Lab Final MC Flashcards
What pieces of information are needed for molecular weight?
- mass
2. number of moles
How can you determine number of moles of a gas?
pressure and volume at a specific temp
Water displacement method
can calculate volume of gas
How do you get mass of gas?
weigh the lighter before and after dispensing
analytical balance
measures to 0.0001 g
Pieces of information to record in fuel of a lighter
atmospheric pressure
temperature
mass of the gas
volume of the gas
2 forms of bromothymol blue
yellow and blue
Acid base reaction experiment
use bromothymol blue
add 0.1M HCl (acid) and 0.1M NaOH
HCl makes blue turn yellow
NaOH makes blue
What color is bromothymol blue at first?
green
Sodium alginate
polymer that builds cell walls of seaweed and kelp, used as a gel, thickens products
C6 H7 O6 Na
Calcium chloride
CaCl2
Synthesize calcium chloride overall formulas
calcium metal + water = calcium hydroxide
calcium hydroxide + HCl = calcium chloride
Molarity of HCl used to synthesis calcium chloride
3M
What happens when calcium chloride and sodium alginate interact?
Jelly like product
strands of sodium alginate are connected by Ca in middle
Molarity (M)
moles / volume
What happens when calcium metal is added to water?
bubbling fizzing, white grain on bottom
What does calcium solid look like?
Gray and flaky
What wavelength to use for urine absorbance?
470 nm
What is in urine that we measured?
phosphate
Error
measured value - true value
Random error
results from limitations of measurement device
has an equal chance of being positive or negative
statistical variation
take the average to reduce
Systematic error
bias in the system
may be either positive or negative
can be detected and corrected
Finding uncertainty
calculate % errors
then add calculated random error to find uncertanity in %
How to calculate random error
the uncertainity is half of the smallest division of a scale
Precision
refers to the closeness of replicate measurements
Alum
potassium aluminum sulfate dodecahydrate
KAl(SO4)2 * 12H20
Overall formulas of synthesis of alum
Al(s) + KOH (aq) + H2O = KAl(OH)4 (aq) + H2 (g)
oxidation-reduction reaction
KAl(OH)4(aq) + H2SO4(aq) + H2O = KAl(SO4)2*12H2O(s)
acid-base reaction
What happens when KOH is added in synthesis of alum?
white bubbles form
fizzing
turned slight gray
What happens when H2O is added in synthesis of alum?
Smoke forms
gray bubbling
dark gray layer on bottom
what happens in second part of synthesis of alum?
white kind of slush initially
became more clear
Qualitative analysis
the process of figuring out what something is by interrogating the qualities of the substance
pH of alum
slightly acidic
can use pH test to determine
Determining if product has aluminum ions
add aluminon to solution
if it turns red, it contains aluminum ions
Determining if product has sulfate ions
add barium chloride to solution
if precipitate forms, it contains sulfate ions
Determining if alum contains water
heat to a constant weight
measured mass loss should equal 12 moles of water
Density
mass / volume
Intensive property
it is independent of the quantity of the substance measured
ex: density is intensive
Using a volumetric pipette to determine density
- measure the mass of the empty beaker
- use volumetric pipette to dispense the correct amount of liquid
- measure the mass of the full beaker, subtract
make sure to record temperature
What indicates precision?
standard deviation
How should you round standard deviation
to one significant figure
then the number gets put in the same PLACE as the standard deviation
3 factors that influence if something is significant
- absolute difference
- number of replicate determinations (n)
- precision of the data
What does a 2 sample t test conclude?
if two means are significantly different between two populations
Mixture that produces the most energy…
has the least number of moles of reactant left over
one closest to the stoichiometric ratio
What do data points on the job’s plot represent?
amount of energy released
Different sides of the job plot
represent different limiting reagents
Stoichiometric point
where the two lines meet on the jobs plot
no excess
how is mole fraction calculated?
calculated by dividing the moles of one component by the total number of moles of all the components
reaction to be studied by job’s plot
yA + xB = AyB
mohr graduated cylinder
like the volumetric pipette
can use to measure various volumes
make sure going the correct direction when using
volume fraction (theta)
volume A / total volume
What does the intensity of the color depend on
- kind of molecule doing the absorbing
- the concentration
- the path length the light passes through
- the solvent the molecule is dissolved in
Beer’s Lambert Law
A=ecl
e= extinction coefficient
c= concentration molarity
l = path length (centimeters)
A = absorbance
What color was the solution that we used for the jobs plot?
light red
How to determine concentration of NaOH solution?
use titration with KHP
Potassium hydrogen phthalate
abbreviated KHP
formula = KC8H5O4
burette
squeeze bottle used for titrations
quantitative transfer
using water/solution to make sure all of a substance is transfered
What has to be added to solution for titrations?
phenolphtalein
Steps of titration
- weigh acid
- quantatively transfer
- dillute to 50mL
- add phenolphtalein
- stir
- add base
- measure how much base used to achieve pink
What does the titrant refer to?
NaOH
the base
Concentration of NaOH in our titration experiment
roughly .1 moles per kg
volumetric flask
looks like a bulb with a skinny top
Retention of cations
need to figure out the overview of the experiment
why we did what
ammonia
NH3
What color did soil solution turn when ammonia was added?
blue
Which zeroes are significant in a decimal?
trailing zeroes only
ex: 0.03 (no significant zeroes)
sig fig rules for addition and subtraction
answer must be the least precise
sig fig rules for multiplication and division
answer will be the same as the one with the least number of sig figs
idea behind synthesizing calcium chloride
- add water to metal
- add HCl to product
hydrogen gas is given off as side product
finding concentration of something that was dilluted
use the absorbance to back solve for concentration with the curve, if you are starting with absorbance
use formula V1C1=V2C2
relationship between starting aluminum and final alum product
positive, linear relationship until the graph flattens out at around 1.7g
at this point KOH acts as a limiting reagent and there is not enough to yield more alum
amphoteric molecule
can act as an acid or a base
example of an amphoteric molecule
alum
can act as an acid in the presence of OH-
donates a proton to the hydroxide
this is why the precipitate turns clear as more base is added
net ionic equation of test for sulfate ions
barium chloride + sodium sulfate
Ba2+ + SO4 2- = BaSO4 (solid)
that is why precipitate forms
can disregard chloride and sodium when writing net equation
just use metal and sulfate to show what made the precipitate
extinction coefficent units
M-1 * cm-1
neutralization equivalent
the mass of acid required to react with one mole of hydrogen ion in aqueous solution
how much acetic acid is present
relationship between neutralization equivalent and molecular weight
NE = molecular weight / (# of acidic hydrogens)
neutralization equivalent units
g / mol
