Experimental techniques Flashcards
True or false: only a strong acid will 100% deionize
true
Idiometric titrations
used to determine the concentration of an oxidising agent in solution. A starch solution is used as an indicator since it can absorb the I2 that is released
Why should KIO3 be added in excess
to keep iodine dissolved
What does the AA solution contain?
HCl (5mL), KI (5mL), starch (2mL)
What happens to the KI in the solution?
reacts with the potassium iodate, leaving I2
What happens to the concentration of Vitamin C as temperature/pH/light/metals/oxygen increases?
decreases (Degradation)
Why do we work in fumehoods?
protect us from inhaling toxic gasses
How do you know if the fumehood is pulling air from inside?
the paper will start blowing inwards
Where must the window sash be?
Under the black arrow
can you put your head under the glass?
NO
Where can the work be done?
behind the blue line
What do you have to do to the solution in a flask before taking it out of the fumehood?
Stopper it
What temperature does the solution need to be at before pouring into a seperatory funnel
room temperature (20)
How many times should you vent and rock the funnel?
at least 5 times
Where do you hold the top when you vent?
Away from you or other people
What do you leave out from the beaker you pour your seperated solution to?
the bubble layer
What is sublimation?
technique used to purify a solid chemical substance
Steps for sublimation
- the substance is placed into a vacuum filter flask that has been fitted with a cold finger, and then the flask is placed on an electric hotplate
- the water pump is turned on to lower the pressure within the vacuum filter flask, and simultaneously the heat is turned on
Sublimate
The condensed substance
Where does the sublimate form?
The hot chemical vapours rise until they hit the cold finger, where the vapours condense onto the cold finger.
What happens to the impurities
impurities will either not sublime and remain at the bottom of the filter flask, or will not condense and be sucked out of the flask by the water pump.
Melting point analysis
used for the identification of a compound and its purity
If a substance contains impurities
will melt at a lower temperature than the pure compound, and melts over a wide range of temperatures
In general
the smaller the range of melting
temperatures, the higher the purity of the sample
Steps for melting point
- load a sample into a melting point
capillary tube and then slowly heat up the tube in a melting point apparatus. - record the temperature at which the sample begins to melt AND the temperature at which all of the sample has melted.
What are rotary evaporators used for
to remove solvents from a solution through evaporation
Steps for rotary evaporation
An RBF is clamped to the rotary. The vacuum is turned on, and the RBF is lowered into the hot water bath. The rotary is then turned on.
How does the rotary evaporation work
The solvent in the RBF is heated and evaporates out of the top of the flask which goes in the condensor, where the solvent cools due to the cold water that is in the condensor, which evaporates. The solid is then left in the RBF
why do we use calorimetry?
so we can identify solutes in a coloured solution and very accurately determine their concentrations
How Does Colourimetry Work?
Colourimetry is a form of spectroscopy, which measures how atoms or molecules respond when exposed to electromagnetic radiation of a certain wavelength within the visible light spectrum.
Beers law
A = ε l c
analytical wavelength
wavelength of max absorbance
SEROLOGICAL PIPET
Pipets with graduations along the length of the tube, kinda similar to a syringe
how do you measure on a serological pipette?
You measure backwards, for example if you want 3 ml, you measure to the 7 ml mark
How to calibrate analytical wavelength
Select all wavelengths in advanced settings and then run a blank. Then click on absorbance and run a 10 mL sample of dye. Record the highest wavelength
How to collect data using spectrophotometer
Click the wavelength and all the boxes in the same column. Run a blank the set the time interval to 5 seconds. Turn the stirring on and reversing off.
Measuring pH
measured with a pH probe, which is a sensor containing a combination of two electrodes. first electrode has a fixed voltage and the other (glass) electrode uses it as an electrode. the pH should match with the voltage on the glass second electrode
When not in use where should the pH probe be kept
stored in the pH 7 buffer solution
What do we measure in a pH titration?
the change in pH of the solution being titrated
- plot the volume of the titrant added on the x-axis and the pH on the y-axis
Drop dispenser
A liquid is put in it and the flow rate is set so that you can determine the size of the drop that comes out of the tip. This way drops can be converted to mL.
Drop counter
Each drop that comes out passes by a sensor on the drop counter and is counted and plotted on the pH curve by adding a formula
Where does the pH probe go when the titration happens?
on the side of your solution, dont let it touch the magnetic stirrer
Formula
Volume = counter * mass of drops / number of drops
How many drops should you weigh and measure?
100
How do you set up a microlab drop counter
Click on add sensors and set it to “counter”. Click “set counter options” and click “continually increasing count”. Finish and go down further. Make sure it is says “count every drop”. Then add another sensor and click pH, the add a new calibration point by changing the 0 to a 7 and wait until the red line is in between the green section. Then drag the sensors to the graph.
How do you callibrate the drop dispensor
Fill the drop dispenser with water and make sure it flows. Weigh an empty beaker and record it. Let the water flow until 100 drops are counted then re-weigh the beaker. Enter the formula into the program.
