The volume of a rock is 29 ml. The mass of the rock is 5 grams. What is its density

d =  

m

V

m = d×V

V =  

m

d

DENSITY

Density is defined as mass per unit volume.

d =  

m

V

Example:

A brick of salt measuring 10.0 cm x 10.0 cm x 2.00 cm has a mass of 433 g. What is its density?

Step 1: Calculate the volume

V = lwh = 10.0 cm × 10.0 cm × 2.00 cm = 200 cm³

Step 2: Calculate the density

d =  

m

V

=  

433

g

200

c

m

³

= 2.16 g/cm³

MASS

d =  

m

V

We can rearrange this to get the expression for the mass.

m = d×V

Example:

If 500 mL of a liquid has a density of 1.11 g/mL, what is its mass?

m = d×V = 500 mL ×  

1.11

g

1

m

L

= 555 g

VOLUME

d =  

m

V

We can rearrange this to get the expression for the volume.

V =  

m

d

Example:

What is the volume of a bar of gold that has a mass of 14.83 kg. The density of gold is 19.32 g/cm³.

Step 1: Convert kilograms to grams.

14.83 kg ×  

1000

g

1

k

g

= 14 830 g

Step 2: Calculate the volume.

V =  

m

d

= 14 830 g ×  

1

c

m

³

19.32

g

= 767.6 cm³

Explanation:

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.