A mixture of lithium and sodium hydrides reacted with 193 cm3 of water. The weight of the solution obtained by 1 gram is less than the sum of the masses of all starting compounds. Mass fraction in the percentage of alkalis in the solution amounted to 8%. Calculate the mass of the hydrides.

 

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Tell me the way solution task. Where to start solving the task?

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14 hours ago, KirMaloy said:

A mixture of lithium and sodium hydrides reacted with 193 cm3 of water.

How hydride reacts with water?

 

Edited December 16, 20196 yr by Sensei

I can write the reaction equations

LiH + H2O = LiOH + H2

NaH + H2O = NaOH + H2

The weight of all substances after the reaction decreased by 1 gram. I understand that this is hydrogen
Hydrogen has a total mass. How can I calculate the mass of hydrides?

LiH + NaH + 2H2O = LiOH + NaOH + 2H2

m(LiH+NaH) = (M(LiH) + M(NaH)) * m(H2) / 2M(H2) = (7.95 + 24) * 1 / 4 = 8 г.

How to find the mass of each hydride in a mixture?

 

What is molar mass (or atomic mass) of each compound in your equation?

If you know mass of Hydrogen that escaped, you can calculate combined mass of LiH and NaH.

 

I calculated the combined weight of the hydrides above.
I don't know what to do next.

The total weight of hydrides is 8 grams. How to find out the mass of each hydride?

LiH + NaH + 2H2O = LiOH + NaOH + 2H2

m(LiH+NaH) = (M(LiH) + M(NaH)) * m(H2) / 2M(H2) = (7.95 + 24) * 1 / 4 = 8 г.