Lab exam 1 Flashcards
What are the basic safety rules to follow in a chemistry lab?
-Always wear safety goggles and gloves.
-Tie back long hair and avoid loose clothing.
-Know the location of safety equipment (fire extinguisher, eye wash, first aid).
-Handle chemicals with care and read labels for proper handling.
-Always add acid to water (AAW), to prevent violent splashes
-Always pour base into acid, this allows us to avoid splashing, prevent boiling, and spattering
-dispose chemicals in the acid-waste container
How do you calculate the density of a substance? How can we calculate V and M from density? Explain the factors to density.
Density = Mass / Volume
V = M/D
M = V x D
-When volume is higher density is lower, this is due to them being inversely related
Example: If mass = 50g and volume = 25mL, then density = 50g / 25mL = 2 g/mL.
What is the procedure for measuring the density of a liquid or solid?
- Measure the mass of the sample using a balance.
- Measure the volume of the sample (use a graduated cylinder)
- Calculate density using the formula Density = Mass / Volume.
What are some sources of error in density measurements?
Incorrect measurement of mass or volume.
Air bubbles in liquid measurements.
Temperature variations affecting the volume of the sample.
How can density be calculated using a graph?
-Plot mass on the X-axis and volume on the Y-axis.
-The slope of the line represents density, as slope = Δy / Δx = m2-m1 / v2-v1.
-If graph is a straight line, the substance has a constant density (homogenous)
-If graph is a curved line, the density is not constant (heterogenous)
-Steeper slopes means higher density, flatter slope means lower density
What are the steps to separate components of a mixture?
- Identify the physical properties that can be used (e.g., solubility, boiling point).
- Use appropriate separation techniques (filtration, evaporation, distillation).
Explain the procedure for the separation of mixtures lab.
Goal: separate sand, NaCL, benzoic acid
1st. dissolve NaCl in cold water, this makes it dissolve
2nd. filter out the solid, then boil the salt water, this makes it solid NaCl
3rd. wash off the solid, add water, and boil the benzoic acid
4th. filter out the sand, let benzoic acid water cool down until crystals are formed
What type of crystals do NaCl and benzoic acid make?
-Benzoic acid forms needle crystals and NaCl form cubic crystals.
How do you calculate the percent recovery of components in a mixture?
Percent Recovery = (mass of recovered component / initial mass) × 100.
What are possible sources of error in separating mixtures?
Loss of material during separation (e.g., filtration, transfer).
Impurities in recovered components.
Incomplete separation due to improper technique.
Improper temperatures.
What is the purpose of paper chromatography?
To separate compounds, has two phases stationary and mobile phase.
What physical property does paper chromatography rely on?
Paper chromatography relies on the adhesion of substances to the paper and the cohesion between solvent molecules.
What are the steps to separate dyes in food colors using paper chromatography?
- Draw a baseline on chromatography paper. (1.5 cm)
- Apply a small spot of the dye mixture.
- Place the paper in a solvent (e.g., water, alcohol, NaCl) and allow it to travel up the paper.
- The different dyes will move at different rates due to their varying affinity for the solvent and paper.
How do you calculate the retardation factor (Rf) in paper chromatography? How can we find distance traveled by analyte and solvent using Rf?
Rf = Distance traveled by analyte / Distance traveled by solvent.
-Solvent = analyte/Rf
-dye= Rf x solvent
-Rf ranges from 0-1
Rf is a unitless ratio that helps identify compounds in a mixture.
What technique is used to determine the formula of copper chloride?
Use moles and molar mass to find the ratio of copper to chloride in the compound. Then use % composition and empirical formula to find the chemical formula.
What are potential sources of error in determining the formula of copper chloride?
Loss of copper chloride during heating.
Incomplete reaction of copper with chlorine.
Contamination of the product.
What is the general result of a double replacement precipitation reaction?
Two aqueous solutions react to form an insoluble solid (precipitate).
How do you classify a chemical reaction as a redox or non-redox reaction?
Redox reaction: Involves the transfer of electrons (oxidation and reduction).
Non-redox reaction: No electron transfer; typically involves acid-base or precipitation reactions.
How do you write ionic and net ionic equations for precipitation reactions?
- Write the full ionic equation, showing all ions in solution.
- Identify the spectator ions (ions that don’t change).
- Remove spectator ions to write the net ionic equation.
What are is the purpose of a titration experiment?
A titration is used to determine the concentration of an unknown solution by reacting it with a known solution (titrant).
What is the procedure for a titration experiment?
- Add a known concentration of titrant to the solution of unknown concentration.
- Use an indicator to detect the end point.
- Calculate the molarity of the unknown solution based on the volume of titrant used.
What are standard solution, endpoint, and indicator?
- Standard solution is a solution with a precisely known concentration that helps to determine concentration of an unknown substance
-Endpoint is when both reactions are used up and there’s no excess of either reactant
-Indicator is a compound that has an acid (Protonated) form and a base (deprotonated) form with a different color for each form
For this experiment we used phenolphthalein (this is clear in acid and pink in base)
What are some possible sources of error in titration experiments?
Inaccurate volume measurements.
Inconsistent endpoint determination.
Impurities in the titrant or unknown solution.
