Density and specific gravity

What is Density?

Mass per unit volume of a substance.

What are the Units of Density?

Grams per cubic centimeter (g/cc) or grams per milliliter (g/mL).

What is the Density of Water?

Density = 1 g/cc (since 1 cc = 1 mL, also 1 g/mL).

What is the Density of Mercury?

Density = 13.6 g/mL

What is the Density Formula?

Density = Mass / Volume.

10 mL of sulfuric acid weighs 18 g. Density = 18 g / 10 mL =

1.8 g/mL

A piece of copper metal weighs 53.6 g, and has a volume of 6 mL. Calculate its density?

8.933 g/mL

If 250 mL of alcohol weighs 203 g, what is its density?

0.812 g/mL

Specific Gravity

Ratio of a substance's weight to the weight of an equal volume of a standard (usually water for liquids/solids, hydrogen for gases), both at the same temperature.

Specific Gravity Formula

Weight of substance / Weight of equal volume of water.

10 mL of sulfuric acid weighs 18 g, 10 mL of water weighs 10 g. Specific Gravity=18g/10g=

1.8

sp gr < 1:

Lighter than water

sp gr > 1:

Heavier than water

If 150 mL of a sorbitol solution weigh 170 g, what is its specific gravity?Solution:

1.1333

If 2 fl. oz. of glycerol weighs 74.1 g, what is its specific gravity?

1.25

What is a Pycnometer?

A special glass bottle used to measure specific gravity.

What are the Sizes of a Pycnometer?

Available in 1 to 50 mL volumes for laboratory use.

A 50-mL pycnometer weighs 120g when empty, 171g when filled with water, and 160g when filled with an unknown liquid. Calculate the specific gravity of the unknown liquid.

0.78

What is the cost of 1000mL of glycerin, specific gravity 1.25, bought at $5.43 per pound?

$14.93

If a pharmacist dissolves 1.2 g of a medicinal agent in 60 mL of a cough syrup having a specific gravity of 1.20, what is the specific gravity (to 3 decimal places) of the product if the addition of the medicinal agent increases the syrup's volume by 0.2 mL?

1.216 g / mL

LWQ =

(SR / % Error) 100%

LWQ method

(amount read / aliquot (w%) ) = (drug weighed / total mix (x))

A torsion prescription balance has a sensitivity requirement of 0.004 g. Explain how you would weigh 0.008 g of a substance with an error not greater than 5%?

0.08

If a liter of a cough syrup weighs 1285 g, what is its specific gravity?

1.285

If 500 mL of a solution weigh 650 g, what is its specific gravity?

1.3

A formula for an anesthetic ointment is;

Benzocaine 200 g

Polyethylene glycol 400 600 g

Polyethylene glycol 3350 ad 1000g

Polyethylene glycol 400 is a liquid, sp gr. 1.13, benzocaine and polyethylene glycol3350 are powders. How many milliliters of polyethylene glycol would be used in the formula?

531

Cocoa butter (theobroma oil), which is solid at room temperature and melts at 34°C, has a specific gravity of 0.86. If a formula calls for 48 mL of theobroma oil, what would be the corresponding weight of cocoa butter to use?

41

A patient added a 17-g measured dose of polyethylene glycol 3350 (MIRALAX®) to 180mL of water to use as a laxative. If the volume of the resultant mixture was 195.6 mL, calculate the apparent density of polyethylene glycol 3350 and the specific gravity of the mixture.

1.1, 1.01