Elements compounds and mixtures

Question 1

What are atoms?

Answer 1

-the smallest pieces of an element that can exist

Question 2

What are compounds?

Answer 2

-2 or more atoms chemically joined together

Question 3

What is a mixture?

Answer 3

-2 or more substances (elements or compounds) that haven’t been chemically combined

Question 4

What is a pure substance?

Answer 4

-a specific element or compound with specific melting and boiling points

Question 5

What is simple distillation?

Answer 5

-Separates 2 liquids with different boiling points.
The mixture is heated until the liquid with the lower boiling point starts to boil.
-The vapour released passes through a condenser, where the gas cools back into a liquid.

Question 6

What is fractional distillation?

Answer 6

• Separates lots of liquids with different boiling points.
• The mixture is slowly heated until the liquid with the lowest boiling point boils and then condenses.
• Then we increase temperature slowly to collect (boil then condense) the other fractions.

Question 7

What is crystallisation?

Answer 7

-Separates solutions into different parts: dissolved solids (solutes) and liquids (solvents).
-Heat the mixture so that the solvent evaporates.
Eventually, crystals of the solute (dissolved solids) will form.
-We can collect the solvent (liquid) by condensing it as it evaporates.

Question 8

What is filtration?

Answer 8

• Separates mixtures of insoluble solids and liquids.
• Done by pouring the mixture through filter paper:
• The insoluble solid is trapped.
• The liquid runs through the paper and is collected below.

Question 9

What is chromatography?

Answer 9

-Separates solutions with a number of different solutes (solids) in the solvent (liquid)

Question 10

List the steps of chromatography.

Answer 10

• Place a drop of the solution to be separated near the bottom of a piece of chromatography paper.
• Dip the very bottom of the paper into a suitable solvent.
• The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it.
• Different solutes (solids) move at different speeds, so they separate on the paper.

Question 11

What is paper chromatography?

Answer 11

-mixtures of soluble substances are separated

Question 12

List the steps of paper chromatography.

Answer 12

-Use a pencil to draw a horizontal line near the bottom of the chromatography paper.
-Place samples of known food colourings (A-D) next to an unknown substance (X) on this ‘start line’.
-Place the paper in a beaker containing a small volume of solvent.
Let the solvent move to a few cm below the end of the paper.
-By comparing spots produced by X with those produced by A-D, you will be able to identify the unknown substance.

Question 13

How do you work out the Rf value?

Answer 13

-distance travelled by substance/distance travelled by solvent

Question 14

What is a reference substance in chromatography?

Answer 14

-a pure sample that’s run next to the tested substance to see if it’s a component in the mixture