1. Chemistry Science 3rdESO
Units and Measurement
Chemistry
Science 3rdESO

2. A) SI Units, Scientific Notation, Measurement, Accuracy, Precision, Error

3. Math and Units Math- the language of Science
SI Units – International System
MKS
Meter m
Mass kg
Time s
National Bureau of Standards
Prefixes

4. SI Unit Prefixes Name Symbol giga- G 109 mega- M 106 kilo- k 103 deci-
10-1
centi- c
10-2
milli- m
10-3
micro- μ
10-6
nano- n
10-9
pico- p
10-12

5. Length

6. Click the image to watch a short video about the meter.km m cm mm
Metric Units
The basic unit of length in the metric system in the meter and is represented by a lowercase m.
Standard: The distance traveled by light in absolute vacuum in 1⁄ of a second.
Metric Units
1 Kilometer (km) = 1000 meters
1 Meter = 100 Centimeters (cm)
1 Meter = 1000 Millimeters (mm)
Click the image to watch a short video about the meter.
Which is larger?
A. 1 meter or 105 centimeters
B. 4 kilometers or 4400 meters
C. 12 centimeters or 102 millimeters
D millimeters or 1 meter

7. Measuring Length How many millimeters are in 1 centimeter?
1 centimeter = 10 millimeters
How many millimeters are in 1 centimeter?
What is the length of the line in centimeters? _______cm
What is the length of the line in millimeters? _______mm
What is the length of the line to the nearest centimeter? ________cm
HINT: Round to the nearest centimeter – no decimals.
Ruler:

8. Measuring Instruments
Measuring Tapes:
Long distance (up to 1metre) are available in closed and open reel configurations.  The open reel is good for outside or dirty environments. Calibrations are in centimetres or in millimetres.
Straight Rules:
Straight rules available in a large variety of materials, scales and graduations. 
Lengths typically don't exceed 1m. It is used to measure in centimetres of length.
Calliper rule
A variation to the more traditional caliper is the inclusion of a vernier scale; this makes it possible to directly obtain a more precise measurement.
Vernier calipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and depending on the manufacturer, depth measurements by the use of a probe that is attached to the movable head and slides along the centre of the body.
The vernier scales may include both metric and inch measurements on the upper and lower part of the scale.
Vernier calipers commonly used in industry provide a precision to a hundredth of a millimetre (10 micrometres), or one thousandth of an inch.

9. Mass

10. Click the image to watch a short video about mass.kg g cg mg
Metric Units
Kilogram Prototype
Mass refers to the amount of matter in an object.
The base unit of mass in the metric system in the kilogram and is represented by kg.
Standard: 1 kilogram is equal to the mass of the International Prototype Kilogram (IPK), a platinum-iridium cylinder kept by the BIPM at Sèvres, France.
Metric Units
1 Kilogram (kg) = 1000 Grams (g)
1 Gram (g) = 1000 Milligrams (mg)
Click the image to watch a short video about mass.
Which is larger?
A. 1 kilogram or 1500 grams
B milligrams or 1 gram
C. 12 milligrams or 12 kilograms
D. 4 kilograms or 4500 grams

11. _______ + ______ + _______ = ________ g
Measuring Mass
We will be using triple-beam balances to find the mass of various objects.
The objects are placed on the scale and then you move the weights on the beams until you get the lines on the right-side of the scale to match up.
Once you have balanced the scale, you add up the amounts on each beam to find the total mass.
What would be the mass of the object measured in the picture?
_______ + ______ + _______ = ________ g

12. Measuring Mass – Triple-Beam Balance
1st – Place the film canister on the scale.
2nd – Slide the large weight to the right until the arm drops below the line. Move the rider back one groove. Make sure it “locks” into place.
3rd – Repeat this process with the top weight. When the arm moves below the line, back it up one groove.
4th – Slide the small weight on the front beam until the lines match up.
5th – Add the amounts on each beam to find the total mass to the nearest tenth of a gram.
Click here to try an online activity.

13. Volume

14. Click the image to watch a short video about volume.
Metric Units kL cL mL L
Volume is the amount of space an object takes up.
The base unit of volume in the metric system in the liter and is represented by L or l.
Standard: 1 liter is equal to one cubic decimeter
Metric Units
1 liter (L) = 1000 milliliters (mL)
1 milliliter (mL) = 1 cm3 (or cc) = 1 gram*
Which is larger?
Click the image to watch a short video about volume.
A. 1 liter or 1500 milliliters
B. 200 milliliters or 1.2 liters
C. 12 cm3 or 1.2 milliliters*

15. Measuring Instruments
Differentiate volume-capacity
Volume and capacity are sometimes distinguished, with capacity being used for how much a container can hold (with contents measured commonly in litres or its derived units), and volume being how much space an object displaces (commonly measured in cubic metres or its derived units).

16. Measuring Volume
We will be using graduated cylinders to find the volume of liquids and other objects.
Read the measurement based on the bottom of the meniscus or curve. When using a real cylinder, make sure you are eye-level with the level of the water.
What is the volume of water in the cylinder? _____ml
What causes the meniscus?
A concave meniscus occurs when the molecules of the liquid attract those of the container. The glass attracts the water on the sides.

17. Parallax Error
Parallax error
Parallax is a deceptive change of the position of an object which is observed while the position of the observer changes. Position of eye at all volumetric vessels must be at the same level as the meniscus. If not, the parallax will cause an error while reading the position of the meniscus of a liquid in a burette. It will be a positive mistake if the eye is lower, and negative if the eye is higher than the meniscus plane.
If you are measuring the volume of liquid in a measuring cylinder for example, make sure you positioned your eye to take readings at the bottom of menicus for water and top of menicus for mercury.

18. Measuring Liquid Volume
What is the volume of water in each cylinder?
Images created at A B C
Pay attention to the scales for each cylinder.

19. Measuring Solid Volume
10 cm
9 cm
8 cm
We can measure the volume of regular object using the formula length x width x height.
_____ X _____ X _____ = _____
We can measure the volume of irregular object using water displacement.
Amount of H2O with object = ______ About of H2O without object = ______ Difference = Volume = ______
Click here for an online activity about volume. Choose Lessons  Volume & Displacement

20. M x 10n Scientific Notation M is the coefficient 1<M<10
10 is the base
n is the exponent or power of 10

21. Other Examples:
5,45E+6
5,45 x 10^6

22. Numbers less than 1 will have a negative exponent.
A millionth of a second is:
0, sec 1x10-6
1,0E ,0x10^-6

23. Limits of Measurement
Accuracy and Precision

24. Accuracy - a measure of how close a measurement is to the true value of the quantity being measured.

25. Example: Accuracy
Who is more accurate when measuring a book that has a true length of 17,0cm?
Susan:
17,0cm; 16,0cm; 18,0cm; 15,0cm
Amy:
15,5cm; 15,0cm; 15,2cm; 15,3cm

26. Precision – a measure of how close a series of measurements are to one another. A measure of how exact a measurement is.

27. Example: Precision
Who is more precise when measuring the same 17,0cm book?
Susan:
17,0cm; 16,0cm; 18,0cm; 15,0cm
Amy:
15,5cm; 15,0cm; 15,2cm; 15,3cm

28. Example: Evaluate whether the following are precise, accurate or both.
Not Precise
Not Accurate
Precise
Accurate
Precise

29. Precision= Significant Figures
Accurancy
Absolute error
Relative error
Precision= Significant Figures

30. Absolute Error Error= experimental –accepted value
It is the amount of physical error in a measurement.
It uses the same units than the measurement.

31. Relative error (Percent Error)
% Error= |experimental –accepted| x100
accepted value
(value of thing measured)
Relative error gives an indication of how good a measurement is relative to the thing being measured.
If a have two students measuring two objects with a metre stick the comparative accurancy of these measurements can be determined by looking at their relative error.

32. Absolute- relative error
Students measured time in an experiment. These measurements are: 3,01 s; 3,11 s; 3,20 s; 3,15 s
True value? (Valor que se considera exacto)
Absolute and relative error for each measurement?
Measurement
Absolute Error
Relative Error
3,01 s
3,01 - 3,12 = - 0,11 s
-0,11 / 3,12 = - 0,036    (- 3,6%)
3,11 s
3,11 -3,12 = - 0,01 s
-0,01 / 3,12 = - 0,003    (- 0,3%)
3,20 s
3,20 -3,12 = + 0,08 s
+0,08 / 3,12 = + 0,026    (+ 2,6%)
3,15 s
3,15 - 3,12 = + 0,03 s
+0,03 / 3,12 = + 0,010    (+ 1,0%)

33. B) Significant Figures= Precision

34. Significant Figures= Precision
The significant figures in a measurement include all of the digits that are known, plus one last digit that is estimated.

35. Centimeters and Millimeters

36. Graduated Cylinder - Meniscus

38. B) International System of Units and Prefixes

39. Base SI Units
Quantity
Unit
Symbol
Length
meter m
Mass
kilogram kg
Temperature
kelvin K
Time
second s
Amount of Substance
mole
mol
Luminous Intensity
candela cd
Electric Current
ampere a

40. Derived SI Units (examples)
Quantity
unit
Symbol
Volume
cubic meter m3
Density
kilograms per cubic meter
kg/m3
Speed
meter per second
m/s
Newton
kg m/ s2 N
Energy
Joule (kg m2/s2) J
Pressure
Pascal (kg/(ms2) Pa

41. Units for Volume m3
cm3
dm3
L Liter mL
1 dm3 = 1L
1cm3= 1mL

42. Temperature A measure of how hot or how cold an object is.
SI Unit: the kelvin ( K )
Note: not a degree
Absolute Zero= 0 K

43. Temperature Scales

44. Celsius and Kelvin
K= oC + 273

45. Farenheit and Celsius
oF= (1,8 oC ) +32

46. Unit for Weight
1 Newton
1 N= kg m/s2

47. Units for Energy Joule J calorie 1 cal= 4,184 J
1 cal = quantity of heat needed to raise the temp of 1g of water by 1 oC.

48. Note:
1 Cal = 1kcal =1000cal

49. SI Unit Prefixes Name Symbol giga- G 109 mega- M 106 kilo- k 103 deci-
10-1
centi- c
10-2
milli- m
10-3
micro- μ
10-6
nano- n
10-9
pico- p
10-12

50. SI Unit Prefixes for Length
Name
Symbol
Analogy
gigameter Gm
109
megameter Mm
106
kilometer km
103
decimeter dm
10-1
centimeter cm
10-2
millimeter mm
10-3
micrometer μm
10-6
nanometer nm
10-9
picometer pm
10-12

51. C) Factor Label Method of Unit Conversion- Dimensional Analysis

52. Factor-Label Method Example: Convert 5km to m: NEW UNIT
5km x 1000m =5000m km
OLD UNIT

53. Convert 7000m to km
7000m x 1 km = 7 km
1000m

54. Convert 2,45cs to s
2,45cs x 1 s = 0,0245s
100cs

55. Convert 55,00 km/h to m/s 55,00 km x 1000 m x 1 h___ = 15,28m/s
h km s