Chemistry - Chemical analysis Flashcards
Definition of pure in chemistry
Only contains one compound or element throughout - not mixed with anything else
What tells you how pure a substance is
A chemically pure substance will melt or boil at a specific temperature
How can you test the purity of a sample
Measure its melting and boling point and compare it with the melting or boiling point of the pure substance. The closer your measured value is to the actual melting or boiling point, the purer the sample is
What are formulations
Mixtures with exact amounts of components, useful with precise purpose eg. paint
What is chromatography
An analytical method used to separate the substances in a mixture. You can then use it to identify the substances
What are the phases of chromatography
A mobile phase - where the molecules can move. This is always a liquid or a gas
A stationary phase - where the molecules can’t move. This can be a solid or a really thick liquid.
During the chromatography experiment what phase are the substances in
The substances in the sample constantly move between the mobile and the stationary phase - an equilibrium is formed between the two phases
How do the two phases of chromatography interact with each other
The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it
What determines how quickly a chemical moves in chromatography
The chemicals that spend more time in the mobile phase than the stationary phase will move further. A chemical will spend more time in the mobile phase if it is more soluble in the mobile phase
What is the stationary phase in paper chromatography
The paper
What is the formula to calculate the Rf value
distance travelled by the substance divided by the distance travelled by the solvent
What is the Rf value specific to
The Rf value of a substance is specific to a particular mobile phase and stationary phase, if these phases changed then so would the Rf value
Test for chlorine gas
Chlorine bleaches damp litmus paper- will turn it white
Test for oxygen
Put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint
Test for carbon dioxide
Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of lime water causes it to turn cloudy
Test for hydrogen gas
Hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop”.
How do we test for carbonates in anions
Put a sample in a test tube and them using a dropping pipette add a couple of drips of dilute acid. You should then connect the test tube to a test tube of limiter. If carbonate ions are present, co2 will be released and will turn the limewater cloudy when it bubbles through it
What safety precautions are required for testing chlorine gas
Do the experiment in a fume cupboard
Wear a mask
How do we test for sulphates in anions
Use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution a test tube containing the mystery solution. If sulphate ions are present a white precipitate will form.