CHEM100L EXAM2
what are the units for R in PV=nRT
0.0821 (atm)(L)/(mol)(K)
What is the concentration of hydrochloric acid if 16.00 ml of the acid was neutralized with 35.90 ml of 0.152 M Sodium Hydroxide? Considering the rules for significant figures, choose the correct value.
0.341
what is mL to L
1000 mL = 1 L
What are the two common types of titrations
Acid-Base titrations and redox titrations
Why must the crucibles be allowed to cool to room temperature before weighing in experiment 11?
Analytical balances do not weigh hot objects correctly due to the lower weight of the hot air on the balance pan.
Why must the crucibles in experiment 11 be further heated with a gentle flame after the tin has all reacted? What would be affected if this was not done?
Any excess nitric acid needs to be removed from the crucible. Not using a low flame would cause the oxide to splatter making the final weight of the crucible and tin oxide to be too low.
Three weighings are done in experiment 8. The sequence of weighing is (1) empty flask + foil; (2) flask + foil after boiling water bath; (3) flask + foil + water to fill flask. Why is no weighing done when the unknown is initially added to the flask, before it is placed in the boiling water bath?
Because a large excess of unknown liquid is added to the flask, and this excess evaporates and leaves the flask taking the air in the flask with it. So there is no need to weigh the excess liquid.
Which of the following is an example of an intensive property? a. Volume b. Mass c. Concentration d. Length
Concentration
What is stated by Avogadros Law?
Equal volumes of different gases contain the same number of molecules (or moles) of the gas under the same conditions of pressure and temperature.
TRUE OR FALSE The neutralization reaction of sodium hydroxide and hydrochloric acid is H2O + NaCl --> NaOH + HCl
False
A 1.000 gram sample of iron(Fe) is heated in air, during which it unites with an oxygen of the air to produce 1.430 grams of the oxide. What is the empirical formula of the oxide.
Fe2O3
What is the purpose of the titration technique?
It is used to find the concentration of a solution of unknown concentration.
What must be true about the boiling point of the liquid in order for the method in experiment 8 to provide an accurate molecular weight?
It must be below the boiling point of water.
Why was the indicator added to the Erlenmeyer flask with the unknown HCl solution?
It was used to identify when the solution passed the equivalence point.
what are the units for T in PV=nRT
K
how do you convert celsius to kelvin
K = C + 273.15
what are the units for V in PV=nRT
L
A Bunsen burner is used in experiment 11. What precaution should be taken in using the burner if you have long hair?
Long hair must be tied back so that it does not get into the flame
How do you determine the concentration with different stoichiometry
M1V1/a=M2V2/a a is the coefficients of the titrant and the analyte
How do you determine the concentration of an unknown with 1:1 stoichiometry
M1V1=M2V2 Concentration of acid x volume of acid = concentration of base x volume of base
Concentrated nitric acid is used in experiment 11 and must be handled with extreme caution. Select the reasons why and two precautions to be used in its handling.
Nitric acid is extremely caustic and can cause chemical burns to the skin and eyes, and if inhaled to the respiratory system. Proper PPE must be worn at all times, which includes goggles, lab coat and gloves and work must be performed in a fume hood.
What is the ideal gas law equation?
PV=nRT
What are the numerical values for conditions at STP, and what is the value for R? Include units
Pressure = 1 atm, Temperature = 273 K, R = 0.08206 L atm/mol K
In the procedure of experiment 11, you were asked to cut up the tin foil into smaller pieces after weighing it and placing in the crucible. What is the reasoning behind this? units
Smaller pieces of tin allow the nitric acid to react with the tin more easily allowing more of it to come into contact with the acid, making it a more efficient and complete reaction.
what are the products that occur when hydrochloric acid reacts with sodium hydroxide
Sodium chloride and water
What states of matter do not obey the mathematical laws described in this experiment?
Solids and liquids
What happens at the equivalence point during a titration?
The added titrant neutralizes all of the analyte in the flask.
How would the calculated molecular weight of the unknown be affected if 20 mL of the unknown liquid had been placed in the flask at the start, rather than 15 mL in experiment 8?
The calculated molecular weight would not be affected since the excess would leave the flask if the experiment is performed correctly
What is the purpose of performing a coarse and a fine titration?
The coarse titration gives an approximation of where the end point occurs, whereas the fine titration gives the exact volume of titrant needed.
How is the temperature of the gas in the flask maintained at a constant level and measured in experiment 8?
The flask is kept in a boiling water bath. The temperature of the boiling water is a constant and can be measured with a thermometer.
What is the purpose of adding an indicator during an acid-base titration?
The indicator changes color according to the pH of the solution and can be used to monitor the acid-base reaction.
How would the calculated molecular weight of the unknown be affected in experiment 8 if the flask were left in the boiling water bath for too short a time before being removed?
The molecular weight would be too high because too much of the excess liquid would still remain.
How is the pressure in the flask determined in experiment 8?
The pressure is the same as the atmospheric pressure in the room since the flask is not actually sealed and can be read using a barometer.
Why are two different pieces of metal foil used in experiment 8 and what is the function of each?
The smaller piece stays over the mouth of the flask at all times and prevents air currents from blowing the contents of the flask. The larger piece helps keep the smaller piece dry and is removed before weighing
Quantities of tin and tin oxide weighed in experiment 11 are relatively small compared to quantities you weigh in other experiments. Why must these weighings be done accurately, to at least 3 significant figures?ude units
There is uncertainty present with using such a small quantity of the limiting reagent. So the more accurate we can be in weighing to report more significant figures, the better the reported results and less uncertainty
TRUE OR FALSE molarity is concentration
True
What is Avogadro's Law?
Volume is proportional to number of moles the same number of moles will always occupy the same volume under a given set of conditions.
When is the equivalence point reached in experiment 15?
When moles of acid equals the moles of base
When is the endpoint reached in experiment 15?
When the indicator changes color
what are the safety precautions for experiment 11?
a bunsen burner is used so be cautious, eye protection is mandatory, don't touch hot objects, hydrochloric acid and nitric acid are use din this lab so wear eye protection and proper PPE
what does the empirical formula of a compound represents
a forumla generated with the smallest whole number ratio between the two elements
what are the units for P in PV=nRT
atm
Phenolphthalein is ______________ in acidic solution and _____________ in basic solution
clear, pink
what are the safety precautions in experiment 15?
glass is used so don't break anything and the acids and bases are not dangerous if washed off quickly but they are dangerous to the eyes so you need to wear eye protection
What is the formula for Molecular weight
grams/ moles
What is Charles' Law?
if the pressure of a gas is held constant, the volume of a gas is directly proportional to its temperature.
what does the reaction between a song base and a strong acid look like
it starts of basic, then ince it reaches its equivalent point, a pH of 7, it becomes acidic
What does the reaction between an strong acid with a strong base look like
it starts off acidic and when it reaches its equivalent topic, it has a pH of 7, then it becomes basic
what are the units for n in PV=nRT
moles
What does concentration mean?
moles/liters
Which indicator was used to determine the end point of the titration?
phenolphthalein
What color does the indicator change to during the course of the titration?
pink
what is constant in Charles' Law
pressure and number of moles
What is oxidation?
removal of electrons
what is constant in Avogadro's law
temperature and pressure
what is constant in Boyle' Law
temperature and the number of moles
What is concentration?
the amount of the substance dissolved in a certain volume of solution M=n/V the number of moles divided by the volume
What is the purpose of the concentrated nitric acid and hydrochloric acid used in experiment 11
the concentrated nitric acid is used as we will oxide tin with the nitric acid and then heat the product to evaporate all of the unreacted nitric acid so that we are only left with tin and oxygen. The hydrochloric acid is used to clean the crucible after the lab is completed
What is the safety precautions in experiment 8?
the proper PPE and some objects in the lab are flammable so be careful and cautious
what is the purpose of performing titrations
the purpose is to determine the unknown concentration of a solution by using the known concentration of another
what is the analyze in a titration
the solution of the unknown concentration
what is the titrant is a titration
the solution with the known concentration
If temperature increases, what happens to the volume of that gas
the volume could increase
What is Boyle's Law?
the volume of a gas is inversely proportional to its pressure. As pressure increases, volume decreases. when a gas is under pressure, it takes up less space
If pressure increases, what happens to the volume of that gas
the volume would decrease
what is changing in Avogadro's law
volume and number of moles
what is changing in Boyle's Law
volume and pressure
what is changing in Charles' Law
volume and temperature
If the number of moles increases, what happens to the volume of that gas
volume would increase as well
what happens in an Acid Base titration
when an acid reacts with a base, a neutralization reaction occurs