Practical Stuff To Learn Flashcards
(33 cards)
What’s control variable
Variable that’s kept constant throughout experiment
What’s independent variable
Factor that’s changed during experiment to see effect it has on another factor
What’s dependent variable
A factor that’s measured/observed in experiment due to changing of independent variable
When plotting graph what variables go on what axis
Independent variable - x axis
Dependent variable - y axis
How do you measure the gradient of either tangent or line of best fit
Gradient =
Change in y
——————
Change in x
What’s can anomaly
Deviation of value from its expected value
(I.e. value that doesn’t fit trend)
Why should anomalies be ignored when calculating mean
Not including anomalies in mean value make it much more accurate
What is precision
Set of precise measurements will have very little spread about mean
But precision gives no idea of how close values are to actual, true-value - only how close values are to each other
What’s accuracy
More accurate data, closer it is to actual value
What’s an uncertainty
Uncertainty in a measurement is interval within which actual value is expected to lie
What’s % uncertainty + how to calculate it
% uncertainty in a measurement
Absolute uncertainty
—————————— X 100
Calculated value
What are diff ways to improve apparatus to govern more accurate results
Increase number of readings
Control external variables
Use measuring devices/equipment with greater precision
How do you use laboratory equipment to carry out titration
• A pipette is used to accurately measure out the volume of a reactant before transferring it to a conical flask.
• A burette is a measured, controlled and easy way to add small volumes of one reactant to another reactant.
How do you use laboratory equipment to heat under reflux
Quickfit apparatus is used to heat a substance under reflux.
- The substance is boiled in a pear-shaped or round-bottomed flask.
- As it evaporates, it is cooled by the water in the liebig condenser and so condenses back into a liquid and drips back down into the flask to be heated again.
Why’s heating under reflux used
• Allows heating for a long period of time
• Prevents the flask from boiling dry
• Prevents volatile reactants/products escaping
• Ensures even heating
How do you use laboratory equipment to carry out distillation
• The substance you want to distill is heated in a pear-shaped or round-bottomed flask, causing it to evaporate.
• When it reaches the condenser it will cool and condense back into a liquid which will then drip out into the collecting flask.
How do you use laboratory equipment to filter under reduced pressure
Using a Buchner funnel and Buchner flask, connected by rubber tubing to the vacuum source.
• The funnel contains a layer of filter paper.
• Pour the substance onto the filter paper and the liquid will be sucked through via vacuum filtration into the flask.
• The solid will remain on the paper.
What’s a standard solution
Solution of known conc
How to make standard solution
• Measure, using a balance, the mass of solid required.
• Transfer this to a volumetric flask and rinse the remaining weighing bottle content into the flask so no solid is lost.
• Add a volume of distilled water to dissolve the solid. Swirl to mix.
• Then add more distilled water up to the line on the neck of the volumetric flask. Invert multiple times to mix.
What are concordant results
Titres within 0.1cm3 of each other
Why are acid-base indicators used
To detect when a reaction reaches completion/becomes neutral, usually by presence of colour change
How do you purify solid product
By recrystallisation.
• Add minimum amount of warm solvent to the impure sample until it has dissolved.
• Allow to cool, crystals should form.
• When no more form you can filter under reduced pressure to obtain a dry crystalline solid.
How do you purify a liquid product
• You can use a separating funnel to isolate the organic layer from the aqueous layer.
• You can then purify the liquid by distillation, which separates the substances by boiling point.
How to determine MP of substance and why can this be useful
• Place a small sample of the solid in a capillary tube.
• Melt using the melting apparatus available, measuring the temperature with a thermometer.
• A pure substance will usually melt at a single temperature (or a very small range) but an impure substance will melt over a range of temperatures (usually lower than that of the pure substance).
• Record the starting and ending points of the melting, when the first crystal can be seen to melt and when the last crystal becomes liquid respectively.
• You can then compare the melting point to known values to identify the substance.
