Question

experiment 2
pre - lab questions
name:
section:
answer all calculation questions to the correct number of significant figures.

1. define density. in what units is density most often expressed for solids, for liquids?
2. what method can be used to determine the volume of an irregularly - shaped solid?

3a. the mass of a sample bottle is 27.32 g. when filled with water, the bottle weighs 46.85 g. the density of water is known to be 0.9976 g/ml. calculate the capacity (volume) of the bottle.
3b. the sample bottle in question 3a is emptied, then filled with an unknown liquid. the mass of the bottle and the liquid is 41.27 g. calculate the density of the unknown liquid.

Explanation:

1. Density is defined as mass per unit volume of a substance. For solids, it is most often expressed in grams per cubic centimeter ($\text{g/cm}^3$); for liquids, it is most often expressed in grams per milliliter ($\text{g/mL}$).
2. The water displacement method (submerging the irregular solid in a measured volume of water and measuring the change in volume) is used to find the volume of an irregularly-shaped solid.

(for 3a and 3b):

Step1: Find mass of water

$\text{Mass of water} = 46.85\ \text{g} - 27.32\ \text{g} = 19.53\ \text{g}$

Step2: Calculate bottle volume

Use $V = \frac{m}{
ho}$.
$V = \frac{19.53\ \text{g}}{0.9976\ \text{g/mL}} = 19.58\ \text{mL}$

Step3: Find mass of unknown liquid

$\text{Mass of liquid} = 41.27\ \text{g} - 27.32\ \text{g} = 13.95\ \text{g}$

Step4: Calculate liquid density

Use $
ho = \frac{m}{V}$.
$
ho = \frac{13.95\ \text{g}}{19.58\ \text{mL}} = 0.7125\ \text{g/mL}$

Answer:

1. Density is mass per unit volume. Solids: $\text{g/cm}^3$; Liquids: $\text{g/mL}$
2. Water displacement method

3a. $19.58\ \text{mL}$
3b. $0.7125\ \text{g/mL}$