Headstart Flashcards
Accuracy
How close a measured value is to the true value of the quantity being measured
Precision
How close two or more measurements are to each other.
Repeatability
How closely two successive measurements of the same quantity match, when carried out under the same conditions of measurement (observer, procedure, instrument, location).
Reproducibility
How closely two measurements of the same quantity match, when carried out under changed conditions of measurement (observer, procedure, instrument, location)
Resolution
The smallest change in the quantity being measured that results in a perceptible change on the measuring instrument. For example, the resolution of a burette is 0.05 mL.
Validity
The extent to which an experiment investigates what it aims or claims to investigate. This is affected by both experimental design (eg controlled variables) and how it is conducted (eg observer bias).
Random Errors
Unpredictable variations in the measurement process resulting in a spread of readings. Eg subjective human judgement
Systematic Errors
Systematic Errors cause inaccuracy in a systematic manner so that when a value is measured repeatedly, the error is the same. Eg incorrectly calibrated instruments or parallax error.
Rules for Significant Figures (in Chemistry)
All digits where a number is expressed in standard form. For other numbers, all digits between the first non-zero digit and the final digit including trailing zeros. Whole numbers without a decimal point have the same number of sig-figs as digits in the number.
Outliers
Data points or observations that differ significantly from other data points or observations. These may be caused by mistakes (and therefore omitted) but should be accounted for before omission as an ethical approach to dealing with data.
Steps for stoichiometry problems
- Calculate the number of moles of ‘known’ (or limiting reagent, where applicable)
- Use the molar ratio to determine the number of moles of ‘unknown’
- Answer the question with appropriate sig figs and units.
How to calculate % (w/v)
Determine the mass in grams of the solute that would be present in 100 mL of the solution
How to use the ideal gas equation to calculate volume in L
V = nRT/P
How to use the ideal gas equation to calculate pressure in kPa
P = nRT/V
How to use the ideal gas equation to calculate moles
n = PV/RT
How to use the ideal gas equation to calculate temperature in Kelvin
T = PV/nR
Standard conditions
25 degrees celsius and 100kPa
Units in the ideal gas equation (except R)
Pressure in kPa, Volume in L, Amount in moles, Temperature in Kelvin
Evidence for oxidation
Loss of electrons; Increase in oxidation number; gain of oxygen (except F); loss of hydrogen (eg organic molecules)
Evidence for reduction
Gain of electrons; decrease in oxidation number; loss of oxygen (except F); gain of hydrogen (eg organic molecules)
What happens to the oxidant (oxidising agent) in a redox reaction
It is reduced
What happens to the reductant (reducing agent) in a redox reaction?
It is oxidised
What is the site of oxidation?
The Anode
What is the site of reduction?
The Cathode
What is always present at the cathode?
The oxidant
What is always present at the anode?
The reductant
Steps for balancing a half equation
- Balance the Key Element (changes oxidation number)
- Balance Oxygen using water
- Balance Hydrogen using H+
- Balance charge using electrons
- Add state symbols
Reliability
How consistently an experiment is able to produce consistent results even when conditions are varied (observer, procedure, instrument, location)
Equivalence Point
The point in a titration when the solutions have reacted in the exact mole ratio as shown by the reaction equation - neither is in excess. (in fact neither reactant is present at all - only products!)
End Point
The point in a titration where an observation (eg colour change of the indicator) signals the end of the titration itself. Good experimental design will ensure that the end point is near the equivalence point in terms of volume of titrant delivered.
Total range of concordant titres
Up to 0.10 mL
Which of these is a correctly shown titre value? 10.59 mL, 10.55 mL, 10.4 mL
10.55 mL (2 decimal places with the second being 0 or 5)
What should you rinse a burette with?
The solution to be used in the burette (titrant). Rinsing with water would dilute the titrant.
What should you rinse a volumetric pipette with?
The solution to be used in the volumetric pipette (analyte). Rinsing with water would reduce the amount of analyte delivered in the aliquot.
What should you rinse a volumetric flask with?
Water. Rinsing with the solution being measured out would increase the amount of that solution in the volumetric flask by an unknown quantity.
What should you rinse a conical flask with?
Water. Rinsing with the analyte would increase the amount of analyte present in the conical flask by an unknown quantity.
