Practical & Investigative Skills Definitions

Question 1

atom

Answer 1

a small independent particle which makes up all matter

Question 2

element

Answer 2

a substance made up of only one type of atom

Question 3

compound

Answer 3

a substance made from different kinds of atoms chemically joined (bonded) together. they have a fixed ratio of atoms e.g. NaCl = 1 Na for every 1 Cl, C6H12O6 (glucose) = C:H:O is always in the ratio of 6:12:6

Question 4

mixture

Answer 4

containing more than one different type of particle (elements or compounds) that aren’t chemically joined together. there is never a fixed ratio of components in a mixture.

Question 5

solvent

Answer 5

a substance (usually a liquid) in which another substance dissolves e.g. water is the solvent in all aqueous solutions

e.g. NaCl(aq) - sodium chloride is dissolved in the solvent water
e.g. tetrachloromethane (CCl4) is the gaseous solvent that dissolves grease when clothes are dry cleaned

Question 6

solute

Answer 6

the substance that dissolves in a solvent

e.g. NaCl(s) is the substance that dissolves in water in NaCl(aq)

Question 7

solution

Answer 7

a mixture of a solute dissolved in a solvent. solutions can have different concentrations (amount of solute dissolved in a known amount of solvent)

Question 8

saturated solution

Answer 8

a solution in which no more solute can dissolve at a given temperature. generally more solute can dissolve in a solvent at a higher temperature.

Question 9

solubility

Answer 9

a measure of how much solute can dissolve in a solvent. solubility is measured in g of solute per 100g of solvent at a given temperature

Question 10

solubility curve

Answer 10

a graph showing how the solubility of a solute varies with temperature

Question 11

purity

Answer 11

a pure substance is one in which all the particles are the same - ie all elements of the same type or all compounds of the same type. a pure substance has a fixed melting and boiling point whereas a mixture may melt or boil over a range of temperatures e.g. pure water freezes/ melts at 0 degrees celsius and boils at 100 degrees celsius. however, if salt is added to ice, the mixture melts at a lower temperature than 0 degrees celsius. if salt is added to water, the mixture boils at a higher temperature than 100 degrees celsius.

Question 12

independent variable

Answer 12

what you change

Question 13

dependent variable

Answer 13

what you are measuring

Question 14

controlled variable

Answer 14

what you keep the same

Question 15

reliability

Answer 15

getting repeated reproducible results, even though your answer may not be quite the right one

Question 16

accuracy

Answer 16

getting the answer you should be getting (or very close)