Chemistry, 05.07.2019 22:10 thesleepycat

A40.15 gram sample of a hydrate of na2so4 was heated thoroughly in a porcelain crucible, until its weight remained constant. after heating, 21.27 grams of the anhydrous compound remained. what is the formula of the hydrate?

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Answer from: aiti48

The formula of the hydrate of the sodium sulfate is : Na_2SO_4.7H_2O

Explanation:

Mass of hydrated sodium sulfate = 40.15 gram

Mass of completely dehydrated sodium sulfate = 21.27 gram

Mass of water molecules present in hydrated sodium sulfate =x

40.15 gram = 21.27 gram + x (Law of conservation of mass)

x = 40.15 gram - 21.27 gram = 18.88 g

Moles of water = $\frac{18.88 g}{18 g/mol}= 1.04mol$

Moles of sodium sulfate = $\frac{21.27 g}{142.04 g/mol}=0.1497 mol$

Whole number ratio of sodium sulfate and water:

Sodium sulfate = $\frac{0.1497 mol}{0.1497 mol}=1$

Water = $\frac{1.04 mol}{0.1497 mol}=6.9 a\\rox 7$

The formula of hydrate be Na_2SO_4.7H_2O

So, the formula of the hydrate of the sodium sulfate is : Na_2SO_4.7H_2O

Answer from: Quest

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.

Answer from: Quest

when the volume of gas is changed from 717.73 ml to 852 ml the temperature will change from 315 c to 452 c

calculation

this is calculated using the charles law formula

that is, v1/t1 = v2/t2

v1=?

t1 = 315 c into kelvin = 315 +273 = 588 k

v2 = 852 ml

t2 = 425c + 273 =698 k

make v1 the subject of the formula ( by multiplying both side by t1)

v1=( v2 xt1) / t2

v1= (852 ml x 588 k)/ 698 k= 717.73 ml

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A40.15 gram sample of a hydrate of na2so4 was heated thoroughly in a porcelain crucible, until its w...

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