Describe an experiment to show that water contains hydrogen and oxygen only

Electrolysis

Explanation:

The electrolysis of water is one such experiment that shows that water is made up of hydrogen and oxygen atoms only in the ratio of 2 to 1.

In the electrolysis of water, electricity is passed through acidified water to cause it to decompose.

The electrolysis of water is also known as the electrolysis of dilute tetraoxosulphate  (VI) acid.

At the cathode, H⁺ ions are discharged and hydrogen gas is liberated:

               2H⁺       +     2e⁻     →        H₂

At the anode, both the sulfate ion and hydroxyl ions migrate to this electrode. Only the OH⁻ is selected for preferential discharge due to its lower position in that activity series.

         4OH⁻  →   2H₂O    +    O₂     +     4e⁻

Oxygen gas is produced at the anode.

This electrolysis demonstrates the volumetric composition of water that is, 2 volumes of hydrogen at the cathode and 1 volume of oxygen at the anode.

i'm wiling to try and you : )

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2