Question

how many oxygen atoms will be on the reactant side of the chemical equation shown after it is balanced?
(nh₄)₃aso₃ + li₂co₃ ⟶ li₃aso₃ + (nh₄)₂co₃
○ 6
○ 24
○ 15
○ 9
which list of coefficients will balance the chemical equation shown?
_ca + _al₂o₃ ⟶ _al + _cao
○ 3,1,2,3
○ 3,2,1,1
○ 2,1,3,1
○ 1,1,3,2

Explanation:

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First Question:

Step1: Balance ammonium ions

Balance $\text{NH}_4^+$: add coefficient 2 to $(\text{NH}_4)_3\text{AsO}_3$, coefficient 3 to $(\text{NH}_4)_2\text{CO}_3$

$$2(\text{NH}_4)_3\text{AsO}_3 + \text{Li}_2\text{CO}_3 ightarrow \text{Li}_3\text{AsO}_3 + 3(\text{NH}_4)_2\text{CO}_3$$

Step2: Balance arsenic ions

Balance $\text{AsO}_3^{3-}$: add coefficient 2 to $\text{Li}_3\text{AsO}_3$

$$2(\text{NH}_4)_3\text{AsO}_3 + \text{Li}_2\text{CO}_3 ightarrow 2\text{Li}_3\text{AsO}_3 + 3(\text{NH}_4)_2\text{CO}_3$$

Step3: Balance lithium ions

Balance $\text{Li}^+$: add coefficient 3 to $\text{Li}_2\text{CO}_3$

$$2(\text{NH}_4)_3\text{AsO}_3 + 3\text{Li}_2\text{CO}_3 ightarrow 2\text{Li}_3\text{AsO}_3 + 3(\text{NH}_4)_2\text{CO}_3$$

Step4: Count reactant oxygen atoms

Calculate total O: $(2\times3)+(3\times3) = 6 + 9 = 15$
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Second Question:

Step1: Balance oxygen atoms

Balance O: add coefficient 3 to $\text{CaO}$

$$\_\text{Ca} + \text{Al}_2\text{O}_3 ightarrow \_\text{Al} + 3\text{CaO}$$

Step2: Balance calcium atoms

Balance Ca: add coefficient 3 to $\text{Ca}$

$$3\text{Ca} + \text{Al}_2\text{O}_3 ightarrow \_\text{Al} + 3\text{CaO}$$

Step3: Balance aluminum atoms

Balance Al: add coefficient 2 to $\text{Al}$

$$3\text{Ca} + \text{Al}_2\text{O}_3 ightarrow 2\text{Al} + 3\text{CaO}$$

Step4: Match coefficients

Identify coefficients: 3, 1, 2, 3
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Answer:

1. 15
2. 3, 1, 2, 3