72 drops were 1ml for stearic acid the container was 8.5 cm wide and filled with hexane Trial 1 was 20 drops Trial 2 was 2

Question

72 drops were 1ml for stearic acid
the container was 8.5 cm wide and filled with hexane
Trial 1 was 20 drops
Trial 2 was 21
trial 3 was 16
The concentration of steric solution in hexane was :1.64*10^-4 g/ml
Area of single molecule of steric acid is: 0.21 mn^2
Molar mass of steric acid is: 284 g/mol
-What is the moles of stearic acid used?
-What is the number of stearic acid used to make the lens?
-how many molecules of stearic acid would there be if its it was 1 mole of stearic acid on that lense?

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Thu Giang 5 years 2021-08-27T07:25:25+00:00 1 Answers 14 views 0

Answers ( )

  1. RuslanHeatt
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    2021-08-27T07:26:33+00:00
    Reply

    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 = 1.6×10^-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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