CHEM 112 lab practical questions and correct detailed answers

Chemicals from the laboratory should never be taken _________ the laboratory. - correct answers outside Determine the correct sequence of steps used in carrying out a measurement using a pH probe. Rank them from first to last. - correct answers Remove probe from storage solution Rinse probe with distilled water and blot dry Place probe in solution to be measured Observe readout on meter of sample solution pH Rinse probe, blot dry, then place in storage solution If pH 8.3, the phenolphthalein will be - correct answers colorless Examples of Lewis acids - correct answers Fe3+ BeCl2 SO3 Examples of Lewis bases - correct answers O2- H2O Examples of Bronsted acids - correct answers HCOOH HNO3 Examples of Bronsted bases - correct answers CH2COOCH3- HCOO- Calculation of pH from [H+] - correct answers pH = -log([H+]) What are risks of filling chemical waste containers past the recommended level? - correct answers Overflowing waste containers can drip down the sides Chemical vapors need room to expand Chemicals can easily splash out when moved What is the reason that the cuvette must be placed in the same orientation each time that it is used? - correct answers The transmittance of the cuvette must be measured in the same place each time. A in Beer-Lambert Law - correct answers absorbance no units e in Beer-Lambert Law - correct answers molar absorptivity L/(mol x cm) b in Beer-Lambert Law - correct answers path length cm c in Beer-Lambert Law - correct answers concentration mol/L Lambda max is the wavelength of - correct answers maximum absorbance for a compound. A student fills a beaker with stock solution, and uses half. What should be done with the other half? - correct answers It should be disposed of in the proper waste container. The buret is rinsed with the ________ before being filled with solution. - correct answers Titrant (ensures that it will not be diluted with water) The endpoint is a change that indicates... - correct answers equivalence is observed in the analyte solution. What equals 1mg/mL? - correct answers 10^-3 mg/uL 10^3 ug/mL 1g/L What is the best method to determine the identity of an unknown chemical in lab? - correct answers Perform a series of experiments. Elevation affects - correct answers boiling point Depression affects - correct answers freezing point and vapor pressure Examples of strong electrolytes - correct answers HBr FeCl2 Example of weak electrolyte - correct answers H2CO3 Why use molality rather than molarity in dT=Kf(m)? - correct answers As the temperature changes, its volume will also change, which affects its molarity but not its molality. What factors influence the rate of a chemical reaction? - correct answers changing the concentration of reactants adding a catalyst changing the temperature the nature of the reactants Rate increases if... - correct answers temperature is increased or a catalyst is added Rate decreases if... - correct answers concentration of the reactant decreases or the surface area of a solid reactant decreases Rate of reaction units - correct answers amounts per time (M/s or M/min) Zero order units - correct answers M/s First order units - correct answers 1/s Second order units - correct answers 1/(M)(s) Third order units - correct answers 1/(M^2)(s) What is the most appropriate action if a chemical has just splashed on a person's face in lab? - correct answers Wash face without removing goggles if the eyes are not yet affected. What is the correct method for drawing liquid into a pipet? - correct answers Place a pipet bulb at the top of the pipet to draw up liquid. What conditions must occur when a chemical reaction is at equilibrium? - correct answers The forward and reverse reactions are happening at equal rates. What is an isosbestic point? - correct answers A point on an absorption spectra where two species have the same molar absorptivity. If a compound is yellow in color, - correct answers it absorbs violet light. If a large portion of a person's body are exposed to harmful chemicals, what two things should be done? - correct answers remove clothing and use a safety shower How does a buffer resist change in pH upon addition of a strong acid? - correct answers The strong acid reacts with the weak base in the buffer to form a weak acid, which produces few H+ ions in solution and only a little change in pH. How can you experimentally determine the pKa of acetic acid? - correct answers Determine the pH of the solution half way to the end-point on the pH titration curve for acetic acid. Which acid would be the best buffer at pH = 3.7? - correct answers Formic acid; Ka = 1.8 x 10^-4 When should you put on safety goggles? - correct answers when working with chemicals and/or glassware What are two reasons why you do not discard broken glass in regular garbage? - correct answers broken glassware could still contain chemicals and potential injuries could occur if janitorial staff do not see the broken glass. A voltmeter is used to measure - correct answers electrical potential A galvanic (voltaic) cell is - correct answers an electrochemical cell that produces electricity from a spontaneous oxidation-reduction reaction. OIL RIG - correct answers oxidation is losing (e-) reduction is gaining (e-) Red Cat, An Ox - correct answers Cathodes go through reduction Anodes go through oxidation Electrons in the wire flow - correct answers towards the cathode and away from the anode (to the right) Cations from the salt bridge - correct answers flow towards the cathode (to the right) Na+ is formed by the ______ of Na(s). - correct answers oxidation Br- is formed by the __________ of Br(l). - correct answers reduction