Lab calculation - Non-volatile residue - convert to requested format

[GaryJ]

Doing a lab experiment (let me know if this is in the wrong category and I'll move it) to calculate non-volatile residue in a cleaned tube.
I have a control beaker and sample beaker and tube which is rinsed in a solvent then that sample is evaporated and compared against a control to determine how "dirty" the tube is.
Inner diameter of tube: .2565" (its open ended)
Length of tube: 45"
Pi: 3.14159654
Inner surface area in sq inches: 36.2618
sample weight in grams: .0135
Control weight in grams: .0131

In need to submit this expressed in milligrams per square feet.

Depending on what order I do the conversions I get different answers.

thanks in advance.

 

[stapel]

Doing a lab experiment (let me know if this is in the wrong category and I'll move it) to calculate non-volatile residue in a cleaned tube.
I have a control beaker and sample beaker and tube which is rinsed in a solvent then that sample is evaporated and compared against a control to determine how "dirty" the tube is.
Inner diameter of tube: .2565" (its open ended)
Length of tube: 45"
Pi: 3.14159654
Inner surface area in sq inches: 36.2618
sample weight in grams: .0135
Control weight in grams: .0131

In need to submit this expressed in milligrams per square feet.

Depending on what order I do the conversions I get different answers.

Please reply showing your two different conversions. Thank you!

 

[GaryJ]

Where I'm having the issue is where the conversion takes place. I have an example where the calculation is performed and then the answer converted.
e.g.
.0004 grams / 36.2618 sq. inches = 0.0000110 grams per sq inch
0.0000110/144*1000 (to convert sq in to sq ft and grams to mg) = 0.000766 mg/sq ft
I don't believe this is correct.

Also it depends on if you calculate like this: 0.000110 / (144*1000) = extremely small number...


I believe you should convert the units then do the calculation.
e.g.
.0004 *1000 = 0.4 mg
36.2618 sq in / 144 = 0.251818 sq ft
0.4 mg / 0.251818 sq ft = 1.588447 mg/sq ft

As you can see they are vastly different answer.

the formula given to me is:
(C-A)-(D-B) grams / Pi*E*L
where:
A = initial mass of sample container
B = initial mass of control container
C = Mass of sample container after evaporation
D = Mass of control container after evaporation
E = Diameter of tube measured in inches
L = Length of Tube measured in inches

NVR in grams/Square Inch/144*1000 = mg/Sq Ft

 

[Deleted member 4993]

Where I'm having the issue is where the conversion takes place. I have an example where the calculation is performed and then the answer converted.
e.g.
.0004 grams / 36.2618 sq. inches = 0.0000110 grams per sq inch

= 1.10309E-05 * 144 grams per sq ft (amount in a sq.ft. must be larger than the amount in sq.in)

= 1.10309E-02 * 144 mg per sq ft

= 0.001588 gms/sq.ft

0.0000110/144*1000 (to convert sq in to sq ft and grams to mg) = 0.000766 mg/sq ft
I don't believe this is correct.

Also it depends on if you calculate like this: 0.000110 / (144*1000) = extremely small number...


I believe you should convert the units then do the calculation.
e.g.
.0004 *1000 = 0.4 mg
36.2618 sq in / 144 = 0.251818 sq ft
0.4 mg / 0.251818 sq ft = 1.588447 mg/sq ft

As you can see they are vastly different answer.

the formula given to me is:
(C-A)-(D-B) grams / Pi*E*L
where:
A = initial mass of sample container
B = initial mass of control container
C = Mass of sample container after evaporation
D = Mass of control container after evaporation
E = Diameter of tube measured in inches
L = Length of Tube measured in inches

NVR in grams/Square Inch _* (144*1000) = mg/Sq Ft

If done correctly, the sequence of conversion does not matter

 

[GaryJ]

Subhotosh,
Thank you for your reply.
I don't understand this statement, "(amount in a sq.ft. must be larger than the amount in sq.in)"
This doesn't make sense to me. 1 sq foot = 144 sq inches
Please explain.
Thank you!

 

[stapel]

I don't understand this statement, "(amount in a sq.ft. must be larger than the amount in sq.in)"
This doesn't make sense to me. 1 sq foot = 144 sq inches

Surely, since there are 144 square inches in one square foot, then there should be 144 times as much in one square foot as there is in one square inch...?

 

[mmm4444bot]

I believe you should convert the units then do the calculation.

.0004 *1000 = 0.4 mg
36.2618 sq in / 144 = 0.251818 sq ft
0.4 mg / 0.251818 sq ft = 1.588447 mg/sq ft

I also get 1.588 mg/ft².

(The measurements are not precise enough to justify reporting six decimal places.)

NVR in grams/Square Inch/144*1000 = mg/Sq Ft

The division highlighted in red above is incorrect. That should be a multiplication.

g/in² * 144000 = mg/ft²

:idea: Google the following:

convert 1 g/in^2 to mg/ft^2