MediumChemistryHigh School (9–10)GeneralAtoms and Molecules › Molecules, Ions and FormulaeNumericalBoard Exam
Write the formula of calcium phosphate. Calcium has a valency of 2, and the phosphate group, PO₄…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
- Write the formula of calcium phosphate. Calcium has a valency of , and the phosphate group, , has a valency of . Check that the charges add up to zero.
- Write the formulas of magnesium phosphate and aluminium phosphate (aluminium has a valency of ).
Need a reminder? The key ideaShow
Valency is the combining capacity of an atom or group. Criss-cross: write the symbols and valencies, cross the valencies over, simplify, and put a group in a bracket if there is more than one of it. Names: the metal first, then the non-metal ending in ide, or the group's name.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Cross over: . Charges: .
Step 2. (b) Magnesium. Magnesium also has a valency of : .
Step 3. (b) Aluminium. Crossing and gives , which simplifies to .
Answer: , and .
Discussion (0)
Log in to join the discussion.
Loading…