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LABORATORY ACTIVITIES FOR REGENTS CHEMISTRY

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

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

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

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

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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.).

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A metric ruler cm. marks mm. marks

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

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

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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.

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

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

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

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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

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The triple beam balance:

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The dial-a-gram balance:

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

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

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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.)

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

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

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CHEMISTRY PART DEUX

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COMMON PROCEDURES Techniques used for various Activities

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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.

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

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

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

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

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Graphing Label the X and Y axis The X axis is the independent variable (consistent variable such as time) The Y axis is the changing variable

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Temp. C Time in Sec

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Temp. C Time in Sec

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Temp. C Time in Sec

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

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

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

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

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FINIS

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