Chemistry Lab Manual Name: _____________

In this task, we will work in groups to learn about the measuring tools in the Chemistry Lab. This booklet will help you in future tasks and assessments. Record all your work in this booklet.

Submit for checking at the end of the session – it will be formatively assessed for Criterion E: Processing Data and Criterion F: Attitudes in Science.

Related Concepts: 01.2 Accuracy, Precision, Error, Uncertainty (Quia quiz: http://www.quia.com/quiz/3507626.html) 01.3 SigDigs and Notation (Quia quiz: http://www.quia.com/quiz/3504378.html)

Criterion E: Processing DataLevel Level descriptor

0 The student does not reach a standard described by any of the descriptors below.

1–2 The student collects some data and attempts to record it in a suitable format.The student organizes and presents data using simple numerical or visual forms.The student attempts to identify a trend, pattern or relationship in the data.The student attempts to draw a conclusion but this is not consistent with the interpretation of the data.

3–4 The student collects sufficient relevant data and records it in a suitable format.The student organizes, transforms and presents data in numerical and/or visual forms, with a few errors or omissions .The student states a trend, pattern or relationship shown in the data.The student draws a conclusion consistent with the interpretation of the data.

5–6 The student collects sufficient relevant data and records it in a suitable format.The student organizes, transforms and presents data in numerical and/or visual forms logically and correctly.The student describes a trend, pattern or relationship in the data and comments on the reliability of the data.The student draws a clear conclusion based on the correct interpretation of the data and explains it using scientific reasoning.

Criterion F: Attitudes in ScienceLevel Level descriptor

0 The student does not reach a standard described by any of the descriptors below.

1–2 The student requires some guidance to work safely and some assistance when using material and equipment.The student requires some guidance to work responsibly with regards to the living and non-living environment.When working as part of a group, the student needs frequent reminders to cooperate with others.

3–4 The student requires little guidance to work safely and little assistance when using material and equipment.The student works responsibly with regards to the living and non-living environment.When working as part of a group the student cooperates with others on most occasions.

5–6 The student requires no guidance to work safely and uses material and equipment competently.The student works responsibly with regards to the living and non-living environment.When working as part of a group, the student cooperates with others.

There’s no such word as ‘amount’!What do you really mean when you say “amount”?

Matter is anything that has mass and volume (takes up space): We measure mass in kilograms (kg), or grams (g). We measure volume in litres (l) or millilitres (ml) (sometimes cm3).

But we also describe other quantities: Time in seconds (s) Length or distance in metres (m) Energy in joules (J) or kilojoules (kJ) Heat/temperature in degrees Celcius (oC) (the SI* unit is Kelvin, K) Amount of a substance in moles (mol) Concentration of a solution in moles per litre (M) Acidity or alkalinity in pH (0 is a strong acid, 7 is neutral, 14 a strong base) Electrical conductivity in Siemens (S)

*Standard International (SI) units are based on the metric system – numbers that divide easily into tens and hundreds. Most countries in the world use these units and it makes calculations more straightforward.

In this activity, we’ll learn how to measure some of these physical quantities using the appropriate tools in the lab. Complete this lab manual as you go along – you will use it as a tool throughout the course.

Safety FirstWe must be safe in the lab at all times. Check that you can find these:

Goggles Fire blanket Fire extinguisher Phone

Safe Bunsen ‘driving license’ How do you turn on the Bunsen?

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What is the ‘safety flame’?……………………………………………………………………………………………………………………………………………………………………………………………………

What is the ‘roaring flame’ and which part is the hottest?……………………………………………………………………………………………………………………………………………………………………………………………………

NEVER point a hot container towards yourself or others. ALWAYS be careful in the Chemistry Lab!

What should you do if there is an accident in the lab?

Do not try to clean up broken glass – MrT will do it.

Visual guide to Chemistry Lab equipmentAs you work through the tasks, draw some simple diagrams of the lab equipment to help you remember the names.

Beaker Conical flask Test tube

Tripod & Gauze mat Test tube tongs Wash bottle

Pasteur (dropping) pipette Filter funnel Spatula

Units and Uncertainty (Quia quiz: http://www.quia.com/quiz/3507626.html)

All measurements have uncertainties – a range of values in which the true measurement could lie. More precise measuring tools have a smaller degree of uncertainty.

Significant Digits (or Significant Figures ) Tutorial: http://is.gd/sigfigsWe use significant digits to communicate how precise a measurement is – how certain we are in our measurement. In the example above, there are 4 significant digits. Significant digits are:

All non-zero digits (and all the zeroes in-between non-zeroes!) Any digits after a decimal point

But they are NOT: Leading zeroes, e.g. 0.000345 has only 3 sigdigs: 345 Trailing zeroes with no decimal, e.g. 10,000 has only 1 sigdig

How many significant digits in these numbers? 123.45 _________ sig digits 123000 _________ sig digits 1.008 _________ sig digits 01.67 _________ sig digits 1000 _________ sig digits 1000.0 _________ sig digits

Write these numbers to 3 sigdigs:

12420 = _______________

0.03209 = _______________

4050.0 = _______________

0.0101010 = ______________

Calculating Significant Digits We can only report values to the minimum degree of certainty so:

When adding or subtracting, use the number of decimal places of the weakest value. When multiplying or dividing, use the number of sigdigs of the weakest value.

1. 2.01 - 1.0 =

2. 123 + 456.789 =

3. 1.2 x 3.45 =

4. 34.678 /3.33 =

Measuring VolumeWe use graduated cylinders to measure volumes of a liquid. We do not use beakers or conical flasks – the marks on those are estimates only.

We read the volume at the bottom of the meniscus – label it on the diagram.

Observe these different-sized measuring cylinders. Complete the table. Size Markings every… Recorded volume (ml) Uncertainty (± )

5ml

10ml

50ml

100ml

Which of the cylinders has:1. The most precise gradations (markings)? _______2. The biggest uncertainty? _______

Add up the total volume of water in the four cylinders. Present your working and give the answer to the most appropriate significant digits. Explain your answer.

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Measuring MassWe use digital balances to measure the mass of a substance.

Never get the balance wet or dirty. Check the range of the balance – do not press on it or add a

mass that is heavier than the maximum. You will break it. Use a measuring tray or paper on top of the stage. “Zero” it if you need to. Do not stack balances or drop them.

Choose one known mass and measure it using three different balances. Complete the table. Balance Range (g) Recorded mass (g) Uncertainty (± ) What is this balance good for?

A

B

C

Accuracy, Precision & Errors (Quia quiz: http://www.quia.com/quiz/3507626.html)

There is always an element of error in our measurements. The accuracy of a measurement is how close it lies to the true value (“correct answer”). The precision of a measurement is how repeatable that measurement is.

Which of the dartboards shows: 1. High precision and high accuracy? Top - Middle - Bottom2. Low precision and low accuracy? Top - Middle - Bottom3. High precision but low accuracy? Top - Middle - Bottom

Systematic error is an error that is the same for all measurements and can be adjusted. For example, a digital balance that is poorly calibrated might measure 0.5g too much each time. Random error is not consistent between measurements and cannot be adjusted. For example, errors introduced by using different recording tools or people.

Which of the dartboards shows: 4. Random error? Top - Middle – Bottom 5. Systematic error? Top - Middle - Bottom

Dartboard diagrams from http :// preparatorychemistry.com /Bishop_Book_1_eBook.pdf

Measuring TemperatureCompare the glass thermometer with the temperature probe on the data logger. Remember: Thermometers and dataloggers are NOT for stirring!

Measure the temperature of the solution/ liquid – NOT the container Don’t touch the thermometer or probe against the glass Wait for the temperature to stabilize before taking the reading

Glass thermometer oC (± )

Temperature probe oC (± )

What is a Solution? A solution is a homogenous* mixture of a substance in a liquid.

The solvent is the liquid, e.g. water or alcohol, which dissolves the… Solute, which is the solid, e.g. salt or sugar.

Label the solvent and the solute in the diagram to the right.

*mixtures can be: Homogenous = evenly distributed, like solutions Heterogeneous = unevenly distributed, like soup or the oceans.

Beaker from: http://www.wpclipart.com/science/beaker/beaker.png.html

Which would you choose to get quick readings of a reaction that changes temperature?

Measuring pHWe use pH probes on the datalogger to measure the acidity or alkalinity of a solution. Strong acids have low pH, neutral pH is 7 and strong bases have high pH.

Measuring ConductivtyIn some solutions, ions form. These are positive ions (cations +) or negative ions (anions -). When these ions move, they carry electrical charge, which can be detected with the conductivity probe. A high concentration of ions will give a high conductivity.

pH scale from: http://www.ec.gc.ca/acidrain/kids.html

Take care of the probes: Make sure the electrolyte bottle is secure when not being used. Rinse gently with distilled water between every reading. Do not stir or shake the probe.

Taking readings: Submerge the probe and wait for the reading to stabilize Record the pH to an appropriate level of precision

Record the pH and conductivity of these three solutions: Solution A B C

pH (± )

conductivityμS (± )

Conductivity and pH probes need to be calibrated regularly. This avoids systematic error. What do we mean by systematic error?

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This symbol means ‘micro’ or one-thousandth. 1 μS = 0.001 S (Siemens is the unit of conductivity)

Scientific Notation (Quia quiz: http://www.quia.com/quiz/3504378.html)

Often we produce measurements or readings with a large number of zeroes. We use scientific notation to present these numbers in a clear, standard format.

Simple rules: There is always one digit before the decimal It always ends x 10x (“times ten to the power of x”) The value of x tells us how many places the decimal has been moved.

If you are making a large number small, x is positive. If you are making a small number (less than zero) larger, X is negative.

e.g. 1230000000000 can be written as 1.23 x 1012

The decimal has moved 12 places to the left.

e.g. 0.000000000123 can be written as 1.23 x 10-10

The decimal has moved 10 places to the right.

Expand the following notations:

1.0 X 103 = _____________________________

1.0 X 10-6 = _____________________________

4.56 X 105 = _____________________________

7.01 X 10-4 = _____________________________

Record the following in scientific notation to 3 significant digits:

• 12340000 = _____________________________

• 00012340 = _____________________________

• 10101010 = _____________________________

Compare the following measurements: 3.04 x 104 kJ 3.040 x 104 kJ 3.0400 x 104 kJ

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