or inconsistent results
- evaluate presented results or experimental data by applying scientific knowledge and interpret and draw appropriate conclusions from practical observations and data in relation to the hypotheses
- analyse anomalous or inconsistent results, discuss trends in results, identify sources of error and their of error (random and systematic errors)
- suggest possible preventative measures of errors
- plan an experiment or investigation, including making reasoned predictions of expected results and suggesting suitable apparatus and techniques
- name appropriate apparatus for the measurement of time, temperature, mass and volume, including burettes, pipettes and measuring cylinders
- recall of familiar, and unfamiliar, techniques to record observations and make deductions from them
- describe or comment on experimental arrangements and techniques
- recall of simple chemical tests, e.g. for food substances and the use of hydrogen carbonate indicator, litmus and universal indicator paper
- draw an appropriate conclusion, and justify it in line with the data, using an appropriate explanation
- recognise, observe, record and measure images of familiar, and unfamiliar, biological specimens make a clear line drawing from an image of a specimen, calculating the magnification and adding labels as required
- record readings from diagrams of apparatus, Including reading a scale with accuracy and precision and taking repeated measurements, where appropriate, to obtain an average value
- describe, explain or comment on experimental arrangements and techniques.

Basic units and derived units
These terms will be used by examiners during the setting of question papers. You should be made aware ot the terminology during teaching, learning and practical work.
Numbers
The best way to count numbers of objects or organisms is as follows. Small objects, such as flower parts or different coloured seeds, should be placed on a dark-coloured background. Use black paper or black cloth, because the dark background helps to show up the light coloured object. Count in fives, making five barred gates, as shown in below.
Thus, four gates equal 20 in total, and so on. Each stroke represents one item and each gate is five items. Tally Counters with a push button are used to count large numbers of objects.

Length
Length is measured by means of a metre (m) rule (100 cm in length), which has every centimetre divided into ten millimetres (mm). When taking a reading, it is essential that the eye is vertically over the mark to be read and you are not looking from the side, which would cause a reading error. See figure below. Callipers are used to measure the thickness of objects. The open calliper is then measured against a metre rule.

 Area
Area is measured in square metres (m²), square centimetres (cm²) or square millimetres (mm²). Most biological specimens have an irregular form, and their surtace area is difficult to measure exactly.
 The area-by-weighing method
The surface area of a leaf is found by tracing around the outline on thick card and then cutting out the outline, which is carefully weighed as a grams. A square of the same card is measured and its area is calculated by multiplying the square's length by its width. The square of card is weighed carefully (*b* grams).
- The leaf surface area will be found as follows:
● The square card weighs b grams and has an area x cm²
● The leaf outline weighs a grams and its surface area will be (a grams x square area x cm²) ÷  *b* grams,  square card weight = y cm² or area of one leaf surface. Total leaf surface area =y cm² x 2.
 The squared-graph-paper method
For the squared-graph-paper method, graph paper is made up of one millimetre (1 mm²) and larger, one centimetre (1 cm²) squares (1 cm²). A leaf can be placed on the graph paper and its outline drawn on the paper. The number of large (1 cm²) squares within a leaf tracing is counted, then every small (1 mm²) Square that does not form part of a large cm square is counted using the gate method.
- The leaf area will be calculated as follows:
● Total number of large (1 cm²) squares = 32 cm²
● Total number of small (1 mm²) squares outside of large squares =725 mm²
● Total area of one leaf surface
= 32 cm² + 725/100
= 32 + 7.25
= 39.25 cm²
● Two leaf surfaces
= 39.25 × 2
 Volume
Volume is mainly measured by means of a graduated measuring cylinder or graduated cylinders. They are available as: 10 cm³ capacity in 0.2 cm³ graduations, 50 cm³ capacity in 1 cm³ graduations, and up to 100 cm³ capacity in 19 cm³ graduations. Reading the liquid level is an important technique in which the eye must be level with the lower Iliquid of the meniscus, as shown in Figure below, otherwise reading errors will occur. Non-living biological specimens can be lowered into a half-filled measuring cylinder of water until completely submerged. The increase in water level is noted as *b* cm³ . The volume of the object will then be obtained by subtracting the reading for the half-filled cylinder *a* cm³ from *b* cm³.

 Mass or weight
Mass or weight can be determined by spring balances with a capacity of 100 g graduated in 1 g divisions, the specimen being supported on a small pan attached to the balance hook. Larger-capacity spring balances weighing up to 1000 g (1 kg) are available. A simple lever balance, with a range up to 1000 g or 250 g in 1 divisions, will weigh objects directly with reasonable accuracy. Double pan balances require a box of weights, and they weigh to an accuracy of 10 mg or 0.01 g.
 Time
Time is recorded by means of a stopwatch or the learner's personal watch.
 Energy
Energy contained within a substance, for example, food is measured in joules (0), kilojoules (k), and megajoules (MJ). It depends on the body's mass (weight), as well as its temperature. Various methods are used to measure energy using a calorimeter apparatus.
Temperature
Temperature is a measure of how hot or cold an object or substance is with reference to some standard value. There are three temperature scales in use today: Fahrenheit, Celsius and Kelvin. The Fahrenheit temperature scale is a scale based on 32 for the freezing point of water and 212 for the boiling point of water, the interval between the two being divided into 180 parts.

 Burettes
A burette (also spelled buret) is laboratory apparatus used in quantitative chemical analysis or in analytical chemistry to measure the volume of a liquid or a gas. It is a long, graduated glass tube with a stopcock at its lovwer end and a tapered capillary tube at the stopcocks outlet.

 How to use a burette:
- Before you start using a burette, first rinse it with water.
- Then, rinse it with distilled water using a washing bottle.
- Then, rinse it twice with a standard solution.
- Rotate the burette in your hands, while holding it horizontally in order to wet all sides.
- Make sure you are eye level with the bottom of the meniscus; always read the bottom of the meniscus.
- Have your burette completely upright.
- Hold a white piece of paper behind the burette to improve the recognition of the bottom of the meniscus.
Pipettes
Pipettes are used for transporting small amounts of liquid.

How to use a pipette:
- Make sure you have enough samples, at least four for titration.
- Put a clean 100 ml conical flask next to the sample container. It must have been rinsed with distilled water, but it does not have to be dry.
- Re-set your pipe filler and then suck up your sample material to just above the calibration mark.
- Fine-adjust the level so that the bottom of the meniscus is level with the mark.
- Withdraw the pipette gently from the sample container, while keeping contact between the pipette tip and the beaker wall.
- Make sure you do not lose any solution from the pipette through hasty movement.
- You may tilt the pipette and allow an air bubble to get sucked in when you move the pipette to the conical flask. Make sure you do not lose any liquid.
- After inserting the pipette in the conical flask, deliver the measured amount by pressing the fast release lever of your pipette filler. Your pipette tip should be in contact with the flask wall.
- It is important to leave the tip in contact with the wall for 3 more seconds after the solution has been drained from the pipette. This allows for the exact delivery of the volume.
Measuring cylinders
A graduated cylinder, measuring cylinder or mixing cylinder is a common piece of laboratory equipment used to measure the volume of a liquid. It has a narrow cylindrical shape. When taking readings from the measuring cylinder, the bottom of the water meniscus must be read horizontally at eye level to avoid parallax error.

Units
We use the International System of Units (SI units). Units will be indicated in the singular and not in the plural, for example 28 kg. 

Errors and accuracy and uncertainty
Errors and mistakes may occur in experiments and investigations, just as in any other human activity. You cannot have complete confidence about the reliability of every individual observation you make. For example, an incorrect amount of reagent may accidentally be measured out and the mistake not noticed, a stopwatch may be misread, or a reading from an instrument may be inaccurately taken. You need to be confident that your results are accurate. The more replicate readings you can take, the more confidence you can have.
Anomalous data
The first thing you should do when analysing data is to look at the data set as a whole, and see if you can find patterns and outliers. Anomalous data points that are outside the general trend could point to something interesting, or could just be a mistake or random fluctuation. Always have a closer look at an outlier to determine the cause of the unexpected result.
 Experimental Techniques
 Planning an experiment or investigation
When you are choosing an investigation, you need to keep a record of your ideas. You also need to briefly say what your investigation is about. For example, you may want to show the action of the enzyme amylase in the digestive system. Every investigation has a number of important steps to follow. First, get together everything you need, including ordering equipment, materials and laboratory space and pencils, graph paper, calculator, laboratory coat, relevant textbooks, and so on. Now you are ready to start.
1. Title: Choose a working title, for example, 'The effect of amylase inside the digestive system.'
2. Aims: Write a clear aim or aims - this is what your investigation will determine.
• For example, 'to determine whether amylase can break down starch.
• Keep the investigation relatively simple. The in-depth nature will come from the quality, not the breadth of your investigation.
3. Variables (factors or external factors)
• ldentify the variables or factors that you are investigating.
•  Changes in these factors will determine the outcome of your investigation.
• ldentify the factor (or factors) that:
• you are going to vary-the independent variable(s)
• will be caused to change - the dependent variable(s).
As an example, in digestion the effect of temperature and pH of the reaction mixture are the independent variables, while yield of time taken is the dependent variable. Are there any other factors that might affect your reslts? Write down the other factors that might affect your results. Suggest now you mignt deal with them to ensure a 'fair test'.
These will need to be kept constant or controlled during the investigation; a 'fair test' means that only the independent variable can have an effect on the dependent variable. For example, if amylase is varied, temperature, pH and time must be kept the same for each starch concentration investigated. A good control is often to leave out the factor that you are testing, to see the effect (if any) of the other factors.
4. Experimental hypothesis: This is a prediction of the outcome, which is a testable statement. It usually takes a form that connects the independent and dependent variables.
5. Briefly outline how you are going to collect your data.
You will need to:
• alter the independent variable
• measure the changes in the dependent variable
• keep other factors constant or controlled
• repeat, preferably at least twice, to check the reliability of your method.
You will need to consider:
• how precise (number of significant figures) your • measurements need to be and how you will obtain this level of precision
• the range and number of measurements you need to make
• the equipment and materials you will need and if they are available.
6. Collate, analyse and display your results:
• You could use graphs or tables.
• You could use a spreadsheet like Microsoft Excel.
7. Carry out a risk assessment
• What are the hazards and how will you reduce risk to acceptable levels?
8. Carry out trials:
• Do this as soon as you can. This will test for unforeseen problems and help you to plan. Trials check that the method works; they are not to obtain a full set of results at this stage. They will help you to decide the range and number of your results.
9. Do the main investigation:
• Collect the data that you need, including checking its reliability by repeating. It is good practice to design a table for recording your results and doing preliminary calculations. This may take longer than you expect.
• Plan to graph data as you obtain it.
• Check that the data is satisfactory (that is, not too many anomalies).
10. Make notes to help evaluate your investigation:
• Make notes of anything in the procedure that affects your data. If possible, construct error bars on graphs and/or use statistical tests.
11. Analyse and present the data:
• Consider using Microsoft Excel to help speed things up and avoid errors.
• Change the method if results are unexpected or unsatistactory.
• Draft your report and match it against the marking criteria.
• Do this as early as you can, so you have time to address omissions.
• Write against the marking criteria and meet the deadline.
In the real world, sCientists often find that things do not work out as they expected. Iif t happens to you, do not consider that the 'experiment did not work'. Rather, 'the results were not as expected'.
It is then your task to take your data, your record of what happened during the investigation and evaluate what you did. Your results are genuine results obtained in the conditions that you provided at the time. If your results did not contorm to accepted scientific theories, there will be a reason for this. You should look hard at your method and try to explain why you got this particular data arnd suggest modifications to overcome the problems. If you have planned well, such problems will appear in trials and you will have time to use your modifications.

 Simple chemical tests
There are a number of simple chemical tests that can be carried out on biological solutions. We will look at justa few of them.
1. Clear limewater turns milky when you pass carbon dioxide through it because a reaction that produces a white precipitate takes place.

2. Hydrogen carbonate indicator is a mixture of dilute sodium hydrogenate solution with the dyes cresol red and thymol blue. It is a pH indicator; an increase in atmospheric carbon dioxide makes it more acidic and it changes from orange to yellow. A decrease in atmospheric air makes it less acid and causes the colour to change to red or purple.

3. Litmus paper is used to test whether a solution is acidic or alkaline in nature. Litmus paper is very cheap to use as an indicator to find acidity and alkalinity. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the colour change oCcurring over the pH range 4.5-8.3 at 25 °C (77 °F). Neutral litmus paper is purple.

4. A universal indicator is a pH indicator composed of a solution of several compounds, which exhibits several smooth colour changes over a pH value range from 0 to 14, to indicate the acidity or alkalinity of solutions, where 7 indicates neutral.

5. Sodium carbonate is a water-soluble sodium salt of carbonic acid with alkalinising properties. When dissolved in water, sodium carbonate forms carbonic acid and sodium hydroxide. As a strong base, sodium hydroxide neutralises gastric acid, thereby acting as an antacid. It can be used to lower the pH, for example, when investigating the effect of temperature on the activity of lipase.
6. Bromothymol blue is a dye used as an indicator in determining pH. Bromothymol blue is a weak acid. It can be in acid or base form, depending on the pH of the solution. This reagent is yellow in acidic solutions, blue in basic solutions and green in neutral solutions. It can be used for testing the pH of sewage water or the quality of water.

7. DCPIP can be used to measure vitamin C concentration. You can measure the vitamin C content of a sample of fruit juice by measuring the volume of the sample required to decolourise a solution of DCPIP. Calibrate the results by comparison with a known Concentration of vitamin C.
8.Blue cobalt chloride: Cobalt (II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl₂. It is usually supplied as the hexahydrate CoCI₂. 6H₂O. The hexahydrate is deep purple in colour, whereas the anhydrous form is pale blue. Cobalt chloride paper is useful because the hydration/dehydration reaction occurs readily, making the paper an indicator for water. For example, to test whether a plant is losing water during transpiration, a blue cobalt chloride paper is placed on the leaf of the plant and turns pink in the presence of water.

9. Benedict's solution iIS used to test for simple sugars (for example, glucose) and double sugars, Such as sucrose, after hydrochloric acid is added. The solution is used to test for the presence of glucose in urine, a symptom of diabetes. One litre of Benedict's solution Contains 173 g sodium citrate, 100 g sodium carbonate, and 17.3 g cupric sulphate pentahydrate.

10. lodine solution: A chemical test for starch is to add iodine solution (brown solution) and see if it turns black in colour. It is possible to distinguish starch from other carbohydrates using this iodine solution test. For example, if iodine is added to a peeled potato, it will turn black.
11. Ethanol/alcohol and water: Lipids are insoluble in water and soluble in ethanol (an alcohol). After lipids have been dissolved in ethanol and then added to H₂0, they will form tiny dispersed droplets in the water, which is milky. This is called an emulsion.

 The End, posted by Miss Fang Xiu.