quantative chemistry

Question 1

what is an example of a closed system

Answer 1

a stoppered flask

Question 2

what is a closed substance

Answer 2

where no substances can enter or leave

Question 3

what closed systems happen in an open beaker

Answer 3

acid-alkali neutralisation reactions

Question 4

what is an example of a non-enclosed system

Answer 4

open flasks or boiling tubes

Question 5

example of a non-enclosed system

Answer 5

magnesium reacts with oxygen gained from the air to from magnesium oxide

Question 6

what is thermal decomposition

Answer 6

substance that breaks down into 2 or more substances when heated

Question 7

what is uncertainty

Answer 7

interval within which the true value of a quantity can be expected to lie

Question 8

what can be causes of uncertainty

Answer 8

• if a thermometer is showing the accurate temp

- exactly when a chemical reactions has finished

Question 9

how to calculate uncertianty from instruments

Answer 9

take half the resolution and put ± e.g. resolution of 1.0cm = ±0.5cm

Question 10

how to write down result with uncertainty from instruments

Answer 10

e.g. measured 24.0 degrees from thermometer, answer is 24.0 degreesC ± 0.5 degreesC

Question 11

how to calculate uncertainty from sets of repeat measurements

Answer 11

use ± half the range

Question 12

when is a solution formed

Answer 12

when a solute dissolves in a solvent

Question 13

how can concentration of a solution be found

Answer 13

-mass of dissolved solute
./
-volume of solution

Question 14

how to convert from cm^3 to dm^3

Answer 14

divide by 1000

Question 15

how to convert from dm^3 to cm^3

Answer 15

multiply by 1000

Question 16

what units must be used for volumes in concentration calculations

Answer 16

dm^3

Question 17

how to calculate mass of solute

Answer 17

concentration in g/dm^3 * volume in dm^3

Question 18

how can concentration of solution be changed

Answer 18

• dissolving more solute

- evaporating solvent

Question 19

how to calculate number of particles

Answer 19

amount of substance in moles * avogadro constant * subscript number

Question 20

when to use Ar instead of Mr

Answer 20

for metals or separate atoms

Question 21

how to calculate masses of substance in a balanced equation

Answer 21

relative formula mass * amount

Question 22

what is a limiting reactant

Answer 22

a reactant that has been used up

Question 23

what is excess

Answer 23

reactant that is left after a reaction

Question 24

what does the mass of a product depend on

Answer 24

the mass of the limiting reactant

Question 25

how to calculate balancing numbers

Answer 25

1- write the formula of substances
2-calculate the amount in moles
3-divide both by the smaller amount

Question 26

how to convert from mol/dm^3 to g/dm^3

Answer 26

multiply by relative formula mass

Question 27

how to convert from g/dm^3 to mol/dm^3

Answer 27

divide by relative formula mass

Question 28

how to calculate atom economy

Answer 28

(total Mr of desired product / total Mr of all reactants) * 100

Question 29

what is the theoretical yield

Answer 29

maximum possible mass of a product that can be made in a reaction

Question 30

reasons why mass of product is less than theoretic yield

Answer 30

• reaction not completing as it is reversible
• product may be lost when separated from reaction mixture
• some reactants may react in different ways different to expected

Question 31

what factors depend what chosen pathway you take

Answer 31

• percentage yield
• atom economy
• rate of reaction
• equilibrium position
• usefulness of by-products

Question 32

what is avagadro’s law

Answer 32

in a given temperature and pressure equal volumes of different gases contain equal numbers of molecules

Question 33

what is the molar volume

Answer 33

volume occupied by one mole of any gas at room temp and pressure (24dm^3)

Question 34

how to calculate volume of gas

Answer 34

amount in mol * molar volume

Question 35

how to calculate amount of gas

Answer 35

volume / molar volume