atom economy

Question 1

What is atom economy?

Answer 1

The mass of the product that we want as a % of the mass of all the products we make.
Atom economy= mass of desired product/ mass of all products x 100

= mass of the reactants

Question 2

What is the atom economy for the production of CH2Cl2 for the following reaction: 2Cl2+CH4-> CH2Cl2 + 2HCl

Answer 2

A.e.: desired/all x 100
Mr of (ch2cl2) 
= 12 +2+71
=85
Mr of hcl 
=1+35.5
=36.5
X2
= 73
85+73 = 158
A.e. 85/158 x100
= 53.8%

Question 3

what is the importance of atom economy?

Answer 3

Chemical reactions produce unwanted by-products. These are waste products. Improving atom economy can reduce this waste to make it more sustainable , minimize waste and maximize efficiency.

Question 4

What is the atom economy of addition reactions?

Answer 4

100% atom economy with no by-products

Question 5

What is the atom economy of substitution and elimination reactions?

Answer 5

<100% atom economy

Question 6

Ethanol is a valuable chemical. It can be made in a number of ways, one such way is through the fermentation of glucose according to the equation : C6H12O6(aq) -> 2C2H5OH (aq) + 2CO2(g)
Calculate the atom economy of the above reaction

Answer 6

A.e: mr desired / mr of all. X100
Mr of ethanol : 24+6+16
=46 
Mr of CO2: 12+32
= 44
46x2 +44x2 
=180
46x2=92
92/180 x100
=51.1%

Question 7

Another method used in the production of ethanol is the hydration of ethene as shown in the reaction: C24+H2O -> C2H5OH
Compare the atom economy of this reaction to that of the fermentation (51.1)
Which reaction is preferable?(industrially)

Answer 7

This reaction is preferable as no waste products or by-products are formed unlike the reaction in a .

Question 8

Magnesium hydroxide Mg(OH)2 us used to treat indigestion. It is made using magnesium chloride MgCl2 and sodium hydroxide NaOH. There is one by-product of this reaction which is the same as table salt. ‘Write a balanced equation for the reaction and calculate the atom economy of this reaction’

Answer 8

MgCl2+ 2 NaOH -> Mg(OH)2 + 2 NaCl
Mr of Mg(OH)2 
\: 2+32+24.3
->58.3
Mr of NaCl
\: 35.5 +23
-> 58.5
A.e. : 58.3/58.3+58.5x2 x100
= 33.3%

Question 9

A scientist reacts 10g of MgCl2 with an excess of NaOH. What is the maximum mass of Mg(OH)2 he could make?

Answer 9

Moles=mass/mr
Mol of MgCl2:
10/24.3+71
=0.105mols
1:1 so Mg(OH)2 = 0.105mols
Mass = moles x mr
= 0.105 x 58.3
6.1g

Question 10

The actual mass he obtains is 5G what is the yield of the experiment (6.1g was theoretical) in this experiment how does atom economy relate to yield?

Answer 10

5/6.1 x100
=82.0%
Atom economy is separate from the yield. The yield of this reaction is high however the atom economy is low.