[ANAL-LEC-MID-01] CALCULATIONS OF RESULTS AND ERRORS

THIS FLASH CARDS IS ABOUT ANALYSIS II; CALCULATIONS OF RESULTS AND ERRORS.

Recording

When we say calculations of results, it is about?

Error

Measurements invariably involve _____ and uncertainties.

No — impossible.

Is it possible to perform a chemical analysis that is totally free of errors or uncertainties?

Acceptable accuracy

We can only hope to minimize errors and estimate their size with?

Errors

These are caused by faulty calibrations or standardizations or by random variations and uncertainties in results.

• Faulty calibrations

• Standardizations

• Random variations

• Uncertainties in results

Errors are caused by?

• Frequent calibrations

• Standardizations

• Analyses of known samples

These three (3) can sometimes be used to lessen all but the random errors and uncertainties.

Error

Refers to the difference between a measured value and the “true” or “known” value.

• Measured value

• True or known value

Errors refer to the difference between a?

Errors

These can often denotes the estimated uncertainty in a measurement or experiment.

| absolute error - true value |
————————————— x 100%
true value

What is the formula for error and percentage error?

Measured value

What is the synonym of absolute error?

Researcher

Example only:

Who is the one that determined the measured value?

Manufacturer

Example only:

Who is the one that determine the true value?

Numerical value

Source and Nature of Errors:

It is only in rare cases that this value of an experimental result can be directly determined.

Different measurements and observations

Source and Nature of Errors:

As a rule, it is necessary to calculate the result from these measurements and observations that have been made.

Statistics

The side of experimentation involves?

Statistics

This is the science of collecting and analyzing data to test hypotheses, identify patterns, and determine whether results are real or due to chance.

Duplicate results

Source and Nature of Errors:

These results that check very closely are not an assurance of accuracy.

Reliability of the methods

Results that agree closely when obtained by two different methods of analysis are a good indication of the?

Accuracy

This indicates the closeness of the measurement to the true or accepted value and is express by the error.

Result and the accepted value

Accuracy measures agreement between a?

Accuracy

This is often more difficult to determine because the true value is usually unknown.

Accepted value

Since the true value is usually unknown, this value must be used instead.

Absolute or relative error

Accuracy is expressed in terms of either?

Precision

This describes the agreement among several results obtained in the same way.

Reproducibility of measurements

Precision describes the?

Precision

This is readily determined by simply repeating the measurement on replicate samples.

• Standard deviation

• Variance and coefficient of variation

Precision of a set of replicate data may be expressed as?

Acceptable accuracy

“We can only hope to minimize errors and estimate their size with?”

Low accuracy, low precision

Low accuracy, high precision

High accuracy, low precision

High accuracy, high precision

Source and nature of errors

The results of repeated analyses or measurements will fail to agree, in general, when made by the same analyst or by different analysts to the full precision of which the method or instrument is capable.

Discrepancies

The __________ in the results are caused by various sources of error to which all experimental data are subject.

Subject

The discrepancies in the results are caused by various sources of error to which all experimental data are?

• Indeterminate errors

• Determinate errors

What are the two (2) different types of errors?

Indeterminate errors

This type of error manifest themselves by slight variations in a series of observations made by the same observer under identical conditions..

Sligh variations

Indeterminate errors manifest themselves by?

• Differences in the judgement

• Skill of the analyst

Indeterminate errors results from causes difficult to detect, such as?

1. Intangible

2. Impossible

Indeterminate errors are (1)_____, and their elimination by the analyst is (2)_____.

Determinate errors

This type of error is of such nature that they recur in a constant manner in each of a series of determinations.

Constant manner

Determinate errors recur in a?

Yes — possible.

In determinate errors, is it possible partially to determine their value and reduce their effect on the final result?

Personal errors

Errors:

Made by the individual analyst.

(e.g., inability to judge color changes sharply, resulting in habitual reading of end points in titration too late).

Errors of method

Errors:

Caused by faulty procedure.

(e.g., incorrect sampling, contamination of precipitates, and improper selection of indicators).

Apparatus errors

Errors:

Due to poor construction or calibration.

(e.g., inaccuracy in the calibration of burets or pipets, inequality in the length of the arms of the balance, and incorrect weights).

Apparatus errors

Errors of this type are usually detectable and so may be eliminated to a large extent.