Ch4 Chemical calculations

Question 1

Avogadro constant

Answer 1

6.02 x 10^23 atoms in one mole

Question 2

mole formula

Answer 2

mass/ (Mr)

Question 3

mass formula

Answer 3

mole x Mr

Question 4

Mr

Answer 4

relative formula mass

sum of mass numbers of elements within

Question 5

percentage yield formula

Answer 5

(actual mass/ theoretical mass) x 100%

Question 6

Factors affecting percentage yield

Answer 6

1. reaction may be reversible
2. may produce unexpected or unwanted products in alternative reactions
3. some products may be lost during separation
4. reactants may no be pure

Question 7

atom economy

Answer 7

measure of the amount of starting materials that end up as useful products

Question 8

atom economy formula

Answer 8

(Mr of desired product/ Mr of all reactants) x 100%

Question 9

concentration of a solution g/dcm^3

Answer 9

(mass of solute/ volume of solution cm^3) x 1000

mass of solute/ volume of solution dm^3

Question 10

concentration of a solution mol/dcm^3

Answer 10

moles in solute/ volume of solution dm^3

(mass/Mr) / volume of solution dm^3

Question 11

Volume of a gas dm^3

Answer 11

mole of gas x 24 dm^3

(Mass/Mr) x 24 dm^3

Question 12

1dm^3

Answer 12

1000cm^3

Question 13

mole of gas

Answer 13

vol of gas/ 24dm^3 or 24,000^3

Question 14

volume of one mole of gas

Answer 14

24dm^3 at room temperature and pressure

Question 15

Titration method

Answer 15

1. Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
2. Add a few drops of indicator(pink phenolphthalein) and put the conical flask on a white tile.
3. Fill the burette with acid and note the starting volume.
4. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5. Stop adding the acid when the indicator phenolphthalein changes to colourless. Note the final volume reading.
6. Calculate the titre by finding the difference between the end and starting volume
7. Repeat steps 1 to 5 until you get concordant titres(within 0.1cm^3 of each other)
8. Calculate the mean titre