How many total numbers of atoms in the following unit cell? A solution containin

Question

How many total numbers of atoms in the following unit cell? A solution containing more than the equilibrium amount is called an unsaturated solution a supersaturated solution a concentrated solution a saturated solution. Give the term for the amount of solute in moles per liter of solution. Molality molarity molefraction mole percent What mass (in g) of NH_3 must be dissolved in 475 g of methanol to make a 0 250 m solution? 4.94 g 2.02 g 1.19 g 8.42 g Calculate the molarity of a solution that contains 0.250 moles of KF in enough water to give 0.500 of solution. 0.500 M 2.00 M 0.125M 8.00 M Give The freezing point is lowered and the boiling point is elevated. The freezing point is elevated and the boiling point is lowered. The freezing point and the boiling point are elevated. The freezing point and the boiling point are lowered. What volume of a 0.716 M KBr solution is needed to provide 30.5 g of KBr? 21.8 mL 42.7 mL 184 mL 357 mL Identify the colligative property, vapor pressure lowering freezing point depression boiling point elevation all of the above

Explanation / Answer

(17) In face centered cubic we have 8 corners and six. For the corners, each atom is shared by 8 corners and so its contribution is 1/8, so, 8 x 1/8 = 1(atom per unit cell)

We also have 6 faces in the fcc and each face has one atom, So, in total we have 6 face atoms and the contribution of each of these face atoms is 1/2. So, 6 x 1/2 = 3 (atoms per unit cell)

Hence, the total atoms per unit cell for fcc = 1+3 = 4 (Answer)

(18) let's say at equilibrium only 20 grams of a solute could be dissolved in 100 grams of solvent. So, if exactly 20 grams of solute are dissolved then we call it saturated solution. If less than 20 grams are dissolved then we call it unsaturated solution, and if more than 20 grams could be dissolved by making some changes to other parameters like temperature of pressure then it is called super saturated solution.

A concentrated solution means more solute is dissolved in the solvent but it does not saturated or super saturated.

So, from above examples/definitions, the correct choice Super saturated solution.

(19) Molality is the moles of solute per kg of solvent.

molarity is the moles of solute per liter of solution.

mole fraction is the moles of solute divide by total moles of solution (sum of moles of solute + solvent).

mole percent is (moles of solute/moles of solute + moles of solvent) x 100

So, from the definitions the correct choice is Molarity.

(20) mass of solvent = 475 g = 0.475 kg

m stands for molality, so, molality of solution = 0.250m.

we know that, molality = moles of solute/kg of solvent

let's say we have X moles of solute that is ammonia.

so, 0.250 = X/0.475

on cross multiply...

X = 0.250 x 0.475 = 0.11875 mol

molar mass of NH3 is 17 g/mol.

So, mass of NH3 = 0.11875mol x 17g/mol = 2.01875 g, this could be round to 2.02 g (three sig figs)

So, the correct answer is 2.02 g.

(21) Information for this one is not clear as it does not say what is 0.500 of solution. (Could only be solved if we know what is this number).

(22) Pure water freezes at 0 degree C. So, would be a problem for the places where the temperature is below zero degree C. To overcome this problem, antifreezing agents are used that decreases the freezing point of water and keep the radiayor safe. Antifreeze also increases the boiling point of water as it try to hold the water molecules in liquid phase, so to bring them in vapor phase we need more temperature so it helps to stop the water boiling which is not good for vehicles.

hence the correct choice is "The freezing point is lowered and the boiling point is elevated."

(23) molarity is given = 0.716 M

mass of solute, KBr = 30.5 g

we know that, molarity = moles of solute/liter of solution

molar mass of KBr is 119 g/mol

so, moles of KBr = 30.5 g x 1 mol/119g = 0.256

plug in the values in the molarity formula..Let's say the volume is X.

0.716 mol/L = 0.256 mol/X

X = 0.256 mol x 1L/0.716mol = 0.357 L

1 L = 1000 ml, so, 0.357L x 1000ml/1L = 357 ml

So, the correct choice is 357 ml

(24) Colligative proties depends on number of particles of the solute dissolved in the solution.

Vapor pressure lowering depends on how many particles of solute are dissolved, So, it is a colligative prperty.

we know that, delta Tf = i * m * kf

where delta Tf stands for freezing point depression, i stands for Van't hoff factor, a theoretical number of ions that we get when the solute is dissociated into its ions. m stands for molality and kf is molal freezing constant.

So, as freezing point depression also depends on number of particles so it is also a colligative property.

Similar to freezing point lowering, boiling point elevation also depends on number of particles of solute, delta Tb = i * m * kb.

where delta Tb is elevattion in boiling point and kb is molal elevation constant.

So, the correct choice is "All of the above."

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