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Higher Chemistry > Calculations > Flashcards

Calculations Flashcards

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1
Q

what does it mean if a reactant is in ‘excess’

A

some left over/ extra after the reaction has occured

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2
Q

why is it called a ‘limiting’ reagent

A

limits how much product can be formed

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3
Q

what is the mass of 1 mole

A

gfm

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4
Q

steps in excess calculations

A
  1. find no of moles for each reactant
  2. write down molar ratio
  3. sub in actual no of moles of reactant 1 and see how much reactant 2 is needed
  4. if have enough then r2 is in excess and r1 is limiting reagent, if not sub in other way around
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5
Q

steps on how to find mass of product formed

A
  1. work out which reactant is in excess and which is limiting reagent
  2. work out no of moles of product will be produced based on moles of LIMITING REAGENT
  3. use mass,n,gfm triangle to calculate mass of product formed
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6
Q

purpose of percentage yield calculations

A

chemical reactions do not produce 100% of the product expected and the actual yield is less than this.

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7
Q

percentage yield equation

A

%yield=actual yield/theoretical yield x100

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8
Q

what is generally considered to be a good %yield?

A

above 70%

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9
Q

steps for percentage yield calculation?

A
  1. write out molar ratio
  2. work out number of moles of reactant
  3. work out number of moles of product
  4. work out mass of product (theoretical yield)
  5. find %yield using theoretical and actual yield
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10
Q

what is molar volume?

A

the volume occupied by one mole of gas

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11
Q

units of molar volume

A

litres/mol

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12
Q

the molar volume is the same…

A

for all gases at the same temperature and pressure

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13
Q

approximate molar volume of gases at 20 degrees is…

A

24 litres/mol

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14
Q

approximate molar volume of gases at 0 degrees is…

A

22.4 litres/mol

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15
Q

molar volume equation

A

molar volume = volume/no. of moles

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16
Q

determining molar volume experimentally

A
  1. work out mass of gas (mass of flask+gas-mass of flask)
  2. work out no. of moles n=m/gfm
  3. sub in no. of moles to molar volume equation
17
Q

way to work out mass of reactant mixture without calculator

A

molar ratio

18
Q

reacting volumes (gas in a reaction) steps

A
  1. calculate no of moles of substance in the question
  2. use molar ratio
  3. use molar volume relationship
19
Q

excess and molar volume steps

A
  1. find the limiting reagent
  2. use molar ratio to find moles of what you are looking for
  3. use molar volume relationship
20
Q

2 ways the efficiency of reactants being converted into products can be measured:

A
  1. percentage yield

2. atom economy

21
Q

%yield: after a chemist makes a new product…

A

they allow the product to ‘dry’ so that any water/solvent is removed.
watch glass weighed again with new substance on - difference in masses = actual mass of product
can then carry out %yield calculation

22
Q

percentage yield provides a measure of…

A

the degree in which the limiting reagent is converted to the desired product

23
Q

what does percentage yield not take into account

A

by-products formed that could be problematic and wasteful

24
Q

atom economy measures the…

A

proportion of the total mass of reactants converted into the desired product.

25
Q

reactions which have a high percentage yield may have a low atom economy if…

A

large quantities of unwanted by-products are formed

26
Q

atom economy equation

A

%atom economy= mass of desired products / total mass of reactant x100

27
Q

100% atom economy means that…

A

all reactants are turned into products. This is desirable

28
Q

Situation where there is 100% atom economy

A

if there is only 1 product

29
Q

steps for calculating atom economy

A
  1. work out mass of desired product (no. of moles x gfm)
  2. work out total mass of reactants
  3. atom economy equation
30
Q

clean by-products that are easy to dispose of

A

water

31
Q

comparing two processes

A

work out atom economy for each and compare by-products - are they wasteful, toxic, flammable etc?

32
Q

steps for redox titration calculations:

A
  1. work out no. of moles of substance of known concentration
  2. use molar ratio to work out no. of moles of substance of unknown concentration
  3. calculate concentration using c=n/v

Higher Chemistry (16 decks)

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