Chapter 1-Measurement

Why is it that important to study chemistry?

What is chemistry?

What is matter?

What is energy and how does it relate to chemistry?

The law of conservation of mass, says that mass, or quantity of matter, remains constant during any chemical change.

There are two principal ways of classifying matter

1. By its physical state as a solid, liquid, or gas. A physical property is a characteristic that can be observed for material without changing its chemical identity.

• Examples of physical properties are melting point, density(for a pure substance), and color.

2. By its chemical constitution as an element, compound or mixture. A chemical property is a characteristic of a material involving its chemical change.

• A chemical property of iron is its ability to react with oxygen to produce rust.
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Hints for recognizing chemical change.

1. Color change.

2. gas is given off.

3. heat is given off or absorbed. (substance or surroundings get hot or cold)

4. light is emitted.

Hints for recognizing physical change.

1. melting-freezing, evaporating-condensing,

2. subdividing (making smaller pieces)

3. dissolving a substance like salt in water

Elements, Compounds and Mixtures-see chart and definitions in the textbook.

Measurement and Significant Figures

The term precision refers to the closeness of the set of values obtained from identical measurements of a quantity. It may also refer to the number of decimal places your device measures.

Accuracy is a related term; it refers to the closeness of a single measurement to its true value or average.

Significant Figures (sf.)

Number of significant figures refers to the number of digits reported for the value of a measured or calculated quantity, indicating the precision of the value.

• When multiplying and dividing measured quantities, give as many significant figures as the least found in the measurements used. Count!
• When adding or subtracting measured quantities, give the same number of decimals as the least found in the measurements used.

To count the number of significant figures in a measurement, observe the following rules:

• All nonzero digits are significant.
• Zeros between significant figures are significant.
• Zeros preceding the first nonzero digit are not significant.
• Zeros to the right of the decimal after a nonzero digit are significant.
• Zeros at the end of a non-decimal number may or may not be significant. (Use scientific notation.)

Examples

14.0 g /102.4 mL = 0.136718 g/mL ==> ______ g/mL

4.56cm * 1.4cm = 6.384 cm² ==> ______ cm²

13.34 in + 87.266 in = 100.606 in ==> _______ in

A tricky one! Just like lab experiment 2.

(14.25 g – 10.25 g)/ (68.3 mL – 64.245mL) = 0.986436 g/mL ––> ______ g/mL

An exact number is a number that arises when you count items or when you define a unit.

2.54 cm= 1 in, 12 items = 1dozen

Note that exact numbers have no effect on significant figures and you use the numbers given to determine s.f.'s.

In 1960, the General Conference of Weights and Measures adopted the International System of units (or SI), which is a particular choice of metric units. See your text for a list.

Table 1.5 Relationships of Some U.S. and Metric Units

Which of the above are exact numbers?

Temperature scales- see textbook for diagrams.

ºF = 1.8 ºC + 32

K = ºC + 273.15

Body temperature is about 98.6ºF. Calculate that temperature in ºC and in K.

Derived Units

Volume is defined as length cubed and has an SI unit of cubic meters (m³). 1 mL = 1 cm³

Density in g/cm³

Density = mass/volume

Example:

1. A sample of the mineral galena (lead sulfide) weighs 12.4 g and has a volume of 1.64 cm³. What is the density of galena?

2. If a block of wood is 2.54 cm on each side, what is the volume? What is the density if the mass is 14.27 g?

Units: Dimensional Analysis

The ratio (2.54 cm/1 inch) is called a conversion factor. It is also an exact number.

Examples:

1. How many centimeters are there in 9.00 inches?

2. How many inches are there in 765 cm?

3. If a 544 g sample of Al has a density of 2.7 g/cm³ calculate the volume in cm³ and in L.

4. Sodium hydrogen carbonate (baking soda) reacts with acidic materials such as vinegar to release carbon dioxide gas. Given that an experiment calls for 0.348 kg of sodium hydrogen carbonate, express this mass in milligrams.

5. Convert 0.547 lb to grams.

6. How many cm³ in 1 yd³?

Percent Calculations:

Parts per thousand

Parts per million ?

An air sample contains 1.2 x 10¹⁸ molecules of a pollutant for every 6.02 x 10²³ particles of air collected. Calculate the % and the ppm of the pollutant.

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Updated Jan. 3,2004. Questions or comments on this Web site should go to Robin Terjeson.