LABORATORY ACTIVITIES FOR REGENTS CHEMISTRY

Many laboratory activities require measurements. Science uses the S.I. (Metric System) of measurements.

Types of measurements: –Linear (length or distance) –Mass (weight) –Volume –Temperature

All measuring instruments have calibrations. These are the markings or divisions on the measuring tool.

Linear measurements are made using a Meter Stick or Metric Ruler. Metric Ruler Meter Stick

The basic unit for linear measurement is the meter (m.). Other commonly used units are the centimeter (cm.) and millimeter (mm.). One advantage of the metric system is that everything is based on the number, 10, or some multiple of mm. = 1 cm. (and 1 mm. = 0.1 cm.) 100 cm. = 1 m. (and 1 cm. = 0.01 m.) Also, 1000 m. = 1 kilogram (kg.).

A metric ruler cm. marks mm. marks

When making measurements, scientists use a concept and a practice known as significant figures (Sig. Figs.)

Significant figures include an estimated digit that is always one place beyond the calibrations on any measuring instrument.

Estimating the last digit in a measurement You might estimate the end of the cylinder to be half-way between the lines or 0.05 cm. This digit must be included in the measurement.

Estimating the last digit in a measurement This measurement should be read as 4.95 cm. This measurement has 3 significant figures.

Reading a metric ruler correctly: This point can be read as 1.65 cm. or 16.5 mm.

Reading a metric ruler correctly: This point can be read as 6.70 cm. or 67.0 mm.

How to read the volume of a liquid in a buret or graduated cylinder

Reading a meniscus When a liquid is placed in a piece of laboratory equipment such as a graduated cylinder, buret, or a beaker, you will notice a "curve" at the surface of the liquid. This curve is known as the meniscus. As the diameter of the container decreases, the meniscus becomes more pronounced. The meniscus may be convex (curving upward) or concave (curving downward). Most of the time you will find that the meniscus is concave. The most notable exception is the meniscus that forms from mercury. When taking measurement readings it is important that the reading is done properly. The following rules must be adhered to: Read the meniscus at eye level. Do not read the meniscus from above or below eye level. Significant measurement errors may occur Read the bottom of a concave meniscus and the top of a convex meniscus. For the following picture, the bottom of this meniscus is between 6.0 and 6.1 mL. If the instrument is accurate to +/-.05 mL, then The correct reading is 6.05 mL.

Mass measurements are made using a balance. There are several kinds of balances: Triple beam balance Dial-a-gram balance Electronic/ digital balance Analytical balance

The triple beam balance:

The dial-a-gram balance:

The electronic/ digital balance: When using this balance, it is not necessary to estimate any places.

The analytical balance: This is used for very technical, precise applications.

Mass, in the metric system, is measured in grams (g.), centigrams (cg.) or milligrams (mg.). 10 mg. = 1 cg. (and 1 mg. = 0.1 cg.) 100 cg. = 1 g. (and 1 cg. = 0.01 g.) Also, 1000 g. = 1 kilogram (kg.)

As with all measuring instruments, Sig. Fig. Rules must be followed when reading a balance. How would you read this measurement?

This should be read as grams (g.) How would you read this measurement?

CHEMISTRY PART DEUX

COMMON PROCEDURES Techniques used for various Activities

FILTRATION Purpose and Definitions Used to separate suspensions. Filtrate is the liquid portion which passes through the filter paper. Residue (precipitate) is the portion which remains in the paper.

1. Fold a circular piece of filter paper into quarters to form a cone. 2. Insert into a funnel and dampen

Diluting Acids ALWAYS DILUTE BY ADDING ACID TO WATER Do what ya oughta add the acid to the water.

Constructing Data Tables 1. Identify the variables in the experiment. 2. Set up tables using appropriate labels and state units of measurements.

Sample Data Table for Melting Pt. Lab. Time in sec. Temp. O C

Graphing Label the X and Y axis with name & units The independent variable is on the X-axis. (it is the only variable you choose to change in the experimental setup) The dependent variable is on the Y-axis. It changes during the experiment in response to the changes of the independent variable.

Temp. C Time in Sec

Temp. C Time in Sec

Temp. C Time in Sec

Temp. C Time in Sec The melting point of this substance is 15 0 C as indicated by the plateau.

Final Review of Specific Labs Heating / Cooling Curve Density of solids and liquids Solubility Curves % Composition

Temp. C Time in Sec HEATING / COOLING CURVE Solid Liquid Gas Plateaus indicate change of phase. Two phases co-exist Solid-liquid Liquid-gas

KNO 3 saturated 60 0 C Unsaturated 80 0 C Super Saturated C

FINIS