Basic Chemistry Chapter 2 Measurements Chapter 2 Lecture 2.7 Density Fifth Edition Chapter 2 Measurements 2.7 Density Learning Goal Calculate the density of a substance; use the density to calculate the mass or volume of a substance.

Density Density compares the mass of an object to its volume. is the mass of a substance divided by its volume. is defined as

Density Substances that have higher densities contain particles that are closely packed together. lower densities contain particles that are farther apart. Metals such as gold and lead have higher densities because their atoms are packed closely together.

Density: Units In the metric system, densities of solids, liquids, and gases are expressed with different units. The density of a solid or liquid is usually given in grams per cubic centimeter (g/cm3) or grams per milliliter (g/mL). The density of a gas is usually given in grams per liter (g/L).

Density of Common Substances

Guide to Calculating Density

Calculating Density A 0.258-g sample of high-density lipoprotein (HDL) has a volume of 0.215 cm3. What is the density of the HDL sample? STEP 1 State the given and needed quantities. STEP 2 Write the density expression.

Calculating Density A 0.258-g sample of high-density lipoprotein (HDL) has a volume of 0.215 cm3. What is the density of the HDL sample? STEP 3 Express mass in grams and volume in cm3. STEP 4 Substitute mass and volume into the density expression and calculate the density.

Link to Health: Bone Density A condition of severe thinning of bone known as osteoporosis may occur. Scanning electron micrographs (SEMs) show (a) normal bone and (b) bone with osteoporosis due to loss of bone minerals.

Link to Health: Bone Density Bone density is often determined by passing low-dose X-rays through the narrow part at the top of the femur (hip) and the spine (c). Bones with high density will block more of the X-rays compared to bones that are less dense.

Density of Solids Using Volume Displacement The density of a solid is calculated from its mass and volume. When a solid is submerged, it displaces a volume of water equal to the volume of the solid.

Density of Solids In the figure below, the water level rises from 35.5 mL to 45.0 mL after the zinc object is added.

Using Volume Displacement to Calculate Density A lead weight used in the belt of a scuba diver has a mass of 226 g. When the weight is carefully placed in a large graduated cylinder containing 200.0 cm3 of water, the water level rises to 220.0 cm3. What is the density (g/cm3) of the lead weight?

Using Volume Displacement to Calculate Density STEP 1 State the given and needed quantities. STEP 2 Write the density expression.

Using Volume Displacement to Calculate Density STEP 3 Express mass in grams and volume in cm3. Mass of lead weight = 226 g STEP 4 Substitute mass and volume into the density expression and calculate the density.

Guide to Using Density as a Conversion Factor

Using Density as a Conversion Factor Greg has a blood volume of 5.9 qt. If the density of blood is 1.06 g/mL, what is the mass, in grams, of Greg’s blood? STEP 1 State the given and needed quantities. STEP 2 Write a plan to calculate the needed quantity.

Using Density as a Conversion Factor Greg has a blood volume of 5.9 qt. If the density of blood is 1.06 g/mL, what is the mass, in grams, of Greg’s blood? STEP 3 Write the equalities and their conversion factors including density. STEP 4 Set up the problem to calculate the needed quantity.

Specific Gravity Specific gravity (sp gr) is a relationship between the density of a substance and the density of water. Specific gravity is calculated by dividing the density of a sample by the density of water, which is 1.00 g/mL at 4 °C. A substance with a specific gravity of 1.00 has the same density as water (1.00 g/mL).

Specific Gravity A hydrometer is used to measure the specific gravity of urine. The normal range of specific gravity for urine is 1.003 to 1.030. The specific gravity can decrease with type 2 diabetes and kidney disease. Increased specific gravity may occur with dehydration, kidney infection, and liver disease.

Specific Gravity In a clinic or hospital, a dipstick containing chemical pads is used to evaluate specific gravity.

Concept Map