module 2 - foundations in chemistry

Question 1

charge of ammonium ion

Answer 1

(NH4) +

Question 2

charge of hydroxide ion

Answer 2

OH -

Question 3

charge of nitrate ion

Answer 3

(NO3) -

Question 4

charge of carbonate ion

Answer 4

(CO3) ^2+

Question 5

charge of sulfate ion

Answer 5

(SO4) ^2-

Question 6

define molecular formula

Answer 6

number of atoms of each element in a molecule

Question 7

define empirical formula

Answer 7

simplest whole number ratio of atoms of each element in a compound

Question 8

relative molecular mass

Answer 8

• compares the mass of a molecule with the mass of an atom of carbon-12

Question 9

relative formula mass

Answer 9

mass of a formula unit with the mass of an atom of carbon-12

Question 10

relative atomic mass

Answer 10

weighted mean mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12

Question 11

method to work out formula of hydrated salt

Answer 11

• weigh empty cruicible
• add hydrated salt to crucible and weigh
• heat the crucible and contents using bunsen burner, gently for 1 min, then strongly for 3 mins
• leave to cool and weigh again
• repeat till theres no change in mass of the cruicible
• then calculate.
  subtract initial mass of cruicible from the final mass. this is mass of water that would have evapourated.
  use to calculate.

Question 12

assumptions made for the molecules when using the ideal gas equation

Answer 12

• no intermolecular forces
• random motions
• elastic collisions
• negligible size

Question 13

reasons why 100% yield is not achieved

Answer 13

• reaction might have not gone to completion
• other side reactions may have taken place alongside main reaction
• purification of product might result in loss of some of product

Question 14

advantages of having reactions with high atom economies

Answer 14

• produces large proportion of desired products and few unwanted waste products
• important for sustainability as they make use of natural resources

Question 15

what is an acid

Answer 15

proton donor

Question 16

what are titrations used for

Answer 16

• finding conc of solution
• identifyng unknown chemicals
• finding purity of substance

Question 17

method to prepare standard solution

Answer 17

• weigh solid accuratey
• dissolve solid in beaker with distilled water (use less distilled water than needed to fill volumetric flask)
• transfer solution to volumetric flask
• rinse the beaker with distilled water to get the last traces of the solution into the flask
• fill flask carefully to graduation line by adding distilled water drop at a time
• if too much added, solution becomes too dilute and would need to be prepared again
• invert volumetric flask several times to mix solution thoroughly. if this is missed out, titration results are unlikely to be consistent.

Question 18

why are standard solutions used

Answer 18

• they have a known concentration so they can help identify the concentration of unknown substances

Question 19

method for acid-base titration

Answer 19

• add measured volume of one solution to conical flask using pipette
• add other solution to burette and record initial burette reading to nearest 0.05 cm cubed
• add few drops of indicator to conical flask
• run solution in burette into conical flask, swirl to mix two solutions
• stop when indicator changes colour - this is end point
• record final burette reading

FINISH OFF FLASHCARD. PG 44.

Question 20

oxidation number rules

Answer 20

-

Question 21

define strong acid

Answer 21

acid that fully dissociates in water

Question 22

define weak acid

Answer 22

acid that only partially dissociates in water