Amount of Substance

Question 1

What is molecular formula?

Answer 1

Actual number of atoms of each element in a compound

Question 2

What is empirical formula?

Answer 2

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

Question 3

What is the formula for atom economy

Answer 3

(mr of desired product/ mr of all reactants) x 100

Question 4

what is the calculation for NUMBER of moles

Answer 4

number of molecules/ avogadro

Question 5

What is %yield?

Answer 5

Tells us about the practical efficiency of the process

Question 6

What is the formula for % yield?

Answer 6

(actual yield/mass/ theoretical mass) x 100

Question 7

What is the formula for actual yield?

Answer 7

(percentage yield x theoretical yield) / 100

Question 8

How do you carry out a %yield calculation

Answer 8

1. work out moles of reactant
2. use mole ratio from the balanced equation work out the theoretical moles of product
3. using the theoretical moles of product calculate the theoretical maximum mass of product.
4. use equation to work out %yield

Question 9

What is the equation for %purity?

Answer 9

(actual mass/impure mass) x 100

Question 10

How do you carry out a % purity calculation

Answer 10

1. work out the moles of the product (reactant is impure)
2. use mole ratio from the balanced equation work out the actual moles reactant that reacted
3. use actual moles of reactant calculate its actual mass
4. use equation to work out %purity

Question 11

what is the formula for apparatus error?

Answer 11

(margin of error/quantity) x100

Question 12

what is the ideal gas equation?

Answer 12

pv = nRt

Question 13

How do you convert KPa to Pa

Answer 13

x 1000

Question 14

How do you convert cm3 to m3

Answer 14

divide 1,000,000

Question 15

How do you work out empirical formula

Answer 15

• divide the percentage of the element by its Mr
• Work out the ratio of all elements by dividing by the smallest number
• Ratio should be whole numbers

Question 16

How do you calculate molecular formula from empirical formula and molecular mass

Answer 16

Mr of molecule
————————— = multiplier
Empirical Mr

Multiply empirical values by multiplier

Question 17

how can you calculate the limiting/excess reactant?

Answer 17

• work out the moles of both reactants
• reactant with the smallest value is limiting

Question 18

how do you calculate the average titre

Answer 18

titres (volume) within 0.1 of eachother

subtract them then divide by 2

Question 19

what is a back titration?

Answer 19

A base is treated with an excess of acid on the leftover acid is titrated (vice versa)

You can then work back to find the original base that reacted

Question 20

How can you use the limiting reagent to work out the maximum mass of products that can be made?

Answer 20

• after working out the limiting use the ratio to calculate moles of the product
• use moles to calculate mass

Question 21

define atomic number

Answer 21

number of protons in an atom

Question 22

how do you convert mg to g

Answer 22

divide by 1000

Question 23

how do you convert t into kg

Answer 23

x 1000

Question 24

What is the equation for density

Answer 24

Mass/volume

Question 25

What is the equation for concentration

Answer 25

moles/volume

Question 26

how do you convert m3 to dm3

Answer 26

x 1000

Question 27

how do you convert cm3 to dm3

Answer 27

divide 1000

Question 28

How do you express concentration in g dm^-3

Answer 28

Conc (g dm-3) = Conc in (mol dm-3) x Mr

Question 29

What are the stages of making a volumetric solution

Answer 29

Transfer known mass of solid Dissolve in water Transfer and wash

Question 30

How do you transfer a known mass of solid

Answer 30

1. Place a weighing boat on the balance and tare. 2. Transfer the solid to the weighing boat. 3. Record the mass.

Question 31

How do you dissolve solid in water to make volumetric solution

Answer 31

1. Transfer the solid into the beaker and rinse weighing boat with deionised water and transfer the washings to the beaker. 2. Add 100 cm3 of deionised water to the beaker. 3. Stir with a glass rod until the solid has dissolved.

Question 32

How do you transfer and wash when making a volumetric solution

Answer 32

1. Transfer the solution to a volumetric flask using a funnel. 2. Rinse the beaker stirring rod and funnel with deionised water and transfer the washings to the volumetric flask 3. Add deionised water to the volumetric flask to make up to the graduation mark. Use a dropping pipette when close to the mark 4. Invert flask to make sure the solution is thoroughly mixed.

Question 33

Why is a rough titration carried out first

Answer 33

used to determine the approximate amount of standard needed to neutralise an unknown solution.

Question 34

How do you set up and carry out a titration

Answer 34

1. Rinse the burette with deionised then with standard solution 2. Fill the burette including the area below the tap with the standard solution 3. Take initial reading and record to 2 decimal places (ending in a 5 or 0.) 4. transfer solution to conical flask and add indicator 5. add the solution from the burette, with constant swirling of the conical flask, until the indicator just changes colour. (indicates neutralisation)

Question 35

Why should you only add few drops of indicator

Answer 35

indicators are weak acids, and any more would affect the end point.

Question 36

Why is a conical flask used?

Answer 36

so no solution spills when swirling.

Question 37

Why should you remove the funnel before starting the titration

Answer 37

ensures no additional drops enter from the burette and lower your titre.

Question 38

How do you calculate the concentration of the solution in the conical flask after a titration

Answer 38

1. use table to work out concordant results and work out the avg titre 2. use avg titre and conc of the standard solution (a) to workout moles of (a) 3. use ratio from balanced equation to calculate moles of solution in conical flask (b) 4. calculate concentration of (b) using worked out moles and given volume

Question 39

How do you calculate the original mass and Mr from a titration

Answer 39

1. write balanced equation 2. the volume and concentration of HCl to calculate the moles of standard solution (a) 3. use the ratio from the balanced equation to deduce the moles solution in conical flask (b) 4. calculate the sample factor and calculate the number of moles in the original 250 cm3 solution 5. using these moles calculate the original mass of (b)

Question 40

How to do calculate moles of an acid from a back titration

Answer 40

1) Work out the excess moles of acid in the titration equation 1 2) Work out the moles of NaOH base required to neutralise the left-over acid. (ratio from equation 2 will allow you to determine the left-over moles of acid) 3) Use ratio and moles of NaOH to calculate moles of left-over acid 4) Subtract your left-over moles from excess moles of acid to determine how many moles of acid actually reacted in equation 1 5) Use your ratio in equation 1 to work out the moles of your carbonate base. (not NaOH) 5) Use your carbonate moles to determine an answer

Question 41

What colour is Phenolphthalein in an acid

Answer 41

Colourless

Question 42

What colour is Phenolphthalein in an alkali

Answer 42

pink

Question 43

What colour is Methyl orange in an acid

Answer 43

Red

Question 44

What colour is Methyl orange in an alkali

Answer 44

Yellow