The Mole & the Avogadro Constant (CIE A Level Chemistry)

5.0 g of an unknown Group 2 nitrate was decomposed to produce 0.0843 moles of gas.

2X(NO₃)₂ (g) → 2XO (s) + 4NO₂ (g) + O₂ (g)

Identify the unknown element in the unknown Group 2 in part (a).

X = ............................

State and explain whether strontium nitrate would need to be heated more or less strongly than X(NO₃)₂ to decompose.

Relative strength of heating .......................................................................................

Explanation ..................................................................................................................

Barium sulfate is a white insoluble solid and is used in stomach X-rays and as a pigment for paint.

Calculate the number of atoms in 74 mg of barium sulfate.

.............................................. particles

State the ionic equation for the formation of barium sulfate.

A different barium compound, barium carbonate, was reacted with hydrochloric acid. 

When magnesium reacts with hydrochloric acid, the following reaction occurs:

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)  

During the reaction, the hydrogen produced occupies 103 cm³ at 25.0 ^oC and 100 kPa. 

Calculate the amount, in moles, of hydrogen gas produced during the reaction. 

....................................... moles

A student completed the same reaction as in part (a), using 3.75 g of magnesium.

Calculate the mass, in grams, of magnesium chloride produced by the student during this reaction. Give your answer to 3 significant figures.

.............................. g

Calculate the number of hydrogen atoms produced during the student's reaction in part (b).