A student is using colored beads to make a model of calcium dihydrogen phosphate, Ca(H2PO4)2. Calcium atoms are represented by white beads, hydrogen atoms by black beads, phosphorus atoms by green beads, and oxygen atoms by red beads.

Question

What combination of beads should the student use for the model?

A 2 white, 2 black, 1 green, 2 red2 white, 2 black, 1 green, 2 red
B 1 white, 4 black, 2 green, 8 red1 white, 4 black, 2 green, 8 red
C 2 white, 12 black, 4 green, 6 red2 white, 12 black, 4 green, 6 red
D 1 white, 8 black, 8 green, 4 red

Answer 1

To build a model of calcium dihydrogen phosphate, which has the formula Ca(H2PO4)2, we need to determine the number of each type of atom present in the compound:

1. Calcium (Ca): There is 1 calcium atom in the formula.
2. Hydrogen (H): Each dihydrogen phosphate (H2PO4) group contains 2 hydrogen atoms, and since there are 2 of these groups, there are a total of \(2 \times 2 = 4\) hydrogen atoms.
3. Phosphorus (P): Each dihydrogen phosphate group contains 1 phosphorus atom, and with 2 groups, there are \(2 \times 1 = 2\) phosphorus atoms.
4. Oxygen (O): Each dihydrogen phosphate group has 4 oxygen atoms, and with 2 groups, there are \(2 \times 4 = 8\) oxygen atoms.

Now we can summarize the counts of each type of atom:

• Calcium: 1
• Hydrogen: 4
• Phosphorus: 2
• Oxygen: 8

Now we can match this to the options provided for the beads:

• A: 2 white, 2 black, 1 green, 2 red (Incorrect)
• B: 1 white, 4 black, 2 green, 8 red (Correct)
• C: 2 white, 12 black, 4 green, 6 red (Incorrect)
• D: 1 white, 8 black, 8 green, 4 red (Incorrect)

The correct answer is B: 1 white, 4 black, 2 green, 8 red.