LAB 2 & 3: Measurement & Conversion in Chemistry (Chem 2070)

Chemistry Laboratory Manual | General, Organic, and Biological Chemistry

CHEMISTRY LABORATORY REPORT COLLECTION Student: Mariela Aguilar | Course: Chem 2070 | Date: 09/02/22

KEY CONCEPTS COVERED

✓ Conversion Factors & Problem Solving ✓ Significant Figures

✓ Density & Specific Gravity ✓ Measurement & Calculations

LAB 2: Conversion Factors and Problem Solving A. Rounding Off

Initial Number Student’s Rounded Value Correct? Corrected (if needed) 143 144 yes —

532,800 533,000 no 533,000

0.583 0.6 no 0.58

45.08 45.1 yes —

■ Rounding Rules: Round to the specified number of significant figures. If the digit after the rounding position is ≥5, round up; if <5, round down.

B. Significant Figures in Calculations

B.1 Multiplication and Division Calculation Student Answer Significant Figures

(0.8)(0.8) × (42)(15) 604.8 → 600 1 sig fig

(35)(1.2) / (4.0)(5) 2.1 2 sig figs

B.2 Addition and Subtraction Calculation Student Answer Decimal Places

13.45 mL + 0.2 mL 13.7 mL 1 decimal place

145.5 m + 86.58 m + 1045 m 1277 m 0 decimal places

245.625 g − 80.2 g 165.4 g 1 decimal place

36.8 cm − 3.45 cm 33.4 cm 1 decimal place

■ SIG FIG RULES: • Multiplication/Division: Answer has same number of sig figs as measurement with fewest sig figs • Addition/Subtraction: Answer has same number of decimal places as measurement with fewest decimal places

C. Area and Volume Measurements

C.1 Area of Rectangle Measurement Student 1 Student 2

Length 13.3 cm 13.2 cm

Width 3.1 cm 3.0 cm

Area (L × W) 41.23 cm² → 41 cm² 39.6 cm² → 40 cm²

Why different values? Two students could obtain different calculated areas due to: (1) slight differences in measurement precision, (2) different measuring instruments, (3) human error in reading measurements, or (4) variations in rounding methods.

C.2 Volume of a Cube Property Value

Shape Cube

Length 2 cm

Width 2 cm

Height 2 cm

Formula V=L×W×H

Volume 2 × 2 × 2 = 8 cm³

D. Problem Solving Using Conversion Factors

Metric Height Conversion: Measurement Value Conversion

Height (inches) 64 in —

Height (cm) 162.6 cm 64 in × (2.54 cm / 1 in) = 162.56 cm

Height (m) 1.63 m 162.6 cm × (1 m / 100 cm) = 1.626 m

■ COMMON CONVERSION FACTORS: • 1 inch = 2.54 cm • 1 kg = 2.205 lb • 1 qt = 946.4 mL • 1 pt = 473.2 mL

Practice Problems: Q1 A pencil is 16 cm long. What is its length in inches? 16 cm × (1 in/2.54 cm) = 6.3 in

Q2 A person has a mass of 63 kg. What is the weight in pounds?63 kg × (2.205 lb/1 kg) = 139 lb

Q3 A bottle contains 1.5 qt of olive oil. Volume in mL? 1.5 qt × (946.4 mL/1 qt) = 1420 mL

Q4 How many liters of plasma in 8.5 pt? 8.5 pt × (473.2 mL/1 pt) × (1 L/1000 mL) = 4.0 L

LAB 3: Density and Specific Gravity Pre-Lab Study Questions

Q1 What property of oil makes it float on water? Oil has a lower density than water (ρ_oil < ρ_water), so it floats.

Q2 Why does heating gas in a hot air balloon make it rise?

Heating decreases gas density (warm air is less dense than cool air), creating buoyant forc

Q3 Difference between density and specific gravity? Density = mass/volume (g/mL). Specific gravity = density of substance / density of water (n

Q4. Density Calculations: Given Mass = 18 g, Volume = 11 mL

(a) Density ρ = m/V = 18 g / 11 mL = 1.6 g/mL

(b) Specific Gravity SG = ρ_object / ρ_water = 1.6 / 1.0 = 1.6

(c) Float or Sink? Sink (density > 1.0 g/mL, object is denser than water)

■ DENSITY FORMULA: Density (ρ) = Mass (m) / Volume (V) • Units: g/mL or g/cm³ • Water density = 1.0 g/mL at 4°C • If ρ > 1.0 g/mL → object sinks • If ρ < 1.0 g/mL → object floats

Q5. Volume and Mass Calculations:

Given 15 g sample, density = 0.85 g/mL

(a) Volume V = m / ρ = 15 g / 0.85 g/mL = 17.6 mL

(b) Mass in 34 mL m = ρ × V = 0.85 g/mL × 34 mL = 28.9 g

C. Experimental Determination of Density ■ Water Displacement Method: Used to find volume of irregular solids. Volumesolid = Final water level − Initial water level

Measurement Value

Mass of solid 45.2 g

Initial water level 20.0 mL

Final water level 25.6 mL

Volume of solid 25.6 − 20.0 = 5.6 mL

Density 45.2 g / 5.6 mL = 8.1 g/mL

Metal identified Brass (ρ ≈ 8.0-8.5 g/mL)

Metal Density Reference Table

Metal Density (g/mL) Common Uses

Aluminum 2.70 Aircraft, cans, foil

Iron 7.87 Construction, tools

Brass 8.0-8.5 Musical instruments, fittings

Copper 8.96 Electrical wiring, plumbing

Lead 11.34 Batteries, radiation shielding

Gold 19.32 Jewelry, electronics

D. Graphing Mass and Volume ■ Mass vs. Volume Graph: Plotting mass against volume produces a straight line. The slope of this line equals the density of the material.

Slope = ∆m / ∆V = Density

Trial Total Mass (g) Total Volume (mL) Mass of Metal (g) Volume of Metal (mL) Density (g/mL)

Initial 125.0 50.0 — — —

1 145.2 52.5 20.2 2.5 8.08

2 165.4 55.0 40.4 5.0 8.08

3 185.6 57.5 60.6 7.5 8.08

4 205.8 60.0 80.8 10.0 8.08

Calculate Density from Graph: Choose any two points: (Volume2, Mass2) and (Volume1, Mass1) Density = (Mass2 − Mass1) / (Volume2 − Volume1) Example: (205.8 − 125.0) g / (60.0 − 50.0) mL = 80.8 g / 10.0 mL = 8.08 g/mL

Additional Practice Problems

Q1 A metal object has mass of 19.3 g. When placed in graduatedVolume 23 −20 cylinder= with 20mL = 3water, mL
Density level rose to = 19.3 23 mL. g / What 3 mL is = 6.4 density g/mL
Metal and identity?

Q2 What is mass of solution with density 0.85 g/mL and volume 50 m= ρ × V = 0.85 g/mL × 50 mL = 42.5 g mL?

■ KEY TAKEAWAYS: • Significant figures maintain precision in calculations • Conversion factors help translate between measurement systems • Density is an intensive property that identifies substances • Graphing mass vs. volume yields density as the slope • Water displacement measures volume of irregular objects