QCA7e_ch03_szb_handouts

# QCA7e_ch03_szb_handouts - Daniel C Harris Quantitative...

This preview shows pages 1–7. Sign up to view the full content.

1 Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 3 Experimental Error Daniel C. Harris Daniel C. Harris Topics in this Chapter • Accuracy and precision • Significant figures • Types of error – Random error – Systematic error • Error propagation

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 Measured volume = 1.13 ± 0.05 mL Measured mass = 4.635 ± 0.002 g Density = mass / vol. = 4.10 g mL 1 ± ?.?? Experimental Error • Suppose that you determine the density of a mineral by measuring its mass and volume. The uncertainties in measured mass and volume are given, but what is the uncertainty in the computed density?
3 Significant Figures • The number of significant figures is the minimum number of digits needed to write a given value in scientific notation without loss of accuracy. • The number 142.7 has four significant figures • The number 1.4270 10 2 has five significant figures. Significant Figures • The number of significant figures is the minimum number of digits needed to write a given value in scientific notation without loss of accuracy. • Zeros are significant when they occur – in the middle of a number or – at the end of a number on the right-hand side of a decimal point.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
4 Minimum uncertainty • The last significant digit (farthest to the right) in a measured quantity always has some associated uncertainty. • The minimum uncertainty is ± 1 in the last digit. Minimum uncertainty • The needle is at an absorbance of 0.234. • This number has 3 significant figures: – the numbers 2 and 3 are completely certain – the number 4 is an estimate • The value might be read 0.233 or 0.235 by other people!
5 Significant Figures • The number of significant figures in the answer may exceed or be less than that in the original data: Significant Figures • If the numbers being added do not have the same number of significant figures, we are limited by the least- certain one: • The number 121.7948064 should be rounded to 121.795 as the final answer.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
6 Rounding • When rounding off, look at all the digits beyond the last place desired: – If larger than half round up – If smaller than half round down – If exactly half round to even number: 0.0345 0.034 0.575 0.58 – Reason: to avoid systematically increasing
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 19

QCA7e_ch03_szb_handouts - Daniel C Harris Quantitative...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online