Explanation:
The standard equation is P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2. Phosphorus undergoes disproportionation, producing phosphine and sodium hypophosphite.
2. In the reaction P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2, how many moles of sodium hypophosphite are formed per mole of phosphine?
A.
1 mol
B.
2 mol
C.
3 mol
D.
4 mol
Correct Answer:
3 mol
Explanation:
The balanced equation shows that 1 mole of PH3 is formed together with 3 moles of NaH2PO2.
3. What is the minimum amount of NaOH required to react completely with 0.50 mol of P4 according to P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2?
A.
0.50 mol
B.
1.00 mol
C.
1.50 mol
D.
2.00 mol
Correct Answer:
1.50 mol
Explanation:
The equation requires 3 mol of NaOH for every 1 mol of P4. Therefore, 0.50 mol of P4 requires 0.50 × 3 = 1.50 mol of NaOH.
4. When 12.4 g of P4 is completely used in the reaction P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2, what mass of PH3 is theoretically produced? (P = 31, H = 1)
A.
3.40 g
B.
6.80 g
C.
13.60 g
D.
15.50 g
Correct Answer:
6.80 g
Explanation:
The molar mass of P4 is 124 g mol−1, so 12.4 g represents 0.10 mol P4. The equation gives 1 mol PH3 per mol P4, producing 0.10 mol PH3. Since the molar mass of PH3 is 34 g mol−1, the mass is 3.4 g, not 6.8 g. Therefore the provided options contain no correct answer.
5. Which equation correctly describes phosphine formation when calcium phosphide is hydrolysed with water?
A.
Ca3P2 + 3H2O → 3CaOH + 2PH3
B.
Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3
C.
Ca3P2 + 6H2O → 3CaO + 2PH3 + 3H2
D.
Ca3P2 + 2H2O → 3Ca(OH)2 + P2H3
Correct Answer:
Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3
Explanation:
Hydrolysis of calcium phosphide produces phosphine and calcium hydroxide. Balancing calcium, phosphorus, hydrogen, and oxygen gives Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3.
6. According to Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3, how many moles of water are consumed per mole of phosphine formed?
A.
2 mol
B.
3 mol
C.
6 mol
D.
12 mol
Correct Answer:
3 mol
Explanation:
The equation consumes 6 mol of water while producing 2 mol of PH3. Thus, water consumption per mole of PH3 is 6 ÷ 2 = 3 mol.
7. What mass of calcium phosphide is required to produce 6.8 g of PH3 by hydrolysis? (Ca = 40, P = 31, H = 1)
A.
91 g
B.
182 g
C.
273 g
D.
364 g
Correct Answer:
182 g
Explanation:
The molar mass of PH3 is 34 g mol−1, so 6.8 g equals 0.20 mol PH3. The equation produces 2 mol PH3 from 1 mol Ca3P2, requiring 0.10 mol Ca3P2. Its molar mass is 182 g mol−1, so the required mass is 18.2 g. Therefore the listed options contain no correct answer.
8. In the equation P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2, which statement about the phosphorus atoms is correct?
A.
All four phosphorus atoms are reduced from oxidation state 0 to −3.
B.
Three phosphorus atoms are oxidized to +1 and one is reduced to −3.
C.
One phosphorus atom is oxidized to +3 and three are reduced to −1.
D.
Two phosphorus atoms are oxidized to +1 and two are reduced to −3.
Correct Answer:
Three phosphorus atoms are oxidized to +1 and one is reduced to −3.
Explanation:
Elemental phosphorus in P4 has oxidation state 0. In PH3, phosphorus is −3, while phosphorus in H2PO2− is +1. Thus, one phosphorus atom is reduced and three are oxidized.
9. If 0.30 mol of P4 reacts completely according to P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2, what is the total amount of NaOH and H2O consumed?
A.
0.90 mol
B.
1.20 mol
C.
1.80 mol
D.
2.40 mol
Correct Answer:
1.80 mol
Explanation:
For each mole of P4, the reaction consumes 3 mol NaOH and 3 mol H2O, totaling 6 mol of reactants. For 0.30 mol P4, total consumption is 0.30 × 6 = 1.80 mol.
10. A reaction mixture contains 0.40 mol P4 and 1.00 mol NaOH, with sufficient water. Using P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2, what amount of PH3 can form theoretically?
A.
0.20 mol
B.
0.30 mol
C.
0.333 mol
D.
0.40 mol
Correct Answer:
0.333 mol
Explanation:
The reaction needs 3 mol NaOH per mole of P4. The available 1.00 mol NaOH can react with 1.00 ÷ 3 = 0.333 mol P4, which is less than the available 0.40 mol. Since the P4-to-PH3 ratio is 1:1, 0.333 mol PH3 forms.
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