Molality is a measure of number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution.
A commonly used unit for molality in chemistry is mol/kg. A solution of concentration 1 mol/kg is also sometimes denoted as 1 molal. The unit mol/kg requires that molar mass be expressed in kg/mol, instead of the usual g/mol or kg/kmol.
Homework Statement
Freezing point depression question[/B]
student determines molar mass of acetone using the method used in this experiment. She found that the eq temp of water and ice was 1 deg C. She then adds 11.1g of the sample to mixture and temp falls to -3 deg C. Mass of solution was...
Homework Statement
Commercial grade HCl solutions are typically 39.0% (by mass) HCl in water. Determine the molality of this HCl solution, if it has a density of 1.20 g/mL.
Homework Equations
molality = moles solute / kg solvent
The Attempt at a Solution
39.0g HCl (1mol/36.46g/mol) =...
Homework Statement
What is the molality of 1M NH4OH dissolved in 70.092ml of water? What is the total mass of the solution? What is the total volume? What is the concentration percent? What is the molar concentration?
1M NH4OH = 35.046g
density of water = 1g/ml
density of NH4OH = 0.88 g/ml...
Homework Statement :[/B]
The density of a 2.05 molar solution of acetic acid is 1.02g/ml. The Molality of the solution is:
(a) 1.14 mole/kg
(b) 3.28 mole/kg
(c) 2.28 mole/g
(d) 0.44 mole/kg
Homework Equations :[/B]
The Attempt at a Solution :[/B]
I tried it out very simply using unitary...
Homework Statement
Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 gram of lauryl alcohol in 0.100Kg of benzene freezes at 4.1 degrees Celsius. What is the molar mass of the lauryl alcohol?
Kf for benzene = 5.12, Freezing point of benzene is 5.5...
Say for example you have take a sample of 500ml from a bulk saline solution (NaCl and H20). If you know that for every 100 grams of water there is 10 grams of NaCl, can you calculate the amount of NaCl in 500ml of the final mixture?
Question
A 1.392 M sodium carbonate solution has a density of 1.1353 g/mL. Calculate the molality of the solution.
Attempt
1.392 M Na2CO3 = 1.392 mol Na2CO3 per 1 L solution
I can't really make sense out of this. What would be the next step?
Homework Statement
Screenshot of some prof's website. This is just ridiculous.
http://i.minus.com/jnUa604Tz6bKX.png
Homework Equations
Molarity to molality.
Molality is moles / kg of solvent.
Molarity is moles / volume of solution.
The Attempt at a Solution
Pretty sure all the ones...
Homework Statement
The molality of an aqueous sodium nitrate solution is 2.14 m. What is the mole fraction of sodium nitrate?
Homework Equations
Molality = moles of solute / kg of solvent.
Mole fraction of A = moles of A / total number of moles (in this case, moles of solute +...
Homework Statement
Consider the following aqueous solution at 25°C
Cr2(SO4)3, 1.26 mol/L, 1.37 mol/kg
Calculate the mole fraction, density and % w/w
Homework Equations
χ = n Cr2(SO4)3 / n Cr2(SO4)3 + n H2O
Unit conversions
ρ= g solvent / mL solution
% w/w = mass solvent / 100 g...
Can someone explain why we take the number of particles into account after we have determined our molality? I feel like I'm just memorizing this and not understanding why you need to determine # of particles for molality in the problem below.
The observed boiling point was elevated by 1.02...
Homework Statement
How many grams of NaCl must you add to 750g of water to make a 0.35 molal solution?
Ans. 7.59g
Homework Equations
molality=\frac{mol_{solute}}{kg_{solvent}}
MW of NaCl = 23 + 35.45 = 58.45 g/mole
The Attempt at a Solution...
I have seen in my textbook that most colligative properties are defined in terms of molality. This must mean that there is some relation between molality and the von Hoff factor, since von Hoff factor is directly related to the colligative properties.
However, as far as I know, the only...
Homework Statement
When carbon dioxide "dissolves" in water, essentially all of it reacts to form carbonic acid, H2CO3:
CO2(s) + H2O(l) <--> H2CO3(aq).
The carbonic acid can then dissociate into H+ and bicarbonate ions,
H2CO3(aq) <--> H+(aq) + HCO3-(aq).
Consider a body of otherwise pure...
hello,
i had been comparing the molarity and molality of a solution.
i know molarity is moles of solute per L of solution, and molality is moles of solute per kg of solvents.
but what i m interested to know is- which of the two is more concentrated- 1molal solution or 1 molar solution.
my...
Homework Statement
A 10% (by wt) solution of KNO3 would have what molality and what mole fraction
Homework Equations
mole fraction = moles of KNO3/total moles
wt % = # g of solute/total g
molality = # moles KNO3/kg H2O
The Attempt at a Solution
1 g KNO3/10 g total
1 g KNO3/101.1...
Homework Statement
Hi. This is a question based on a lab I did.
We mixed an unknown solute in a solution of pure cyclohexane. Based on numbers we got from our lab, we were asked to find the molal concentration of the unknown. The freezing point of the unkown was found to be 1.5 C and the...
Homework Statement
In a lab, 40.3 mL Mn2+ is mixed with 5 mL H3PO4. 0.4g of potassium periodate is added. The flask is heated and then diluted to 100mL. The final solution prepared is a permanganate solution. Calculate the final molarity of the solution.
C Mn2+ = 0.06061 M (60.61...
Is molality equal to moles of solute / kg of solvent
or is it equal to mole of particles of solute / kg of solvent?
example: is the molality of 0.5 mol of NaCl dissolved in 1 kg of water 0.5 m or 1 m?
Homework Statement
hey guys just wondering how to do this.
Lithium tetrafluoroborate (LiBF4) is sold as a 1.00 M solution in
acetonitrile. If the solution has a density of 0.852 g/mL,
the molality of the solution is?
i tired using denisty=m/v and concentration=n/v but always had 2...
Homework Statement
You have a 10.4g mixture of sugar (C12H22O11) and table salt (NaCl). When this mixture is dissolved in 150g of water the freezing point is found to be –2.24 degrees centigrade. Calculate the percent by mass of sugar in the original mixture.
Homework Equations
delta...
Homework Statement
Find the molality of a sulfuric acid solution which contains 27,0% by mass of H2SO4 and a density of 1,198 g/mL
Homework Equations
molality = moles of solvent / mass of H2SO4 (kg)
The Attempt at a Solution
If we have 1kg of the solution, then we have 0,270 kg of...
Having a massive brain fart... SIMPLE "molarity -> molality" conversion...
This isn't even a homework question per se, I'm just trying to understand how the question converted the molarity to the molality value, via the density given. I just got a different value of molality when trying to...
Homework Statement
A solution containing equal masses of glycerol, C3H8O3, and water has a density of
1.10 g/mL. Calculate the (a) molarity; (b) mole fraction of glycerol; (c) molality of
the solution.
Homework Equations
M=moles of solute/liters of solution
mole fraction = n1/n(total)...
Just having some problems understanding why one is dependent on pressure and temperature and the other is not. If molarity is moles of solute/litres of solvent, why would this change with pressure and temperature? A litre of water will remain a litre of water at any given temperature and...
Hi.
How many grams of antifreeze must be dissolved in 300 g of water in order to reduce the freezing point of water to –13.02o C under 1 atm pressure (Kf: 1.86 o C/molal and C3H5(OH)3: 92.09 g/mol).
I have not learned molality yet and I am completely confused as to where to start. I...
Molality creating problems for me!
calculate the molality and osmotica pressur of a 0.5% solution of urea (Mol Mass=60) in water at 0 degree celsius.
R-0.0821
now my dear friends!
i have calculated successfuly the osmotic pressure in this question which is
osmotic pressure = 1.86...
I haven't taken chemistry in over 3 years so I have forgotten a lot of the very basic concepts (even while understanding the higher level stuff) and am having problems with this simple thing! Please help :(.
Question 1- At 20°C, a 2.32 M aqueous solution of ammonium chloride has a density of...
How do I find the molality of an aqueous solution containing 1g/L of a certain protein with molar mass 9.0 x 10^4 g/mol if the density of the solution is 1g/(cm^3)??