CHEM 101L QUESTIONS AND ANSWERS
when should you not wear gloves in the laboratory setting?
when using your laptop, opening the door
what should you do if you get solution on your gloves and up your arm
notify the TA, rinse arm under distilled water for at least 15 min
when is it acceptab...
when should you not wear gloves in the laboratory setting?
when using your laptop, opening the door
what should you do if you get solution on your gloves and up your arm
notify the TA, rinse arm under distilled water for at least 15 min
when is it acceptable to eat at the lab bench?
NEVER! if you are hypoglycemic take your snack outside of the lab
define accuracy
How close data measurements are from the accepted or "true" value.
define precision
how close individual measurements are from each other. Can be determined by
calculating mean, standard deviation, and CV
define systematic error
Error that arises from a flaw in equipment or experiment design. They can be detected
and correct. Usually has to do with own out equipment or incorrect calibrations.
define random error
Error arises from uncontrolled and uncontrollable variables which has an equal chance
of being positive or negative. This type of error cannot be detected and corrected.
Examples include temperature fluctuations, incorrect readings, scale output that records
various readings for the same mass.
Why does ice float?
less dense than water. The oxygen atoms repel one another causes the volume to
increase and the density to decrease.
measure NaOH by difference. The NaOH bottle is 5.042 g, once the NaOH
removed it is 4.812 g. Calculate mass of NaOH.
5.042-4.812 = 0.230 g
how to you calculate density and what units should be used?
D=M/V, kg/cm^3
how to calculate mean
add up all values and divide by the number of values.
how to calculate standard deviation
shows how close the data numbers are to each other (precision).
1. find mean
2. subtract mean from all numbers and square each value.
3. add up all square values. Divide this number the numbers in the data set minus 1 (n-
1)
4. square root the new mean
how to calculate coefficient of variation
this shows the variability and dispersion of data
1. find mean and standard deviation
2. standard deviation/ mean, and then multiply by 100
how does temperature affect density
,as temperature increases density decreases because molecules are farther apart and
the volume is larger. When temperature decreases density increases because
molecules slow down and pack tightly to each other, decreasing the volume.
what do calibration standards define
accuracy and quality of measurements
conversions
tetra (10^12)
giga (10^9)
mega (10^6)
kilo (10^3)
base
deci (10^-1)
centi (10^-2)
milli (10^-3)
micro (10^-6)
nano (10^-9)
pico (10^-12)
femto (10^-15)
atto (10^-18)
how to find displacement volume (Vd)
initial volume reading (Vi) - volume reading with T probe (VT)
how to find corrected volume with buret
largest volume increment (Vb) - volume reading with probe (VT) - displacement value
(Vd)
dependent variable is what your are measuring and goes on the _______ axis
while independent variable is what you manipulate and goes on the _______ axis
y axis, x axis
temperature and pressure are ________ related
directly
in experiment 2, the system was the
reactants and products, direct reaction
the surroundings was the
water, cups, everything outside of the cups
in an exothermic reaction
the system gives off energy to the surroundings. There is more bond formation than
breaking of bonds. The solution in the calorimeter heats up. The reactants have more
energy than the products.
in an endothermic reaction
the system gains heat from the surroundings. There is more bond breaking than bond
forming. The solution in the calorimeter loses heat because it is being supplied to the
reaction. the products have more energy than the reactants.
draw diagram for endothermic
diagram
draw diagram for exothermic
diagram
how to find the change in temperature DT
, Tf - Ti
for endothermic reactions, the final temperature will be
lower
for exothermic reactions, the final temperature will be
higher
Should you add water to acid or acid to water?
add acid to water; this minimizes heat that can cause dangerous fumes or chemical
reactions
which is larger quantity, solvent or solute
solvent (dissolving medium)
what is solute
what is being dissolved in the solvent, smaller quantity
in an aq solution of NaCl, is water the solute or solvent
solvent
draw soluble chart
in notebook
spectator ions
do not play a direct part in the reaction, can be eliminated
net ionic equations
ions directly part of the reaction
what is a precipitate
insoluble solid
why do we use two cups in the coffee cup calorimeter setup
to limit the escape of heat, making results more accurate. Styrofoam was used because
it's a good insulator of heat
why do you need a stir bar in the calorimeter
to thoroughly mix up reactants in order to a chemical reaction to occur
true or false: to calculate temperature change you do initial temperature minus
final
false
does making a bond release or requiring energy
forming bonds releases energy
why do bond forming reactions release energy
represents a stable configuration for atoms
breaking bonds__________ energy
requires energy; bonds do not spontaneously break
forming bonds is a characteristic of
exothermic reactions
breaking bonds is a characteristic of
endothermic reactions
what is the balanced equation for the neutralization of barium hydroxide with
sulfuric acid
Ba(OH) (aq) + H2SO4 (aq) ----> Ba(SO4) (s) + 2H2O (l)
neutralization reactions are:
between an acid and a base, normally salt and water are produced. the cation from the
base is combined with the anion from the acid (salt) and water is produced
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