Lab Safety and Equipments
You need to transfer exactly 10.00 mL of a solution. Which laboratory equipment should you choose for the most accurate measurement?
A volumetric pipette
A solution is prepared by mixing 15 g of NaCl with 85 g of water. What is the mass fraction of NaCl expressed as a percentage?
15%
Classify the following compounds:
CaO, H₂SO₄, KOH, Na₂CO₃
CaO - oxide
H₂SO₄ - acid
KOH - base
Na₂CO₃ - salt
Calculate the molar mass of Ca(OH)₂.
74 g/mol
A reaction produces 40 mL of gas in 20 seconds. Calculate the average rate of gas formation.
2 mL/s
A student needs to dilute a solution to exactly 250.0 mL. Which piece of glassware should be used for the final preparation, and why?
A 250 mL volumetric flask, because it is calibrated to contain an exact volume.
A solution contains 24 g of solute and 96 g of water. What is the total mass of the solution, and what is the mass percentage of the solute?
120 g; 20%
Which of the following oxides reacts with water to form a base: SO₃, CaO, CO₂, P₂O₅? Write the reaction.
CaO
CaO + H₂O → Ca(OH)₂
Calculate the molar mass of Al₂(SO₄)₃.
342 g/mol
Two experiments use the same mass of CaCO₃ and the same volume of HCl. Experiment A uses 1.0 M HCl, while Experiment B uses 2.0 M HCl. Which experiment should have a higher initial reaction rate, and why?
Experiment B, because the higher concentration of HCl results in more frequent effective collisions.
A student reads the liquid level in a graduated cylinder while looking at it from above. What type of measurement error can this cause?
Parallax error
How many grams of NaCl and water are required to prepare 300 g of a 12% NaCl solution?
NaCl = 36 g
Water = 264 g
Complete and balance the reaction:
FeCl₃ + NaOH → ?
FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl
Calculate the equivalent mass of Ca(OH)₂ in an acid-base reaction.
Meq=74/2=37 g/eq
Why does powdered CaCO₃ react faster with HCl than the same mass of CaCO₃ in large pieces?
Powdered CaCO₃ has a larger surface area exposed to the acid, increasing the frequency of effective collisions.
A student accidentally adds more distilled water than the calibration mark while preparing a standard solution in a volumetric flask. Can the student simply remove the extra liquid with a pipette and continue? Explain.
No. Some of the dissolved solute would also be removed, so the concentration would no longer be reliably known. The solution should be prepared again.
A student prepares 150 g of a 20% solution. After heating, 10 g of water evaporates. What is the new mass percentage of the solute?
Approximately 21.4%
When solutions of BaCl₂ and Na₂SO₄ are mixed, a white precipitate forms. Identify the precipitate and write the balanced molecular equation.
The precipitate is BaSO₄.
BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl
Calculate the equivalent mass of H₃PO₄ if all three acidic hydrogen ions participate in the reaction.
Approximately 32.7 g/eq
The concentration of a reactant decreases from 0.80 mol/L to 0.50 mol/L in 30 seconds. Calculate the average rate of disappearance of the reactant.
0.010 mol·L⁻¹·s⁻¹
During an experiment, a student heats a closed test tube containing a liquid. Identify the main danger and explain why this procedure is unsafe.
Pressure can build up inside the closed test tube during heating, which may cause the tube to burst.
You have 200 g of a 10% NaCl solution. How many grams of water must evaporate to obtain a 20% NaCl solution?
100 g of water
You are given three unlabeled solutions: HCl, NaOH, and NaCl. You have only blue and red litmus paper. How can you identify all three solutions?
The equivalent mass of a metal is 12 g/eq. The metal forms MCl₂. Determine the molar mass of the metal.
24 g/mol
A student wants to investigate the effect of temperature on reaction rate using HCl and CaCO₃. Name two variables that must be kept constant to make the experiment fair.
Any two appropriate controlled variables, for example: HCl concentration, HCl volume, mass of CaCO₃, or surface area/particle size of CaCO₃.