4 Researching Chemistry Flashcards
what are precise results?
if experiments can be repeated several times and their values are numerically similar
what are repetable results?
if the same experimenter obtains these numerically similar values
what are reproducible results?
if a number of different experimenters obtain these numerically similar values
what is a systematic error?
an error repeated in each measurement made by the experimenter
what is a random error?
they are made by the experimenter
how can you reduce random errors in experiments?
repeated measurements and averaging
what are uncertainties?
uncertainty of measurements results from the scale or digital reading not being an exact or precise measurement
what is the equation for percentage error?
uncertainty/actual measurement made X 100
what are types of spectral data which can be organised?
absorption spectroscopy
mass spectroscopy
IR spectroscopy
portion NMR spectroscopy
why is a control experiment carried out?
to validate a technique or procedure is accurate
what does parts per million refer to?
1 mg per kg
or
1 mg per L
how many mg are in a kg?
1,000,000 mg = 1 kg
what is percentage by mass?
the mass of solute made up to 100cm3 of solution
what is percentage by volume?
the number of cm3 of solute made up to 100cm3 of solution
how is percentage by yield reduced?
mass transfer or mechanical losses
purification of product
side reactions taking place
equilibrium position
what can gravimetric analysis determine?
the mass of an element or compound in a substance
what are weighing boats?
used to measure substance on a balance without contamination
what is the function ‘tare’ on a balance used for?
allows the balance to be set to zero when an object is on top of the balance pan
what is weighing by difference?
the mass of an empty weighing boat is measured and the chemical is added to the boat and reweighed. the difference is the mass of the substance in the bottle.
what is weighing accurately approximately?
weigh within the region of the calculated mass, but record exactly what you used
heating to a constant mass steps
the substance is initially weighed and recorded
the substance is heated to remove moisture
the substance is allowed to cool in a desiccator
the substance has its mass measured on a balance
repeating the steps of weighing, heating, cooling and reweighing until constant mass is obtained
what is the purpose of a desiccator?
prevents reabsorption of water
what is a constant mass?
the mass is no longer changing
what are two types of gravimetric analysis?
precipitation
volatilisation