In-class Prac Validation

Question 1

density formula

Answer 1

d = (P x Mr) / (R x T)

Question 2

Molar mass - equation 1

Answer 2

Mr = (m x R x T) / (P x V)

Question 3

Molar mass - equation 2

Answer 3

Mr1 / Mr2 = m1 / m2

Question 4

% Error

Answer 4

( l T - E l / T ) x 100

Question 5

Apparatus Uncertainty Percent

Answer 5

% Apparatus Uncertainty = (uncertainty of apparatus) / (measured value) X 100

Question 6

Uncertainty of Final Value

Answer 6

Final Value Uncertainty = (AU% / 100) x final value

Question 7

Concordant value

Answer 7

values that are within 0.1mL of each other

Question 8

Reliability of an experiment

Answer 8

Reliability refers to the ability of a titration to produce consistent results when repeated by the same operator in the same conditions.

Question 9

Accuracy of an experiment

Answer 9

Accuracy refers to how close the experimental or calculated value is to the true/original value.

Question 10

Precision

Answer 10

Precision refers to spread of the data/results. Essentially, how closely two or more measurements are together, and is also known as repeatability of the results.

Question 11

How to improve the accuracy of a titration? OR What conditions promote the accuracy of a titration?

Answer 11

1) cleaning of apparatus - residual substances can effect results
2) using appropriate apparatus - calibrated volumetric glassware
3) correct/suitable indicator - appropriate pH range (equivalence)
4) controlled temperature - solution temp must be controlled
5) vigorous stirring - ensure rxn is complete & homogenous
6) repeatable trials - multiple trials (UP precision/accuracy)
7) slow & steady addition of titrant - must be very precise volume

Question 12

What is standardisation?

Answer 12

Standardization of a solution is determining the exact concentration of the solution. This is done through titration (e.g. acid to base), with a primary substance of a known concentration. A primary standard is a highly pure, stable and readily available substance that can be used to accurately determine the concentration of another substance through titration.

Question 13

Comment on the size of apparatus uncertainty compared to the percentage of error?

Answer 13

The experimental error was significantly higher than the AU, which indicates that the appropriate apparatus was utilised and the source of error is another variable (e.g. instrumental, systematic, environmental)

Question 14

Types of Error

Answer 14

Systematic Error - incorrect/inaccurate measurements of the meniscus throughout the experiment due to parallax error

Instrumental Error - incorrect calibration of apparatus (calibration of auto dispenser incorrectly)

Environmental Error - other external factors within the lab (e.g. changes to pressure, temp)