chem work,ridiculously difficuly

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1. Ruth has a solution of ammonium phosphate. It is found that the exact halfway point between its freezing point and its boiling point (at sea level) is 49.832 degrees celsius.What is the mass percent of the solution?

2.samuel starts with a 3.0M solution of barium chloride. He adds 22.0 ml of this solution to 100.0 ml of water to make solution A. He then takes 25.8 ml of solution A and adds it to 150.0 ml of water to make solution B. Finally he takes 30.7 ml of solution B and adds it to 300.0 ml of water to make solution C. What is the molarity of solution C?

3.Rachel adds together 450.9 grams of a 22.0% solutionof pottasium carbonate and 275 grams of barium chlorate. How many grams of precipitate does she produce?

4.Arron gas 0.800 kg of a 5.00% solution of pottasium carbonate. A plastic cube which has a side length of 3.00 cm and a mass of 30.807g sinks in the solution, and another plastic cube which has a side length of 3.25cm and a mass of 39.134g floats in it. What is the molarity of the solution?

5. Isaac dissolves 8.00 liters of nitrogen gas in 9.00 liters of water at standard pressure to produce a solution which remains solution which remains liquid over a range of 100.306 degrees celcius. What was the temperature of the gas, in kelvins when he dissolved it

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@courage,

One at a time.

Quote:

1. Ruth has a solution of ammonium phosphate. It is found that the exact halfway point between its freezing point and its boiling point (at sea level) is 49.832 degrees Celsius.What is the mass percent of the solution?

Approach

Ammonium phosphate
water soluble salt
ionic and dissociates---ammonium phosphate -> ammonium ion + phosphate ion
molecular weight--add it up

Water @ sea level--1 atm pressure midpoint mp bp temp=50 degC

now know fp depression--use to calc conc (molar fp depression)

convert into desired terms using water density and molecular weights solute and solvent.

wanna spreadsheet?

Wet lab qual.

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@courage,

Quote:

2.samuel starts with a 3.0M solution of barium chloride. He adds 22.0 ml of this solution to 100.0 ml of water to make solution A. He then takes 25.8 ml of solution A and adds it to 150.0 ml of water to make solution B. Finally he takes 30.7 ml of solution B and adds it to 300.0 ml of water to make solution C. What is the molarity of solution C?

This one is easier as it is a chain calculation

Solution A molarity [A]=3.0M*(22/(22+100))

Solution B molarity =[A]*(25.8/(25.8+150.0))

Solution C molarity [C]=*(30.7/(30.7+300))

[C]=3.0M*(22/(22+100))*(25.8/(25.8+150.0))*(30.7/(30.7+300))

note as the worst accuracy is the 2 significant digits in the starting molarity the molarity of [C] is two significant digits

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@courage,

Quote:

3.Rachel adds together 450.9 grams of a 22.0% solution of potassium carbonate and 275 grams of barium chlorate. How many grams of precipitate does she produce?

soln method

get the molecular formulas of barium chlorate and potassium carbonate
find their molecular weights
write the balanced substitution reaction for
potassium carbonate + barium chloride -> potassium chloride + barium carbonate
identify the precipitate
crunch the numbers

450.9*0.22 gives you the grams of potassium carbonate
dividing this by the mw gives mols of potassium carbonate

using balanced chemical substitution use molar ratios of reactants determine how many mols of barium chloride is required--
convert this to grams

if less than 275 grams potassium carbonate is limiting reactant
if more then barium chloride is limiting

use molar ratios of balanced reaction for precipitate and limiting reactant (in mols)--multiply his by the mw of precipitate product.

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Did Summer school start already?

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Quote:

4.Arron gas 0.800 kg of a 5.00% solution of potassium carbonate. A plastic cube which has a side length of 3.00 cm and a mass of 30.807g sinks in the solution, and another plastic cube which has a side length of 3.25cm and a mass of 39.134g floats in it. What is the molarity of the solution?

This one has to much information-a 5% by weight potassium carbonate pretty much gives the solution molarity. Get the mw of potassium carbonate and churn.

The cubes give nothing more than the solution density range
39.134/(3.25)^3 g/cm^3 <sol den< 30.807/(3^3) g/cm^3

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Quote:

5. Isaac dissolves 8.00 liters of nitrogen gas in 9.00 liters of water at standard pressure to produce a solution which remains solution which remains liquid over a range of 100.306 degrees celsius. What was the temperature of the gas, in kelvins when he dissolved it

Use molar freezing point depression to determine the nitrogen concentration in the water solution. This should be in mols/l. With 9 liters how much nitrogen is in the solution in mols.

Now use the ideal gas law (PV=nRT) to calculate T, you have pressure, volume, and number of mols. Remember that T in the ideal gas law is absolute.

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Good basic chemistry problems. Four explored multi step algebraic processes. The fifth was a common too much information situation.
Neither ridiculous or particularly difficult when you think about what you already know.

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chem work,ridiculously difficuly

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