C5 - Chemical analysis

Question 1

what is pure substance?

Answer 1

a substance is something that only contains one compound or element throughout

Question 2

what are mixtures?

Answer 2

substances that contain more than one element or compound which isn’t chemically bonded

Question 3

what are formulations?

Answer 3

are useful mixtures with a precise purpose that are made by following a “formula”

Question 4

what is filtration?

Answer 4

to separate an insoluble solid from a liquid

Question 5

what is crystalisation?

Answer 5

separates a soluble solid from a solution

Question 6

what is simple distillation?

Answer 6

is used for separating out a liquid from a solution, or to separate liquids that have very different boiling points

Question 7

how do you calculate the relative atomic mass?

Answer 7

sum of (isotope abundance x isotope mass number) / sum of abundances of all isotopes

Question 8

how do you calculate the percentage of mass of an element in a compound?

Answer 8

(atomic mass x amount of element ÷ atomic mass total of compound) x 100%

Question 9

what are the 2 reasons why mass could change?

Answer 9

1. if the mass increases, because some of the atoms in gaseous reactants end up in solid, liquid, or aqueous products
2. if the mass decreases, because some of the solid/liquid/gas or aqueous reactants end up in gaseous products

Question 10

what is the equation to work out the number of moles?

Answer 10

Number of moles = mass grams / relative formula mass

Question 11

what is Avogadro’s constant?

Answer 11

6.0 x 10 to the power of 23

Question 12

what is an acid?

Answer 12

is a substance that dissolves in water to release H+ ions

Question 13

what is an alkali?

Answer 13

is a substance that produces hydroxide (OH-) ions when it dissolves in water

Question 14

acid + alkali →

Answer 14

acid + alkali → salt + water

Question 15

does the salt from the reaction contain the negative or positive ion?

Answer 15

negative

Question 16

does the acid from the reaction contain the negative or positive ion?

Answer 16

positive

Question 17

HCI + NaOH →

Answer 17

HCI + NaOH → NaCl + H₂O

Question 18

what is concentration?

Answer 18

the amount of substance in a given volume of solution is called its concentration

Question 19

how do you calculate the concentration of a solution?

Answer 19

g/dm concentration = mass of solute (g) / volume of solvent in dm3

Question 20

how do u calculate the concentration for it to be in mols?

Answer 20

concentration (mol/dm) = number of moles solute (mol) / volume of solvent (dm)

Question 20

what is chromotography?

Answer 20

analytical method used to separate the substance in a mixture
used to identify substances

Question 21

what is the mobile phase in chromatography?

Answer 21

when particles of the phase can move in a mixture
liquid / gas

Question 22

what is the stationary phase in chromatography?

Answer 22

where the particles of the phase can’t move
solid / very thick liquid

Question 23

how do you do paper chromatography?

Answer 23

1. draw a line near the bottom w pencil
2. add a spot of test substance to the line & place into solvent
3. place a lid on top of container to minimise evaporation of solvent
4. when solvent has nearly reached the top take it out and let it to dry
5. if the chromatogram has more than 1 substance, it was impure

Question 24

what to do if there is colourless chemicals in the chromatograms?

Answer 24

locating agents: - if the mixture contains amino acids, u can spray - ninhydrin solution - dip the completed paper in a few iodine crystals

Question 25

what is an RF value?

Answer 25

is the ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent

Question 26

what is the calculation for calculating the Rf value?

Answer 26

Rf = distance travelled by solute / distance travelled by solvent

Question 27

what are titrations?

Answer 27

let you find out how much acid is needed to neutralise a quantity of alkali or acid

Question 28

what is the calculation for the number of moles in the other substance in titration?

Answer 28

moles = concentra x volume