Question

Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. How many grams of calcium hydride are needed to form 8.5 grams of hydrogen?

Answer 1

Hint: Generally metal hydrides react with water and form respective metal hydroxides and hydrogen gas are as the products. If we know how many moles of hydrogens is liberated during the chemical reaction we can calculate the amount of calcium hydride involved in the reaction.

Complete step by step answer:
- In the question it is asked to calculate the amount of calcium hydride needed to form 8.5 grams if hydrogen.
- The balanced chemical reaction of representing the chemical reaction of calcium hydride with water is as follows.
\[Ca{{H}_{2}}+2{{H}_{2}}O\to Ca{{(OH)}_{2}}+2{{H}_{2}}\]
- In the above chemical reaction one mole of calcium hydride reacts with two moles of water and forms one mole of calcium hydroxide and two moles of hydrogen as the products.
-The molar mass of hydrogen is 2.016 g/mol.
- The number moles form 8.5 gm of hydrogen is $=\dfrac{8.5}{2.016}=4.216 mol$
- One mole of calcium hydride produces two moles of hydrogens, then the number of moles of calcium hydride required for the above reaction is as follows.
\[\begin{align}
  & \text{number of moles of calcium hydride = }\dfrac{\text{number moles of hydrogen}}{\text{2}} \\
 & =\dfrac{4.216}{2}=2.108 moles \\
\end{align}\]
- Now we have to calculate the number of grams of calcium hydride required in the above chemical reaction.
- The molar mass of the calcium hydride = 42.094 g/mol.
- The mass of the calcium hydride required to react with 8.5 g of hydrogen = (42.094) (2.018) = 88.73 grams.
- Therefore the amount of calcium hydride required to react with 8.5 grams of hydrogen is 88.73 grams.

 Note: first we should convert the given amount of hydrogen into a number of moles then only we will get the amount of calcium hydride required to react with a particular amount of hydrogen for balanced chemical reaction.