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3 years ago

72 drops were 1ml for stearic acid

Chemistry

1 answer:

Svetach [21]3 years ago

6 0

CaseAnswer:

-Mole of stearic acid used = 1.3*10^-3 mol

-Molecules of stearic acid there would be in 1 mole of stearic acid = 7.994*10^20 molecules

Explanation:

Know information from the problem are:

Mass concentration of C18H32O2 = 1.6x10^-4 g/ml, Molar mass of C18H32O2 = 284 g/mol.

Unit factor from drops to ml is 72 drops = 1ml. Therefore, for every drop, n, given, there would be n drops (1ml/ 72drops). The problem tells that stearic acid was added to hexane and that the addition process was done three-time with different amounts of drops. Think of this as releasing a substance from a burette during titration. If we convert the drops into millimeters, we would have 20 drops (1ml/72drops)= 0.28 ml, 21 drops (1ml/72drops)= 0.29 ml, and 16 drops (1ml/72drops)= 0.22 ml. [We need these volumes to determine the mass of stearic acid from mass concentration given.]

Unknown informations are:

V (volume in ml) =?

The mole of stearic acid used =?

Strategy

To calculate the mole of stearic acid used, we need the mass of stearic acid from the mass concentration. To get this we need a volume. Notice that those volumes (drops) are not the same ( it is safe to say that there is an error in the readings, as they were done independently). Therefore, we would find two or three values whose difference is smaller ( there is a little error). Subtract the smaller number from the larger number till you get a smaller difference ( do this for all three values).

The set of numbers with the smallest difference is 0.29 - 0.28=0.014, our concordant value.

Solutions

Now we us this set of numbers, 0.29-0.28, to determine an average volume :

V = (0.29-0.28)/2 (ml)

V= 0.285 ml

Now we can calculate the mass of stearic acid from the mass concentration:

m = C*V; m is the mass, C is the concentration in g/ ml, and V is the volume in ml.

m = (1.64*10^-4 g/ml)*(0.285 ml)

m = 4.674*10^-5 g

The mole of stearic acid used:

n = m/MM l; n is the mole of stearic acid, m is the mass of stearic acid, and MM is the molar mass of stearic acid.

n = 4.674*10^-5 g (284 g/mol)

n = 1.3274*10^-3

How many molecules of stearic acid would there be if it was 1 mol of stearic acid?

1 mol = 6.02214*10^23 molecule

Therefore, a conversion fraction would be:

6.02214*10^23 molecule/ 1 mol

Solution

Molecules of stearic acid in 1 mol =

1.3274*10^-3 mol (6.02214*10^23 molecule/ 1 mol)

= 7.994*10^20 molecules in 1 mol of C18H16O2

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