C8 Chemical analysis Flashcards
What is an element?
A substance containing only one type of atom
What is a compound?
Two or more elements chemically joined together
What is a mixture?
Two or more substances (elements and/or compounds) that are mixed up but NOT chemically joined together
What is an atom?
The smallest part of an element which is still definitely from that element (electrons for example are identical no matter which type of atom they come from).
What is a molecule?
Two or more atoms joined together
What is a pure substance?
Elements are pure substances as they contain only one type of atom but so are compounds if they are not mixed with anything else.
How can melting points and boiling points be used to determine the purity of a substance?
Pure substances have a fixed melting point and boiling point. For example, pure water boils at 100 degrees centigrade and melts at 0 degrees centigrade
What happens to the boiling point of a substance when an impurity is added?
The boiling point rises when an impurity is added. We can use this to make pasta cook faster by adding salt to the water - as the boiling point rises the water gets hotter and so the pasta cooks faster too.
What happens to the melting point of a substance when an impurity is added?
The melting point lowers when an impurity is added. We use this idea when we spread salt onto icy roads. The salt means that the ice will melt at a lower temperature (and also freeze at the same, lowered temperature). This means the ice will no longer be frozen and so will melt.
What is a formulation?
A formulation is a mixture that has been designed as a useful product.
What types of substances are made to a formulation?
Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
What is chromatography?
Chromatography is a process used to separate mixtures and can give information to help identify substances. See here for more details
Give two examples of substances that can be identified using chromatography.
- coloured inks in a mixture of coloured inks 2. It is used in the sequencing of DNA and RNA
What is an Rf value?
The Rf value is the ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent. Different compounds have different Rf values in different solvents, which can be used to help identify the compounds.
What is the formula for an Rf value?
Rf value = distance moved by substance
distance moved by solvent
What is the test for hydrogen gas?
The squeaky pop test. This is carried out by collecting a tube of gas and then holding a flame close to the end of the tube - if the tube contains hydrogen it will burn with a a squeaky pop. Watch this short video to see and hear it
What is the test for oxygen gas?
Oxygen will relight a glowing wooden splint. This means if you have a tube you suspect contains oxygen you should light a splint, blow it out and put the glowing embers into the tube. If they relight it is oxygen (watch this test here)
What is the test for carbon dioxide gas?
This is the limewater test. Bubble the gas through limewater and if it goes cloudy / milky it is limewater (The cloudiness is a precipitate of calcium carbonate). Watch this test here
What is the test for chlorine gas?
Put damp, blue litmus paper into the gas. If the litmus paper turns red and then bleaches to white it was chlorine gas - watch this test here.
What colour does the flame go when testing lithium compounds?
crimson like this:
What colour does the flame go when testing copper compounds?
green - like this:
What colour does the flame go when testing potassium compounds?
lilac like this:
What colour does the flame go when testing sodium compounds?
Yellow - like this:
What colour does the flame go when testing calcium compounds?
Orange-Red - like this:
