Question

Homework to 1. How many grams of 75% solution can you prepare from 12.300g of glucose? 2. How many g of Na S, are in 125ml of 0.25M solution? 3. How many grams of water do you need to add to 350g of 15% solution to prepare 6.0% solution? 4. Please assign a physical state fitting this description: - constant volume, variable shape: - variable volume, variable shape - constant volume, constant shape 5. You fill a party balloon with helium at the ground where the pressure is 760 torr, temperature is 22 deg.c. and the balloon has a volume of 5 L. What volume will the balloon have at altitude of 25,000 ft, where the temperature is -50 (that's "negative 50) deg. C and pressure is 300 torr? The pressure of the gas inside the balloon is always equal to the outside pressure. Page 1 of 2

Answer 1

Q1)

w/w % of a solution = weight of solutex100 / weight of solution

Given w/w% = 7.5%

weight of solute = 12.3 g

weight of solution = ??

thus weight of solution = weight of solute x100/ w/w%

= 12.3g x100/ 7.5 = 164 g of solution.

q2)

molar mass of Na2SO4 = 142 g/mol

molarity = moles of solute /Volume of solution(L)

given

Volume = 125mL = 0.125 L

mass of Na2SO4 = ??

molar mass = 142g/mol

molarity = 0.25mol/L

thus

0.25mol/L = (mass/142g/mol) / 0.125L

thus mass of Na2sO4 = 4.4375 g

Q3)We have 350g of 15% solution.

That is 15g os solute is present in 100 g of solution.

Thus 350 g of solution has = 350x15/100 g of solute

When we dilute the solution, the solute mass remains the same , but we add only water.

Thus mass of solute = 350x15/100 g

new percentage after dilution = 6%

Thus w/w% = mass x100/ mass of solution

6% = (350x15/100 g) x100 / massos solution

Massof solution = 875 g

So the water to be added = 875 -350 = 525 g