CHM110 Midterm 1 Flashcards
What is
1) %w/w
2) %w/v
3) %v/v
1) g solute/100g solution
2) g solute/100mL solution
3) mL of solute/100mL solution
NOTICE that it’s always solute to solution
Define molarity and molality and explain temperature dependence
Molarity: mol solute/ L solution (temp dependent
Molality: mol solute/ kg solvent (not temp dependent)
Temp dependent becuase volume of solution changes which temperature, most liquids expand with increases. Molality is dependent on mass though
Given %w/w and density, find molairity, molality and mole fraction
1) MOLAIRITY:
- 98%w/w is simply 98g solute in 100g of solution. Multiply by density to cancel out solution
- Units are in g/mL, multiply by 1000 to make g/L
- Divide by molar mass to cancel out the g for a final unit of mol/L
2) MOLALITY
- If 98% solute then 2% is solvent. 98% = 98g and 2% = 2g.
- Multiply molariity by 1000 to make g/kg and then divide by the molar mass of the solute to get mol of solute/mass of solvent
3) MOLE FRACTION
- If 98% solute then 2% is solvent. 98% = 98g and 2% = 2g. Set up as 98/2 and find the moles of each using the molar mass
- Divide desired mole value by total moles (total moles can be greater than 1 but the mole fractions SHOULD equal 1) to find the mole
Given molairity and molality, find mole fraction, density and %w/w
1) MOLE FRACTION:
- Use molality since it is in mol mol solute/kg solvent
- Find moles of solvent by converting to g and then using molar mass to convert to mol
- Add moles together to find total moles
- Divide mol of solute by total moles to find mole fraction
2) DENSITY:
- Calcualte mass of solute (moles is the molairity value given multiplied by molar mass of solute)
- Calcualte mass of solvent is moles divided by molality (mol x kg/mol) and turn into g
- Add both masses and assume volume of solution is 1L
- Density = total mass/volume
3) WEIGHT BY WEIGHT
- Calculate mass of solute (use molairity for moles and molar mass)
- Calculate mass of solute (use moles of solute/molality which is mol * kg/mol and convert to g
- Find the total mass of the solution
- Divide desired mass by total mass and multiply by 100
Equation for density
Density (g/L) = mass/volume
Unit conversion of L to M^3
1L = 0.001 cubic meter
Divide by 1000
Given density and mole fraction, find, molairity and molality, %w/w
1) %W?W (FIND THIS ONE FIRST)
- Use mole fraction to find the moles of each reactant. So XA = nA/nT (total moles) and then you can find the mass by multiplying by the molar mass but KEEP IN MIND the nT doesn’t cancel out till the end when you divide both values with the molality
- Then use these moles and calculate the mass of each in g
- Add both these grams together
- Divide solute in grams by total and multiply by 100%
2) & 3) Just follow same method as above
Given molality and density, find molairity, mole fraction and %w/w
**even without asking to find %w/w this method is still useful
1) MOLAIRITY
- Calcualte moles of solute using the molality
Moles = molality x mass of solvent (assume 1kg)
= mol/kg x kg and convert to grams
- Calculate mass of solute by multiplying by molar mass
- Combine both mass of solute and mass of solvent (assumed to be 1kg)
- Divide mass of solution by density to obtain the volume
- Molairity is moles of solute/divided by volume
2) %W/W
- Use previous mass numbers obtained
3)
What does 1 mol equal
6.022 x 10^23
Determine empirical formula from combustion analysis
- Convert masses of compounds to moles of compounds
- Calcualte mole of element in compound (H2 is multiply by 2 for example)
- Convert to mass of element
- Continue as usual
Mass percent formula
mass of element (moles x molar mass)/molar mass of compound
Why is theoretical yield not obtained?
Side reactions, reaction stopping before complete, physical losses (like solid clinging to another paper)
Why does water dissociate ionic compounds into ions
Attraction between O in water attracted to cations and H attracted to anions is strong enough to break attraction between ions
Electrolyte and strong, weak, and non
When dissolved in water produced ions and conducts eletricity
Strong - acid/base and ionic
Weak - acid/base
Non - covalent
Why is molality greater than molarity usually?
With molairity, adding more solent increases TOTAL volume so smaller fraction
Using couloumb’s law, distinguish between bonding and IMF
Bonding forces stronger because larger charges closer together
IMF weaker becuase smaller charges father apart
What is LDF
Electron charge is distributed unevenely on atom so creates temporary dipole which induces other temporary dipoles resulting in weak attractions
Does weak IMF cause high or low vapour pressure?
High because it is easy for molecules to escape to vapour phase
Define polariziability and what kinds of atoms have higher polariziability
How easily electron cloud distorted by other ions or dipoles to cause induced dipole
Heavier, alrger, and negative ions are more polarizable
If you need to produce 100mL solution of 4 solutions of 0.250mol/L each and you are provided by four 25mL flasks containing the solutions with 1.00mol/L.
Would pouring the contents into a 100mL beaker provide desired final solution with high precision?
5 points
- Combining solutions of four 25mL flasks would give approximate final volume of 100mL
- Calculate mol of final (0.025) of 0.1L so concentration would be 0.25 mol/L
- Pouring liquid out of volumetric flask is not quantitative transfer (one of those would be using pipette or funnel) and total volume would be less than 100mL
- Adding additional water to rinse the flasks would give final solution volume greater than 100mL
- Not appropriate method for producing desired final solution
When do moles of solution change?
When pressure or temperature changes, but not with volume or concentration
Starting with an equation for molality and mole fraction of solute A in water, express mole fraction as a function of ONLY molality!
1) Find nw
- mass w = nw x MMw
- assume mass of 1kg (1000)
- should be around 55.5 mol
2) Find na
- molality = nA/massw
na = molality x mass (1)
na = m
3) Combine to mole fraction equation
- molality / molality + 55.6
Mixture of two salts (mass given) in excess other salt creates a percipitatte of a given mass. Calculate moles of each
1) Find moles of percipitate
2) Set x + y = answer from 1 and rearrange to isolate y
REMEMEBER when to double if 2 moles makes 1 mol
3) mass salt A + mass salt B = mass of two salts
Mass = (x and molar mass)
Rearrange and solve for x
What is the equation for molar volume of a gas
MV = volume/moles
Two different gases, which has higher average kinetic energy
Temperature is a measure of average kinetic energy so they would be the same
Temperature is proportional to average kinetic energy
Avogardro’s principle
Equal volumes of gases at the same temperature and pressure will contain equal number of molecules (even when they are different gases!)
equation for partial pressur eof a gas A
pA = mole fraction A times total pressure
Deviations from real gases
Low temperature and high pressure
- Gases do indeed have volume
- Attractive and repulsive forces exist among gas particles (because atoms exist as charged subatomic aprticles and many bonds are polar
Volume required for neutralization?
Normality 1 x volume 1 = normality 2 x volume 2
Normality: equivalents bsaed on how many hydrogen it donates, multiply molairity by this value
Then isolate and solve like c1v1 = c2v2 problem
