Chem Unit 2 Flashcards
Number of moles =
Actual mass (g) / molar mass
OR
of particles / Avogadro’s number
Absolute uncertainty is expressed as:
+/- [uncertainty value]
When adding or subtracting, uncertainty should be:
added together in the sum/difference
When multiplying or dividing, uncertainty should be:
converted into percent uncertainty, and then added
The formula for converting absolute uncertainty into percent uncertainty is:
absolute uncertainty / measurement value * 100
The formula for determining experimental error is:
( |actual measurement - expected measurement| / expected measurement ) * 100
The empirical formula of a compound, when given the # of grams of its components, can be determined by:
- Converting mass into moles
- Taking the mole ratio
- Finding the whole number ratio
The empirical formula of a compound, when given the percent composition of its components, can be determined by:
- Assuming that you have 100g of the compound
- Converting mass into moles
- Taking the mole ratio
- Finding the whole number ratio
The molecular formula of a compound, when given the empirical formula, can be determined by:
- Using the given molar mass of the molecular compound
- Determining the molar mass of the empirical formula
- Comparing (e.g. EF = 30, MM = 180)
- Multiplying components as needed
Percentage composition by mass of a given element within a compound can be determined by:
- Find the molar mass of each element in the compound
- Given the molar mass, find the molecular mass of the entire compound
- Divide the molar masses by the molecular mass and multiply by 100%
Determine the percentage composition by mass of H2O.
%H = 2/18 = 11.1%
%O = 16/18 = 88.9%
The Law of Definite Proportions was stated by whom? What does it mean?
- Joseph Proust
- That a compound will always have a fixed ratio of elements (H2O will always be 2:1)
Explain how empirical formula can be determined via combustion?
- Find mass of CO2 and H2O produced by combustion process
- Find mass of carbon in CO2 and mass of hydrogen in H2O (mass * percent composition)
- Determine number of moles of carbon and hydrogen
- Take the mole ratio
- Take the whole number ratio
The relationship between uncertainty and experimental error is:
Experimental error - uncertainty = error% that can be attributed to systemic error. Uncertainty is based in precision, whereas experimental error is based in accuracy.
Formula for molarity?
c = n/v where c is concentration in mol/L, n is # of moles, and v is volume in litres
Molarity is also known as
molar concentration
Practical applications of the molarity formula:
in soap, food industry, hot chocolate, iced tea, medicine, etc
Formula of mass-volume concentration:
c = m/v where c is concentration in g/L, m is mass of solute in g, and v is volume of solution in L
Liters can also be expressed in
dm^3
Mass-volume concentration can be used when
the solution has a solid solute and a liquid solvent
Formula for %(mass/volume) concentration:
mass of solute (in g) / volume of solution in mL all * 100%
Formula for %(mass/mass) concentration:
mass of solute (in g) / mass of solution (in g) all * 100
Formula for % volume/volume concentration:
volume of solute (in mL) / volume of solution (in mL) all * 100
Mass/mass concentration is used when
solutions are solid or liquid
Mass/mass concentration applications in real life include
IV, personal care, spinal fluid, CaCl2 and slush, drugs, toothpaste
Volume/volume concentration is used when
both chemicals are liquid
Volume/volume concentration applications in real life include
Diluting acids, alcohol
Formula for trace concentrations (ppm, ppb, ppt):
m/m
mass of solute/mass of solution all * 10^6/9/12/etc
Trace concentration is used to
find small amounts of things (in water, medication, etc.)
Formula for density is:
d = m/v
Find density using gas constant?
alphabet first
d = PM/RT
Pressure, molar mass, gas constant, temperature
High pressure outside, low pressure inside =
thing gets crushed (can)
High pressure inside, low pressure outside =
attempt to balance out (ears pop)
Why does the human body not crumple from high pressure?
Skeletal system
Bernoulli’s principle:
As speed of a moving fluid (liquid/gas) increases, pressure within fluid decreases
Pressure formula:
Pressure (total) = pressure (partial a) + pressure (partial b)
The ideal gas model assumes:
That gases are in constant, random, straight-line motion; attraction between particles is negligible; volume of particles is negligible; no energy is lost on collision; average kinetic energy is directly proportional to temperature
Under STP, one mole of gas will always take up how many litres of volume?
22.7
Pressure is determined by
how frequently the particles collide with the container
density
Molar volume (gas) formula:
V = M/d (molar volume = molar mass / density)
How to find limiting reagent?
- Take the masses of your reactants.
- Convert them into moles.
- Moles of reactant 1 = moles of reactant 2 .. etc, therefore cross-multiply reactant 2 by coefficients.
- If the product is less than the moles calculated in step 2, then reactant 1 is the limiting reagent.
2 Fe2O3 + 3C
* Moles of R1 = 1.35; moles of R2 = 3.53
* 3/2(1.35) = 2.025. Thus, Fe2O3 is the limiting reagent.
Percent yield is:
(Actual yield / theoretical yield) * 100%
The three gas laws are:
- Boyle’s Law (P1V1 = P2V2)
- Charles’ Law (V1/T1 = V2/T2)
- Gay-Lussac’s Law (P1/T1 = P2/T2)
The combined gas law is:
(P1V1/T1) = (P2V2/T2)
100 kPa conversions:
bar, psi, mmHg, atm, torr
- 1 bar (div 100)
- 14.5 psi (pounds per square inch)
- 7.5 mmHg
- 1 atm (div 101.3)
- 750 torr
What is STP? (IB)
100 kPa, 273 K
When do ideal gases act more like real gases?
High pressure, low temperature
Ideal gas law?
PV = nRT
Universal gas constant?
R
8.314 kPa * L / mol * K
1 mole of any gas at STP occupies a volume of:
22.7 L
How to find number of particles?
number of moles = number of particles / 6.022 * 10^23
N = nNa
Why use moles?
A mole is the number of particles of a substance that must be present in a sample such that the sample’s mass in grams is equal to the substance’s atomic weight in AMU.
