College Chemistry 1, Lab Exam 1

Goggles

Protective eyewear that must be worn during experiments.

Strong acid spill response

Rinse with running water for 15 minutes.

Unused chemicals

Must never be returned to the stock bottle to avoid contamination.

Cleaning broken glassware

Use a broom and dustpan to clean up broken beakers.

Heating test tubes

The mouth of the tube should never be pointed at anyone to prevent injury.

Standard curve equation

A = 2.15C + 0.010

Slope in experiments

Represents the change in absorbance per unit concentration.

Y-intercept in experiments

Represents the absorbance when concentration is zero.

R² value

Indicates how well the data fits the model; closer to 1 means a better fit.

Absorbance measurement

A sample with absorbance 0.575 has a corresponding concentration that needs to be calculated.

Effect of concentration on absorbance

If concentration is increased

Approximate volume measurement glassware

Examples include beakers and graduated cylinders.

Precise volume delivery device

A pipette is used to deliver one precise volume only.

Graduated cylinder reading

Correct measurement from a graduated cylinder marked every 0.1 mL and reading slightly above 12.7 mL is 12.7 mL.

Density calculation

Density = mass/volume; for a metal cylinder with mass 15.62 g and volume 5.95 mL

Precision vs. accuracy

Accuracy refers to how close measurements are to the true value

Percent error calculation

Percent error = |(measured value - accepted value)| / accepted value × 100.

Statistical measure for precision

Standard deviation is commonly used to quantify precision.

Double displacement reaction

Example: 2HCl(aq) + Na₂CO₃(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g).

Balanced molecular equation prediction

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).

Total ionic equation

Shows all ions present in the reaction

Net ionic equation

Shows only the ions that participate in the reaction.

Precipitate formation

Using solubility rules

Activity of metals

A more active metal is one that is easier to oxidize.

Conductivity comparison

0.10 M CaCl₂ will have greater conductivity than 0.10 M NaCl due to more ions produced.

Conductivity probe units

Units used are typically microsiemens per centimeter (µS/cm).

Sugar solutions conductivity

Sugar solutions show almost no conductivity because they do not dissociate into ions.

Total ion concentration (TIC)

The total concentration of all ions in a solution.

Higher TIC comparison

0.20 M NaNO₃ has higher TIC than 0.10 M MgCl₂ due to the number of ions produced.

Solution preparation

To prepare 250 mL of 0.400 M NaOH

Volumetric flask usage

Describe the process of making a solution using a volumetric flask.

Molar mass NaOH

40.00 g/mol

CuSO₄•5H₂O molar mass

249.7 g/mol

Concentration of CuSO₄ solution

0.200 M

Volume of CuSO₄ solution

100 mL

Dilution formula

C1V1 = C2V2

Initial concentration (C1)

0.800 M

Final volume (V2)

50.0 mL

Beer's Law

A = εbc

Absorbance units

Absorbance has no units.

Color of light absorbed by a yellow solution

Purple light.

Sample absorbance

A = 0.350

Cuvette preparation

Must be wiped before inserting into the spectrophotometer.

Slope in absorbance graph

Change in absorbance per unit concentration.

y-intercept in absorbance graph

The absorbance when concentration = 0.

Density formula

Density = mass ÷ volume

Analytical balance

More precise than top-loading balance.

Accuracy

Closeness of a measurement to the true/accepted value.

Precision

Reproducibility of measurements.

Example density calculation

Density ≈ 2.63 g/mL.

Percent error

Percent error = ((|measured - accepted|) ÷ accepted) × 100%

Absolute error

Absolute error = |measured - accepted|

Standard deviation

Standard deviation is used to quantify precision (spread of repeated values).

Gas-evolution reaction

A reaction where a carbonate reacts with an acid to produce CO₂ and H₂O.

Molecular (balanced) equation

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Precipitate

A solid that forms from a solution during a chemical reaction.

More active metal

A metal that is easier to lose electrons (i.e.

Conductivity

The ability of a solution to conduct electricity

Absorbance

Absorbance (A) is proportional to concentration (c) as per Beer's Law.

Cuvette care

Wipe the cuvette to remove fingerprints

Ion dissociation in CaCl₂

CaCl₂ dissociates to 3 ions (Ca²⁺ + 2 Cl⁻) per formula unit.

Ion dissociation in NaNO₃

0.20 M NaNO₃ dissociates to Na⁺ + NO₃⁻ → 2 ions → TIC = 0.40 M (ions).

Ion dissociation in MgCl₂

0.10 M MgCl₂ dissociates to Mg²⁺ + 2Cl⁻ → 3 ions → TIC = 0.30 M (ions).

Solution preparation steps

Accurately weigh solute

Grams of NaOH for 0.400 M solution

4.00 g NaOH for 250 mL of 0.400 M.

Grams of CuSO₄·5H₂O for 0.200 M solution

≈ 4.99 g of CuSO₄·5H₂O for 100 mL of 0.200 M.