Chapter 2 - Measurment and Purity Flashcards
When measuring where do put the decimal points to.
The 1st or 2nd decimal point
Are mercury thermometers or digital thermometers more accurate
Digital thermometers are.
In terms of mass what is used more for chemistry
Grams are used more than kilograms.
In measuring when do mostly use the measuring cylinder
When measuring volumes of liquids where accuracy isn’t an important factor
What is the apparatus pipette used for
Pipettes are the most accurate way of measuring the fixed volume of liquids.
What is the apparatus Burette used for
It’s most accurate way of measuring a variable volume of liquid.
E.g titration
What apparatus is most used for measuring gas
The volume of a gas sometimes needs to be measured and is done by collecting it in a graduated measuring apparatus
A gas syringe is usually the apparatus used.
What is a graduated cylinder inverted in water used for
When measuring a gas a graduated cylinder inverted in water, provided the gas isn’t water-soluble can be used to measure gas.
When is the appropriate time to flip the cylinder upright
when measuring gas.
If the gas happens to be heavier than air and is colored, the cylinder can be used upright.
What is paper chromatography
This technique is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)
What are steps for paper chromotography
A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples.
The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don´t wash into the solvent container
The solvent travels up the paper by capillary action, taking some of the coloured substances with it
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart. Those substances with higher solubility will travel further than the others
This will show the different components of the ink / dye
What is the simplified steps of chromatography
- First set up the chromatography experiment
- Secondly lower paper into beaker with appropriate solvent and wait for solvent to travel up the paper.
- Lastly analyse chromatogram to see the different components of ink/dye
What happens if you use an impure substance in chromatography
An impure substance will show up with more than one spot, a pure substance should only show up with one spot
If a substance used is a mixture in chromatography what happens
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
If two substance that are identical are used in chromatography what will happen
If two or more substances are the same, they will produce identical chromatograms
What’s the difference between paper chromatography and chromatogram
Paper chromatography is the name given to the overall separation technique while a chromatogram is the name given to the visual outcome of
What do pure substances melt and boil at
Pure substances melt and boil at specific and sharp temperatures. Eg water has a boiling point of 100°C and a melting point of 0°C
What is range of melting and boiling for mixtures
Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures. Therefore the melting points and boiling points of substances can be used to check whether something is a pure substance or is mixture.
What is a pure substance
A pure substance consists of only one substance and contains nothing else.
In food and drugs why is having a pure substance important
as impurities could be dangerous even in small amounts
What are Melting and boiling points used for for with food and drugs
It’s used to assess the purity of food and drugs
If something is impure what will happen e.g water
For example, if a sample of water melts at exactly 0°C and boils at exactly 100°C then the water is pure, but If the melting and boiling points of the water aren’t these exact values then the water must be impure and contain other substances i.e. it must be a mixture
What are retention factor values
These values are used to identify the components of mixtures
What does calculating the retention factor value (Rf) do
Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions. The Rf value of a particular compound is always the same
How do you calculate retention factor value (Rf)
Retention factor = distance moved by compound ÷ distance moved by solvent
The Rf value is a ratio and therefore has no units
It’s kinda like chromatography.
What are locating agents
For chromatography to be useful the chemist needs to be able to see the components move up the paper, which is not the case for invisible samples such as proteins
Locating agents are substances which react with the sample and produce a coloured product which is then visible
When is the chromatogram treated with locating agent
The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye
How do you seperate a mixture of solids
For a difference in solubility, a suitable solvent must be chosen to ensure the desired substance only dissolves in it and not other substances or impurities
What are immiscible liquids
They are liquid solutions that do not dissolve in one another. They are liquids that do not mix in equal proportions.
How can immiscible liquids be separated
Immiscible liquids can be separated using a separating funnel or by decanting
What is decanting
It’s gradually pouring out a liquid from another liquid.
What’s filtration
Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water). Centrifugation can also be used for this mixture. Pouring insoluble mixture of solid and liquid in the filter tunnel Using the filter the liquid particles will gradually fall through and sold particles will not
What’s residue in filtration
The solid particles that can’t get through the filter paper
What’s filtrate in filtration
It’s the liquid particles that pass through the filtrate
What’s crystallisation
Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper sulphate from a solution of copper (II) sulphate in water)
How does crystallisation work
The solution is heated, allowing the solvent to evaporate to leave a saturated solution behind.
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod
What’s simple distillation
Used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids
How does simple distillation work
The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask
The vapour passes through the condenser, where it cools and condenses, turning into pure liquid H2O which is collected in a beaker
After all the water is evaporated from the solution, only the solid solute will be left behind
What is fractional distillation
Used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)
How does fractional distillation work
The solution is heated to the temperature of the substance with the lowest boiling point
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
What does miscible mean
Miscible means liquids that can be mixed together in all proportions
