C8 Flashcards
What is a pure substance ?
A pure substance is a single element or compound , not mixed with any other substance
What is a formulation ? Give examples
A formulation is a mixture of compounds in measured quantities that has been designed as a useful product.
- Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
Describe paper chromatography required practical
a) A start line is drawn near the bottom of the paper. The mixture is spotted on the line.
b) A beaker is filled with small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)
c)Paper is hung on a rod and placed in a beaker.
d) Solvent travels up the paper, thus separating the components.
e) Before solvent level reaches the end, the paper is taken out and the finish line is marked. The paper is dried.
f)The procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent etc.
g) Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.
How is Rf calculated ?
Distance moved by substance/ distance moved by solvent
In a paper chromatography experiment a compound A was found to have an Rf value of 0.85 - what does it tell you about the compound ?
It has a higher affinity for the solvent than for the paper
What is the test for hydrogen ?
The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.
What is the test for oxygen ?
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.
What is the test for carbon dioxide?
The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).
What is the test for chlorine ?
The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.
How do pure substances melt and boil ?
A pure substance melts at a specific fixed temperature.
A pure substance also has a specific fixed boiling point.
Impure substances melt and boil over a range of temperatures..
What is chromatography?
Chromatography can be used to separate mixtures and can give information to help identify substances. Chromatography involves a stationary phase and a mobile phase. Separation depends on the distribution of substances between the phases.
What is an impure substance ?
A mixture (impure substance) consists of two or more elements or compounds that are physically placed together, they are not chemically combined and so the chemical properties of the substances in a mixture remain unchanged.
What is the paper in Paper chromatograhy?
The paper is the stationary phase because it does not move
What is the solvent in paper chromatography
The solvent is the mobile phase becuase it does move
What will a pure compound produce in paper chromatography
A pure compound will produce a single spot in all solvents
Whereas , the compounds in a mixture may separate into different spots depending on the solvent
