INTRO CHEMISTRY I CHEM 1305

Matter - anything that has mass and occupies space.
Mass - the quantity of matter in a particular body.

Scientific notation is a method that allows one to write very large or small numbers in shorthand. 

For example, the number 27000000000000 can be written in scientific notation as 2.7 x 10¹³ or the number 0.00000073 can be written as 7.3 x 10^{- 8}.

 To do this,  write the number as a factor between 1 and 10 multiplied by 10 raised to a power.

 Procedure:

• Move the decimal point in the original number so that it is located after the first non-zero digit.

 Example:      2468   ------->   2.468

• Multiply this new number by 10 raised to the proper power.  The power of 10 is equal             to the number of places that the decimal point was moved.

         Example:      2468   ------->   2.469 x 10^?    ------->  2.469 x 10³

The decimal point was moved three places.
Therefore the power of ten is 3.

• Determine if the power of 10 is positive or negative.

If the decimal point was moved to the left, the exponent is positive. 

Example: 2468 = 2.468 x 10 ³

 If the initial number is larger than 1, the power of 10 will be positive.

 If the decimal point was moved to the right, the exponent is negative.

 Example: 0.000123 = 1.23 x 10 ^{- 4}

If the initial number is less than 1, the power of 10 will be negative.

Sometimes, numbers have more digits than one needs or can realistically use.  For example, the bank may calculate that after paying you interest your saving account has $314.873 .  The problem is that there is no currency under a penny, so they round the the pennies down to 87 cents because they cannot give you three tenths of a penny.  This is an example of rounding off to a certain significant figure.  In this case, one hundredth of a dollar ($314.87).

There are various rules which can be used for rounding off, but in this course we will use the following.

• Rule 1

 If the digit is less than 5, DO NOT change the last digit.

 Example: 74.693 rounded off to 4 digits

Count 4 digits from the left .... to the digit "9".

74.693

Drop the 3.  It is less than 5.

Answer:  74.69

 Example: 1.00629 rounded off to 4 digits.

Count 4 digits from the left ... to the digit "6".

1.00629

Drop the 2 and the 9.  2 is less than 5.

Answer: 1.006

• Rule 2

If the digit is greater than or equal to 5, increase the last digit by 1.

Example: 12.879 rounded off to 4 digits.

Count 4 digits from the left ... to the digit "7".

12.879

The digit immediately to the right of the "7" is "9" which is greater than 5.

12.879

Drop the 9 and add 1 to the 7.

Answer: 12.88

Example: 1.025868 rounded off to 4 digits

Count 4 digits from the left ... to the "5"

1.025868

This digit "5" is equal to 5.

 Drop the remaining digits (....868)

1.025868  ----->  1.025

Add 1 to the 5.

Answer: 1.026

The metric system was developed in 19th century France. The United States is one of the few countries not using the metric system.

The metric system has three basic units for measuring matter:

• gram  (mass)
• liter (volume)
• meter (distance)

The units are expressed in multiples of 10.

The metric system uses prefixes to define multiples or fractures of the basic units.

Conversion of metric to metric

Metric conversions uses dimensional analysis (factoring) to convert one metric prefix to another.   The conversions is accomplished by conversion factors:

Example: Convert 4 grams to mg.

 

Example: Convert 80 ml to kl.

You have two sets of conversion factors.

or

or

Since we do not know how to convert directly from ml to kl, we first convert ml to liters then liters to kiloliters.

Example: Convert 5 cm to um

You have two sets of conversion factors:

or

or

Since we do not know how to directly convert from cm to um, we first convert to liters than to um.

Metric - English Conversions

Sometimes it is necessary to convert from the english system to the metric system or vice versa.

To do this we need three conversion factors.

1 in  = 2.54 cm

1 lb  = 454 g

1 qt  = 946 ml

Example: Convert 24 oz. to kg

Example: Convert 8 meters to yards.

There are three commonly used temperature systems:

• Fahrenheit
• Celsius (Centigrade)
• Kelvin

We commonly have to convert from one system to another.

Celsius to Fahrenheit

Fahrenheit to Celsius

Celsius to Kelvin

Fahrenheit to Kelvin

Convert from ^oF to ^oC then to Kelvin

Kelvin to Fahrenheit

Convert from K to ^oC then to ^oF

Density is mass per unit volume.


In science we normally use g/ml (g/ml³) for solids and liquids and g/l for gases.

Example: A cube of iron measures 2 cm x 2 cm x 3 cm and has a mass of 80g. Calculate the density.

Volume = 3 cm x 2 cm x 2 cm = 12cm³

mass = 80g

Example: A substance has a density of 0.9 g/ml and a volume of 100 ml.   Calculate the mass.

Mass = ?

Density = 0.9 g/ml

Volume = 100 ml

Example: A substance has a density of 2.1 g/cm³ and a mass of  50 grams.    Calculate the volume.

mass = 50g

density = 2.1 g/cm³

volume = ?

The specific gravity of a substance is the density of that substance divided by the density of a reference substance (standard).  This allows one to compare the density of one substance with that of a reference substance.

In chemistry, we use water at 4 ^oC as the standard.