10S1 Lesson 5/6 - Experimental design

• Chemistry
• Secondary Education

Lesson 1 - What is IGCSE Chemistry?

1. Name appropriate apparatus for the measurement of time, temperature, mass and volume, including (a) stopwatches,(b) thermometers, (c) balances, (d) burettes, (e) volumetric pipettes, (f) measuring cylinders, (g) gas syringes
2. Suggest advantages and disadvantages of experimental methods and apparatus

Daily Review

Lightning Question

• State at least one insight you learned from the video you watched.
• Write it in your notebook.

The clock's ticking!

Think about these questions

• How much can you depend on measurements?
• Are all measurements trustworthy?
• How can you tell if it is only an approximation? 

The exact number of apples

Calibrated into divisions of 1 cm.

Calibrated into divisions of 0.1 cm.

Calibrated into divisions of 1 cm.

Calibrated into divisions of 0.1 cm.

What length is measured by Ruler A: 4.2 cm or 4.3 cm?

What length is measured by Ruler B: 4.27 cm or 4.28 cm?

REALISATIONS

• All measurements involve uncertainty.
• All measurement's last digit is always an estimate.
• The digits that you record when you measure something are called significant digits.

final, uncertain  digit

sure, certain digits

1

Watch and Learn

Worked example 1:

• 4.27 cm has three significant digits.
• 4 and 2 are certain (sure).
• 7 is the last uncertain digit.

Watch and Learn

Worked example 2:

• 5.201 g has four significant digits.
• _______, _______, and _____ are certain (sure).
• ________ is the last uncertain digit.

Watch and Learn

Worked example 3:

• 27.0 oC has ______ significant digits.
• _______ and _____ are certain (sure).
• ________ is the last uncertain digit.

2

Significant Digits

How many significant digits (SD) are there in:

• 9.776 g = 4 SD
• 23.4 kg = _______ SD
• 208 cm3 = 3 SD
• 45 094 mg = _______SD
• 0.0507 dm3 = 3 SD
• 0.000000000000071 mol = _______ SD
  
• 53 400 km = _______ SD or _____ SD

RULES for Significant Digits

(1) All non-zero digits are significant.

(2) All zeros in between non-zero numbers are significant.

(3) Zeros to the left of a value are NOT significant.

(4) Zeros to the right of a value may OR may not be significant.

(1) Identify the name of the apparatus.

(2) Read and write the measurement.

(3) Convert the measurement to a given unit.

(4) Identify the number of Significant digits.