Metric conversion is a systematic approach to problem solving that uses conversion factors to move or convert from unit ot another.

Many problems in chemistry and health science requires a change of units.You make changes in units everyday. We use metric system which is a common method of measuring system , in 1960 scientists adopted a modification of metric system called International system of Units (SI), to provide uniformity for units used in sciences.

Measurement Metric SI

Length Meter (m) Meter (m)

Volume Liter (L) cubic meter (m^3)

Mass Gram (g) Kilogram (kg)

Time Second (s) Second (s)

Temperature celsius degree Kelvin

The special feature of the metric system of units is that a prefix can be attached to any unit to increase or decrease its size by some factor of 10. For exampl; the prefixes milli & micro are used to make smaller units.A table is attached here lists some of the metric prefixes, their symbols and their values.

Point to note: The relationship of a prefix to a unit can be expressed by replacing the prefix with its numerical value.For exampl: when the prefix kilo in kilometer is replaced with its value of 1000,we find a kilometer is equal to 1000 meters.

Equalities: The comparisons which show the relationship between two units that measure the same quantity.For exampl, in the equality 1m = 100 cm,each quantity describes the same lengthbut in different unit.

meter to cm

1 cm = 10^-2 m

perfix centi value of prefix centi

In the above example you can see a length equality.To write the equality between centimeter and meter , we used the value of prefix centi which is 10^-2 , so then we got the equality between cm and meter(m) that 1 cm = 10^2 x m or this can also be written as 1 m = 100 cm

Writing conversion factors; Conversion factors are the ratio of equivalents values can be generated from equivalence statement.

From the above example of equality the conversion factor can be either

1cm/10^-2m or 10^-2m/1cm

How we use the conversion factor to solve the problems of unit conversion

** given unit x Find unit/ given unit = Find unit

** Given unit x related unit/given unit x Find unit/related unit = Find unit

Arrange the conversion factor so that starting ( given ) units cancels, you can do this by arranging the conversion factors so that the starting units is on the bottom of the conversion factor.

You may find one step unit conversion or two step or chain unit conversions.

Systemetic approach :

Sort information from the problem:by identifying the given quantity and unit , the quantity and unit you want & any relationships implied in problem.

Design a strategy to solve the problem: Devise a conceptual plan.

Apply steps in conceptual plan: Check units properly and multiply terms accross the top & divide by each bottom term.

This should be more clear with these examples;

convert 1.76 yd to centimeter:-

sort info ; Given = 1.76 yd ( yards) & Find : length in cm

Strategy : conceptual plan yd ==> m ==> cm, equivalence : 1m = 1.094 yd , 1 cm = 10^-2 m

conversion factors : 1m / 1.094 yd or 1.094 yd/ 1m and 1cm/10^-2m or 10^-2m/1cm

Solution: Given unit x related unit/given unit x Find unit/related unit

so, we use the conversion factor in which we have given & related units at the bottom so that we can cancel the given & related units.

1.76 yd x 1m / 1.094 yd x 1cm/10^-2m = 160.8775 cm = 161 cm

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