Question

Polymers are large molecules composed of simple units repeated many times. Thus, they often have relatively simple empirical formulas. Calculate the empirical formulas of the following polymers: (a) Lucite (Plexiglas); 59.9% C, 8.06% H, 32.0% O (b) Saran; 24.8% C, 2.0% H, 73.1% Cl (c) polyethylene; 86% C, 14% H (d) polystyrene; 92.3% C, 7.7%

Answer 1

Answer:

(a) C5H8O2

(b) C2H2Cl2

(c) CH2

(d) CH

Explanation:

We need to find the proportion of the atoms in whole numbers. Given the percentages we can calculate the number of moles and find their proportions.

Assume 100 g and given the atomic weights the moles are calculated.

(a) C = 59.9/ 12.01 = 4.98  ≈ 5.00

    H = 8.06/1.007 = 8.00

    O = 32/15.999  = 2.00

C5H8O2

(b) C= 24.8/12.01 = 2.06≈ 2.00

    H = 2.0/1.007 = 1.99 ≈ 2.00

   Cl = 73.1/ 35.453 = 2.06 ≈ 2.00

C2H2Cl2

(c) C = 86/12.01 = 7.16  

    H= 14/1.007 = 13.90

7.16:13.90 ≈ 1:2

CH2

(d) C = 92.30/12.01 = 7.68

    H = 7.7 / 1.007 =   7.65

7.68:7.65 ≈ 1:1

CH

Answer 2

In letter d that's a missing information: it's 7.7% H.

Answer:

a. C₅H₈O₂

b. CHCl

c. CH₂

d. CH

Explanation:

Let's consider a sample that has 100 g of mass, so by that, we can calculate the mass of each component. After that, the number of moles can be find dividing the mass by the molar mass. The molar mass of the elements given are: C = 12 g/mol, O = 16 g/mol, H = 1 g/mol, and Cl = 35.5 g/mol. The empiric formula is the simplest one, so, all the number moles must be divided by the small one. If it's not divisible, then the empiric formula is already done.

a.

mC = 0.599*100 = 59.9 g

mH = 0.0806*100 = 8.06 g

mO = 0.32*100 = 32 g

nC = 59.9/12 = 5 mol

nH = 8.06/1 = 8 mol

nO = 32/16 = 2 mol

Because 5 is not divided by 2, the empiric formula is C₅H₈O₂.

b.

mC = 0.248*100 = 24.8 g

mH = 0.02*100 = 2 g

mCl = 0.731*100 = 73.1 g

nC = 24.8/12 = 2 mol

nH = 2/1 = 2 mol

nCl = 73.1/35.5 = 2 mol

So, all must be divided by 2, and the empiric formula will be CHCl.

c.

mC = 0.86*100 = 86 g

mH = 0.14*100 = 14 g

nC = 86/12 = 7 mol

nH = 14/1 = 14 mol

Dividing all by 7, the empiric formula is CH₂.

d.

mC = 0.923 *100 = 92.3 g

mH = 0.077*100 = 7.7 g

nC = 92.3/12 = 7.7

nH = 7.7/1 = 7.7

Dividing all by 7.7, the empirical formula is CH.