What mass of salt (nacl) should you add to 1.94 l of water in an ice cream maker to make a solution that freezes at -14.4 ∘c ? assume complete dissociation of the nacl and density of 1.00 g/ml for water.

- mass of NaCl used is 439g.

Solution:- Depression in freezing point is a colligative property and the formula used to solve this type of problems is,

delta Tf = i x m x kf

where, delta Tf is depression in freezing point

i is Van't hoff factor. For NaCl, the value of i is 2 as it gives two ions.

m is molality and kf is the molal freezing point constant. For water, kf is 1.86 degree C/m

given, Volume of water = 1.94 L = 1.94 kg

Freezing point of solution = -14.4 degree C

pure water(solvent) freezes at 0 degree C. So, delta Tf = 0 - (-14.4) = 14.4 degree C

Let's plug in the values in the formula..

14.4 = 2 x m x 1.86

m = 14.4/(2 x 1.86)

m = 3.87

molality, m = moles of solute/kg of solvent

moles of solute = m x kg of solvent = 3.87 x 1.94 = 7.51

mass of solute, NaCl used = 7.51 mol x (58.44 g/mol) = 438.88 g that could be round to 439g.

beta decay is the answer

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.