Question

6 moles of BaCl2 reacted with 3 moles of H3PO4. The number of moles of Ba3(PO4)2 formed is
A. 0.5 mol
B. 1 mol
C. 1.5 mol
D. 2 mol​

Answer 1

Introduction

Two dry solids --- barium hydroxide and ammonium nitrate --- are mixed to produce an endothermic reaction.  The temperature of the mixture drops approximately 45oC and is cold enough to freeze the reaction beaker to water on a block of wood

Equations

Ba(OH)2.8H2O(s) + 2NH4NO3(s)   →   Ba(NO3)2(aq) +  2NH3(aq) + 10H2O(l)

To Conduct Demonstration

Mix the two solids together in a 250mL beaker.  Stir for a few seconds with a stirring rod.  (Do not stir with the thermometer.)  The mixture should become moist from the water released by the Ba(OH)2.8H2O.  DO NOT ADD ANY WATER TO THE BEAKER.

Place a drop or two of water on the wooden block.  Place the container on top of the block of wood, covering the water.

Place the thermometer in the beaker.

The mixture will become extremely cold and freeze the reaction beaker to the damp block of wood.  The entire block can be lifted up by lifting the beaker.

This reaction releases NH3 gas.  Students may be able to detect the odor if they are close enough.

Read the final temperature from the thermometer. 

Demo Time: 10 – 15  minutes

Safety and Disposal

Barium salts are toxic.  Avoid inhaling ammonia vapors.

Dispose of waste in the barium waste carboy or the heavy metals waste carboy.

References

Shakhashiri, B.Z. Chemical Demonstrations:  A Handbook for Teachers of Chemistry; 1983.

Acknowledgment

Margaret Asirvatham, Spring 1987.

Thermochemistry

T510: Exothermic Reaction – Thermite

T515: Endothermic Reaction - Ba(OH)2 + NH4NO3

T515: Prep Notes

T520: Exothermic and Endothermic Reactions – Hot and Cold Packs

T525: Hot Packs vs Hydrogen Balloon

T540: Calorimetry – Specific Heat and Molar Capacity

T560: Effects of Temperature – Sublimation

T565: Effects of Temperature -

Answer 2

6 moles of BaCl2 reacted with 3 moles of H3PO4 to form C.1.5 moles of Ba3(PO4)2.

Given,

Moles of BaCl2=6

Moles of H3PO4=3.

To find,

the number of moles of Ba3(PO4)2 formed.

Solution:

• The reaction between BaCl2 and H3PO4 takes place as:
• 3BaCl2+2H3PO4→Ba3(PO4)2+6HCl.
• The stochiometric coefficients of BaCl2, H3PO4, Ba3(PO4)2 and 6HCl are 3, 2 , 1 and 6.
• This means that 3 moles of BaCl2 react with 2 moles of H3PO4 and form 1 mole of Ba3(PO4)2.

• H3PO4 here is the limiting reagent.

2 moles of H3PO4 form 1 mole of Ba3(PO4)2, so 3 moles of H3PO4 will form:

$=\frac{1}{2} X3\\=1.5 moles.$

Hence, the number of moles of Ba3(PO4)2 formed is 1..5 moles.

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