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How should data be reported in Chemistry?

How should data be reported in Chemistry?. There are two kinds of numbers :. Exact numbers : may be counted or defined (they are absolutely accurate). Numbers obtained from measurements are not exact. These measurements involve estimating. You can report one estimated digit. 6.3 5 or

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How should data be reported in Chemistry?

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  1. How should data be reported in Chemistry?

  2. There are two kinds of numbers: • Exact numbers: may be counted or defined (they are absolutely accurate).

  3. Numbers obtained from measurements are not exact. These measurements involve estimating.

  4. You can report one estimated digit. • 6.35 or • 6.36 or • 6.37 • the last number is the best estimate for the 3 students. • Two numbers are certain. • One number is uncertain. • three significant figures!

  5. significant figures indicate the uncertainty in measurements

  6. Scientific notation:

  7. How to countsignificant figures ? • 438 g = 4.38 x 102 3 s.f. 2.2678.42 = 2.67842 x 103 6 s.f. 3. 1.7 2 s.f.

  8. Task 1: Try these! A) Write in scientific notation.B) Determine the number of significant figures • 506 • 10.05 • 900.43 • 60.00 • 1.09 • 0.06 • 0.00470

  9. How do you round off? • If the numbers to be discarded are less than 50  leave the last significant number unchanged : 23.31 23 • If the numbers to be discarded are more than 50  add one to the last significant digit : 23.54 24 • If the numbers to be discarded are 50  round off so that the last significant number is an even number : 23.5024

  10. TASK 2: Complete these multiplication and division problems • 13.7 x 2.5 • 200. x 3.58 • 2.3 x 3.45 x 7.42 • 0.003 / 5 • 5. 89 / 9.0 • 6. 5000 / 55 500 = 1 SF 500. = 3 SF 550 = 2 SF On a measuring device, for example the measurement of 500 ml in a measuring cylinder, for the purposes of accuracy this is assumed to be an absolute value.

  11. TASK 3: Complete these addition and subtraction problems • 0.008 + 0.05 • 4.50 + 3 • 35.89 + 34.6 • 200 – 87.3 • 75.0 – 2.55 • 10.0 – 9.9

  12. TASK 4: Apply your knowledge Write: • 35.270 to 3 significant figures • 0.4140 to 2 significant figures • 87.257 to 3 significant figures • 1.350 to 2 significant figures 5. 62.50 to 2 significant figures

  13. Multiple step problems • When carrying out multiple step problems keep one extra significant figure throughout the whole problem, to reduce rounding errors. • The final result should be consistent with the number of significant figures given in the experimental measurements.

  14. Converted, Measured and Counted Numbers • Unit conversions are infinitely accurate. The number of significant figures does not change because conversions are exact values, not measured values. • Counted numbers are infinitely accurate, such as counting the number of atoms in H2O (there are 3). 3 is an exact value not a measured value. Counting does not need a tool. • Measuring requires the use of a tool: ruler, scale, balance, graduated cylinder etc… Measured numbers are only as accurate as the tool being used. The number of significant figures should indicate this.

  15. A great website for practicing Significant figures can be found at: http://www.sciencegeek.net/Chemistry/taters/sigfigs.htm

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