<< Chapter < Page Chapter >> Page >

Time

The SI base unit of time is the second (s)    . Small and large time intervals can be expressed with the appropriate prefixes; for example, 3 microseconds = 0.000003 s = 3 × 10 −6 and 5 megaseconds = 5,000,000 s = 5 × 10 6 s. Alternatively, hours, days, and years can be used.

Derived si units

We can derive many units from the seven SI base units. For example, we can use the base unit of length to define a unit of volume, and the base units of mass and length to define a unit of density.

Volume

Volume is the measure of the amount of space occupied by an object. The standard SI unit of volume is defined by the base unit of length ( [link] ). The standard volume is a cubic meter (m 3 )    , a cube with an edge length of exactly one meter. To dispense a cubic meter of water, we could build a cubic box with edge lengths of exactly one meter. This box would hold a cubic meter of water or any other substance.

A more commonly used unit of volume is derived from the decimeter (0.1 m, or 10 cm). A cube with edge lengths of exactly one decimeter contains a volume of one cubic decimeter (dm 3 ). A liter (L)    is the more common name for the cubic decimeter. One liter is about 1.06 quarts.

A cubic centimeter (cm 3 ) is the volume of a cube with an edge length of exactly one centimeter. The abbreviation cc (for c ubic c entimeter) is often used by health professionals. A cubic centimeter is also called a milliliter (mL)    and is 1/1000 of a liter.

Figure A shows a large cube, which has a volume of 1 meter cubed. This larger cube is made up of many smaller cubes in a 10 by 10 pattern. Each of these smaller cubes has a volume of 1 decimeter cubed, or one liter. Each of these smaller cubes is, in turn, made up of many tiny cubes. Each of these tiny cubes has a volume of 1 centimeter cubed, or one milliliter. A one cubic centimeter cube is about the same width as a dime, which has a width of 1.8 centimeter.
(a) The relative volumes are shown for cubes of 1 m 3 , 1 dm 3 (1 L), and 1 cm 3 (1 mL) (not to scale). (b) The diameter of a dime is compared relative to the edge length of a 1-cm 3 (1-mL) cube.

Density

We use the mass and volume of a substance to determine its density. Thus, the units of density are defined by the base units of mass and length.

The density    of a substance is the ratio of the mass of a sample of the substance to its volume. The SI unit for density is the kilogram per cubic meter (kg/m 3 ). For many situations, however, this as an inconvenient unit, and we often use grams per cubic centimeter (g/cm 3 ) for the densities of solids and liquids, and grams per liter (g/L) for gases. Although there are exceptions, most liquids and solids have densities that range from about 0.7 g/cm 3 (the density of gasoline) to 19 g/cm 3 (the density of gold). The density of air is about 1.2 g/L. [link] shows the densities of some common substances.

Densities of Common Substances
Solids Liquids Gases (at 25 °C and 1 atm)
ice (at 0 °C) 0.92 g/cm 3 water 1.0 g/cm 3 dry air 1.20 g/L
oak (wood) 0.60–0.90 g/cm 3 ethanol 0.79 g/cm 3 oxygen 1.31 g/L
iron 7.9 g/cm 3 acetone 0.79 g/cm 3 nitrogen 1.14 g/L
copper 9.0 g/cm 3 glycerin 1.26 g/cm 3 carbon dioxide 1.80 g/L
lead 11.3 g/cm 3 olive oil 0.92 g/cm 3 helium 0.16 g/L
silver 10.5 g/cm 3 gasoline 0.70–0.77 g/cm 3 neon 0.83 g/L
gold 19.3 g/cm 3 mercury 13.6 g/cm 3 radon 9.1 g/L

While there are many ways to determine the density of an object, perhaps the most straightforward method involves separately finding the mass and volume of the object, and then dividing the mass of the sample by its volume. In the following example, the mass is found directly by weighing, but the volume is found indirectly through length measurements.

Questions & Answers

What is saturated hydrocarbon?
Ebenezer Reply
Alkane series are saturated Hydrocarbon
Adam
ok
hamza
what is the meaninh of link
Aisha Reply
Yes wish to join am a science ⚗ student
Emmanuel Reply
What is acid
Emmanuel
is agroup of substance that relaise hydrogen ion in the water solution.
mengistu
thanks
Aisha
An acid is a proton donor or an electron pair acceptor
amanda
how can someone understand chemistry vividly
Mercy Reply
Maybe by reading proofs or practical work and application in modern world.
Abdelkarim
what is isotopes
Samuel Reply
whats de shape of water
Amara Reply
water has no shape because it's liquid
Wil
water is a shapeless, odourless, colourless and tasteless substance that only takes the shape of its container.
mikefred
i think they're referring to the molecular shape?
It has no shape but takes the shape of the container
kpadonu
Yeah I think so too and it's a bent shape
amanda
what isthe maening pkw
Wilson Reply
what is the meaning of STP
Laura
introduction to chemistry for beginner
Lansana Reply
hi
noble
through out human history
marwan Reply
Yes?
Esther
hello
noble
yes
Bol
what
noble
is euglena a unicellular organ
Agio Reply
is euglena a unicellular organism
Agio
how is hydrogen can be heated
Buwembo Reply
what is difference between atom and molecule
Aqeela Reply
Atom is the smallest part of matter; it consists of equal number of protons and electrons. It may have neutrons. A molecule is a compound made of atoms covalently bonded.
Abdelkarim
does amoeba has structure
Mercy Reply
what is the effect of green house on the earth 🌎
kolawole Reply
what is the effect of green house on the earth 🌎
kolawole
what's an atom?
Davy Reply
it's the smallest unit of Matter
Orsine
atom
Eden
smallest part of an element
lydia
also, depending on its (atom's) structure, that is the amount of protons and neutrons and electrons, is the determining factors of what element it is.
Richard
is a smallast particals of an element
Buwembo
it is the smallest part of an element that can take part in a chemical reaction
Ayub
is the smallest part of an element
Jonathan
An atom is the smallest indivisible part of a matter
kpadonu

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play




Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry' conversation and receive update notifications?

Ask